CAOS 2018: Papers with Abstracts

Abstract. Total knee arthroplasty (TKA) procedures have recognised differences in knee kinematics and kinetics from healthy knees. This study reports on the less documented knee kinematics and kinetics of uni-compartmental knee arthroplasty (UKA) patients during walking as a secondary outcome measure of a RCT between a fixed bearing UKA robotic procedure versus a mobile bearing UKA manual procedure.
Three dimensional, instrumented, gait analysis was performed 5 years after 49 medial osteoarthritis UKA patients received surgery. 27 were randomised to receive a robotic assisted UKA and 22 to receive a manual implant surgery.
The robotic assisted group showed a significant increased range of motion in stance during walking. 59% of the robotic assisted group achieved a bi-phasic sagittal knee moment, in comparison of 50% of the manual group. Significantly higher peak values of the varus knee and internal rotation moments were measured for the robotic assisted group during early and late section of the gait cycle, respectively. This indicates that larger normalised forces are applied through the knee during flat ground walking in the robotic assisted group.
The robotic assisted group showed biomechanical benefits over the manual group for walking tasks. Poor fixation outcomes are avoided in patients with normal knee moments.

Abstract. Vibroarthrography describes the detection of joint pathologies by analysis of vibrations emitted during joint movement. In our study, 30 healthy volunteers and 39 patients with various degrees of chondromalacia or osteoarthritis were selected and accelerometers and piezoelectric sensors were placed on prominent bone structures of patients’ knee joints (patella, lateral and medial tibial plateau) in order to measure the structure-borne noise during active extension and flexion of the joint. After semi-automatic signal segmentation had been applied to isolate flexion and extension cycles, features based on relative high-frequency components were generated. Using machine learning with a linear support vector machine, these signals were classified as healthy, exhibiting chondromalacia °II-IV or osteoarthritis. 84% of healthy subjects were identified correctly, while the classification accuracy for individual stages of chondromalacia or osteoarthritis ranged from 11% (CM °II) to 50% (CM °III). In order to make results easily interpretable without resorting to machine learning techniques, we propose a normalized score between 0 and 1 and show that this "v-score" for flexion and extension significantly correlates with the achieved multi-class classification. Vibroarthrography may qualify as potent screening tool for the detection and grading of joint cartilage defects and aid physicians in the choice and estimation of urgency of further diagnostic and therapeutic decisions.

Abstract. This study investigated if CAOS TKA cases complicated by challenging patient conditions would negatively impact the perioperative outcomes of surgery. Early outcome data on 51 TKA’s from a multicenter, consecutive series were analyzed. The patients were separated into challenging and standard case groups according to the criteria of age, BMI, and severity of deformity. The two groups did not exhibit significant differences in any of the early outcomes. Our study demonstrates consistent early results using CAOS TKA irrespective of patient conditions.

Abstract. This study employed an advanced method (CUSUM) to analyze the learning curve regarding surgical efficiency (time) in 10 surgeons from different experience levels upon their adoption of a contemporary CAOS TKA system. The first 50 CAOS TKA cases of each surgeon were analyzed to identify the case number when their learning process was stabilized (cases of proficiency). The surgical time increase during the learning phase were compared between senior and novice surgeons. The data demonstrated a short learning duration (12-13 cases) and a moderate learning process (~15min time increase compared to later cases) upon adoption of the CAOS system, without high sensitivity to surgeon’s experience level.

Abstract. This observational study on fifty-six patients presents the coronal knee angular laxity measured during computer-assisted total knee arthroplasty. Varus/valgus knee laxity was assessed at extension, mid-flexion, and high flexion, and compared between arthritic knees and knees following trial TKA implantation. The data represented soft tissue laxity under surgical reality and may be used to further understand the clinical implications of intraoperative soft-tissue management. The findings highlight the potential for CAOS to accurately manage soft tissue balance in addition to bony cuts and overall alignment.

Abstract. This study investigated if CAOS TKA cases in higher risk patients would impact the perioperative outcomes of surgery. Intraoperative and recovery/discharge data on 70 patients (72 knees) from a multicenter, consecutive series were analyzed. The patients were grouped into challenging and standard case groups according to the criteria of age, BMI, and degree of deformity. Despite a general trend observed between the challenging and standard cases, the two groups did not exhibit significant differences in terms of surgical time, blood loss, recovery and time to discharge. The data demonstrated consistent perioperative results by CAOS TKA irrespective of patient conditions.

Abstract. This study investigated the accuracy of a novel CAOS enhanced mechanical instrument system for TKA, and its sensitivity to surgeon’s experience level. Resection errors in varus/valgus alignment were assessed across senior, fellow, and resident surgeon groups, and compared between CAOS guided resections and resections performed with conventional instruments. The findings demonstrated that regardless of surgeon experience level, the CAOS enhanced mechanical instrumentation significantly reduced alignment errors compared to conventional instrumentation, along with substantial increases in the prevalence of optimal resections.

Abstract. This study employed an advanced method (Cumulative sum control chart, CUSUM) to analyze the learning curve regarding surgical efficiency (time) in four surgeons from different experience levels upon their adoption of a mechanical instrument enhanced by computer-assisted orthopaedic surgery (CAOS). The first six CAOS-TKA cases of each surgeon were analyzed to identify the case number when their learning process was stabilized (cases to proficiency). The surgical time increase during the learning phase were compared between senior and fellow surgeons. The data demonstrated a short learning duration (2-3 cases) both senior and fellow surgeons and a mild impact from learning compared to cases performed using conventional instrument system.

Abstract. This study investigated the accuracy and reliability of using full-length lower limb radiographs to measure alignment outcomes of computer-assisted total knee arthroplasty. Simulated radiographs were created from cadaveric whole leg CT scans. Three analysts performed repeated measurement of the hip-knee-ankle (HKA) angle, blinded to the ID of the subject and image repetition. In addition, simulated radiographs with internal- /external- limb rotation were measured to assess sensitivity of the measurements. The result demonstrated high accuracy and reliability of the measurement, with low sensitivity to limb rotation. The findings supported the use of full-length lower limb radiographs to measure clinical outcomes in HKA.

