CAOS 2017: Papers with Abstracts

Abstract. The reported incidence of spondylolysis in athletes varies between 15% and 47%, considerably more than 6% in the general population, with most common types of related sport activities being gymnastics, weight lifting, soccer, swimming, cricket and tennis. (Reitman, Stanitski). The repeated tension stress microtrauma on the ventro-caudal part of the inferior articular facet during lumbar hyperextension and trunk twisting movements, together with anatomical predispositions can result in complete symptomatic fracture defect, preventing further participation in sports activities. Although less common and more benign, unilateral isthmic stress fractures tend to be resistant to conservative management if not properly addressed initially, therefore warranting early operative treatment (Debnath).

Abstract. Total knee arthroplasty (TKA) is considered a highly successful procedure. Survival rates of more than 90% after 10 years are generally reported. However, complications and revisions may still occur for many reasons, and some of them may be related to the operative technique. Computer assistance has been suggested to improve the accuracy of implantation of a TKA (Jenny 2005). Short term results are still controversial (Roberts 2015). However, few long term results have been documented (Song 2016). The present study was designed to evaluate the long-term (more than 10 years) results of a TKA which was routinely implanted with help of a non-image based navigation system. The 5- to 8- year of this specific TKA has already been documented (Jenny 2013).
The hypothesis of this study will be that the 10 year survival rate of this TKA will be improved in comparison to historical papers when analyzing survival rates and knee function as evaluated by the Knee Society Score (KSS).

Abstract. The non-invasive navigation system may help the surgeon to assess the lower limb axis at least as accurately as with the conventional radiographic techniques without exposure. But validation of this system used was only performed experimentally, and the present study is the first step of clinical validation.

Abstract. The survival rate of navigation-assisted unicompartmental knee arthroplasty when mechanical revision was considered as the end-point was 94% after 10 years. These figures compares favorably with previously published literature about conventional implantation. Longer follow-up is required to prove superiority of any technique.

Abstract. The CUSUM analysis allows monitoring the learning curve when introducing PSTs for TKA in an academic department. There may be a significant learning curve to achieve the steady state of accuracy and obtain an acceptable alignment. The decision was taken to discontinue using PSTs for TKA..

Abstract. The fundamental for upper cervical spinal surgery is screws fixation progress, however, anatomical variations of atlantoaxial vertebrae are wide, and the region is adjacent to important organ such as spine cords, oblongata and vertebral artery, all of which make the fixation harder. Robot-assisted navigation can make up for the above shortcomings, and has the potential to more improve the screw placement accuracy.
We recently designed a robot system called TiRobot, which is based on intraoperative three-dimensional images. TiRobot has three components: the planning and navigation system, optical tracking system and robotic arm system. By combining navigation and robot techniques, TiRobot can guide the screw trajectories for orthopedic surgeries.
TiRobot has been used in upper cervical surgeries with the approval from the Ethics Committee. There were 7 screws inserted during the surgeries, 1 screw for posterior C1- 2 trans-articular fixation, 1 screw for anterior odontoid fixation and 5 for C1 or C2 pedicel fixation. All surgeries were smoothly performed using TiRobot. According to the post-operation CT image data, all the screw placements were sufficient because there was no perforation of the spinal canal or any unexpected malposition. According to the Gertzbein-Robbins classification, all screws fell into group A. Furthermore, there was a discrepancy between the planned and the actual placements at the entry points and the end points. The average deviation in entry point and end point were 1.21 +/- 0.45mm and 1.19 +/- 0.36mm. These safe and accurate results make TiRobot the first medical robot could be used in upper cervical spinal surgery.

Abstract. To introduce a new robot-assisted surgical system for spinal posterior fixation which called TiRobot, based on intraoperative three-dimensional images. TiRobot has three components: the planning and navigation system, optical tracking system and robotic arm system. By combining navigation and robot techniques, TiRobot can guide the screw trajectories for orthopedic surgeries.
In this randomized controlled study approved by the Ethics Committee, 40 patients were involved and all has been fully informed and sign the informed consent. 17 patients were treated by free-hand fluoroscopy-guided surgery, and 23 patients were treated by robot-assisted spinal surgery.
A total of 190 pedicle screws was implanted. The overall operation time were not different for both groups. None of the screws necessitated re-surgery for revised placement. In the robot-assisted group, assessment of pedicle screw accuracy showed that 102 of 102 screws (100%) were safely placed (<2 mm, category A+B). And mean deviation in entry point was 1.70 +/- 0.83mm, mean deviation in end point was 1.84 +/- 1.04mm. In the conventional freehand group, assessment of pedicle screw accuracy showed that 87 of 88 (98.9%) were safely placed (<2 mm, category A+B), 1 screw fall in category C, mean deviation in entry point was 3.73 +/- 2.28mm, mean deviation in end point was 4.11 +/- 2.31mm.
This randomized controlled study verified that robot-assisted pedicle screw placement with real-time navigation is a more accuracy and safer method, also revealed great clinical potential of robot-assisted surgery in the future.

Abstract. This study investigated the accuracy of Distal Femoral Cut and Proximal Tibial Cut during navigated total knee arthroplasty on a large cohort of patient. The findings demonstrated that CAOS is an accurate and precise solution to assist the surgeons achieve his/her surgical resection goals with substantial reduction of unacceptable resections.

Abstract. This study investigated the accuracy of TKA alignment during and past learning phase for navigated total knee athroplasty. The findings demonstrated TKA during learning phase can accurately and precisely achieve surgical resection goals with no clinically meaningful compromise in alignment accuracy.

Abstract. INTRODUCTION
Total knee arthroplasty (TKA) is widely performed for improving pain and restoring function for patients with osteoarthritis (OA) and over 50000 primary procedures were performed in Australia in 2015 (Annual report 2016). Computer assisted pre-operative planning (CAPP) was introduced to enhance accuracy of rotational and translational alignment of components (Schep 2003). It can be done with 3D bone surface modelling from CT or MRI scans and take kinematics and surgeon work flow into account. Computer assisted intra-operative navigation is also accessed by some surgeons and consists of three elements: software platform, point positions from reference arrays captured and reference device attached to the patient’s bone (Bae 2011).
By incorporating CAPP with navigation, a correlation between the patient’s anatomy from pre-operative images can be established by gathering intra-operative anatomical landmarks and/or surface points and is known as registration (Chan 2016). However, identifying landmarks and acquiring images intra-operatively and the registration quality can be time-consuming and/or prone to risk. Custom-designed registration software that could reduce the time and error and be incorporated into the surgical workflow is needed (Chan 2016).
The aim of this study was to develop custom registration software using pre-operative planning and intra-operative 3D data capture and validate precision and repeatability using a preliminary Sawbones study.

Abstract. A new atlas-based 2D-3D reconstruction of 3D volumes of lower extremity from a pair of calibrated X-ray images was presented. The approach combines non-rigid 2D- 2D registration based 3D landmark reconstruction with the B-spline parametrization of TPS transformation, incorporating the smoothness property of B-splines for regularization. Efficacy of the present approach was evaluated on the calibrated X-ray images and CT data. Also, we take the knee joint articulation into consideration. Articulated B-spline parameterization leads to the almost same accuracy as individual B-spline parameterization and has the superiority over the latter when it comes to the prevention from the knee joint penetration.

Abstract. The key for a successful total hip replacement (THR) and the longevity of the implant is the correct alignment of the acetabular cup which is to be considered as the most critical component. The alignment of the cup is defined with respect to anterior pelvic plane (APP). The APP defines the reference for the anteversion and inclination angles which sets the basis for the correct alignment of the implant. The angle of the plane is created by three distinct anatomical landmarks which are represented by two anterior superior iliac spines (ASIS) and the symphysis pubis. The angle of the APP in respect to the coronal plane defines the pelvic tilt (PT) which can be anterior or posterior. The rotation of the pelvis highly depends on the individual anatomy of the subject. This means that a neutral pelvic tilt (PT) in supine position is rarely observed and also may be dissimilar in standing position. In this paper we present a non-invasiveness and cost-effective prototype for measuring the patient-specific PT under the use of a navigated smart-device based ultrasound system for supporting surgery planning. In view of the non-invasiveness method the system can be used to measure pre- and postoperative pelvic orientation. With the use of an artificial hip reference model different cases were measured. The computed results look very promising with a standard deviation of ±1°.

Abstract. Postoperative pain and functional limitations after an Anterior Cruciate Ligament reconstruction is usually inaccurate placement of the femoral and tibial tunnel. This paper presents a technology workflow including a software pipeline for patient-specific preoperative planning and analysis of the knee joint including functional-mechanical properties..

Abstract. Purpose. To validate a small, easy to use and cost-effective augmented marker-based hybrid navigation system for peri-acetabular osteotomy surgery.
Methods. A cadaver study including 3 pelvises (6 hip joints) undergoing navigated PAO was performed. Inclination and anteversion of two navigation systems for PAO were compared during acetabular reorientation. The hybrid system consists of a tracking unit which is placed on the patient’s pelvis and an augmented marker which is attached to the patient’s acetabular fragment. The tracking unit sends a video stream of the augmented marker to the host computer. Simultaneously, the augmented marker sends orientation output from an integrated inertial measurement unit (IMU) to the host computer. The host computer then computes the pose of the augmented marker and uses it (if visible) to compute acetabular orientation. If the marker is not visible, the output from the IMU is used to update the orientation. The second system served as ground truth and is a previously developed and validated optical tracking-based navigation system.
Results. Mean absolute difference for inclination and anteversion (N = 360) was 1.34 degrees and 1.21 degrees, respectively. The measurements from our system show a very strong correlation to the ground-truth optical tracking-based navigation system for both inclination and anteversion (0.9809 / 0.9711).
Conclusion. In this work we successfully demonstrated the feasibility of our system to measure inclination and anteversion during acetabular reorientation.

Abstract. In orthopaedic spine surgery pedicle screw systems are used for stabilisation of the spine after injuries or disorders. With an percutaneous operation method surgeons are faced with huge challenges compared to an open surgery, but it`s less traumatic and the patient benefits with a faster rehabilitation and less traumatic injuries. The screw positions and the required rod dimensions for the stabilizing connection between the screws are hard to define without an open view on the operating field. Because of these facts a new smart device based system for rod shape determination was invented. Therefore, an application was developed, which integrates a localizer module to get the position data of the pedicle screws, with help of rigid bodies placed on top of the pedicle screws down-tubes. An algorithm was developed to choose the best fitting rod to connect the pedicle screws with help of calculating the rod length and the rod radius. The system was tested in a test scenario where four pedicle screws were drilled into a wooden plate. The positions of the screws were adjusted to fit a curved and a straight rod. In the test scenario the application chose always the rod correctly.

Abstract. With the advancement of the virtual technologies, three-dimensional surgical simulators are now possible. In this article, we describe an immersive simulation platform, allowing students in orthopedic surgery to learn how to deal with a sample diaphyseal fracture of the femur using LC-DCP plate hole, cortical screw and verbrugge forceps. To reach certain realism, weight of the objects and force feedback are used in addition to the visual scene and the 3D sound. The students feel the weight, the strength of the bone when they pierce the holes, and the vibration of the drill. The simulation is implemented by using CAVE, the CyberGlove, CyberGrasp, and 3D sound system.

