ABSTRACT. Hisham Iqbal, Ferdinando Rodriguez y Baena Imperial College London, SW7 2AZ, UK, hisham.iqbal13@imperial.ac.uk, f.rodriguez@imperial.ac.uk 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. 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 eminent 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 has 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. Abstract Objective: In order to provide an accurate and safe spinal surgery training method, this paper constructs a virtual surgical training system for spinal internal fixation and preliminarily evaluated the validation of the system. Methods: A realistic virtual operation environment was created through geometric modeling[1、2] and texture rendering [3-5] of the spinal model (figure 1). At the same time, based on the body element model of vertebral body, multi-point collision detection algorithm [6] (figure 2) and drill bone force prediction experience model are used to realize the real-time calculation of collision detection and feedback force of drill bone operation. Then, the visual and tactile simulation of pedicle screw implantation was achieved. In order to verify the validation of the system on the surgical training, we selected 10 residents to perform the actual cadaver operation. The participants were divided into control Group A (n=5) and intervention Group B (n=5) randomly. Ten adult fresh cadavers including 5 males and 5 females were collected and randomly allocated to the two groups. Their task was to perform the bilateral L1-L5 pedicle screw instrumentation in the cadaver specimens, respectively. Group A was directly put to the test. Group B was trained on the simulator prior to the test. Accuracy was assessed by CT after instrumentation, and the operation time is also recorded. The screw penetration rates and the operation time of the two groups were compared using statistical analysis. Results: The virtual operation training system realizes the real-time interaction between virtual vision and virtual touch, and can simulate the feel of pedicle screw implantation operation; The screw penetration rate of Group B (10.5%) was significantly lower than group A (35.5%, P<0.05).Compares the operation time, there was a significant difference (p < 0.05) in average operation time between Group A (30.5 ± 10.6 minutes) and Group B (45 ± 15.5 minutes). Conclusions: The virtual surgical training system provides a visual-haptic surgical training simulator for the internal fixation of pedicle screws, and a precise and safe training method is realized. The experimental operation suggested that the simulator training had positive effects on real orthopedic surgery and can be used as a great orthopedic surgery training method.

ABSTRACT. Introduction Pelvic rotation during cup impaction causes excessive cup anteversion should be considered in direct anterior approach total hip arthroplasty (DAA-THA) with supine position. There are two mechanical devices based on functional pelvic plane (FPP) and anatomical pelvic plane (APP). The purpose of this study was to compare the accuracy of two mechanical cup alignment devices based on FPP or APP in DAA-THA. Patients and methods The subjects of this study were 90 hips of 80 patients who underwent DAA-THA in a supine position using HipPointer® based on FPP from July 2016 to December 2017 (Pointer group). Pointer group consisted of 31 males (37 hips) and 49 females (53 hips). The other subjects of this study were 29 hips of 27 patients using HipCOMPASS® based on APP from April 2013 to May 2014 (COMPASS group). COMPASS group consisted of 10 males (11hips) and 17 females (18hips). There are no significant differences in age, gender and BMI between the two groups. Results 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). Discussion Accuracy of cup alignment with use of a new developed mechanical navigation device based on intraoperative FPP by correction of axially rotated pelvis horizontally in the DAA-THA is an easy and useful device that can set the cup alignment accurate compared with the device based on intraoperative APP with reference of pubic symphysis.

ABSTRACT. Background Iliopsoas impingement (IPI) has been alerted a lot of attention as one of the causes of persistent pain after THA. This study aimed to investigate the risk factor regarding IPI after THA. Materials and methods This study included 109 hips of 94 patients who underwent primary cementless THA using the same component and surgical approach by a single surgeon. IPI was diagnosed as follows; presence of persistent groin pain, findings of tendinitis, and relieving pain after injection of anesthetic agents into the iliopsoas tendon. To examine the causes of IPI, the effect of patient characteristics, location of the component, and component sizes were analyzed. To measure the position of the acetabular component, postoperative CT images were used. The functional pelvic plane (FPP) was used as the pelvic coordinate system for cup position, and the anterior and lateral protrusion of the cup above the acetabular rim was measured on the axial plane at the level of the femoral head center. We compared the measured parameters between IPI and asymptomatic groups. Results Occurrence frequency of IPI was 2.8% in this study. No relationship was observed between patient characteristics and components in both groups. The anterior protrusion of the cup in IPI group (mean, 5.1 mm; range, 1.9–8.1 mm) was significantly higher than those in asymptomatic group (mean, -1.7 mm; range, -14.4–6.0 mm) (p = 0.007). The lateral protrusion of the cup in IPI group (mean, 13.4 mm; range, 3.5–21.6 mm) was also significantly higher than those in asymptomatic group (mean, 0.6 mm; range, -9.1–13.2 mm) (p = 0.019). Cup inclination and anteversion did not differ between the both groups. Conclusions The anterior and lateral protrusion of the acetabular components from the acetabular rim with the CT measurement based on the FPP is associated with the risk factor of IPI after THA.