Abstract. The orientation of the cup in Total Hip Arthroplasty plays a major role on the post- operative results. It has been considered for several decades that the cup should be oriented according to the safe zone defined by Lewinnek. However, this safe zone is not always suitable because of the inter-individual variability of the pelvic tilt during daily activities. We propose in this paper a non-invasive ultrasound based solution which can easily measure this patient specific parameter in order to thereafter otimise the cup orientation. The accuracy of this system was assessed with a specific pelvic phantom. A clinical pilot study was also performed on ten patients. The pelvic tilt was measured in three daily positions: the supine, sitting and standing positions. The average error was 1.15°±0.82°. The average pelvic tilt was -97.1°±28.6°, -46.3°±12.8° and -9.0°±8.3° for respectively the supine, the sitting and the standing positions. The high inter-individual variability of the pelvic tilt in different daily positions highlight the need to have a suitable device for the measurement of this patient specific parameter for THA. The proposed system is easy-to-use, portable and allows the pelvic tilt measurement in different positions without any additional x-ray radiation.

Abstract. INTRODUCTION
Bone tumor surgery can be more accurate under the computer assisted navigation. The researches have shown the benefit of margin control in pelvic, joint sparing surgery. The traditional method for bone cutting in limb salvage was by free hand. There was no literature focused on the comparison of cutting accuracy in bone tumors around the knee joint. The aim of this study was to compare the accuracy for bony resection under navigation and by free hand in limb salvage surgery around the knee.

MATERIALS AND METHODS
Thirty-nine cases of bone tumors around the knee joint were resected under navigation (Stryker System) in our department from 2008 Sep to 2017 Nov. All the cases were performed intercalary resection in femur or tibia. The initial aim to use navigation was to make the resection more close to the pre-operative planning. The pre-operative planning was performed with the software OrthoMap at the working station (Stryker Company). The CT and MRI imaging were input to the system. We used intraoperative navigation (Iso-C based) to find the cutting plane and use the jig saw to cut the bone. The post-operative specimen was used for verification and compared with the pre-operative plan. The length difference was defined as specimen length minus planning resection length. The control group included 117 cases of tumors around the knee performed limb salvage surgery when bony cutting was achieved by free hand. This was a non-randomized control study. The method to find the cutting plane was by measuring the length from the joint line to the planned plane by ruler. The length of post-operative specimen by free hand was compared with the surgical plan. The length difference was detected in this control group. Then the differences in two groups were compared and analyzed.

RESULTS
The resection lengths in navigation group ranged from 85-282mm and in the free hand group the length ranged from 90-330mm. The length difference between post-operative verification and pre-operative plan was detected. In the navigation group, the length difference was 0.5±2.5mm (range ,-5～5mm), while in the free hand group the length difference was 3.4±9.6mm (range ,-20～29mm), P<0.01. For the absolute value differences analysis, the difference was 2.0±1.6mm and 8.3±6.0mm for navigation and free hand group respectively, P<0.01.

DISCUSSION
Our study shows that bone cutting with navigation can be more accurate than freehand cutting. The average length difference was 2.0mm (95% CI, 0.4 to 3.6mm) when compared to average 8.3mm (95% CI, 2.3 to 14.3mm). The accuracy with navigation is similar to the previous researches. Our comparison with free hand group gives the data how accurate the navigation can help surgeon to achieve. The result indicates that computer assisted navigation can make a role in limb salvage surgery if the precise resection is required.

Abstract. Pedicle screw fixation is a common yet technically demanding procedure. Due to the proximity of the inserted implant to the spinal column, a malplaced screw can cause neurological injury and subsequent postoperative complications. A common surgical routine starts with preoperative volumetric image acquisition (e.g. computed tomography) based on which the surgeons can highlight the planned trajectory. This process is generally done manually , which is error prone and time consuming.
The primary purpose of this paper is to develop an automatic pedicle region localization based on preoperative CTs. This system can automatically annotate the CT scans to identify the regions corresponding to the pedicles and thus provide important information about the anatomical placement of the CT scan that can be useful for intraoperative implant position assessment (e.g. to initialize the 2D-3D registration). On the other hand, the pedicle localization can be exploited for preoperative planning.
We designed and evaluated a fully convolutional neural network for the task of pedicle localization. A large training, validation and testing datasets (5000, 1000, 1000 images separately) were created using a custom data augmentation process that could generate unique vertebral morphologies for each image. After evaluation on the validation and test data, the Dice similarity coefficients between the pedicle regions detected by the trained network and the ground truth was 0.85 and 0.83 respectively.
The proposed deep-learning-based algorithm was capable of automatically localizing the regions corresponding to the pedicles based on the preoperative CT scans. Therefore, a reliable initial guess for the 2D-3D registration process needed for intraoperative implant position assessment can be achieved. This system also has potential use in automating the preoperative planning.

Abstract. Internal fixation in upper cervical spine (C1 and C2) is a big challenge. There is a large anatomical variation, and the upper cervical region is adjacent to important organs such as spinal cords, oblongata, vertebral artery, nerve roots and other important structures, misplacement of internal fixation might lead not only to an instability of the screws, but also to neurological, vascular, and visceral injuries.
TianJi Robot was used in this study to compare the internal fixation safety and accuracy between using the navigation based robotic system and free-hand. In this randomized controlled study 51 patients were involved.
129 screws were smoothly implanted without intraoperative complications. In the robot-assisted surgery group, the analysis of the screw showed that 58 of 59 screws (98.3%) were safely placed (<2 mm), and the mean deviation between the planned trajectory and the actual path is 1.14 +/- 0.09mm. In the free-hand fluoroscopy-guided surgery and navigation assisted surgery group, assessment of screw accuracy showed that 66 of 70 screws (94.3%) were safely placed (<2 mm), and the mean deviation between the planned trajectory and the actual path is 1.48 +/- 0.14mm. There was no statistical difference in Gertzbein-Robbins classification distribution between these two groups (P value = 0.551), however, the discrepancies between the actual path and planned trajectory in this two groups have statistical difference (P value = 0.047).
The TianJi Robot has demonstrated its safety and accuracy in upper cervical spinal surgery upon free-hand technic and the navigation technic, which will have expanded applications in spinal surgery.