Abstract. We have developed a laser projection system, which can project laser on corresponding position to surgical planning drawn at a fluoroscopic image without an optical tracking system. In this paper, we introduce a spatial calibration method between a laser module and a fluoroscope for the laser projection and evaluate its accuracy with a mimic experimental system. The experimental system consists of a laser module, a distance measurement unit and a CCD camera. The laser modules can project arbitrary line on surface by reflecting a point source laser with two galvanometers. We designed a calibration phantom by combining a collimator for accurate laser pattern positioning and stainless steel ball arrays for calculation of an extrinsic parameter of a C-arm fluoroscopy. We set a projection plane having ruler in 400mm distance from the CCD camera, and set 54 points on the screen. The laser module projects points with respect to the set points, and a distance error between set points and projected points and angular error are calculated. The distance errors is 1.5±1.9 mm (average ± standard deviation). Maximum error was 7.5 mm. Angular error was smaller than 2 degrees. The laser projection system and its calibration method shows clinically acceptable accuracy and the clinical application is the next step.

Abstract. Due to tumors or bone fractures caused by high mechanical impact, the affected tissue has to be removed. The implantation of a stabilizing replacement is a common solution for defect bridging and support of bone ossification. Preserving the physiological mobility after the treatment could prevent stress shielding or overload of the surrounding muscles and ligaments. [1]
In case of a critical vertebral body defect, the body and its attached disks have to be removed. Thereafter the adjacent vertebral bodies are braced together resulting in limited physiological spine movability. A flexible implant adapted to and preserving the patient-specific physiological spine mobility would be a desirable solution. [2] [3]
To realize such an implant additive manufacturing (AM) can be used as a key technology. AM offers the following advantages: The build-up of almost any desired complex geometry shape, without additional costs. A monolithic geometry with enhanced functionalities combined in only one part and one material. A cost-efficient implant individualization based on patient specific requirements. [4]
Relating to flexibility, the integration of solid state hinges tailored to the patient specific physiological mobility is possible. Hereby, assembly work is neglectable and abrasion will be prevented due to the absence of friction partners. A challenge to overcome will be the durability of the design. It is limited by the fatigue of the material caused by implant motion.

Abstract. After a fracture injury a swelling of the skin soft tissue results which prevents an early operation. In order to shorten the waiting time until the decrease of the swelling, the metabolism-reducing effect of mild local hypothermia and the swelling-reducing effect of compression therapy should be used in a device anatomically adjusted to the patient. For the best possible treatment, a regulation of the cooling and compression parameters should be carried out by means of sensor technology in order to allow an adaptation to the individual patient.

After a fracture injury a swelling of the skin soft tissue results which prevents an early operation. In order to shorten the waiting time until the decrease of the swelling, the metabolism-reducing effect of mild local hypothermia and the swelling-reducing effect of compression therapy should be used in a device anatomically adjusted to the patient. For the best possible treatment, a regulation of the cooling and compression parameters should be carried out by means of sensor technology in order to allow an adaptation to the individual patient.
Based on medical studies, parameter areas relevant to patients could be determined. These were implemented in first functional models for a cooling system and a compression system. Anatomically adapted cooling and pressure chambers allow a good physical coupling of the system to humans. The first test results, considering the heat emission and the skin elasticity properties of the human body, show that both rapid cooling can be achieved in a range of between 17 and 20°C of skin temperature within 4 min, and that under a pressure effect of between 10 and 20 kPa in the pressure chambers a pressure on the human tissue can be produced up to 15 kPa. The cooling system based on Peltier elements is capable of transporting a heat flow up to 10 W. The quiet, maintenance-free Peltier elements also increase the patient's acceptance. In the pressure chambers, a temporally overlapping generation of pressure pulses can imitate the process of natural walking by the effect of muscle pumps and contribute to a technical lymphatic drainage. By detecting the inflammation area with the aid of netlike-arranged temperature sensors and measuring the internal pressure of the pressure chambers in the case of a swelling tissue, cooling can be carried out at a determined point and the occurrence of, for example, a compartment syndrome can be prevented by regulating the pressure.
At present still ongoing, promising developments of models for the consideration of the temperature distribution and pressure differences in the cardiovascular system should enable a determination of optimized cooling and pressure curves adapted to the individual human. In this way, the best possible control circuits should be identified using medical expert knowledge.

Abstract. The glenohumeral joint is an important joint with large mobility of the human upper
extremity. In shoulder arthroplasty patients often has an unsatisfactory outcome. In order to understand the biomechanical complexity of the shoulder, a novel computer controlled experimental shoulder simulator with an innovative muscle control were constructed. The main component of the simulator includes the active pneumatic
muscles to replicate
the deltoid and the rotator-cuff function and two springs as passive muscle. The aim of this study is to evaluate the impact of a variation of shoulder joint geometries on shoulder biomechanics in the basis of motion analysis. The radius of the glenoid cavity varied from 28-33mm with 2.5mm increment while the radius the humeral head are varied from 20.1-25.1 with 2.5mm increment. The “teach-in” function of the simulator allows an operator to assign the movement to the simulator where the lengths of the pneumatic muscles are recorded. Then the simulator repeats the assigned movement according to the recorded muscles length. The daily living activities includes abduction/adduction, internal/external rotation with adducted arm, and circumduction. The results show promising repeatability of the simulator with minor deviation. However, damage on the surface of the humeral head has been found which should be further studied for both shoulder behavior investigation and the shoulder simulator optimization. Therefore, this study is a decent initial study toward the verification of the simulator and lead to a better understanding of shoulder biomechanical behavior to cope with the clinical problems in the future.

Abstract. The sagittal orientation of the pelvis commonly called pelvic tilt has an effect on the orientation of the cup in total hip arthroplasty (THA). Pelvic tilt is different between individuals and changes during activities of daily living. In particular, the pelvic tilt in standing position should be considered during the planning of THA to adapt the target angles of the cup patient-specifically to minimize wear and the risk of dislocation. Methods to measure pelvic tilt require an additional step in the planning process, may be time consuming and additional devices or x-ray imaging are necessary.
In this study, the relationship between three functional parameters describing the sagittal pelvic orientation in standing position and seven morphological parameters of the pelvis was investigated. Correlations might be used to estimate the pelvic tilt in standing position by the morphology of the pelvis in order to avoid additional measuring techniques of pelvic tilt in the planning process of THA. For 18 subjects a semi-automatic process was established to match a 3D-reconstruction of the pelvis from CT scans to orthogonal EOS imaging in standing position and to calculate the morphological and functional parameters of the pelvis subsequently.
The two strongest correlations of the linear correlation analysis were observed between morphological pelvic incidence and functional sacral slope (r = 0.78; p = 0.0001) and between morphological pubic symphysis-posterior superior iliac spines- ratio and functional tilt of anterior pelvic plane (r = -0.59; p = 0.0098). The results of this study suggest that patient-specific adjustments to the orientation of the cup in planning of THA without additional measurement of the sagittal pelvic orientation in standing position should be based on the correlation between morphological pelvic incidence and functional sacral slope.

Abstract. The purpose of this paper is to present a clinical validation of a novel technology called ’3XPlan’ which allows for 3D prosthesis planning using 2D X-ray radiographs. After a local institution review board (IRB) approval, 3XPlan was evaluated on 25 patients TKA. Pre-operatively, all the patients underwent a CT scan according to a standard protocol. All the CT images were segmented to extract 3D surface models of both femur and tibia, which were regarded as the ground truth. Additionally, 2 X-ray images were acquired for each affected leg and were used in ’3XPlan’ to derive patient-specific models of the leg. For 3D models derived from both modalities (CT vs. X-ray), five most relevant anatomical parameters for planning TKA were measured and compared with each other. Except for tibial torsion, the average differences for all other anatomical parameters are smaller than or close to 3 degrees.

Abstract. A new mini-display has been developed which is directly mounted to navigated surgical instruments. It receives signals from the navigation system and visualizes information how to guide to the instrument in order to reach the pre-planned target pose. Thus the surgeon does not need to change his eye- focus between the operating area and the computer screen of the navigation system. the proposed visualization symbols provide all information for instrument positioning in an intuitive way.

Abstract. The digitalisation gets more and more important in our daily life. Also in medical technology instruments and devices need to become intelligent and be able to both collect and provide additional data. This research is about the development of an electronic sensor system for sterilisable medical containers. Hereby just a few concepts exist to equip the containers with sensor modules but the high temperature of 135 °C during the sterilisation is still a big challenge.
The objective for this research is to find a heat resistant insulation for an electronic system with a power supply, sensors for both sterilisation and transport and a low power communication module. Furthermore, the thermal energy of the sterilisation shall be used for powering up the system.
In a first step an epoxy resin was used to insulate the electronics and a high temperature battery. By using the temperature sensor of a Bluetooth module the module temperature could be measured during multiple steam sterilisations. Following, a partly insulated thermoelectric generator shall be used to get energy by the achieved temperature difference.
First results show that the used epoxy resin limits the temperature to 81 °C. However, the resin was damaged after 21 sterilisation cycles due to its high mass and entrapped air. Therefore, the insulation needs to be minimized and the electronic components need to be able withstanding higher temperatures. Additionally, insulations with not yet considered materials will be tested. Also the possibility of insulating just heat-sensitive parts like the power elements will be investigated.

Abstract. Orthopaedic oncologic surgery requires resection with a safe margin as inadequate surgical margin leads to unfavorable results with an increased rate of local tumor re- currence [1]. Computer Navigation Assisted Surgery (CAS) and Patient Specific In- strumentation (PSI) have been reported to increase accuracy and predictability of tumor resections [2-6]. The technically demanding joint-preserving surgery that re- tains the native joint with the better function may be benefited from the new tech- niques [7]. CAS has the advantages of real-time intraoperative guidance of the bone resections but requires bulky and costly facilities [5]. PSI is a simple option of repli- cating surgical plan but lacks intraoperative image feedback on the surgery [5,6]. As primary bone sarcoma is uncommon, clinical studies for meaningful comparison of the two techniques may not be feasible. The cadaver study was to investigate the surgical accuracy of CAS and PSI in joint-preserving tumor surgery of knee joint.

Abstract. Consideration of the pre- and post-operative magnitude of the hip joint force R and its orientation Ɵ is of major importance for satisfactory long-term results in total hip arthroplasty. R and Ɵ can be computed by using biomechanical models with adapted geometrical/ anthropometrical parameters taken from clinical X-ray images. The objective of this study was to evaluate the models of Pauwels and Debrunner based on digital reconstructed-radiographs (central projection) from 10 CT-datasets of patients treated with telemetric hip-implants by a comparison to corresponding in-vivo measurements.
R and Ɵ were computed for 10 patients with patient-specific geometric/anthropometric parameters. The model adaption was based on 28 anatomical landmarks. The root-mean-square-error of R is smaller for Debrunner (0.59/vs./0.66), and for Ɵ it is smaller for Pauwels’ (4.47/vs./7.78).
Mathematical models provide potentially valuable information regarding hip joint mechanics. Regarding R, in all of the 10 patients the predictions of Pauwels’ model are consistently higher than the in-vivo measurements. Debrunner computed R in 8 cases higher and in 2 cases lower than the corresponding in-vivo forces. Pauwels’ and Debrunner showed similar tendencies: in 8 cases an overestimation of R and in 2 cases contrary results. Regarding Ɵ we found that in 5 cases the predictions of Pauwels’ are consistently higher than the in-vivo measurements and also contrary to Debrunner.
As previous studies showed, an unambiguous identification of most landmarks in a 2D X-ray image is difficult. The impact of the pelvic tilt on the computational result was not considered in our study. Further investigation of this aspect is part of our ongoing work.