ABSTRACT. INTRODUCTION: There is a need to obtain more information about the effect of balancing on functional outcomes, whether the balancing is measured at the time of surgery or at follow-up time. The aim of our study was to measure the varus and valgus laxities and the functional outcome scores of two groups; well-functioning Total Knee Arthroplasties (TKA) patients and subjects with native knees (NK), with matching age, sex, and body mass index. In this way the laxity and functional scores could be compared between the two groups, and a possible relation between laxity and function determined. METHODS: There were two groups, normal controls and well-functioning total knees. From a specific date, all patients attending the clinic were screened for inclusion in the study. Of the 50 normal patients, a total of 73 knees were evaluated; of the 51 TKA patients, a total of 77 knees were evaluated. All patients completed the Knee Society Score (KSS) questionnaire, a different form for each knee. A validated electronic goniometer was used to measure the varus and valgus angles with a moment of 10 Nm. RESULTS: The mean varus laxity for the NK group was 2.87 degrees and 2.89 degrees for the TKA’s. The mean valgus laxity for NK was 1.89 degrees and 2.14 degrees for the TKA group. There was no statistical difference between the pairs of values. The mean ratio of varus/(varus and valgus) in both groups was 0.59, slightly tighter medially. For KSS functional scores, the large majority of the NK group scored a mean of 93 +/-9, with no cases below 70 points. In contrast, the TKA’s scored an average 81 +/-15. There was a significant difference between the mean scores. CONCLUSIONS: In native knees, the varus laxity was greater than valgus, even though the surgical goal is equal balancing. This might suggest that the surgical balancing goal should be a slightly tighter medial side which might enhance rehabilitation. In order to achieve this, a quantitative means of balancing at surgery will be an advantage. This study also suggests despite high satisfaction scores, the functional score of well-functioning TKA’s can still be improved.

ABSTRACT. CAOS Computer-assisted hip navigation offers the potential for more accurate placement of hip components, which is important in avoiding dislocation, impingement, and edge-loading. The purpose of this study was to determine if the use of computer-assisted hip navigation reduced the rate of dislocation in patients undergoing revision THA. We retrospectively reviewed 72 patients who underwent computer-navigated revision THA between January 2015 and December 2016. 72 patients (48% female; 52% male) undergoing revision THA with a mean age of 70.4 ± 11.2 years and mean BMI was 26.4 ± 5.2 kg/m2. The most common indications for revision THA were instability (31%), aseptic loosening (29%), osteolysis/eccentric wear (18%), infection (11%), and miscellaneous (11%). During revision procedure, polyethylene component was most commonly changed (46%), followed by femoral head (39%), and acetabular component (15%). At 3 months, 1 year, and final follow-up, there were no dislocations among all study patients (0%). Compared to preoperative dislocation values, there was a significant reduction in the rate of dislocation with the use of computer-assisted hip navigation (31% vs. 0%; p<0.05). Our study demonstrates a significant reduction in the rate of dislocation following revision THA with the use of computer navigation. Although the cause of postoperative dislocation is often multifactorial, the use of computer-assisted surgery may help to curtail femoral and acetabular malalignment in revision THA.

ABSTRACT. The purposes of this study were to identify the incidence of activities of daily living (ADL) impairment related to hip flexion after rotational acetabular osteotomy (RAO), and to analyse the relationship between postoperative bony ROM and ADL impairment related to hip flexion at 2 years after RAO. We reviewed 26 patients with DDH who underwent RAO. With the questionnaires, we assessed whether the subjects could perform clipping toenails and putting on and taking off socks that needed hip flexion without weight-bearing. We defined the ADL impairment as difficulty to perform both of these activities. The incidence of ADL impairment related to hip flexion was 69% at 6 months, 35% at 1 year, and 12% at 2 years after RAO. Mean bony internal rotation (IR) ROM at 90º of flexion measured by 3D surface models of the pelvis and femur in subjects with impairment was smaller than that without impairment (10º and 37º, p=0.014). The incidence of impairment was significantly higher in subjects with both 105º or less of bony flexion and 20º or less of bony IR at 90º flexion than that in the remaining subjects (p=0.038). The postoperative femoral head coverage didn’t associate with impairment. Subjects may avoid postoperative ADL impairment related to hip flexion if the subject obtain bony flexion was 105º or more, or bony IR at 90º of flexion was 20º or more after RAO. Preoperative-planning considering not only reorientation of the acetabulum but also postoperative bony ROM is desirable to avoid postoperative ADL impairment related to hip flexion.

ABSTRACT. Purpose The aim of this study was to evaluate the feasibility and accuracy of scaphoid screw guide wire placement using computer-assisted designed and three-dimensional (3D) printed surgical guiding template in cadaver wrists.

Methods CT scans of 12 fresh-frozen cadaver wrists were performed, and the data imported into a surgical planning system. A three-dimensional skin surface template block with a guiding hole was generated from CT data to allow a screw guide wire to be placed in the central third of the scaphoid. This 3D model was printed and then put back into the wrist. A screw guide wire was inserted through the palmar guide hole into the intact scaphoid and then a post-procedure CT scan was obtained. These post-procedure data were introduced into the surgical planning system. Angular and linear deviation between the pre-procedural simulation and image of the guide wire was measured in the system to assess accuracy.