Abstract. Objective: To evaluate the efficacy of intraoperative three-dimensional (3D) Iso-C C-arm- navigated percutaneous radiofrequency ablation (RFA) of osteoid osteomas.
Methods: 35 patients (20 males and 15 females) with osteoid osteomas underwent treatment with intraoperative 3D Iso-C C-arm navigation-guided RFA. The tumour was first biopsied for pathological examination, the core needle was removed and the RFA needle was inserted into the nidus. Post-operative X-rays and CT scans were performed to evaluate the degree of ablation and to assess for recurrence at 3-month follow-up. Patients also completed a visual analogue scale (VAS) both pre-operatively and 3 days post-operatively to subjectively assess pain.
Results: Pathological diagnosis confirmed osteoid osteoma in 19 cases. The other 16 cases were not pathologicallydiagnosed owing to inadequate biopsy specimens. In all cases, localized pain was immediately relieved following RFA. Patients reported significantly decreased pain, with mean pre- operative VAS scores of 3.4 reducing to 0.80 at 3 days post-operatively and further to 0.06 at 3-month follow-up (p ,0.05). The mean follow-up time was 15.5 months (range: 3–38 months).
Conclusion: 3D Iso-C C-arm navigation-guided RFA is a safe and effective option for the treatment of osteoid osteomas and may be considered in place of intra-operative CT-guided and open resection.
Advances in knowledge: C-arm image-guided percutaneous RFA mitigates the need for pre- operative CT as well as intraoperative scintigraphy, provides real-time imaging of the anatomy, facilitates accurate resection of the tumour and enables immediate confirmation of excision.

Abstract. From December 2010 to May 2016, 8 patients with periacetabular tumor (chondrosarcoma 5 cases and GCT 3 cases) were treated by accurate en-bloc resection and precise reconstruction with a novel 3D printing individualized prosthesis.One case suffered dislocation of hip joint and two cases presented deep venous thrombosis. The mean follow-up period was 37.5 months (range, 5-70 months). 6 patients survived free of disease. One patient was subject to local recurrence after one year. One patient died from distal metastasis after three years. No infection, prosthesis loosening and breakage occurred. The MSTS score was 18~27. Our study suggest 3D printing implants might be a promising approach for precision reconstruction and long-term stability.

Abstract. Objective: Midline lumbar fusion with cortical bone trajectory(CBT) screw is a novel technique operation, robot system is the new developed system which can help CBT insertion. In this retrospective study, we compare the CBT accuracy by the assistance of navigation system and robot system. Clinical result is also compared.
Result: 55 patients were involved in this retrospective study, 29 patients are assisted by navigation system, 26 patients are by robot system. Mean follow-up is over 12 months. The mean VAS is significant improved at the final follow up for navigation group from 6.2±1.5 to 3.2±1.1(back pain), 7.5±0.9 to1.8±0.7(leg pain), same as the robot system from 6.8±1.5 to 2.9±0.8(back pain), 7.7±1.0 to 1.6±0.8 (leg pain). The JOA score pre-operation is 14.7±4.5 and 14.5±4.1 for navigation and robot system, at the final follow up, it is 24.3±4.2 and 23.9±4.4. the number of penetration cortex has no difference between 2 groups(n=0.363).
Conclusion: MIDLF with CBT screw is effective for the treatment of lumbar degenerative disease. Using navigation and robot system will help the insertion of CBT screw safety and accurate, robot can release the surgeon from part of aiming work.

Abstract. Both, prosthetic design and implantation have a great influence on the impingement and dislocation risk after total hip arthroplasty (THA). Potential impingement risks should be analyzed during THA planning. In order to analyze bony impingement, often 3D meshes of the bony structures have to be transformed and collision between the 3D meshes is calculated which might be complex and time consuming. This work introduces a simplified collision calculation algorithm based on 2D mapping. Possible impingement points on the femur and the pelvis, which are points on a sphere, are extracted and mapped into a 2D plane. Impingement can be calculated using a 2D distance map.
The method was applied for analysing a dislocation case. A 38-year-old female THA patient had a dislocation 3 months after the surgery. The hip dislocated anteriorly in the standing positon while carrying a load in the front (a child) and turning the upper body slightly towards the contralateral side. The cup orientation was within the so called Lewinnek safe zone. The pelvis in standing position was tilted by 11° posteriorly. The impingement analysis revealed that maximal external hip rotation was less than 15° and even less than 10° when the pelvis is tilted more posteriorly which might have been the case during the dislocation. Considering additional soft-tissue involvement, a minor external rotation could in fact be a potential cause for dislocation.
Using the previously introduced prosthetic ROM-based target zone calculation algorithm, optimized THA parameters were determined. This include changing the CCD angle and the stem or neck antetorsion. Using the modified parameters, external rotation of at least 20° would have been possible without bony impingement. The dislocation could have been avoided.

Abstract. In order to measure anatomic parameters of proximal femur, an automatic femoral measurer, which allows importing the femur models and automatically modeling femoral medullary canal, is developed. The accuracy and reliability are verified according to the intra- and inter-class correlation coefficients and the measured result of standard model.

Abstract. The bone fragment and fracture lines may not clear enough to be visualized after bone reduction and may be hidden behind other bones. A 3D printing technology can be used to deal with this drawbacks. A series of algorithms were developed to ensure that two adjacent bone fragments fabricated can be assembled successfully. In this study, we developed a bone reduction algorithm, and a mesh-overlapping detection and removal algorithm to ensure that two 3D-printed fragments are easily assembled and disassembled. In addition, we also developed a method to detect and extract fracture boundary from two adjacent fragments, and then apply a multi-color 3D printing technology to fabricate the assembled bone fragments. The advantage of the proposed method is that we can show the status of 3D-printed bone fragments before and after bone reduction, with fracture lines printed in different color.