Abstract. Robotic surgical systems reduce the cognitive workload of the surgeon by assisting in guidance and operational tasks. As a result, higher precision and a decreased surgery time are achieved, while human errors are minimised. However, most of robotic systems are expensive, bulky and limited to specific applications.
In this paper a novel semi-automatic robotic system is evaluated that offers the high accuracies of robotic surgery while remaining small, universally applicable and easy to use. The system is composed of a universally applicable handheld device, called Smart Screwdriver (SSD) and an application specific kinematic chain serving as a tool guide. The guide mechanism is equipped with motion screws. By inserting the SSD into a screw head, the screw is identified automatically and the required number of revolutions is executed to achieve the desired pose of the tool guide.
The usability of the system was evaluated according to IEC 60601-1-6 using pedicle screw implementation as an example. The achieved positioning accuracies of the drill sleeve were comparable to those of SpineAssist from Mazor Robotics Ltd., Caesarea (IL) with -0.54 ± 0.93 mm (max: 2.08 mm) in medial/lateral-direction and 0.17 ± 0.51 mm (max: 1.39 mm) in cranial/caudal-direction in the pedicle isthmus. Additionally, the system is cost-efficient, safe, easy to integrate in the surgical workflow and universally applicable to applications in which a static position in one or more DOF is to be adjusted.

Abstract. Bone tumor resection and subsequent reconstruction remains challenging for the surgeon. Obtaining adequate margins is mandatory to decrease the risk of local recurrence. Improving surgical margins quality without excessive resection, reducing surgical time and increasing the quality of the reconstruction are the main goals of today’s research in bone tumor surgical management. With the outstanding improvements in imaging and computerized planning, it is now a standard. However, surgical accuracy is essential in orthopaedic oncologic surgery (Grimmer 2005).
Patient specific instruments (PSI) may greatly improve the surgeon's ability to achieve the targeted resection. Thanks to its physical support, PSI can physically guide the blade yielding to a better control over the cutting process (Wong, 2014). Surgical time might significantly be reduced as well when compared to conventional method or navigated procedure. Finally, reconstruction may gain in rapidity and quality especially when allograft is the preferred solution as PSI can be designed as well for allograft cutting (Bellanova, 2013).
Since 2011, PSI have systematically been used in our institution for bone tumor resection and when applicable allograft reconstruction. This paper reports the mid- to long-term medical outcomes on a large series.

Abstract. The treatment of joint-fractures is a common task in orthopaedic surgery causing considerable health costs and patient disabilities. Percutaneous techniques have been developed to mitigate the problems related to open surgery (e.g. soft tissue damage), although their application to joint-fractures is limited by the sub-optimal intra-operative imaging (2D-fluoroscopy) and by the high forces involved. Our earlier research toward improving percutaneous reduction of intra-articular fractures has resulted in the creation of a robotic system prototype, i.e. RAFS (Robot-Assisted Fracture Surgery) system.
We propose a robot-bone attachment device for percutaneous bone manipulation, which can be anchored to the bone fragment through one small incision, ensuring the required stability and reducing the “biological cost” of the procedure. The device has been evaluated through the reduction of 9 distal femur fractures on human cadavers using the RAFS system.

Abstract. Medical navigation providing intraoperative localization of medical instruments plays a crucial role in computer assisted surgery (CAS). Several different multiple- camera standalone optical localizers are available on the market nowadays. Our aim was to develop, easy-to-use, low-cost and portable medical localizer based on iPhone 6S camera. We decided to develop a specialized smartphone app which is able to detect two rigid bodies (RB) on the camera screen and estimate their position both in devices and global coordinate system using sensor fusion with smartphones accelerometer and gyroscope. In the procedure one RB serve as reference and the other is attached to the tool. The prototype was preliminary calibrated using 2D and 3D VDI/VDE 2634 standard. Validation procedure involved measurements of the position and distance of two RBs placed 500 mm from each other in a distance of 1 meter to the smartphones camera. The measurements were taken from three different angles: -30°, 0°, 30° regarding RBs plane. The standard deviation of the measured distance was 0.62 mm with average measured distance of 498.0 mm. The other tests were made in a test-setup where the virtual offset of ultrasound probe was added to one of the RBs so the distance between probe and reference was 195 mm. The tests showed that the position of ultrasound probe is estimated with standard deviation of 0.70 mm and the average measured distance is 195.18 mm. Due to the promising results of those evaluations, we plan to perform more specific tests in clinical setup in near future.

Abstract. This paper presents the development and validation of an early computational model intended to drive a haptic simulator for knee physical exam skills training. Specifically, an analytical model of knee soft tissues was developed and validated against existing computationally expensive open source software and through cadaveric experimentation.

Abstract. This paper presents the initial assessment of the feasibility of using a Sigma 7 tele- operation haptic device to replicate clinical wrist assessment tests and for the novel assessment of wrist proprioceptive control. Included in this paper is an assessment of the biomechanical suitability of the haptic device, as well as the control techniques that will be used to replicate clinical assessments. Finally, we conclude with proof of concept trials.

Abstract. Pedicle screw fixation is a technically demanding procedure with potential difficulties and reoperation rates are currently on the order of 11%. The most common intraoperative practice for position assessment of pedicle screws is biplanar fluoroscopic imaging that is limited to two-dimensions and is associated to low accuracies. We have previously introduced a full-dimensional position assessment framework based on registering intraoperative X-rays to preoperative volumetric images with sufficient accuracies. However, the framework requires a semi-manual process of pedicle screw segmentation and the intraoperative X-rays have to be taken from defined positions in space in order to avoid pedicle screws’ head occlusion. This motivated us to develop advancements to the system to achieve higher levels of automation in the hope of higher clinical feasibility.
In this study, we developed an automatic segmentation and X-ray adequacy assessment protocol. An artificial neural network was trained on a dataset that included a number of digitally reconstructed radiographs representing pedicle screw projections from different points of view. This model was able to segment the projection of any pedicle screw given an X-ray as its input with accuracy of 93% of the pixels. Once the pedicle screw was segmented, a number of descriptive geometric features were extracted from the isolated blob. These segmented images were manually labels as ‘adequate’ or ‘not adequate’ depending on the visibility of the screw axis. The extracted features along with their corresponding labels were used to train a decision tree model that could classify each X-ray based on its adequacy with accuracies on the order of 95%.
In conclusion, we presented here a robust, fast and automated pedicle screw segmentation process, combined with an accurate and automatic algorithm for classifying views of pedicle screws as adequate or not. These tools represent a useful step towards full automation of our pedicle screw positioning assessment system.

Abstract. Fluoroscopic C-arms are operated by medical radiography technologists (RTs) in the Canadian operating room (OR). While they do receive formal, accredited training, most of this training is theoretical, rather than hands-on. During their first encounters in the OR, new RTs can experience difficulty achieving the radiographic views required by surgeons, often needing several scout X-rays during C-arm positioning before achieving the correct anatomical view. Furthermore, ambiguous language by surgeons often inadequately conveys their request (Pally 2013). The result is often frustration, unnecessary radiation exposure, and added OR time (Booij 2007).
Several groups have tried to address this problem by overlaying artificial X-ray images on a live video feed (Chen 2013, Reaungamornat 2012, Müller 2011). Others have used artificial X-rays for simulation training (Bott 2008, Gong 2014, Cleary 2004). Though the intent is to improve C-arm positioning accuracy and efficiency during orthopaedic procedures, these systems have primarily been evaluated on system accuracy and not on their potential to decrease radiation exposure inside the OR or C-arm positioning time.
The purpose of this study was therefore to evaluate the value of artificial X-rays in enhancing C-arm positioning performance using inexperienced users.

Abstract. Component position and sizing in total knee replacement (TKR) could be improved by patient specific instrumentation (PSI). The purpose of the study was to evaluate the reliability of the manufacturer plan in predicting final component sizes for TKR.
Forty-five TKRs were prospectively enrolled and data on component size were recorded from the initial manufacturer’s proposal, the final plan modified after surgeon’s and from the actually implanted prostheses.
Pre-operative modifications were required in more than 50% of the cases, with the tibial tray size requiring more frequent changes. The surgeon’s planning showed a significantly higher accuracy than the manufacturer’s one regarding tibial tray size (p < 0.05) but not femoral components size (p: n.s.). Careful evaluation by an experienced knee surgeon is recommended when planning TKR with PSI.

Abstract. Patient Specific Instrumentation (PSI) may contribute to reduce blood loss after total knee replacement (TKR) by avoiding violation of the medullary canal. The purpose of the study was to compare the hemoglobin (Hb) decrease in two groups of patients undergoing TKR with PSI and conventional instrumentation.
Pre- and post-operative blood samples were collected for twenty-two patients randomly assigned to receive a PSI-assisted or conventional TKR. Post- to preoperative Hb difference was calculated.
A significant difference in Hb reduction in favor of the PSI group was registered on the last day of stay but not on the previous post-operative days: these promising results suggest a beneficial effect of PSI in blood loss reduction. PSI may hence be considered among the strategies available to control and reduce blood loss related to TKR.

Abstract. Improving the accuracy of measuring 6 degree of freedom tibiofemoral kinematics is a crucial step in gait analysis. The skin-marker estimated kinematics is subject to soft tissue artefacts. Fluoroscopic systems have been reported to achieve high accurate kinematics, but induced irradiation and a limited field of view and its high cost hampers routine usage on large patient cohorts. The aim of this study is to assess the feasibility of measuring tibiofemoral kinematics using multi-channel A-mode ultrasound system in cadaver experiment and assess its achievable accuracy. A full cadaver was placed on the surgery table and legs were hanging in the air. Upper body was fixated and right leg was pulled by rope to generate a movement. To track the ground truth of the motion, two bone pins with optical markers were mounted to the femur and tibia separately. Six custom A-mode ultrasound holders containing 30 A-mode ultrasound transducers and 18 optical markers were mounted on six anatomical regions. Calculating the bone to each ultrasound transducer distance from ultrasound echo, and using the spatial information of the optical markers on the holders, 30 points were determined. The segmented bone models acquired from CT or MRI were registered to the corresponding points. Then the tibiofemoral kinematics were determined from the positions of registered femur and tibia per frame. This study has presented a multi-channel A-mode ultrasound system and proven its feasibility of reconstructing tibiofemoral kinematics in cadaver experiment. Although the reconstructed tibiofemoral kinematics is less accurate than fluoroscopic system, it outperforms skin-mounted markers system. Thus, this A- mode Ultrasound approach could provide a non-invasive and non-radiative method for measuring tibiofemoral kinematics, which may be used in clinic gait analysis or even computer-aided orthopedic surgery.

Abstract. Typically, Flexoscopes are used in interventions that require minimal number of ports and maneuverability in the target area such as natural orifice transluminal endoscopic surgery. In orthopedic surgeries, these endoscopes are not used because interventions like drilling and osteotomy necessitate large forces. Laser osteotomy does not require mechanical contact with the bone therefore flexible tools can be used for cutting. GG-1 is a custom-designed robotic platform that allows precise control of the flexoscope’s pose. The robot is anthropomorphically inspired from a human arm. The robot will be able to move and orient the laser accurately, while following an uneven bone surface in the target area of the osteotomy.

Abstract. Proper component alignment is crucial for a successful total hip arthroplasty (THA). Some studies found safe cup orientations and corresponding stem antetorsions based on a defined desired range of motion (ROM) suitable for activities of daily living. These studies either used complex and time consuming 3D simulations or more simple mathematical formulas which cannot be extended to combined motions.
With the method introduced in this work, any arbitrary motion can be applied. The ROM specified as the ROM of the femur relative to the pelvis is transformed into the ROM of the prosthesis neck relative to the cup for each cup orientation. For this transformation, the orientation and design of the stem are considered. The comparison of the neck and cup orientations is done using a 2D mapping of a 3D spherical surface which reduces the complexity of the calculation.
We found that the femoral antetorsion as well as the neutral stem flexion and adduction have an influence on the resulting safe zone. The result is not just a combined anteversion but a combined orientation. For validating the plausibility of the algorithm, the resulting safe zones are compared to literature. Same results can be achieved using the same input data. Using this technique, a patient-specific safe zone based on the ROM can be derived and adjusted to the stem orientation.