Results Mean angular deviation was 3.85 ±1.32 degrees (1.56−5.35 degrees), and linear deviations of 12 specimens were less than 1.1mm. No specimen required a repeat drilling of the scaphoid. All the screw guide wires were considered to be centrally placed in the scaphoid  based on our criterion of central placement of the scaphoid screw.

Conclusions The use of computer-assisted 3D printing surgical guide template to assist screw guide wire placement into an intact scaphoid mimicking non-displaced scaphoid fracture showed acceptable accuracy in cadaver wrists.

ABSTRACT. ‘Grand piano sign’ has been used as a popular benchmark to facilitate correct rotational alignment during mechanically-aligned total knee arthroplasty (TKA). The purpose was to quantitatively determine discernable morphological patterns on anterior femoral condylar resection surface in mechanically aligned (MA-) and kinematically aligned (KA-) TKA. CT scans of knees were reconstructed into 3-D models for 60 TKA candidates. Using a 3-D imaging program, femoral resections were virtually performed. For MA-TKA, the anterior femoral condylar resection was performed parallel to the surgical epicondylar axis (SEA), at an external rotation (ER), and internal rotation (IR) of 3° relative to SEA, respectively. For KA-TKA, the anterior femoral condylar resection was performed parallel to the cylindrical axis (CA), at an ER, and IR of 3° to CA, respectively. Vertical distance from the anterior margin of distal femoral condylar resection to the most proximal peak of each medial and lateral condyle was measured and the ratio of two distance was defined as AC/BC ratio In MA-TKA, the AC/BC ratio in the anterior condylar resection surface parallel, at ER of 3° to SEA, and at IR of 3° to SEA were 0.60, 0.51, and 0.70, respectively (p < 0.01 for all). In KA-TKA, the AC/BC ratio in the surface parallel, at ER, and at IR of 3° to CA were 0.74, 0.63, and 0.89, respectively (p < 0.01 for all). Surgeons can accessorily use the quantifying method for patterns of anterior resection surface intra-operatively to ensure that correct rotational alignment of femoral resection is obtained in both mechanically and kinematically aligned TKA.

ABSTRACT. This is a case series of 26 operations performed in our hospital from March 2017 via Phecda (3rd generation robot developed independently in China).There were 26 cases in our group, including 28 fracture vertebrae. 156 screws were used, of which 150 screws were put in successfully, but position shifted occurred in putting in the other six screws. This could be that the first-time insertions were inaccurate. Re-design should be done, and the entry points should be adjusted. The operation time is range from 60 to 90 minutes. The blood loss is less than 50ml. All the patients can step off the bed at the second day after operation with the support of brace and leave hospital at the third day after operation. No wound infection occurred.The shift, an adverse reaction, also exists in application of robot, just like navigation system. If the shift occurred, neurological injury, vascular injury and even patient death may result. We concluded five common reasons for shift:1.The spinal process clip might not be fixed tightly enough or might be moved in operation without notice. The solution is that the spinal process clip should be fixed tightly. The surgeon should operate softly and avoid touching the clip. If the clip be touched, stop the operation, re-tighten the clip and repeat the procedure.2.The traction of soft tissue could cause resistance at placing the guide sleeve. The solution is to cut off the skin and deep fascia according to the direction designed by robot to reduce the resistance. 3.The screw entry point might be too close to steep bone, so that slip may occur at placing the guide sleeve. The solution is that do not choose the steep bone as screw entry point at the design phase before operation and enhance the holding strength between the guide pin and bone surface. Drill a dent by guide sleeve before putting in guide pin to reduce the slip of pin.4.The vertebrae could move with the respiratory movement after routine general anaesthesia. The solution is to suspend the respirator at the location procedure. But the degree of blood oxygen saturation should be monitored at higher than 95% at all times. Alternatively, respiratory compensation technique can be adopted to ensure the relative position between the robot and vertebrae by software system support.5.The limitation of instrument.  The light reflection ball should be replaced after a certain period of usage.These are what the authors believe may contribute to the shift, sorely based on our understanding of the scenario and experience with the robot over the past cases. They should be tested in the further robot application and study.

ABSTRACT. Objective: To explore the procedures of minimally invasive spinal tubular grading osteotomy(MIS-TGO) in the patient with degenerative spinal scoliosis. METHODS:We performed 9 MIS-TGOs including 7 cases with Grade-1 to Grade-2 osteotomy, 1 case with Grade-3 osteotomy and 1 case with Grade-4 osteotomy. Then we reported a typical Grade-3 MIS-PSO in the patient with progressive back pain and limitation of motion in thoracolumbar spine for 3 years. Preoperative radiographs of total spine showed stiffness degenerative kyphoscoliosis in thoracolumbar spine and marked sagittal and coronal imbalance. The main spinopelvic parameters were measured pre- and postoperatively including the sagittal vertical axis(SVA), C7 plumb line to certer sacral vertical line(C7PL-CSVL), pelvic tilt(PT), pelvic incidence(PI), sacral slope(SS), lumbar lordosis(LL) and thoracic kyphosis(TK). The patient underwent curve correction using navigation-assisted tubular minimally invasive spinal pedicle subtraction osteotomy(MIS-PSO) in the level of L2 with piezosurgery combined with percutaneous bilateral pedicle screws fixation from T9 to L5 segments. The neuroelectrophysiological monitoring was used during the operation. RESULTS:The patient relieved the back pain as well as the radiographs showed sagittal and coronal imbalance were corrected 1 week postoperatively and during the follow-up period lasted for 12 months. The main spinopelvic parameters were at normal ranges. CONCLUSION:MIS-TGO is a reliable technique for the correction of rigid degenerative spinal kyphoscoliosis with exquisite manipulations that must have abundant open and tubular surgical experiences.