Abstract. Advances in augmented-reality (AR) technologies have seen their increased adoption in robotic-assisted procedures in a surgical environment, as they provide both cognitive benefits through improved information management, as well as potential reductions in operating times with the removal of manually operated physical displays. A crucial component of successfully transferring AR-based technologies from a research environment into operating theatres is a robust back-end communication system capable of rapidly communicating information between surgical robots and head-mounted displays.
A system capable of carrying out this task was constructed by coding a server program written in C#, which communicated via WiFi with a HoloLens™ (Windows, USA) app coded in C# deployed via Unity (Unity Technologies, USA). The system architecture utilised User-Datagram Protocol to take raw input data, format it into packets, and then wirelessly transmit it to the HoloLens™. The constructed system was tested against a benchmark frequency (>10Hz) to examine its suitability in a real-time application.
Data varying in size from from 0.128 KB - 4.69 MB was successfully transmitted above the real-time benchmark, with the lowest recorded frame-rate registering at 14.13Hz, indicating that the system shows promise in transmitting surgical navigation workflow information and coordination-transformation data in a surgical environment. Future work on the system will aim to further streamline the communication architecture in order to smoothly integrate any additional hardware into the communication network whilst maintaining a low communication-latency, with an overarching aim of progressing towards a more mixed-reality experience in a surgical environment.

Abstract. We present a method to address the challenging problem of automatic segmentation of lumbar vertebrae from CT images acquired with varying fields of view. Our method is based on cascaded 3D Fully Convolutional Networks (FCNs) consisting of a localization FCN and a segmentation FCN. More specifically, in the first step we train a regression 3D FCN (we call it “LocalizationNet”) to find the bounding box of the lumbar region. After that, a 3D U-net like FCN (we call it “SegmentationNet”) is then developed, which after training, can perform a pixel-wise multi-class segmentation to map a cropped lumber region volumetric data to its volume-wise labels. Evaluated on publicly available datasets, our method achieved an average Dice coefficient of 95.77 ± 0.81% and an average symmetric surface distance of 0.37 ± 0.06 mm.

Abstract. Bi-cruciate retaining knee implants are anatomically designed for use in early surgical intervention, for patients with less severe arthritic disease. Patient satisfaction after total knee replacement is directly related to knee stability and proprioception, particularly for high-demand, active patients. While preservation of all intact and healthy ligaments may be the key to achieving such results of satisfaction, balancing four ligaments in a bi-cruciate procedure is more technically challenging then a conventional total knee replacement. Robotics-assisted arthroplasty has been gaining popularity as a tool to increase accuracy and precision of implant positioning. Robotics-assisted systems can provide surgeons with virtual tools to make informed decisions for knee replacement, specific to the needs of the patient. Here, we are introducing a semiautonomous handheld robotic system support for a bi-cruciate retaining knee implant design. The system supports image-free anatomic data collection and streamlined intraoperative surgical planning with dynamic gap balancing before any bone preparation. In this study, we evaluate the surgical technique and accuracy of implant placement in synthetic bone and cadaver experiments.

Abstract. The survival rate of navigation-assisted total knee arthroplasty when mechanical revision was considered as the end-point was 98% after 10 years and 96% after 15 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 survival rate of navigation-assisted mobile bearing total knee arthroplasty after 13 years when mechanical revision was considered as the end-point was significantly improved when compared to conventionally implanted mobile bearing total knee arthroplasty. Longer follow-up is required to prove superiority of any technique.

Abstract. The survival rate of navigation-assisted total knee arthroplasty was superior to conventionally implanted after 12 years for knees with initial severe coronal deformation when mechanical revision was considered as the end-point. Longer follow- up is required to prove superiority of any technique.

Abstract. Alignment of the bones in standing position provides useful information in surgical planning. In total hip arthroplasty (THA), pelvic sagittal inclination (PSI) angle in the standing position is an important factor in planning of cup alignment [1] and has been estimated mainly from radiographs. Previous methods for PSI estimation [2], [3] used a patient-specific CT to create digitally reconstructed radiographs (DRRs) and compare them with the radiograph to estimate relative position between the pelvis and the x-ray detector. In this study, we developed a method that estimates PSI angle from a single anteroposterior radiograph using two convolutional neural networks (CNNs) without requiring the patient-specific CT, which reduces radiation exposure of the patient and opens up the possibility of application in a larger number of hospitals where CT is not acquired in a routine protocol.

Abstract. Objective The second sacral segment iliosacral screw (S2 screw) insertion is a demanding technique, with a high rate of screw malposition due to the complex pelvic anatomy. TiRobot™ is an orthopedic surgery robot which can be used for S2 screw fixation. We carried out a retrospective analysis of the accuracy of S2 screws using robot-assisted navigation.
Methods A retrospective analysis of 16 patients admitted and managed by S2 screw fixation for unstable pelvic fractures was carried out for evaluation of its efficacy and safety. all patients with pelvic ring disruptions and sacral dysmorphism were evaluated radiographically and S2 screws were placed using a robot-assisted navigation technique. Screw position was assessed and classified using postoperative computed tomography. Fisher’s exact probabilities test was used to analyse the screws’ positions. Surgical time after reduction of the pelvis, insertion time for guide wire, number of guide wire attempts, and radiation exposure without pelvic reduction were also assessed.
Results The excellent and good rate of screw placement was 100%. The fluoroscopy time after pelvic reduction was 7 (7, 9) seconds. The operation time after reduction of the pelvis was 29 (27,33). Time for guide wire insertion was 2.0 (2, 2) minutes. The number of guide wire attempts was 0.0 (0, 0). No postoperative complications or revisions were reported.
Conclusion S2 iliosacral screws can be safely and accurately accomplished using a robot-assisted navigation technique in patients with unstable posterior pelvic ring disruptions and sacral dysmorphism.

Abstract. Use of computer-assisted Total Knee Arthroplasty systems enable more accurate implant placement, better tissue balancing and improved leg alignment. Image-free computer-assisted TKA systems rely on accurate identification of femoral and tibial landmarks to guide the implant planning process. Previously, researchers have studies the variability in collection of these landmark positions and the impact of this variability on the final implant position. Here, for the first time, we present a study assessing the variability of seven landmarks during anonymized clinical cases. Of all the landmarks, we found that there was maximum variability in collection of the femoral anterior notch point.