Abstract. The Interosseous Membrane (IOM) is a fibrous ligament bundle connecting the ulna and the radius. It is well known that the IOM allows transferring partial load from the radius to the ulna (Pfaeffle 2005). It also influences the kinematics of the radioulnar joint (Yasutomi 2002, Tarr 1984).
Three-Dimensional (3D) computer-assisted methods for preoperative planning of osteotomy have been applied successfully on forearm pathologies (Fürnstahl 2010, Murase 2008, Vlachopoulos 2015). However, to the best of our knowledge, models and studies of the influence of the IOM during pro-supination are limited to a kinematics analysis of the system, either with actual bone geometry (Fürnstahl 2009) or without it (Kasten 2002). In this work, we present a physical simulation of the forearm pro-supination involving the IOM biomechanical properties, for providing insights on the influence of the IOM on the radioulnar motion. We demonstrate a preliminary validation using a sample simulation performed on a healthy forearm by comparing its outcome with literature, and analyze the kinetic data that our method allows.

Abstract. In robot-assisted orthopaedic surgery, registration is a key step, which defines the position of the patient in the robot frame so that the preoperative plan can be performed. Current registration methods have their limitations, such as the requirement of immobilising the limb or maintaining the line of sight (LOS). These issues cause inconvenience for the surgeons and interrupt the surgical workflow in the operating room.
Targeting these issues, we propose a smart camera-robot registration system for joint replacement. The bone geometry, which is measured directly by a depth camera, is aligned to a preoperatively obtained bone model to calculate the pose of the target. Simultaneously, in order to avoid registration failure caused by LOS disruptions, the depth camera tracks objects that may occlude the target bone, and a robot manipulator is used to move the camera away from the nearest obstacle. An appropriate camera motion to “escape” the obstacle is calculated based on the position and velocity of the obstacle, with the aim of avoiding the occlusion efficiently without changing the general target position in the camera frame. The inverse kinematics of the robot is used to project the Cartesian velocity of the end-effector into the joint space, with kinematic singularities considered for stable robotic control. An admittance controller is designed as the human-robot interface so that the surgeon can directly set the robot configuration by hand according to a given intraoperative scenario.
Simulations and experiments with a redundant manipulator were conducted to test the performance of a proof-of-concept implementation. The results show that the proposed obstacle avoidance method can effectively increase the distance between the obstacle and the LOS, which lowers the risk of registration failure due to obstacle occlusion. This pilot study is promising in reducing distractions to the surgeon and could help achieve a fluent and surgeon-centred workflow.

Abstract. Despite of the high success of TKA, 20% of recipients remain dissatisfied with their surgery. There is an increasing discordance in the literature on what is an optimal goal for component alignment. Furthermore, the unique patient specific anatomical characteristics will also play a role. The dynamic characteristics of a TKR is a product of the complex interaction between a patient’s individual anatomical characteristics and the specific alignment of the components in that patient knee joint. These interactions can be better understood with computational models. Our objective was to characterise ligament characteristics by measuring knee joint laxity with functional radiograph and with the aid of a computational model and an optimisation study to estimate the subject specific free length of the ligaments.
Pre-operative CT and functional radiographs, varus and valgus stressed X-rays assessing the collateral ligaments, were captured for 10 patients. CT scan was segmented and 3D-2D pose estimation was performed against the radiographs. Patient specific tibio-femoral joint computational model was created. The model was virtually positioned to the functional radiograph positions to simulate the boundary conditions when the knee is stressed. The model was simulated to achieve static equilibrium. Optimisation was done on ligament free length and a scaling coefficient, flexion factor, to consider the ligaments wrapping behaviour.
Our findings show the generic values for reference strain differ significantly from reference strains calculated from the optimised ligament parameters, up to 35% as percentage strain. There was also a wide variation in the reference strain values between subjects and ligaments, with a range of 37% strain between subjects. Additionally, the knee laxity recorded clinically shows a large variation between patients and it appears to be divorced from coronal alignment measured in CT. This suggest the ligaments characteristics vary widely between subjects and non-functional imaging is insufficient to determine its characteristics. These large variations necessitates a subject-specific approach when creating knee computational models and functional radiographs may be a viable method to characterise patient specific ligaments.

Abstract. Component alignment cannot fully explain TKA performance with regards to patient reported outcomes and pain. Patient specific variations in musculoskeletal anatomy are one explanation for this. Computational simulations allow for the impact of component alignment and variable patient specific musculoskeletal anatomy on dynamics to be studied across populations. This study aims to determine if simulated dynamics correlate with Patient Reported Outcomes.
Landmarking of key anatomical points and 3D registration of implants was performed on 96 segmented post-operative CT scans of TKAs. A cadaver rig validated platform for generating patient specific rigid body musculoskeletal models was used to assess the resultant motions. Resultant dynamics were segmented and tested for differentiation with and correlation to a 6 month postoperative Knee injury and Osteoarthritis Outcome Score (KOOS).
Significant negative correlations were found between the postoperative KOOS symptoms score and the rollback occurring in midflexion (p<0.001), quadriceps force in mid flexion (p=0.025) and patella tilt throughout flexion (p=0.009, p=0.005, p=0.010 at 10°, 45° and 90° of flexion). A significant positive correlation was found between lateral shit of the patella through flexion and the symptoms score. (p=0.012) Combining a varus/valgus angular change from extension to full flexion between 0° and 4° (long leg axis) and measured rollback of no more than 6mm without roll forward forms a ‘kinematic safe zone’ of outcomes in which the postoperative KOOS score is 11.5 points higher (p=0.013).
The study showed statistically significant correlations between kinematic factors in a simulation of postoperative TKR and post-operative KOOS scores. The presence of a ‘kinematic safe zone’ in the data suggests a patient specific optimisation target for any given individual patient and the opportunity to preoperatively determine a patient specific alignment target.

Abstract. Provision of prehabilitation prior to total knee arthroplasty (TKA) through a digital mobile application is a novel concept. Traditionally, prehabilitation is provided face to face by a Physiotherapist. Kwok et al (2015) in a systematic review concluded future research should be directed at methods of prehabilitation that are cost effective method. Our research evaluates a resource effective and cost effective method of delivering prehabilitation. DoironCadrin et al 2016 have reported a randomised control trial protocol involving pre-habilitation through audio-visual software, this protocol still requires a health care practitioners time in real time, whereas our methodology enables multiple patients to be managed simultaneously, optimising health care utility.
Prehabilitation is believed to have multiple benefits for the patients’ recovery and outcome. Prehabilitation may impact on length of stay (LOS) through aspects of Social Cognitive Theory (SCT). A mobile application allows a patient’s exercise participation to be recorded, monitored continuously and progressed drives greater self-efficacy, outcome expectation, self-regulation and motivation which could be a mechanism by which patients receive benefit (Brown et al 2014). Another mechanism may be through lower levels of pain and function in the early period after TJR surgery, as reported in the meta-analysis completed by Wang et al (2016). The primary aim of our research is to determine whether provision of prehabilitation through a mobile digital application impacts inpatient LOS after TKA. The secondary objective is to understand the effect of digital prehabilitation on hospital costs.

Abstract. Dental implants are in 96% positioned free hand including a risk of suboptimal placement. A miniaturized navigation system has been developed to overcome these limitations by fixing two stereo cameras to the drill to guide the surgeon during implant insertion. The aim of the present study was to develop and analyse a dual-mode marker with a highly precise, high contrast optical pattern, visible by the camera system, on a precise substrate clearly identifiable on Cone Beam CT (CBCT) images and sterilisable. The marker was developed with a laser engraved optical pattern brought to a ceramic substrate containing two holes to ensure clear identification of the position of the marker within CBCT images.
The substrate dimensions were verified with a micrometer gauge and compared to the expected tolerances. The position and angular error of the optical pattern on the substrate was analysed on optical microscope images. Six markers were exposed to 20 cleaning and steam sterilization cycles and changes were analysed on optical and scanning electron microscope (SEM) images. Energy dispersive X-ray spectroscopy (EDX) analysis was performed to study the percentage composition of the different elements.
Substrate dimensions and angular errors remained always within the defined tolerances. Positioning errors were higher than the tolerances for some of the measurements. The error distribution indicates a systematic error. Results were reproducible over the samples. No changes could be observed visually on the optical microscope images between the initial marker and the 20th sterilization cycle. EDX results show slight percentage variations of the different elements between the different cycles. Fluctuations were most important for the carbon-content.
A dual mode marker could be developed with a very accurate optical pattern very precisely positioned on a ceramic substrate making any marker calibration procedure un- necessary. Precision analysis confirmed a reproducible position of the pattern on the substrate, indicating a stable and robust process. Systematic errors can be corrected directly at the used Laser system. Cleaning and sterilization tests confirmed the stability of the dual-mode marker after cleaning and sterilization. The present study has shown that highly accurate, high contrast and robust markers can be manufactured using laser- engraving technology on ceramic substrates.

Abstract. Although physical and ultrasound (US)-based screening for congenital deformities of the hip (developmental dysplasia of the hip, or DDH) is routinely performed in most countries, one of the most commonly performed maneuvers done under ultrasound observation - dynamic assessment - has been shown to be relatively unreliable and is associated with significant misdiagnosis rates, on the order of 29%.
Our overall research objective is to develop a quantitative method of assessing hip instability, which we hope will standardize diagnosis across different raters and health-centers, and may perhaps improve reliability of diagnosis. To quantify dynamic assessment, we propose to use the variability in femoral head coverage (FHC) measurements within multiple US scans collected during a dynamic assessment. In every US scan, we use our recently-developed automatic FHC measuring tool which leverages phase symmetry features to approximate vertical cortex of ilium and a random forest classifier to identify approximate location of the femoral head. Having estimated FHC in each scan, we estimate the change in FHC across all the US scans during a dynamic assessment and compare this change with variability of FHC found in previous studies.
Our findings - in a dynamic assessment on an infant done by an orthopaedic surgeon, the femoral centre moved by up to 19% of its diameter during distraction, from 55% FHC to 74% FHC. This change in FHC is slightly greater than its variability in static US scans reported in previous studies, suggesting that the distraction force likely produced a real lateral displacement. Our clinician’s qualitative assessment concluded the hip to be normal as this degree of distraction was not indicative of instability. This suggests that our technique likely has sufficient resolution and repeatability to quantify differences in laxity between stable and unstable hips, although this presumption will have to be confirmed in a subsequent study with additional subjects. The long-term significance of this approach to evaluating dynamic assessments may lie in increasing early diagnostic sensitivity in order to prevent dysplasia remaining undetected prior to manifesting itself in early adulthood joint disease.

Abstract. Biomechanical models of the knee have the potential to predict joint mechanics and improve the therapeutic outcome. In case of total knee arthroplasty (TKA) knowledge on post-operative acting joint forces and its consideration in pre-operative planning might increase implant longevity and patient satisfaction. The goal of this study was to evaluate 2D biomechanical models of the knee suitable for pre-operative TKA planning and to validate them based on in vivo measurements of 9 patients treated with instrumented knee implants.
An extensive literature research on 2D biomechanical models of the knee with the requirement that patient-specific model adaption can be performed with data available in the conventional clinical workflow revealed the models of Maquet and Minns. Both models require one-leg stand AP long-leg radiographs and they output the resultant tibiofemoral joint force. For model validation, data from the freely accessible OrthoLoad database (www.orthoload.com) containing forces acting in orthopaedic implants have been used.
Looking at the results, Minns’s model was in the same range as the reference forces (deviation: -55 %BW to +80 %BW) as well as Maquet’s (deviation: -80 %BW to +50 %BW). Overall, the root-mean-square error (RMSE) was smallest for Minns’ model (48.36 %BW against 51.48 %BW). The patient-specific adaptation process plus simulation took 7 to 8 minutes making the models applicable in the conventional clinical workflow with acceptable costs.
In terms of clinical application, the models’ output might be consulted, e.g. to minimize the magnitude of the resultant joint force, target a specific orientation or load distribution in order to consider mechanical factors which might be associated with premature implant failure.