ABSTRACT. Background Fractures of the distal radius are among the most common fractures. Irritation and rupture of the extensor tendons are major complications. Most of the time they are due to inappropriate length of epiphyseal screws. Questions/Purpose We modelized distal radius using CT-scans (1) to determine if the length of the diaphyseal screw was predictable of the length of the epiphyseal screws where comminution make measurements unreliable and (2) to assess the variability of the measurements realised in the oblong hole at different heights.

Methods Forty CT-Scans exams were semi-automatically segmented. The plate was affixed to the distal radius with 3D computed simulation. The measurements were realised at the level of the oblong hole and at the level of 4 distal epiphyseal screws. A linear regression analysis was carried out for each epiphyseal screw length with reference to the diaphyseal screw length of the oblong hole. Two groups were distinguished according to the length of the suitable diaphyseal screw: 14mm and 16mm.

Results The correlation coefficients were [0.64; 0.67; 0.59; 0.73] from ulnar to radial. The choice of a 14mm/16mm long diaphyseal screw implied mean values of epiphyseal measures of respectively [19.1; 19.9; 21.7; 17.8] / [21.5; 22.6; 23.7; 20.6] mm from ulnar to radial, SD [1.3; 1.3; 1.3; 1.1] / [1.3; 1.1; 1.6; 1.3] with statistically significant differences.

Conclusions This relationship between the size of the diaphyseal screw chosen and the spectrum of the epiphyseal screws aims to decrease the rate of screws penetrating the dorsal cortex.

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. To evaluate the clinical application of Renaissance robotic-assisted system for spinal pedicle screw insertion, to compare the placement accuracy & safety of robotic-assisted insertion with traditional free-hand technique. Twenty consecutive patients with spinal disorders, who underwent pedicle screws insertion between 12/2015 and 03/2016, were enrolled in the robotic-assisted group (n=124 screws). Another 20 patients were enrolled in the free-hand group (n=198 screws). CT scan was used for all patients concerning preoperative & postoperative. Renaissance robotic-assisted system was used in the robotic-assisted group for preoperative planning. Intraoperative fluoroscopy was applied to match the information with the robotic-assisted system during the procedure. Average (7 ± 2.5) times for intraoperative fluoroscopy per procedure in the robotic-assisted group (platform mounting and registration), and average (12.6 ± 4.5) times for intraoperative fluoroscopy per procedure in hand-free group (P < 0.05). Average (18.9 ± 7.2) min for mounting the platform and registration. Average (3.7 ± 1.5) min to insert each screw of robotic-assisted, and average (4.3 ± 0.8) min to insert each screw of free-hand (P > 0.05). According to Dr. Rampersaud classification, 100% of robot-assisted and 91.8% of free-hand placed screws were found to be accurate (P = 0.032). Average operation time of the robotic-assisted group was (268.3 ± 74) min, while free-hand group (267.5 ± 65.3) min with no statistical significance (P = 0.980). Average blood loss of robotic-assisted group was (285.0 ± 240.2) ml, while (640.0 ± 389.3) ml in the free-hand group with statistical significance (P = 0.031). Robotic-assisted system improves the accuracy of implant and the safety of spinal surgery. The times and radiation dosage of intraoperative fluoroscopy are reduced. It is of a great prospect to be applied not only in spinal percutaneous surgery, but also revision and deformity.

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. 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 intraoper-ative 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 oste-oma in 19 cases. The other 16 cases were not pathologically diagnosed 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 percutane-ous 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. CLINICAL VARIABILITY OF LANDMARK COLLECTION IN AN IMAGELESS ROBOT-ASSISTED TOTAL KNEE ARTHROPLASTY SYSTEM Rahul Khare, and Branislav Jaramaz Smith & Nephew, Pittsburgh, PA 15222, USA, Rahul.Khare@smith-nephew.com

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. A method and a device for preparing the distal femur in a knee joint in a patient undergoing total knee arthroplasty (TKA) surgery. It has a 15 different machinery actions (cuts and drilling) that are performed by surgeons for formal implantation in TKA. It involves a preoperative planning and production of patient-specific template that transfers planning to intraoperative implementations of the 15 machinery actions (distal cut, anterior cut, posterior cut, anterior chamfer cut, posterior chamfer cut, notch cut, three cuts for box cut making and two lug holes) which are located in the device. It includes locating probes and cutting block.