Abstract. This paper describes novel methods of auto-calibration and auto-registration of 3D imaging and navigation, implemented in a fully integrated device made of a motorized C-arm and a navigation system. Preliminary results are presented. Benefits in terms of saved time, increased accuracy, reasonable x-ray dose, and surgeon satisfaction are reported.

Abstract. Low back pain is one of the most common reasons for outpatient service. It is associated with high costs, and can cause loss of labor and the indirect economic. In Europe and the United States, lower back pain has the corresponding guideline for diagnosis and treatment. But, the hierarchical medical system and process of China is not established at present, and there is lack of guidelines. So, a large number of patients with low back pain have outpatient service in the superior hospital, and it caused a conflict between the increasing demand for outpatient visits and limited medical resources and wasted a lot of public health resources. So, we want to apply the artificial intelligence on the diagnosis of low back pain to help doctor diagnosis and reduce the burden of clinic work.

Abstract. Computer Aided Surgery (CAS) is helpful, but it clutters an already overcrowded operating theatre, and tends to disrupt the workflow of conventional surgery. In order to provide seamless computer assistance with improved immersion and a more natural surgical workflow, we propose an augmented-reality based navigation system for CAS. Here, we choose to focus on the proximal femoral anatomy, which we register to a plan by processing depth information of the surgical site captured by a commercial depth camera. Intra-operative three-dimensional surgical guidance is then provided to the surgeon through a commercial augmented reality headset, to drill a pilot hole in the femoral head, so that the user can perform the operation without additional physical guides. The user can interact intuitively with the system by simple gestures and voice commands, resulting in a more natural workflow. To assess the surgical accuracy of the proposed setup, 30 experiments of pilot hole drilling were performed on femur phantoms. The position and the orientation of the drilled guide holes were measured and compared with the preoperative plan, and the mean errors were within 2mm and 2°, results which are in line with commercial computer assisted orthopedic systems today.

Abstract. Pelvic rotation during cup impaction causes excessive cup anteversion should be considered in direct anterior approach or anterior lateral approach total hip arthroplasty (THA) with supine position. There are two intraoperative support mechanical devices for THAs in supine position, one is based on functional pelvic plane (FPP) and the other is based on anatomical pelvic plane (APP). The purpose of this study was to compare the accuracy of two mechanical devices based on FPP or APP in THA with supine position.
The subjects of this study were 90 hips of 80 patients who underwent DAA-THA in a supine position using HipPointer® based on FPP (Pointer group). The other subjects of this study were 29 hips of 27 patients using HipCOMPASS® (Lexi, Tokyo) based on APP (COMPASS group). There are no significant differences in age, gender and BMI between the two groups.
Cup inclination and anteversion angle in Pointer group and COMPASS group were 40.2° (33-48°), 40.7° (33-47°), and 16.5° (9-26°), 17.5° (10-27°), respectively. There are no significant differences in cup inclination and anteversion angle between Pointer group and COMPASS group. Nor were there any significant differences in the absolute value errors for cup inclination and anteversion angle (inclination angle; 2.5°±2.1 vs 2.4° ±2.0、P=0.45) (Anteversion; 2.7°±2.4 vs 3.0°±2.0、P=0.23).
New developed mechanical navigation device based on intraoperative FPP by correction of axially rotated pelvis to surgical bed plane in the DAA-THA is an simple and useful device which accuracy of cup alignment didn’t show significant differences compared with the device based on intraoperative APP with reference of pubic symphysis.

Abstract. Background Some malignant pelvic tumor may affect the anterior or posterior column at the acetabula area. The postoperative recurrenceand complication rate are high. Precise resection with safe surgical margin could cure the patients while saving healthier host bone for relative simple reconstruction.
Questions/Purposes The purpose of this study is to evaluate the effect of precise single column resection and reconstruction with femoral head plus THR for malignant pelvic tumorswith respect to the (1) surgical safety, (2) oncological outcome and (3) prosthesis survivorship and function.
Methods This is a clinical cases study. From 2007 to 2015, 19 patients with primary malignant tumors of the pelvis were enrolled in the study. The diagnosis included 16 cases of chondrosarcoma, 1 case of undifferentiated polymorphic sarcoma, 1 case of Ewing's sarcoma and 1 case of solitary plasmacytoma. All tumors were resected with safe surgical margins, which were proved by the postoperative specimen evaluation. Anterior column was involved in 17 cases and posterior column in 2 cases. Ten of 19 tumors were resected assisted by computer navigation. Femoral heads were used to reconstruct anterior or posterior column defects and fixed by screws; THR was used for the joint reconstruction. Oncologic outcome and function were evaluated by regular follow-up.
Results The follow up time was more than 12 months in 14 cases with the average of 58.4 months (median 61, range 13-118) months. Surgical margins contained wide resection in 12 cases and marginal resection in 7 cases. The bony wide resection rate was 90% (9/10) in the navigation group and 77.8% (7/9) in free hand group respectively. One patient with Ewing's sarcoma died 14 months postoperative due to lung metastasis. There was only one case with chondrosarcoma was found recurrence in 61 months postoperatively, who was in the navigation group and having marginal margin resection. There was one prosthesis removed due to prosthesis infection (14 months postoperatively). There were another two patients with minor wound infection. The average MSTS function score was 24.8 (17-29).
Conclusions The current treatment method is oncological safe and functional with less complications. The hardware is relatively cost effective and right on the shelf. However, this procedure is highly skill needed.