Abstract. Total knee arthroplasty (TKA) is widely accepted as a successful surgical intervention to treat osteoarthritis and other degenerative diseases of the knee. However, present statistics on limited survivorship and patient-satisfaction emphasize the need for an optimal endoprosthetic care. Although, the implant design is directly associated with the clinical outcome comprehensive knowledge on the complex relationship between implant design (morphology) and function is still lacking.
The goal of this study was to experimentally analyze the relationship between the trochlear groove design of the femoral component (iTotal CR, ConforMIS, Inc., Bedford, MA, USA) and kinematics in an in vitro test setup based on rapid prototyping of polymer-based replica knee implants.
The orientation of the trochlear groove was modified in five different variations in a self-developed computational framework. On the basis of the reference design, one was medially tilted (-2°) and four were laterally tilted (+2°, +4°, +6°, +8°). For manufacturing, we used rapid prototyping to produce synthetic replicates made of Acrylnitril-Butadien-Styrol (ABS) and subsequent post-processing with acetone vapor. The morpho-functional analysis of the replicates was performed in our experimental knee simulator. Tibiofemoral and patellofemoral kinematics were recorded with an optical tracking system during a semi-active flexion/extension (~10° to 90°) motion.
Looking at the results, the patellofemoral kinematics, especially the medial/lateral translation and internal/external rotation were mainly affected. During low flexion, the patella had a more laterally position relative to the femur with increasing lateral trochlear orientation. The internal/external rotation initially differentiated and converged with flexion. Regarding the tibiofemoral kinematics, only the tibial internal/external rotation showed notable differences between the modified replica implants.
We presented a workflow for an experimental morpho-functional analysis of the knee and demonstrated its feasibility on the example of the trochlear groove orientation which might be used in the future for comprehensive implant design parameter optimization, especially in terms of image based computer assisted patient-specific implants.

Abstract. In total knee arthroplasty (TKA) the implant design is one key factor for a proper functional restoration of the diseased knee. Therefore, detailed knowledge on the shape (morphology) is essential to guide the design process. In literature, the morphology has been extensively studied revealing differences, e.g. between ethnicity and gender. However, it is still unclear in which way gender-specific morphological differences are sexual dimorphism or explained by differences in size.
The aim of this study was to investigate the morphology of the distal femur under gender-specific aspects for a large group of patients. Statistical analysis was used to reveal significant differences and subsequent correlation analysis to normalize the morphology.
A dataset of n=363 segmented distal femoral bone surface reconstructions (229 female, 134 male) were randomly collected from a database of patients which underwent TKA. In total, 34 morphological features (distances, angles), quantifying the distal femoral geometry, were determined full automatically. Subsequently, graphs and descriptive statistics were used to check normality and gender-specific differences were analyzed by calculating the 95% confidence intervals for women and men separately. Finally, significant differences were normalized by dividing each feature by appropriate distance measurements and confidence intervals were recalculated.
Looking at the confidence 95% intervals, 6 of 34 features did not show any significant differences between genders. Remarkably, this primarily involves angular (relative) features whereas distance (absolute) measurements were mostly gender dependent. Then, we normalized all distance measurements and radii according to their direction of measurement: Features defined in medial/lateral (ML) direction were divided by the overall ML width and those following the anterior/posterior direction were normalized based on the overall AP length. The results demonstrated that gender- specific differences mostly disappear by using an adequate normalization term.
In conclusion, implant sizes (femoral components) should not be linearly scaled according to one dimension. Instead, ML and AP directions should be regarded separately (non-isotropic scaling). Taking this into consideration, gender-specific differences might be neglected.

Abstract. Orthopaedic surgery is one of the first fields where robotic tools have been used and currently their use is growing thanks to the benefits and advantages of robotics. During the last two decades several robotic devices characterized by high accuracy during both the preoperative and intraoperative phases have been developed. The success of the rehabilitation treatment, which is complementary to the surgical phase, is crucial to the complete recovery of functions: however although computer-assisted navigation is more precise than the conventional techniques, it is still subject to errors. The aim of this study is to present an integrated approach, named "Precision Orthopaedic Surgery - Precision Orthopaedic Rehabilitation" (POS-POR), based on new applications for orthopaedic trauma treatment and rehabilitation.

Abstract. Nowadays, foot switches are used in almost every operating theatre to support the interaction with medical devices. Foot switches are especially used to release risk- sensitive functions of e.g. the drilling device, the high-frequency device or the X-ray C- arm. In general, the use of foot switches facilitates the work, since they enable the surgeon to use both hands exclusively for the manipulation within the operation procedures. Due to the increasing number of (complex) devices controlled by foot switches, the surgeons face a variety of challenges regarding usability and safety of these human-machine-interfaces.
In the future, the approach of integrated medical devices in the OR on the basis of the open communication standard IEEE 11073 gives the opportunity to provide a central surgical cockpit with a universal foot switch for the surgeon, enabling the interaction with various devices different manufacturers. In the framework of the ongoing OR.NET initiative founded on the basis of the OR.NET research project (2012- 2016) a novel concept for a universal foot switch (within the framework of a surgical workstation) has been developed in order to optimize the intraoperative workflow for the OR-personnel.
Here, we developed three wireless functional models of a universal foot switch together with a standardised modular interface for visual feedback via a central surgical cockpit display. Within the development of our latest foot switch, the requirements have been inter alia to provide adequate functionalities to cover the needs for the interventions in the medical disciplines orthopaedic surgery, neurosurgery and ENT.
The evaluation has been conducted within an interaction-centered usability analysis with surgeons from orthopaedics, neurosurgery and ENT. By using the Thinking Aloud technique in a Wizard-of-Oz experiment the usability criteria effectiveness, learnability and user satisfaction have been analysed.
Regarding learnability 83.25% of the subjects stated that the usage of the universal foot switch is easy to learn. An average of 77,2% of users rated the usability of the universal foot switch between good and excellent on the SUS scale. The intuitiveness of the graphical user interface has been approved with 91.75% and the controllability with 83.25%. Finally, 86% of the subjects stated a high user satisfaction.

Abstract. Modern operating rooms (OR) undergo a constant rise in the amount and complexity of technical systems. Due to a lack of inter-device communication and integration, each device works stand-alone resulting in redundant sensors, input devices, monitors and—last but not least—crowded ORs and error prone human- machine-interaction. Therefore, various manufacturers such as Brainlab and Karl Storz provide proprietary integrated workstations. However, those “monolithic” solutions restrict the flexibility of the users and the clinical operators regarding integration of innovative third party devices.
In view of this, the OR.NET initiative (www.ornet.org) strives to develop international open standards for secure dynamic networks of medical devices in ORs. In the scope of the OR.NET project, based on service oriented architecture (SOA), the SDC (Service-oriented Device Connectivity) approach is currently in the process of standardization under IEEE 11073 to link medical devices in the OR (short OR.NETwork). It paves the way to interoperability between various medical devices due to its independence of license holders.
However, the SDC network does not suit real time (RT) requirements of a deterministic data transmission and low maximum latency, e.g. for robotic applications. This paper shows an approach to extend the secure dynamic OR by a real-time capable network to allow the integration of robotic systems. Exemplarily, this paper outlines an orthopaedic robotic system that is released by a universal configurable footswitch. This significantly extends the scope of applications for integrated ORs with the IEEE 11073 standard.

Abstract. The long overdue IEEE 11073 Service-oriented Device Connectivity (SDC) standard proposals for networked and surgical devices provide vendor-independent interoperability and therefore room for improved workflow and new functionality in the operating room. Research and development in this domain remain also highly topical in orthopaedic surgery. Due to the novelty and complexity of the SDC standard family, there is currently a lack of open source public implementations. Such implementations have to overcome several non-trivial challenges, mainly because the complexity of the standards has to be reflected in the software design and implementation. The SDC standard family comes in three different parts and all three standard proposals must be considered when designing and implementing standard conform device communication. In this work, we address these challenges and discuss and compare two design approaches for different programming languages (C++ and Java). Suitable software engineering principles are used to ensure a clean design approach. Practical guidelines are given on how to integrate existing third party components and tools in the framework and the development process, respectively. General feasibility is demonstrated by outlining interoperability between two software frameworks developed using different design concepts.

Abstract. Demographic changes will increase the number of surgical procedures in the next years. Therefore, quality assurance of clinical processes, such as the reprocessing of surgical instruments as well as intraoperative workflows will be of increasing importance to ensure patient safety. Surgical procedures are often complex and may involve risks for the patient. For fixation of screws, e.g. in case of pedicle screws, osteosynthesis plates or revision joint replacement surgery implants, the application of defined torques may be crucial in order to achieve optimal therapeutic results and minimal complication rates. In many cases a subjective rating of the surgeon is necessary as no adequate instrumentation is available. With the same subjective feeling, hammering or screwing in are performed to implant e.g. the acetabular component in THA.

Our actual work is dedicated to the implementation of a functional prototypes of sensor-integrated instruments for specific types of intervention (especially in traumatology) and the evaluation of the sensor integrated surgical instruments in combination with RFID technology for smart process optimization in the operating room as well as for reprocessing of surgical instruments and surgical management in combination with a knowledge-based planning, control and documentation system. Complementary (preferably wireless) sensors such for instrument identification, tracking or more complex measurements such as forces, torques, temperature or impacts during surgery as well as during reprocessing of reusable instruments could enable computer network based quality assurance in a much broader and comprehensive manner.

Within the framework of the OR.NET initiative we follow the approach to integrate wireless sensors for measurement of temperature, force-torque as well as inertial sensors for orientation and impact control, depending on the specific type of application for monitoring of workflows during surgery as well as during reprocessing of reusable instruments and devices. The integration of smart surgical instruments into an open networked operating room based on the open communication standard IEEE 11073 knowledge-based workflow system, can help to improve the process and quality management.

Abstract. The purpose of this study is to evaluate the effect of postoperative mechanical alignment on clinical outcomes and revision rate by comparing acceptable mechanical axis group from neutral and an outlier mechanical axis.
Between 2000 and 2006, clinical and radiographic data of 334 primary TKAs were retrospectively reviewed. Post-operative mechanical axis was investigated within 1 month after TKA. The first group was an acceptable group of 286 knees (85.6%, with mechanical axis of 0°±3°). The second group was an outlier group of 48 knees (14.4%, with mechanical axis of beyond 0°±3°). Clinical outcomes before surgery and at the final follow up were analyzed using scoring method such as Hospital for Special Surgery, Knee Society Score, and Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC) score. Radiologic outcomes including changes of mechanical axis between immediate postop and last follow-up were evaluated. Postoperative complications and revision rates were also evaluated.
The mean degrees in change of mechanical axis between immediate postop and last follow-up were greater in the outlier group (1.6°±2.7) than acceptable group (0.8°±2.4). No significance difference in clinical outcome was found between the two groups. The incidence of aseptic loosening, instability, polyethylene wear, polyethylene breakage, and periprosthetic fracture was 2/4/2/2/2 each in the acceptable group and 1/1/2/0/0 each in the outlier group. Six (2.1%) of 286 in the acceptable group and 4 (8.3%) of 48 in the outlier group were revised (p=0.04). The Kaplan-Meier survival analysis showed a tendency towards improved survival with restoration of neutral mechanical axis. However, such improvement was not statistically significant (p=0.25).
Restoration of neutral limb alignment is a factor of total knee arthroplasty that can result in less revision rate and higher longevity. However, there are no significant differences in clinical outcomes between the two groups.