The produced device has a built-in information about sizing, alignment and bone cutting. The device is a versatile and can act an 11-in-1 block to perform all essential surgical cuts of formal component or act as a pin locator to support the surgeon for positioning of conventional instruments of distal cutting block and 4-in-1 cutting block. 15-in-1 femoral cutting guide is a practical and time-saving tool. The procedure is feasible and easy. Planning was controlled by the surgeon. It replace more than 70 pieces by only one piece.

ABSTRACT. Chronic ACL deficient knees can lead to progressive knee dysfunction with accelerated degeneration and gait abnormalities. ACL deficient arthritic knees are predisposed to postero-medial wear of the tibial plateau. Rotational alignment of the femoral component is one of the important factors dictating the long term outcome in total knee arthroplasty (TKA). Multiple intra-operative landmarks have been identified to obtain optimal femoral component rotation. These landmarks are the posterior condylar axis (PCA), epicondylar axis and the Whiteside’s line. We postulated that in ACL deficient knees, posteromedial tibial wear lead to compensatory changes in posterior medial femoral condyle which alters the relationship between PCA and Whiteside line.The aims of our study were to assess the correlation between PCA White side angle and the integrity of the ACL using CAS. MATERIAL AND METHODS: This was a CAS based study of 106 consecutive Indian varus osteoarthritic knees undergoing primary TKA. Aesculap Orthopilot 5.1 software was used with Femur first surgical technique in all cases. The CAS software allows identification of the combined Whiteside PCA angle as a measure of external or internal rotation from 90 degrees. The competency of ACL was documented and was subdivided into intact, linear striations and absent. The posterior condylar anatomy was documented in each case as hypoplastic, hyperplastic and normal in relation to the posterior lateral condyle. We attempted to establish an association, if any between the integrity of ACL and posterior condylar anatomy in turn influencing the PCA Whiteside angle.Results: The mean varus deformity was 12.21° ± 6.9°(95% CI). The mean femoral component external rotation with respect to the PCA was 4.25° ± 2.2°(95% CI). 56 knees had an intact ACL whereas 50 knees had an incompetent ACL. The mean varus deformity and the Whiteside PCA angle were higher in cases with an incompetent ACL in comparison to cases with an intact ACL. There was a statistically significant association between the ACL status and the PCA Whiteside angle.Conclusion: ACL deficiency alters the biomechanics of the knee with increased Whiteside PCA angle. ACL deficient knees also have increased mean values of varus deformity when compared to knees with an intact ACL. While operating a knee with a deficient ACL combined PCA Whiteside angle could be a more reliable guide for femoral component external rotation than PCA alone.

ABSTRACT. Objective: Midline lumbar fusion with cortical bone trajectory(CBT) screw is a novel technique operation, robot system are 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. Purpose: To develop and validate a deep learning based method for automatic segmentation of lumbar vertebrae from CT images acquired with varying fields of view.

Materials and Methods: 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 to find the bounding box of the lumbar region. After that, a 3D U-net like FCN 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. The developed method is evaluaed on publicly available 15 spine CT images obtained from the MICCAI 2016 xVertSeg challenge.

Results: Our method achieved an average Dice coefficient of 95.77 +/- 0.81% and an average symmetric surface distance of 0.37 +/- 0.06 mm.

Conclusions: We presented a cascaded FCN-based approach for fully automatic segmentation of lumbar vertebrae from 3D CT data. Our method achieved equivalent or superior results over the state-of-the-art method.

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. Introduction: Transforaminal percutaneous endoscopic lumbar discectomy (tPELD) is a popular procedure with debated clinical results and steep learning curves. Computer-assisted navigation can improve accuracy and safety in many kinds of surgeries. Few literatures reported tPELD under the guidance of navigation or robot. Materials and methods: TianJi Robot® was the first robot being used in tPELD. The puncture trajectory was planned by surgeons on TianJi Robot based on intraoperative three-dimensional images. The robotic arm guided the surgeon to make an accurate track towards the herniated disc. Clinical results were assessed by VAS, ODI and modified MacNab criteria. Results: Clinical outcomes were acceptable except of one failed operation caused by obesity. VAS and ODI reduced significantly after surgery. Except for one recurrent case, the other seven patients selected excellent or good according to modified MacNab criteria. Conclusion: In this initial study, TianJi Robot assisted tPELD was proved feasible and effective.

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 +/-0.09 mm. 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 +/- 0.14 mm. 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. Purpose 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. We constructed a novel guide template for percutaneous pedicle screw placement. Its feasibility and the accuracy of template-assisted pedicle screw placement were assessed. Methods Five freshly frozen calf lumbar spines (L1–L5) were thawed. In each, two positioning screws were inserted into the spinous processes of L2 and L4 as anchor points for the guide template. CT data of the spine and Mimics software were used to obtain 3D reconstructions, and the optimal trajectories of the pedicle screw guide wires were determined. The guide template was designed in 3-Matic software on the basis of the positioning screws and planned guide wire trajectories and manufactured by 3D printing. After guide wire placement, postoperative CT data were used to determine the angular and distance deviations of the guide wires and templates. Insertion of 6.5 mm-diameter pedicle screws was simulated. The degree of pedicle-cortex breach by the guide wires and simulated pedicle screws was assessed. Results 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°, respectively. These values were significantly higher than those of the guide templates (1.04±0.45 mm and 0.84±0.32°, respectively). Conclusion The novel guide template is technically feasible and enhances the accuracy of percutaneous pedicle screw placement. It may simplify the surgery and minimize intraoperative radiation. Further research on its clinical applications is warranted.