Abstract. Accurately detecting and diagnosing developmental dysplasia of the hip (DDH), a common hip instability condition among infants, requires ultrasound (US) image data that captures the relevant anatomical structures. Our group has recently introduced a technique for automatically processing 3D US scans of the neonatal hip that significantly reduces dysplasia metric measurement variability, but it can be challenging for a clinician to know at the time of acquisition if they have acquired a volume suitable for analysis. We have previously introduced a single-slice-based approach for assessing adequacy of acquired volumes that worked reasonably well, but we believe that more explicitly three-dimensional approaches would be more robust and reliable. Here, we propose a new technique based on a convolutional neural network (CNN) architecture that incorporates inter-slice information and transfer learning. Our classifier labels volumes as adequate or inadequate for subsequent interpretation based on detecting the presence of key hip anatomical structures needed for DDH diagnosis. We validate our approach on 40 datasets from 15 pediatric patients and demonstrate a slice classification rate of 93% (improving on our previous implementation by 3%) with average processing time of 2 seconds per US volume. We expect automatic US scan adequacy assessment to have significant clinical impact with the potential to help in imaging standardization, improving efficiency of measuring DDH metrics, and improving accuracy of clinical decision making.

Abstract. Recent advances have made robotic assistance a viable option in total hip arthroplasty (THA). However, the clinical outcomes of this procedure relative to THA without robotic assistance have yet to be reported. This study presents short-term outcomes of robotically assisted THA compared to a pair-matched control group of patients that underwent THA without robotic assistance.
Data were prospectively collected on all THAs performed from July 2011 to January 2015. Patients were included if they underwent primary THA treating idiopathic osteoarthritis and were eligible for minimum two-year follow-up. Outcomes were measured using Harris Hip Score (HHS), the Forgotten Joint Score (FJS-12), pain on a visual analog scale (VAS), and satisfaction from 0-10. Patients that underwent THA with robotic assistance were matched 1:1 with THA patients without robotic assistance for age, sex, BMI, and approach.
There were 85 patients in each study group. There were no significant differences in the demographic factors matched for. Both HHS and FJS-12 were significantly higher in the robotic assistance group at minimum two-year follow-up. VAS was lower in the robotic assistance group, but this was not statistically significant (p = 0.12). There was a not a significant difference in patient satisfaction. There was no significant difference in the rate of postoperative complications or subsequent revisions between groups.
Robotically assisted THA is safe and may lead to superior short-term outcomes compared to THA without robotic assistance.

Abstract. Glenoid implant position and scapula shape affect the impingement-free range-of-motion (ROM) of a patient's glenohumeral joint. Currently, methods to evaluate the impingement-free ROM during preoperative planning do not result in one overall score, which is required for an objective optimization of the implant position. Therefore, our study aims to quantify the impingement-free ROM so that surgeons can easily compare the result for various implant positions.
250 virtual shapes from a healthy scapula statistical shape model (SSM) were virtually implanted with a reverse glenoid implant in diverse positions. The impingement-free ROM was visualised on a 2D polar plot and quantified based on healthy kinematic motion data.
ROM scores for a neutral implant position resulted in a mean value of 0.84 +/- 0.06. A lateral, inferior and posterior implant position and a negative shape coefficient in the first SSM mode improved the mean ROM score. The impact of implant position and scapula shape was also visible in the 2D polar plots.
Hence, the defined ROM score was sensitive to implant position and scapula shape. A lateral, inferior and posterior implant position resulted in a better ROM, which agrees with many studies in literature. We conclude that the ROM score proposed in this study agrees well with what has been published in literature and is therefore considered as a suitable candidate to objectively evaluate and improve an implant plan during preoperative planning.

Abstract. In order to reduce the total amount of radiation exposure and provide real-time guidance ultrasound has been incorporated as a potential intra-operative imaging modality into various orthopedic procedures. However, high levels of noise, various imaging artifacts, and bone boundaries appearing several millimeters in thickness hinder the success of ultrasound as an alternative imaging modality in assisting orthopedic surgery procedures. Additional difficulties are also encountered during manual operation of the ultrasound transducer during image acquisition. In this work, we proposed a combination of novel scan plane identification method, based on convolutional neural networks, and bone surface localization method. The bone surface localization approach utilizes both local phase information, a combination of three different local image phase information and signal transmission map obtained from an L1 norm based contextual regularization method. The proposed network was utilized on two different US systems and to identify five different scan planes. Validation was performed on scans obtained from 16 volunteers. The correct scan plane identification rate of over 93% has been obtained. Validation against expert segmentation achieved a mean vertebra surface localization error of 0.42 mm.

Abstract. Many infants are born with unstable hips which can cause severe mobility issues as they grow older. This condition is known as developmental dysplasia of the hip (DDH), and although it is the most common hip disorder in infants, its diagnosis using 2D ultrasound (US) is prone to significant variability. This paper presents methods to reliably and automatically diagnose DDH in infants using 3D US. Based on 40 infant hip examinations, we demonstrate a 70% reduction in variability of 3D US-based measurements compared to those of standard 2D US-based measurements.

Abstract. There is currently a lack of a 'Gold Standard' for quantification and modelling of the Pivot Shift test (PST) in anterior cruciate ligament (ACL) deficient knees. A sudden change in state resulting from a small change in a parameter is characteristic of systems that can be modelled using catastrophe theory. Analysis of data obtained from 50 consecutive navigated ACL reconstructions demonstrated statistically significant (p < 0.01) fitting with a cusp type model of catastrophic failure. Modelling the PST as a Cusp catastrophe may enable true evidence based decisions as to which ACL deficient knees should have surgery and guide the decisions as to the optimum type of surgery required. It may also influence the position of the reconstructed ligaments and allow objective comparisons of different ligament types and surgical techniques.

Abstract. Although exercises improve the outcome of patients with osteoarthritis, patient compliance is poor. Behaviour modification and measuring compliance remain the Holy Grail of healthcare professionals. The responses of a focus group of 20 volunteers to a novel automatic compliance recording augmented reality exercise app were studied. Full compliance was achieved in all cases and was measured and recorded by the app. Overall, the app itself received favorable responses regarding the user interface and user experience.