Abstract. Bone drilling is conducted in many surgical disciplines such as orthopedics, maxillofacial, and spine surgery. Most of these procedures involve drilling of different bone materials including hard (cortical) and soft (cancellous) tissues. Identifying these tissues is essential for surgeons to minimize damage to underlying nerves and vessels.
The sound signal generated during drilling is a valuable source of information that could potentially be employed. Such sounds can be captured readily and easily through non-contact sensors. Therefore, our goal in this preliminary study is to investigate whether drilling sounds can enable us to distinguish between cortical and cancellous tissues.
A bovine tibial bone was drilled, and the cortical and cancellous drilling sounds were captured. Each sound record was divided into small windows with a length of 50 ms and a 50% overlap. The window length was selected small, because our intended longer-term application is to provide the surgeon with near-real-time feedback. Short time Fourier Transform (STFT) coefficients were extracted from each window and were averaged accordingly to obtain p features. A support vector machine (SVM) algorithm was used for classification, and its accuracy was evaluated for different number of features (p). Two training/testing scenarios were considered, atlas (ATL) and leave-one-out (LOO).
The total accuracies for ATL and LOO were 100% and 93.8% respectively obtained for p=128. Our study on a single specimen demonstrated that it is possible to discriminate between cortical and cancellous bones based on relatively short 50 ms windows of drilling sounds.

Abstract. Introduction
Scaphoid non-union results the typical humpback deformity, pronation of the distal fragment, and a bone defect in the non-union site with shortening. Bone grafting, whether open or arthroscopic, relies on fluoroscopic and direct visual assessment of reduction. However, because of the bone defect and irregular geometry, it is difficult to determine the precise width of the bone gap and restore the original bone length, and to correct interfragmentary rotation. Correction of alignment can be performed by computer-assisted planning and intraoperative guidance. The use of computer navigation in guiding reduction in scaphoid non-unions and displaced fractures have not been reported.
Objective
We propose a method of anatomical reconstruction in scaphoid non-union by computer-assisted preoperative planning combined with intraoperative computer navigation. This could be done in conjunction with a minimally invasive, arthroscopic bone grafting technique.
Methods
A model consisting of a scaphoid bone with a simulated fracture, a forearm model, and an attached patient tracker was used. 2 titanium K-wires were inserted into the distal scaphoid fragment. 3D images were acquired and matched to those from a computed tomography (CT) scan. In an image processing software, the non-union was reduced and pin tracts were planned into the proximal fragment. The K-wires were driven into the proximal fragment under computer navigation. Reduction was assessed by direct measurement.
These steps were repeated in a cadaveric upper limb. A scaphoid fracture was created and a patient tracker was inserted into the radial shaft. A post-fixation CT was obtained to assess reduction.
Results and Discussion
In both models, satisfactory alignment was obtained. There were minimal displacement and articular stepping, and scaphoid length was restored with less than 1mm discrepancy. This study demonstrated that an accurate reduction of the scaphoid in non-unions and displaced fractures can be accurately performed using computed navigation and computer-assisted planning. It is the first report on the use of computer navigation in correction of alignment in the wrist.

Abstract. The use of assistance functions for diagnosis and surgical interventions has become an evolving area for mastering challenges of contemporary medicine. Inter alia, these assistance functions can help to prevent malpractices and preserve a high level of satisfaction for patients as well as employees.
To enable such functions in context of a computer-assisted orthopaedic surgery (CAOS), we elaborate the use of Markov Logic Networks (MLNs) for modelling surgical phases. In contrast to commonly researched systems for surgical process modelling, MLNs combine rule-based as well as probabilistic approaches. This allows us to integrate soft and hard constraints into our network – which greatly expands the scenery of currently researched models for phase detection in surgical interventions.
In our contribution, we present the necessary fundamentals of MLNs and show the application to a comprehensible test case. The results are promising concerning the use of MLNs for surgical phase detection. In particular, MLNs have shown two advantages: Firstly, due to their template characteristics, few logic rules allow to model numerous interdependencies between the different surgical phases. Secondly, the combination of probabilistic and logic approaches allows to handle sensor inaccuracies and misclassifications of features directly. E.g., the inaccuracy of a sensor can be expressed by reducing the weight of corresponding formulas, allowing for a softening of constraints.

Abstract. Total knee arthroplasty (TKA) typically addresses end-stage osteoarthritis. While TKA procedures have demonstrated clinical success, occasionally intraoperative complications can occur. This cadaver study examined the potential benefits of soft tissue protection in robotic-arm assisted TKA (RATKA). Six cadaver knees were prepared using RATKA by a single surgeon from a high-volume TKA joint center with no former clinical robotic experience, and compared to seven manually performed cases as a control. The presence of soft tissue disruption was assessed by having the surgeon perform visual evaluation and palpation of the medial collateral ligament (MCL), lateral collateral ligament (LCL), posterior cruciate ligament (PCL), and the patellar ligament after the procedures. The amount of tibial subluxation and patellar eversion was recorded for each case.
For all RATKA cases, there was no visible evidence of disruption of any of the ligaments. All RATKA cases were successfully left with a bone island on the tibial plateau, which protected the PCL. Tibial subluxation and patellar eversion were not required for visualization. In two of the seven MTKA cases, there was slight disruption noted of the PCL, although this did not lead to any apparent change in the functional integrity of the ligament. All MTKA cases required tibial subluxation and patellar eversion to achieve optimal visualization.
Aspects of soft tissue protection were noted in this cadaver study for RATKA. Standard retraction techniques during cutting are recommended. This is the first study to have soft tissue injury parameters assessed for RATKA, and may serve as a platform for future studies.

Abstract. While total knee arthroplasty has demonstrated clinical success, final bone cut and final component alignment can be critical for achieving a desired overall limb alignment. This cadaver study investigated whether robotic-arm assisted total knee arthroplasty (RATKA) allows for accurate bone cuts and component position to plan, compared to manual technique. Six cadaveric specimens (12 knees) were prepared by an experienced user of manual total knee arthroplasty (MTKA), who was inexperienced in RATKA. For each cadaveric pair, a RATKA was prepared on the right leg and a MTKA was prepared on the left leg. Final bone cuts and final component position to plan were measured relative to fiducials, and mean and standard deviations were compared.
Measurements of final bone cut error for each cut show that RATKA had greater accuracy and precision to plan for femoral anterior internal/external (0.8±0.5° vs. 2.7±1.9°) and flexion/extension* (0.5±0.4° vs. 4.3±2.3°), anterior chamfer varus/valgus* (0.5±0.1° vs. 4.1±2.2°) and flexion/extension (0.3±0.2° vs. 1.9±1.0°), distal varus/valgus (0.5±0.3° vs. 2.5±1.6°) and flexion/extension (0.8±0.5° vs. 1.1±1.1°), posterior chamfer varus/valgus* (1.3±0.4° vs. 2.8±2.0°) and flexion/extension (0.8±0.5° vs. 1.4±1.6°), posterior internal/external* (1.1±0.6° vs. 2.8±1.6°) and flexion/extension (0.7±0.6° vs. 3.7±4.0°), and tibial varus/valgus* (0.6±0.3° vs. 1.3±0.7°) rotations, compared to MTKA, respectively (where * indicates a significant difference between the two operative methods based on 2-Variances testing, with α at 0.05). Measurements of final component position error show that RATKA had greater accuracy and precision to plan for femoral varus/valgus* (0.6±0.3° vs. 3.0±1.4°), flexion/extension* (0.6±0.5° vs. 3.0±2.1°), internal/external (0.8±0.5° vs. 2.6±1.6°), and tibial varus/valgus (0.7±0.4° vs. 1.1±0.8°) than the MTKA control, respectively.
In general, RATKA demonstrated greater accuracy and precision of bone cuts and component placement to plan, compared to MTKA in this cadaveric study. For further confirmation, RATKA accuracy of component placement should be investigated in a clinical setting.

Abstract. Active Shape Models (ASM) have been widely used in the literature for the extraction of the tibial and the femoral bones from MRI. These methods use Statistical Shape Models (SSM) to drive the deformation and make the segmentation more robust. One crucial step for building such SSM is the shape correspondence (SC). Several methods have been described in the literature. The goal of this paper is to compare two SC methods, the Iterative Median Closest Point-Gaussian Mixture Model (IMCP- GMM) and the Minimum Description Length (MDL) approaches for the creation of a SSM, and to assess the impact of these SC methods on the accuracy of the femur segmentation in MRI. 28 MRI of the knee have been used. The validation has been performed by using the leave-one-out cross-validation technique. An ASMMDL and an ASMIMCP-GMMM has been built with the SSMs computed respectively with the MDL and IMCP-GMM methods. The computation time for building both SSMs has been also measured. For 90% of data, the error is inferior to 1.78 mm and 1.85 mm for respectively the ASMIMCP-GMM and the ASMMDL methods. The computation time for building the SSMs is five hours and two days for respectively the IMCP-GMM and the MDL methods. Both methods seems to give, at least, similar results for the femur segmentation in MRI. However (1) IMCP-GMM can be used for all types of shape, this is not the case for the MDL method which only works for closed shape, and (2) IMCP- GMM is much faster than MDL.

Abstract. Functional approaches for the localization of the hip center (HC) are widely used in Computer Assisted Orthopedic Surgery (CAOS). These methods aim to compute the HC defined as the center of rotation (CoR) of the femur with respect to the pelvis. The Least-Moving-Point (LMP) method is one approach which consists in detecting the point that moves the least during the circumduction motion. The goal of this paper is to highlight the limits of the native LMP (nLMP) and to propose a modified version (mLMP). A software application has been developed allowing the simulation of a circumduction motion of a hip in order to generate the required data for the computation of the HC. Two tests have been defined in order to assess and compare both LMP methods with respect to (1) the camera noise (CN) and (2) the acetabular noise (AN). The mLMP and nLMP error is respectively: (1) 0.5±0.2mm and 9.3±1.4mm for a low CN, 21.7±3.6mm and 184.7±13.1mm for a high CN, and (2) 2.2±1.2mm and 0.5±0.3mm for a low AN, 35.2±18.5mm and 13.0±8.2mm for a high AN. In conclusion, mLMP is more robust and accurate than the nLMP algorithm.

Abstract. Additive manufacturing has enabled a radical change in how surgeons reconstruct massive acetabular defects in revision hip surgery. We report on the early clinical and radiological results from our methods for surgical planning, design, and implantation of 3D printed trabecular titanium implants in a cohort of patients with large unclassifiable pelvic defects.
We set up a prospective investigation involving 7 consecutive patients. Inclusion criteria was the following: 1) A history of previous total hip replacement; and 2) Current imaging showing at least a Paprosky 3B defect. Planned acetabular inclination and version was 40° and 20° respectively. Post operatively all patients had a CT scan which was analysed with software to determine component position and compared to planned. Outpatient review was done at 2 weeks (For wound), 6 weeks (for weight bearing and fixation) and 52 weeks (for fixation and infection) post-operative.
3 Themedianageatsurgerywas:65years(40-78).Themedianbonedefectvolumewas140cm .Median
surgery length was 5.2 hours (3-6.25). Median blood loss was 1300mL (450- 2000). Radiologically, components were stable and no screw breakages were identified. Achieved inclination was 41.0° (29.0- 55.6) and achieved version was 15.8° (3.8-43.6). Median Oxford Hip score improved from 9 (2-44) to 25 (18-32).
We have demonstrated a new series of pre, intra and post-operative methods for reconstruction of unclassifiable acetabular bony defects. Initial clinical and radiological results are excellent considering the severity of the bony defects. We recommend the use of our or similar methods when trying to reconstruct these defects.