ABSTRACT. With the continual development and introduction of new robotic-assisted navigation surgical systems in total knee and hip arthroplasty (TKA/THA), the market would greatly benefit from a compendium of comparative studies and factual data of the major available and leading systems. This comparison entails the evaluation of system-specific properties and attributes that should be taken into consideration from the relative perspectives of patients, surgeons, third party payors, investment analysts, and hospitals. The needs and demands of each party varies. Patients are concerned with the role of the surgeon (pilot vs. co-pilot), risks of potential harm, need for supplemental studies, time under anesthesia, the safety record of the system, and their recovery rate. When using these robots, surgeons must consider factors such as preoperative planning, radiation exposure, execution with haptic guidance, and intraoperative verification of bony cuts. Third party payors have been highly skeptical of advanced technologies. They play a role in the delay of acceptance of robotics by labeling it “experimental”. A compendium of validation studies with economic impact and safety is required. Lastly, hospitals must evaluate the capital and ancillary costs of each system, and make sure that the technology has been validated in several case studies before committing to the purchase of any system. The purpose of this study is to offer a shopping guide in the format of a comparative tabulation of currently available data for existing robotic technology in the applied field of adult reconstructive surgery of the lower extremities.

ABSTRACT. INTRODUCTION Oblique lumbar interbody fusion (OLIF) with robot assisted percutaneous pedicle screw fixation had been widely used in the treatment of lumbar degenerative disease. But for patients with non-contained lumbar disc herniation, the indirect decompression of OLIF is not enough to relieve the nerve root compression. On the other hand, percutaneous endoscopic spine surgery could remove herniated disc directly under visualization. It is a novel idea to combine robot assisted OLIF with endoscopy to achieve direct decompression in a total minimally invasive method MATERIALS AND METHODS Patient with L4/5 disc herniation received anterior surgery first. The endoscopy was placed through oblique approach to remove herniated disc. After fully decompression of nerve, the OLIF cage was inserted and patient received percutaneous pedicle screw fixation under TianJi Robot assisted in a prone position. RESULTS Patient’s left lower leg pain and low back pain resolved completely after the operation, with the VAS score decreased from 10 to 2. The JOA score improved from 7 to 25, and the improvement rate is 81.8%. The ODI score decreased from 24.4 to 9 in 3 month follow-up. MRI scan after operation showed a completely removal of herniated disc. CONCLUSION Robot assisted OLIF combined with endoscopic decompress is a total minimally invasive solution for patients with lumbar disc herniation with excellent clinical efficacy.

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 or available in most hospitals.

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. In vitro validation experiment was done using radiopaque sawbones with imaging measurement method as the reference standard. The validity of measuring ROM in the three axes was as follows: for flexion and extension, for internal and external rotation, for adduction and abduction. The reliability of measuring ROM in the three axes was as follows: for flexion and extension, for internal and external rotation, for adduction and abduction. 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. Introduction: The morphological parameters of proximal femur are essential in the preoperative planning and design of femoral implants since cementless total hip arthroplasty has become commonly used surgical interventions among the orthopedic community. To automatically measure anatomic parameters of proximal femur under the three-dimension coordinate system, the methods for automatic measurement are proposed. Method: The software is developed for measurement on 16 key anatomic parameters of proximal femur, including femoral head radius, neck-shaft angle, anteversion and so on, which needs users to import 3D model and locate anatomic landmarks. The 3D coordinate system of the femur will be established to supporting geometrical computation. Besides, largest-ball searching method is used to model rough shape of femoral medullary canal. A standard model composed of balls, cone and pipeline is established to evaluate the accuracy of aforementioned methods. Result: By experimenting on 150 femur STL models of both left and right femur from 40 males and 35 females at mean age of 44 ± 23 years, the average time cost of automatic measurement for a single femur model is 0.89 seconds. The intra- and inter-class correlation coefficients and relative error coefficient of anatomic parameters of standard model shows the reliability and accuracy of the measurement. Conclusion: The software for three-dimension measurement on anatomic parameters on femur provides an automatic measuring method to help doctors to design and select customized femoral stem in preoperative planning of total hip arthroplasty through a fast, easy and three-dimensional alternative to the traditional measurement on femur.