Abstract. Malunions of the distal radius are often treated with correction osteotomies, which can be challenging to perform.
In this report, 23 patients with symptomatic distal radius malunions were treated using 3D printed patient-specific surgical guides to facilitate surgery. Patients were compared with a control group of 23 patients that underwent similar surgery with a conventional x-ray planning approach.
Postoperatively all patients in the computer-assisted group showed recovery of ROM, with no anatomical abnormalities on x-ray examination. 6 patients in the conventional planning group had reduced ROM with a residual volar tilt on x-ray images.
Computer-assisted planning with the use of 3D printed patient-specific surgical guides enhances results of corrective osteotomies of distal radius malunions.

Abstract. This study determined if robot assisted total knee arthroplasty (TKA) allows for more accurate alignment, better clinical outcome and long term survival rate compared with conventional TKA. 155 consecutive patients who underwent primary TKA were followed more than ten years. Robotic-assisted TKA appears to reduce the number of mechanical axis alignment outliers without any differences in clinical scores, complications and survival rates when compared to conventional manual techniques.

Abstract. Purpose:
Surgical excision is frequently indicated for symptomatic osteochondroma of the proximal femur. The purpose of this study was to describe our experience with computer-navigation aided excision of osteochondromata in the proximal femur and the outcomes of this technique.
Methods:
Seven patients who underwent computer-navigation aided excision of proximal femoral osteochondromata were studied. Computed tomography images of each patient's proximal femur and a size-matched normal proximal femur were fused on a commercially available navigation planning software. The intended resection margins were then plotted using the normal proximal femur as a template, and the plan executed using intra-operative navigation guidance. Patients were followed clinically, radiographically and with functional scoring using the Musculoskeletal Tumor Society (MSTS) score.
Results:
Five patients had isolated exostoses, while two had tumors associated with multiple hereditary exostoses. A posterolateral approach was used for tumors projecting posteriorly or posteromedially, while an anterior approach was used for anteriorly and medially based tumors. Prophylactic fixation was performed in the four patients that required anterior approaches. Mean duration of surgery was 196 minutes. No intraoperative fractures or post-operative complications occurred, and no secondary procedures were necessary. The mean MSTS score at a mean follow up of 13.1 months was 28.8 (out of a maximum of 30).
Conclusions:
This series is the first report of this novel application of computer-navigation, and demonstrates favorable post-operative functional scores and a low complication rate. It demonstrates the applicability, safety and efficacy of this technique, and is particularly applicable in resections involving particularly large tumors that obscure anatomical landmarks and in patients with associated proximal femoral deformity.

Abstract. Intraoperative detection of hip Range of Motion ( ROM ) is the basis for prediction of postoperative functional limits allowed for patients’ daily living. Although computer navigation system for Total Hip Arthroplasty ( THA ) has improved the accuracy of intraoperative ROM evaluation, it has not been able to gain popularity because of its complex and time-consuming procedures. We preliminarily developed a Inertial Measurement Unit based Hip Smart trial system ( IMUHS ) that is easy and simple to use. An in vitro validation experiment was conducted using radiopaque sawbones with imaging measurement method as the reference standard. The validity of measuring ROM in the three axes was as follows: 4.36±4.93°for
flexion and extension, 1.75 ± 5.21°for adduction and abduction, and 6.42 ± 4.32°for internal and external rotation( p = 0.059 ~ 0.550 ). The ICC values of measuring ROM in all three axes
were 1.00. As measuring ROM is the basis for evaluating direction of impingement, subluxation and dislocation, the IMUHS is a promising development direction of THA computer assisted surgery.

Abstract. Objective: To explore the feasibility and accuracy of the new technique of patient-specific 3D printing screws insertion template in the pelvic fractures.
Methods: From January to June in 2017, 6 patients with pelvic fractures were treated by this new type of screw guide templates. Pubis screws and sacroiliac screws were inserted. The patients with external fixation were examined by CT scan before surgery. The patients-specific 3D printing templates were made with photosensitive resin by a 3D printing system to ensure the trajectory of the screws. The templates were sterilized by ethylene oxide and used during surgery. The accuracy and safety of the templates were evaluated by CT scans after surgery.
Results: Totally 10 screws were inserted, including 5 pubis screws and 5 sacroiliac screws. The average surgical time for pubis screw was 12.7 min/screw, and 9.2 min/screw for sacroiliac screw. The average time of X-ray exposure was 13.3±3.6s/screw for public screw and 9.6±4.5s/screw for sacroiliac screw. All the screws were inserted in the trajectory as preoperative design and the screw axis deviation was 1.60 ± 0.2mm and 2 ± 0.3 degrees angle deviation by preoperative and postoperative CT verification. Blood loss during the surgery was minimal (12.2ml/screw). Vascular of neurologic complications or injuries did not happen. And no infection, broken screws or screw pullout occurred.
ConculsionThe patient-specific screw guide template based on the external fixation can insert the screw accurately and safely with very small incision. This technique is a new kind of intraoperative screw navigations. The patient-specific 3D printing screw insertion template was user-frindly, moderate cost and enabled a radiation-reduced pelvic screw insertion.

Abstract. We experienced an anterior dislocation of a lady after THA in standing position during dandling her baby in front of her. The orientations of acetabular cup and femoral stem, measured by 3D image analysis and post-operative CT images, were within the so called safe zone. As it happened, the moment of this dislocation was captured in a smart phone movie. Surface 3D models were created from pre- and post-operative CT images. The pelvic sagittal tilt angle was measured using pre-operative EOS image in standing position and landmark-based 2D/3D registration. The pelvic tilt and the post-operative THA parameters served as input to calculate the cup orientation relative to the prosthetic ROM-based target zone, the bone stock-based target zone, and maximal amount of external rotation until “bony impingement”. The prosthetic ROM- based target zone algorithm calculates impingement free cup orientations dependent on the stem orientation, neck shaft angle and pelvic orientation. The system clearly showed that impingements occurred during the slight hip external rotation and leaning back motions of the patient in standing position as shown in the smart phone movie. This system demonstrated the neck shaft angle of the stem should be reduced from 135° to 130°, and the stem antetorsion should be reduced from 35° to 20° to get optimum target zone without impingements. In addition, the cup should be placed at 6mm posteriorly to get maximum bony coverage. This patient-specific target zone calculation is a powerful tool to decide the optimum orientation and position of THA implants.