Abstract. In pelvic fracture surgeries, percutaneous screws must be placed accurately for effective fixation and to prevent damage to surrounding tissue structures. Fluoroscopy is currently used to image the pelvis to provide guidance, but this produces harmful ionising radiation and does not allow three-dimensional (3D) visualisation. Ultrasound offers three-dimensional, non-ionising, real-time, and inexpensive imaging. It has thus emerged as an alternative to fluoroscopy for intraoperative imaging in computer-assisted orthopaedic surgery (CAOS). However, ultrasound-based surgical guidance is challenging because ultrasound produces inherently noisy images with limited field-of-view. While several techniques have been proposed to improve bone clarity in ultrasound scans, there is limited work on enhancing ultrasound’s field-of-view for CAOS. In particular, improving the field-of-view for surgical guidance for pelvic fracture surgeries would be needed to achieve accurate and reliable registration to preoperative data, and accurate screw placement in the pelvis.
We propose and evaluate the feasibility of a trackerless method for stitching volumetric ultrasound to achieve an extended field-of-view. Stitching is performed using corresponding features in the overlap between three ultrasound volumes, extracted using an implementation of the 3D scale-invariant feature transform. The volumes are processed using confidence-map weighted phase symmetry detection. Alignment between the volumes is calculated using coherent point drift rigid registration.
We succeeded in extending the field-of-view of 3D ultrasound by creating a 39×43×115mm volume from three initial overlapping volumes, with reasonable overall accuracy. We show a mean post-registration surface error of 0.54mm, compared to 0.33mm achieved by previous tracking-based stitching. Our method achieved a mean distance error of 5.1%, compared to 2% in a similar tracked and 3D SIFT-based technique. Our stitching method does not use tracking, thus contributing towards simpler surgical navigation.

Abstract. The hypothesis was that long-term outcomes were satisfactory or superior to the other implants design reported outcomes. This study confirms our initial hypothesis, that the outcomes of the TKA e-Motion FP with ultra-congruent mobile-bearing were satisfactory at more than 10 years of follow-up. Navigation, whose accuracy is well established, probably contributed to the quality of the results.

Abstract. Since the past few years, patient-specific instrumentation (PSI) has been greatly publicized in knee endoprosthetics. Manufacturers propose advantages such as better accuracy of fit and reduction of both surgical time and operation costs due to pre- operative prosthesis planning. Whether these proposed advantages are achieved in medial unicompartmental knee arthroplasty (UKA) remains unclear. This paper presents results from a retrospective analysis of 22 patients (24 knees) who were electively provided with a medial unicompartmental knee arthroplasty using patient- specific instrumentation.

Abstract. Computer navigation systems has provided useful visual guidance for the surgeon to deliberately locate the tools to the anatomy. However, the tool positioning process is still manually performed. Sometimes the tool positioning may cause fatigue, stress and might be of risk to patient too. In this paper we designed a special purpose handheld robot for bone drilling. Meanwhile the coordinated controller assists the surgeon to precisely and safely drill the bone safely. Two force sensors are embedded at the handle and the cutter to measure the human exerted force and bone drilling force, respectively. The velocity command was then computed by the admittance controller for the robot controller. The motion of the control handle is positioned by the surgeon, while the surgical tool driven by the robot end-effector. The coordination between the human operator and the robot was designed so that the bone drilling can be performed more effectively than only imagenavigation scenario. The drill was able to be maintained on the target trajectory with reasonable accuracy within 2 mm although the human operator has deviated the surgical tool up to 5 cm. The compensation function to guide the drill back to the planned path was very useful to prevent the drill’s breakage when penetrating through the holes on the bone plate in bone drilling procedure.

Abstract. The depth gauge is used in many osteosynthesis surgeries to measure drilled bore depth for screw selection, and has significant limitations. Its use has been shown to contribute to placement of incorrectly sized screws, which can lead to adverse outcomes in patients.
We have developed an automatic depth gauge prototype which mounts on an existing surgical drill and makes use of an optical sensor. This builds off previous work in our lab which showed that drilled bore depth could be computed from continuous measurement of drill displacement relative to the bone. We tested our device in animal models and compared it with digital calipers as a gold standard. In a simple porcine model the prototype showed potentially superior performance (mean error 2.05mm, SD 0.67mm) compared with the conventional depth gauge (mean error 0.83 mm, SD 1.55 mm). However, this could not be reproduced in a more realistic porcine model.An automated depth gauge mounted on a conventional surgical drill shows potential as a replacement for the existing depth gauge, but the design needs to be refined for use in an operating room setting.

Abstract. The hip center (HC) in Computer Assisted Orthopedic Surgery (CAOS) can be determined either with anatomical (AA) or functional approaches (FA). AA is considered as the reference while FA compute the hip center of rotation (CoR). Four main FA can be used in CAOS: the Gammage, Halvorsen, pivot, and least-moving point (LMP) methods. The goal of this paper is to evaluate and compare with an in-vitro experiment (a) the four main FA for the HC determination, and (b) the impact on the HKA. The experiment has been performed on six cadavers. A CAOS software application has been developed for the acquisitions of (a) the hip rotation motion, (b) the anatomical HC, and (c) the HKA angle. Two studies have been defined allowing (a) the evaluation of the precision and the accuracy of the four FA with respect to the AA, and (b) the impact on the HKA angle. For the pivot, LMP, Gammage and Halvorsen methods respectively: (1) the maximum precision reach 14.2, 22.8, 111.4 and 132.5 mm; (2) the maximum accuracy reach 23.6, 40.7, 176.6 and 130.3 mm; (3) the maximum error of the frontal HKA is 2.5°, 3.7°, 12.7° and 13.3°; and (4) the maximum error of the sagittal HKA is 2.3°, 4.3°, 5.9°, 6.1°. The pivot method is the most precise and accurate approach for the HC localization and the HKA computation.

Abstract. Background: There are limited previous findings detailed biomechanical properties following implantation with mechanical and kinematic alignment method in robotic total knee arthroplasty (TKA) during walking. The purpose of this study was to compare clinical and radiological outcomes between two groups and gait analysis of kinematic, and kinetic parameters during walking to identify difference between two alignment method in robotic total knee arthroplasty.

Methods: Sixty patients were randomly assigned to undergo robotic-assisted TKA using either the mechanical (30 patients) or the kinematic (30 patients) alignment method. Clinical outcomes including varus and valgus laxities, ROM, HSS, KSS and WOMAC scores and radiological outcomes were evaluated. And ten age and gender matched patients of each group underwent gait analysis (Optic gait analysis system composed with 12 camera system and four force plate integrated) at minimum 5 years post-surgery. We evaluated parameters including knee varus moment and knee varus force, and find out the difference between two groups.

Results: The mean follow up duration of both group was 8.1 years (mechanical method) and 8.0 years (kinematic method). Clinical outcome between two groups showed no significant difference in ROM, HSS, WOMAC, KSS pain score at last follow up. Varus and valgus laxity assessments showed no significant inter-group difference. We could not find any significant difference in mechanical alignment of the lower limb and perioperative complicatoin. In gait analysis, no significant spatiotemporal, kinematic or kinetic parameter differences including knee varus moment (mechanical=0.33, kinematic=0.16 P>0.5) and knee varus force (mechanical=0.34, kinematic=0.37 P>0.5) were observed between mechanical and kinematic groups.

Conclusions: The results of this study show that mechanical and kinematic alignment method provide comparable clinical and radiological outcomes after robotic total knee arthroplasty in average 8 years follow-up. And no functional difference were found between two knee alignment methods durning walking.

Abstract. Total knee arthroplasty using navigation system is known to be more effective than conventional methods in achieving more accurate bone resection and neutral alignment.1 Mobile bearing is also known to reduce wear and automatically correct rotational malalignment of the tibia but the long-term follow-up results of more than 10 years are extremely rare.2, 3 The purpose of this study is to investigate the results of clinical and radiologic long-term follow-up and complications of total knee arthroplasty using navigation and multi-directional mobile bearing.
From 2003 to 2006, a total of 111 navigation TKAs using multi-directional mobile bearing design were carried out and reviewed retrospectively. TKAs were performed by two experienced surgeons at one institute. Of the 111 patients, 102 were women and 9 were men. The mean duration of follow-up was 11.4 ± 1.0 years (range, 10.1 to 14.08 years). Clinical outcomes were evaluated in terms of Knee Society Score, Hospital for Special Surgery score, Western Ontario and McMaster University (WOMAC) score, range of motion and complications. Long-term radiological outcomes and survival rates were evaluated at least 10 years.
Average preoperative HSS score was 66.5 ± 9.8 and KSS pain and function score were 25.0 ± 11.8 and 44.5 ± 12.3, respectively. Scores improved to 94.1 ± 8.2, 46.6 ± 11.6 and 88.2 ± 14.6 at the last follow up, respectively. Mean preoperative WOMAC scores of 75.8 ± 16.5 improved to 13.8 ± 16.0 at last follow-up. Five knees required re-operation, two for liner breakage, one for liner wear, one for distal femoral fracture and one for infection. The estimated 10-year prosthesis survival rates for any reason and for prosthesis-related problems were 95.5% and 97.4% , respectively.
TKAs using each techniques resulted in similar good clinical outcomes and postoperative leg alignments. Robotic and navigation TKA appeared to reduce the number of postoperative leg alignment outliers and revision rate compared to conventional TKA.

Abstract. The Difficulties to obtain acceptable pelvic reference points on bi- planar X-ray images for EOS measurements change as the patient’s pelvis rotated or inclined. The aim of this study was to clarify the effects of pelvic Z-axis rotation (rotation) and X-axis rotation (inclination) on the measurement values of SS, PT, and APP angle by using of EOS. Methods: We obtained anteroposterior and lateral X-ray images of a trunk phantom which was rotated and inclined in standing position by using of the EOS. Sacral slope (SS) and pelvic tilt (PT) as parameters to judge patient’s pelvic alignments by spinal surgeons, and anterior pelvic (APP) angle as a reference to decide patient’s pelvic alignments by hip surgeons were measured with the EOS software. The values of SS and PT and APP angle were compared in the phantom rotation and inclination. Results: PT showed small changes when the phantom was rotated, however, SS decreased and APP angle increased when the phantom was rotated. The values of SS and PT dispersed at 300 rotation among each inclination. APP angle dispersed at -15o and 30o of rotation among each inclination. Conclusion: Measurement variations of SS and PT were small amount under 15 degrees of rotation and inclination. On the contrary, APP angles showed greater variations when the phantom was rotated and inclined. Proper positioning of subjects, by reducing rotational effects, is important to get constant reproducible measurements, even if we use EOS system.

Abstract. Evaluation of the post-operative implant position is not straightforward given the significant scatter during magnetic resonance imaging (MRI) and computed tomography (CT). In the contrary, bi-planar post operative x-rays are standard of care. Using these bi-planar x-rays, the 3D implant can now be determined when combining these images with 3D implant files and pre-operative CT data. Using data from 20 patients, this paper compares the obtained implant positions to the positions obtained from post-operative CT scans. On average, the differences between both measurement techniques are below 1mm and 1degree for the translational and rotational degrees of freedom respectively. It is therefore concluded that using post-operative x-rays is an effective method to assess the implant position and alignment.