ABSTRACT. In total hip arthroplasty, leg length discrepancy is often measured on pelvic anteroposterior radiographs under the assumption that the operated femur is symmetric to the contralateral side. If the shape of the femur is asymmetry, which might cause measurement error of leg length discrepancy. The present study aimed to address whether hips with unilateral end-stage osteoarthritis secondary to DDH have significant asymmetry in length and find its related factors if any. We assessed 90 patients with unilateral end-stage OA secondary to DDH (Crowe I (n = 43), Crowe II/III (n = 32), Crowe IV (n = 13)) and 43 healthy volunteer were used as controls. We measured the vertical distance from the tip of greater trochanter to the knee center, the vertical distance from the most medial prominence of lesser trochanter to the knee center on the anatomical table top plane. To find factors related to asymmetry of femoral length, the following morphological asymmetric factors were measured; vertical distance from the greater trochanter to the lesser trochanter (GL), femoral neck anteversion, femoral neck shaft angle, and femoral anterior and lateral bowing. The side-to-side difference of GL showed positive correlation with that of the GT in Crowe I and II/III and negative correlation with that of the LT in Crowe I and IV groups. In conclusion, hips with unilateral end-stage OA secondary to DDH have significant asymmetry in length compared to normal hips. The GL asymmetry is a morphological factor to determine the femoral length asymmetry in DDH.

ABSTRACT. Based on the concept of integrated robot surgery system, this study aimed to propose the concept of hand-eye robot-assisted surgery (HERAS, Hand-Eye Robot Aided Surgery) model and build the robot-assisted knee replacement system for the shortcomings of the traditional total knee replacement surgery, and explore its applications in the surgery of total knee replacement. A robot-assisted total knee replacement system was designed and developed combined with the basic concept of hand-eye robot-assisted surgery model according to the specific steps of the osteotomy in total knee replacement surgery. A comprehensive error analysis was performed to detect the surgical error. A series of pre-clinical tests about this robot-assisted total knee replacement system were performed using fake bone model, animal bones, bones of bodies and knees of bodies. We initially developed China’s first robot-assisted total knee arthroplasty experimental system-WATO in this study, the average error of its three-dimensional visual positioning was 0.2814mm; the overall average error of the probe positioning is 0.4mm. The average alignment deflection was 0.82 degree in fake bone model test and 0.89 degree in bones of bodies. The alignment deflection in osteotomy testing using knees of bodies was 0.87 degree and 1.24 degree, respectively. The visual positioning accuracy and precision of cutting in this system met the surgical requirements. However, osteotomy operating time of WATO system was significantly longer than the control group (39.5 minutes vs 6 minutes).

ABSTRACT. ACCURACY OF A CAOS ENHANCED MECHANICAL INSTRUMENT SYSTEM FOR TOTAL KNEE ARTHROPLASTY Y Dai*, JI Huddleston III, M Rueff, L Angibaud, DF Amanatullah† *Exactech Inc, Gainesville, FL, 32653, USA, Yifei.dai@exac.com † Dept of Orthopaedic Surgery, Stanford University School of Medicine, Redwood City, CA, USA, dfa@stanford.edu

Adoption of computer-assisted orthopaedic surgery (CAOS) in total knee arthroplasty (TKA) may be challenged by the inconvenience of switching to CAOS-specific instruments. entation. This study investigated the accuracy of a new CAOS system designed to provide enhancement to conventional instrument. Two seniors, two fellows, and four residents each performed TKA resections on at least 3 knee models using a conventional instrument system. The same resection activities were repeated on a matching set of knee models with the addition of the CAOS enhancement. Varus/valgus alignment was measured by comparing digitized knee models before and after resection. Resection error and %optimal resection (<2° error) were compared between CAOS enhanced and conventionally instrumented cases, and between seniors, fellows, and residents. CAOS enhancement improved alignment accuracy from conventional instrumentation. Unlike conventionally instrumented resections, which were impacted by surgeon’s experience, the CAOS enhanced resections were demonstrated to achieved on average ≤1° accuracy All surgeon groups. Significantly higher percentages of optimal varus/valgus alignment were found in the CAOS resections compared to the conventionally instrumented resections (by 8-59%). All cases performed with CAOS guidance achieved optimal alignment, expect for tibial resections from the fellows (92%). The result showed that compared to conventional instrumentation, surgeons with varying experience level can significantly improve coronal alignment accuracy using CAOS enhanced mechanical instrumentation. Furthermore, CAOS enhancement substantially increased the prevalence of optimal resection. The system investigated may provide a streamlined solution to add the benefit of CAOS to the conventional instrumentation with minimum disruption in the surgical tools.

ABSTRACT. Objective To assess the influence of clinical factors on the clinical accuracy of an intraoperative 3D image-based auto-registration active infrared navigation system. Methods We mimicked the navigation assisted spine surgery set using a 1:1 Sawbone model with titanium beads embedded onto the surface and measured the clinical accuracy of the system by recording the coordinates of the target titanium beads in both the images and the navigation system under different clinical factors including the light of shadowless lamps, the movement of the bed, and the distance between the camera and the patient traker. Results Clinical accuracy of the 3D Nav system did not change under exposure to the shadowless lamps. The clinical accuracy of the 3D Nav system did not change when the surgery bed was moved or the position of the camera was changed. Conclusions The 3D Nav system in this study was the same accurate under different status of the shadowless lamps, different posture of surgery bed, and different posture of the camera.