Abstract. This manuscript presents positioning accuracy test of a self-development 2D C-arm image based robotic navigation system for assisting the surgeon to implant pedicle screws to the planned locations. The main difference of the system to the ROSA Spine system or Mazor X system is the use of 2D C-arm images instead of 3D C-arm (O-arm) or CT images, which is because 2D C-arm is more popular and available in most hospitals. The surgeon uses a positioning probe to plan drill paths directly on the patient’s back, which are projected and shown on the computer-displayed C-arm AP and LA images so that the surgeon can make sure the correction of implantation path. The spatial position and orientation of the implantation path are also input to the robot controller to enable the robot to move automatically the guiding device to align with the planned path. Then the surgeon can easily drill and implant pedicle screw into the pedicle by following the guiding sleeve. The positioning results of phantom experiment indicate that the average distance error of probe tip between planned and guided paths within the pedicle is 1.2 + 0.3mm and the average direction error between the two paths is 0.4 + 0.1o.

Abstract. In CAOS, ultrasound imaging has been proposed as a solution for obtaining the specific bone morphology of the patient, avoiding limitations of existing technologies. However, this imaging modality presents different drawbacks that make difficult the automatic bone segmentation. A new algorithm, based on Fully Convolutional Networks (FCN), is proposed. The aim of this paper is to compare and validate this method with (1) a manual segmentation that was performed by three independent experts, and (2) a state of the art method called Confidence in Phase Symmetry (CPS). The FCN based approach outperforms the CPS algorithm and the RMSE is close to the manual segmentation variability.

Abstract. Percutaneous endoscopic spine surgery is popular in recent years because of its minimally invasive manner. After transforaminal approach presented by Kambin in the late 1980s, many specific methods were described to establish an accurate and feasible approach to the target disc. Among them, the techniques of Yeung[1], Hoogland[2] and Ruetten[3] are the most famous ones and each has different design and indications. However, no consensus have been made because of the debated clinical results, steep learning curves, and pitfalls that exist in each approach. Guide needle insertion and subsequent working channel building remain a challenging procedure. Poor accuracy may lead to poor safety as the nerve root and dura are at risk. Many surgeons attempted to optimize the procedure, but few researches have integrated computer-assisted navigation with tPELD (transforaminal percutaneous endoscopic lumbar discectomy). It is time to bring our surgical robot into the field.

Abstract. In open surgery for spine stabilization, the pedicle screws are often placed using patient-specific guide templates since they can improve the screw placement accuracy and simplify surgery. However, the conventional fit-and-lock template requires full exposure of the bony structures and is therefore not suitable for minimally invasive procedures. In this study, we constructed a novel guide template for percutaneous pedicle screw placement. Its feasibility and the accuracy of template-assisted pedicle screw placement were assessed using an excised calf spine model. As a result, all inserted guide wires and 27 of 30 simulated screws (90%) were completely in the pedicle. The remaining screws (10%) penetrated by less than 2 mm. The average distance and angular deviations of the guide wires were 1.46±0.60 mm and 1.10±0.84°. Our study demonstrate that this novel guide template is technically feasible and enhances the accuracy of percutaneous pedicle screw placement. Moreover, it may simplify the surgery and minimize intraoperative radiation. Further research on its clinical applications is warranted.

Abstract. Screw fixation in upper cervical spine surgery is one of the most challenging spinal procedures. For that reason, the free-hand techniques are not a reliable procedure in upper cervical spine. Wei Tian reported the first posterior C1-2 transarticular screw fixation which was assisted by robotic systems using TiRobot system in 2016. Our study was aimed to assess the accuracy and reliability of screw fixation in upper cervical spine prospectively.
All the patients undergoing screw fixation assisted by robotic system (TiRobot) in upper cervical spine were prospectively studied from August 2015 to January 2018 in Beijing Jishuitan hospital. During surgeries, intraoperatively obtained images by C-arm were transferred into the TiRobot system and three-dimensional images were created. Surgeons' plannings of the screw trajectories were performed in TiRobot system. Afterwards, the robot arm with a guidance tube on its end was automatically moved to the entry point of each trajectory and held still. Guiding pins were inserted and followed by cannulated or conventional screws placements. A fluoroscopic re-scan by C-arm was performed, and the merging of two sets of images demonstrated the deviations between the planned and real trajectories. The deviations were analyzed and any intraoperative difficulties or errors were recorded. Postoperatively, any screw perforations were reviewed and recorded on CT scan images.
Twenty-six patients (13 males/13 females) were included in this study. The average age was forty-nine. The underlying diseases of these patients covered dens fractures, Hangman's fractures, congenial and acquired deformities. 64 screws were placed assisted by TiRobot system. The average deviation between the planned and real trajectories was 0.9 mm. No screw perforations were detected on postoperative CT scans.
Cervical spine, particularly the upper cervical spine has small size bony structures, higher accuracy requirements are significantly important. The results of our study showed only 0.9 mm deviations between planned and real trajectories occurred. This level of accuracy allowed safe and accurate placement of screws in upper cervical spine and no screw perforations were observed. For that reasons, screw fixation in upper cervical spine is an accurate and reliable procedure using TiRobot system.

Abstract. Registration of the patient body and virtual 3D plan is an initial but very fundamental procedure for accurately using the navigation system. Currently, there are two commonly used registration methods, i.e., point registration and intraoperative CT registration, which are suitable for different kinds of operative scenarios. By now, there is no literature reporting about how to choose between these two registration methods during using the navigation systems. In this study, we respectively performed 12 simulated osteotomies based on the point registration method and intraoperative registration method during using the navigation system. Two statistical tests were done based on the surgical errors of osteotomy surgeries using these two registration methods. Specifically, T-test result (p<0.001) indicated the intraoperative CT registration performed better than point registration. Besides, equivalence test of the two registration methods (Rg=1.00 mm) suggested that the two registration methods perform equivalently while using the navigation system. Moreover, we have shared the surgeons some practical suggestions about how to choose between these two registration methods during using the navigation system.