Abstract. In vitro evaluation of knee kinematics remains an essential part during pre-clinical testing of new implants and surgical procedures. To assess the kinematics, markers are rigidly attached to the bone segments and tracked using infrared cameras. Subsequently, the position of the markers relative to the bone is determined using computed tomography (CT). Although the accuracy of the aforementioned, CT-based method is not doubted, no real-time information is provided. Therefore, this paper presents a real-time method that uses a registration phase in combination with a pre-operative CT scan to determine the location of the bone relative to the markers. During this registration phase, the bone surface location is identified touching surface points with a tracked pen. The kinematic parameters obtained using this real-time method is compared to the golden standard, CT-based, method. Under optimal conditions, rotational and translational differences around 1mm and 1degree are obtained. This is in the range of the inter- and intra- observer variability in determining the landmarks used for these kinematic calculations. It is therefore concluded that the accuracy of the real-time method allows effectively evaluating the knee kinematics in six degrees of freedom.

Abstract. Correction osteotomy using conventional techniques may lead to under and over correction. The advantage of using patient specific templates for osteotomy is to predetermine the exact direction and degree of deformity before surgery and to estimate postoperative limb alignment which must mimic the physiologic loading to secure favorable clinical outcome.

Abstract. The increased use of pedicle screws in scoliosis creates a challenge for accurate and safe placement of
screw within the pedicle during the scoliosis surgery. Patient-specific templates (PST) is a novel
method to guide the surgeons for allocating and detecting the positions and trajectories of pedicle
screws in scoliosis surgery. Based on CT-scans and according to certain protocol, this technique will
allow the surgeon to construct a 3D model of spine and present the stage and vertebrae which contain
the most deformed bone. With preplanned surgery on specific software, we can develop an accurate
and safe position of pedicle screws and its trajectories. This method has the ability to customize the
placement and the size of each pedicle screw based on the unique morphology and landmarks of the
vertebrae.

Abstract. In the surgical treatment of Lisfranc injuries, percutaneous wire transfixation of the
tarsometatarsal complex can be challenging due to it’s small corridors and complex anatomy. A novel 2D projection-based software application detects Kirschner wires (K- wires) and automatically indicates their intended direction as a colored trajectory. The aim was to investigate whether the software facilitates K-wire placement in the Lisfranc joint for the inexperienced and the experienced surgeon.
In 20 cadaver foot specimens, 5 K-wires were retrogradely placed into the tarsometatarsal complex from D1-D5 by an experienced and an inexperienced surgeon, with and without using the application. The specimens were presented in pairs; surgeons and software use were equally randomized. Number of placement attempts, duration of procedure, fluoroscopy time, and number of individual fluoroscopy images were recorded.
Use of the software by the inexperienced surgeon significantly reduced the number of placement attempts from 14.2 to 8.8 (p=0.008). The application also reduced the number of fluoroscopy images from 44.8 to 40.8 (p=0.230). Duration of procedure and fluoroscopy time were not affected significantly. The experienced surgeon needed more placement attempts using the software (8.2 vs. 9.2; p=0.351). Duration of procedure, fluoroscopy time and number of fluoroscopy images increased while using the software, yet not significantly.
During percutaneous K-wire transfixation of the Lisfranc joint, the novel software is a useful tool for the inexperienced surgeon. In our chosen study setting, the experienced surgeon did not benefit from the software.
Due to its independency on fixed reference markers or registration processes, the software contributes to the procedures in orthopedic surgery.

Abstract. INTRODUCTION
The results of TKA revisions are less good than a primary TKA (1). The TKA revision frequency increases and we must prepare the next standard of these surgeries (4).The aim of this study was to evaluate the CAOS / one stage strategy to treat the knee PJIs (2, 3).
MATERIALS
In this prospective study, between September 2011 and december 2014, 41 patients treated for chronic knee PJI in a one stage revision. An imageless CAOS system (ExactechGPS, Blue-Ortho, Gieres) was used with a personnalized profile. All surgeries were performed with the same protocole and by using the same Optetrak CC knee components (Exactech, Gainesville, FL). All operations were performed by a single senior surgeon.
Indications for the revision TKA were (1) revision of a primary TKA or unicondylar knee arthroplasty (n=27) or (2) revision of revisionTKA (n=15).
The measurement of the HKA angle, the Oxford score and the ROM were evaluated pre and post-operatively.

RESULTS
27 males and 14 females with an average age of 71 years old (55-87) were treated for a PIJ (1 unicompartimental prosthesis, 26 TKA and 15 RTKA). The mean follow-up was 41 months (30 months - 6 years). The average time of surgery was 135 mn (120-195) for an average hospitalisation duration of 10 days (7-16). No postoperative outliers were reported (mean preop.: -1,6°+/_-5,1° - Post-op. -0,3°+/_ -1,4°). The average ROM were 115° (90-130°) (Fig. 1). The rate of success for the infection was 92,7%. We report no specific CAS complications and all the navigations were finalized. In this series of complex cases, the rate of infection healing is 92,7%.

DISCUSSION
Using CAOS is a safe option with no specific complication. Combined with one stage procedures, it should be a optimal medicoeconomical strategy for Knee revisions.

This first series initiated the « GPS RTKA » project to create a dedicated software evaluated since January 2016 with immediate very good functional results and no complications.
2002;(404): 7-13

Abstract. The individual pelvic sagittal inclination (PSI) is an issue for cup alignment in total hip arthroplasty (THA). The pelvic position in supine or functional pelvic plane in supine have been recommended by many reports while some consider a standing pelvic position as the reference to aim an optimal cup alignment. PSI changes in various postures and even in the same posture, aging change it due to spinal degeneration and muscle weakness. The chronological PSI change is larger in standing than that in supine. It is expected that PSI in standing position may improve when spinal long fusion was performed.
Therefore, the purpose of this study was to evaluate the change of PSI between pre- and post- corrective long fusion for adult spinal deformity (ASD). Total eight patients underwent corrective surgery for ASD between May 2014 and October 2016 were the subjects of this study. All are females with the average age of 70 years. There were two cases that underwent bilateral THA before spine surgery. The anterior pelvic plane (APP) through the most anterior aspect of the pubic tubercle and bilateral anterior superior iliac spines (ASISs) was used to measure PSI, which was defined as the angle between the APP and the vertical axis on the sagittal plane DRR. In addition, we measured the cup anteversion in two THA cases by using viewer software. The mean change in the preoperative PSI from supine to standing was 17° posteriorly. The mean change in the supine PSI from pre- to post-operation was 6.9° anteriorly, and that in the standing PSI was 17° anteriorly. The mean change in the postoperative PSI from supine to standing was 6.7° posteriorly. When we measured PSI on standard AP radiographs of the pelvis in two patients who underwent THA, the mean change in postoperative PSI from supine to standing was less than 3°.The mean change in cup anteversion on supine AP radiographs were 2.7°. As we expected, the change in PSI from supine to standing position was reduced by performing corrective surgery. In this study, the mean change of radiographic cup anteversion in supine after corrective long fusion was 2.7°and PSI in standing changed into the direction which reduce posterior impingement and anterior dislocation. Although the change in PSI after corrective spine surgery heavily depends on the spine surgeon’s philosophy of correction, corrective spine surgery should have a positive effect on cup alignment in standing and little influence on cup alignment in supine.

Abstract. In applications such as biomechanical simulations or implant planning, bone surfaces of the knee are most often reconstructed from computed tomography or magnetic resonance imaging data. Here, ultrasound (US) might serve as an alternative imaging modality. However, established methods cannot directly be transferred to US due to differences in imaging quality and underlying physics.

In this paper, we present a generalisation of the well-known active shape model search algorithm (ASM) that allows for segmenting various structures in US volume images that are too large to be captured with a single recording. The multi-view segmentation approach uses a-priori knowledge in the form of a statistical shape model (SSM) as is the case with the classical ASM. This allows to extrapolate missing information and to generate shapes that comply with the underlying distribution of some training data. The main differences are, however, that the SSM is not only adapted to a single image but to multiple images and that the adaption process is interleaved. As a result, within each iteration the surface information of all sub-volumes is propagated and used in all subsequent steps.

In-silico tests were conducted to investigate how this algorithm would perform in real tracked US data. US volume images were split in slightly overlapping sub-volumes, noise was added, and the alignment was distorted. We could show that the algorithm is capable of reconstructing shapes in the lower millimetre range and for some cases even with submillimetric accuracy. The algorithm is hardly affected by orientation errors below 5 degrees and displacement errors below 5 mm; above these limits, the average absolute SDE as well as its associated variance increases.

Abstract. Total knee replacement is the standard treatment for advanced knee osteoarthritis. An improved method of treating an osteochondral defect for knee osteoarthritis of dogs is provided, which is a composite tissue for treating or preventing a disease, disorder, or condition associated with an osteochondral defect with new technique. The new technique of custom made instruments and implants for dog and small animals is applied for different breeds of dogs regardless of their sizes and weights. The tool is a custom made instruments, which is based on capture of image based (CT or computed X-ray) to be transferred to electronic 3D model and apply 3D preoperative planning to design the tools are used to perform the knee surgery.

Abstract. Background
Osteo Fibrous Dysplasia (OFD) like adamantinoma is considered a benign condition that is usually located in the tibia. The condition is mainly found in children and has an association with classical adamantinoma, a malignancy of bone. The preferred treatment is surgical.
The lesion often requires a segment resection to eradicate the tumor as the margins of healthy bone are often too small to save continuity of bone and the lesion is located in the cortical area. Segmental resection in a young child is associated with a high complication rate.
To avoid these complications it would be ideal to spare the continuity of tibial bone by treating the tumor in situ. Radiofrequency Ablation (RFA) may be a safe and reliable option for treatment of OFD like adamantinoma, without vital tumor spill.
To ensure accurate ablation, the guidance and monitoring of antenna placement, planning and execution are performed with computer assisted surgery (CAS).

Results
Two young patients with OFD like adamantinoma of the tibia were treated with CAS guided open intra-operative RFA in our institution. Because of the heat generation and the proximity of the skin we performed the procedures half open. In both patients successful local tumor ablation was achieved without complications. At baseline MRI there was no sign of residual tumor activity in either patient.

Discussion
Follow-up is short and number of treated patients too low to draw definitive conclusions yet.
What we can say is that there is considerable less damage done to the patient if compared to classical open surgery like segmental resection or hemicortical resection.
Another great advantage is that it allows accurate local tumor ablation without tumor spill and it does not prohibit a local resection as a plan b if there still is viable local tumor tissue visible on MRI. It allows classical treatment in case of insufficient ablation.

Conclusion
Local tumor ablation with RFA has the potential to become a safe and effective treatment alternative in OFD like adamantinoma in a child.

Abstract. Robotic assisted fixation of sacral fractures – initial experience

Unstable sacral fractures are challenging for orthopaedic trauma surgeons. In most cases percutaneous fixation techniques are utilized after reduction. However, these techniuqes are not risk free mainly due to anatomical considerations. Screw misplacement is quite common and concerning. As spine surgery evolved, a miniature robotic guidance system was successfully utilized in pedicular screw insertion. The aim of the study was to demonstrate th use of the miniature robot in the fixation of unstable sacral fracutres.
Patients and Methods: 9 patients with unstable sacral fracutres without significant displacement were eligible for percutaneous fixation. These included 7 traumatic fractures and 2 pathological fractures. All fixation constructs were planned using a preoperative CT scans. The patients were placed prone and the robot was mounted on a Dynamic Reference Bridge (DRB) and a 2 verification fluoroscopic images were taken. The robot was mounted on the DRB and was sent by the computer to point to the desired screw(s) trajectory. The guide wires were inserted through stab wounds and screws were placed subsequently. CT scans were made postoperatively and fluoroscopic and operative time were recorded intraoperatively. Results: Mean patient age was 29 (17-63) number of screws ranged 1-6 (average 2). Mean operative time was 50 min (range 15-90), and average fluoroscopic time was 18 sec (7-42). None was the screw was misplaced. Conclusion: Robotic assisted fixation of sacral fracture is promising. At this time it is limited to nondisplaced fractures.