ABSTRACT. Objective: To evaluate component malposition and the pressure distribution at the proximal tibia after total knee arthroplasty (TKA). Methods: A 3D model was established with data from computed tomography of the whole lower limb, and TKA was simulated. The tibial and femoral components were changed to 3°, 5°, and 7° varus and 3°, 5°, and 7° valgus positions in the coronal plane. Finite element analysis was performed after pressure was applied from the femoral head to the ankle (300 N, 1800N) to simulate weight bearing, and the pressure distribution on the surface of the tibia was analyzed. Biomechanical testing was conducted with a weight-bearing rig and 6 cadavers. The positions of the tibial and femoral components were changed in the coronal plane by 3° and 5° varus, and 3° and 5° valgus; and the mechanical alignment of the lower limb was analyzed. Pressure (3, 6, 9, and 12 kg) was applied from the femoral head to the distal tibia on the rig. An NK button sensor was placed between the proximal tibia and the tibial tray to measure the pressure at the tibial surface. Results: Varus or valgus positioning of the tibial or femoral components in the coronal plane led to varus or valgus malalignment of the mechanical axis of the lower limb. The coronal alignment of the lower limb could be normalized by appropriate positioning of the tibial and femoral components. The peak pressure achieved on the medial or lateral side of the tibia was determined by the varus or valgus alignment of the mechanical axis. No peak pressure was detected under conditions where the alignment was normal, even if the tibial or femoral components were malpositioned. Conclusions: Malpositioned femoral or tibial components will change the alignment of the lower limb. The peak pressure of the proximal tibia is positively related to the alignment.

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. Describing a reliable mathematical model for a phenomenon first requires accurate measurements. The key test of knee joint laxity following a ruptured anterior cruciate ligament (ACL) is the Pivot Shift Test (PST). This is usually done manually and there is poor inter observer reliability. There is currently a lack of a 'Gold Standard' for quantification and modelling of the Pivot Shift test (PST). In the literature 25 parameters have been used to describe the Pivot shift test (PST). These have generally measured antero-posterior translation, acceleration and rotation. The mathematical relationship between the various parameters has hitherto not been clarified. However, it is acknowledged that it is the sudden acceleration of anterior- posterior movement resulting from a very small change in flexion during the test that is of clinical significance. A sudden change in state resulting from a small change in a parameter is characteristic of systems that can be modelled using catastrophe theory. The aim of this study is to determine whether the Pivot Shift in the anterior cruciate deficient knee can be modelled accurately using catastrophe theory. The PST was performed on 50 consecutive ACL deficient knees by the senior author at surgery prior to and after navigated ACL reconstruction. Internal/external rotation, flexion/extension and antero-posterior translation were simultaneously recorded using the navigation software. The knees were taken through a continuous range of extension to flexion for a series of internal/external angles. The cusp model was fitted to the data and statistically analysed using the "Cusp" package for the R statistical system. The PST of the ACL deficient knee was successfully modelled as a Cusp Catastrophe. Analysis after stabilisation confirmed the absence of catastrophic behaviour. The fitted model clearly reproduces the sudden acceleration of anterior-posterior movement as flexion crosses the singularity, and all estimated parameters were significant at the p < 0.01 level. Based on this model, there are at least three subcategories of knee behaviour as revealed by the PST. 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. Introduction: Instrumented load sensors have been used for soft tissue calibration of total knee arthroplasty for years. A common criticism of the method has focused on the inert nature of the soft tissue envelope contractility under anesthesia. Furthermore, recent work has emphasized the important role of muscle action in stabilizing the knee and improving function and satisfaction. This study aims to demonstrate the quantitative changes in the load magnitude and relative distribution as patients raise their leg during a wake-up test under spinal anesthesia.

Methods: This study is a pilot study of 25 patients performing a straight leg raising maneuver under verbal command at the conclusion of a total knee arthroplasty. The spinal anesthetic formula was modified to allow earlier return of motor function. Video capture of the event was performed to measure height, knee flexion, duration and speed of the maneuver. The tibial load magnitude and relative compartmental distribution were recorded throughout.

Results: There was found to be sizable variability in the efficiency of the spinal anesthetic recipe. Smaller patients had residual motor block and either could not perform the task satisfactorily or at all. Of the 17 patients who had enough power, the relative increase in magnitude of tibial load force was in the range of 2.8 to 4.3, with an average of 3.4. The relative medial to lateral load distribution was preserved in 15 cases. There were no complications. No patient experienced any negative memory recall from the test.

Discussion: Can the relatively low passive forces and their distribution measured at surgery predict functional stability with forces encountered in weight-bearing activities? This study demonstrates that a well- balanced knee can be expected to have a predictable 3 to 4 fold increase in load across the joint under reasonable isometric muscular contraction, while preserving the medial-lateral load symmetry. The ability to preserve this compartmental load symmetry suggests that balanced load values obtained at surgery could be a predictor of clinical success.

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. 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. Implant position and scapula shape affect the impingement-free range-of-motion (IF-ROM) of a patients shoulder. Currently, methods exist to evaluate the IF-ROM during implant planning but their outcome is still difficult to interpret and quantify. Therefore, our study aims to define a software method that adequately visualises and quantifies the IF-ROM so that surgeons can easily interpret and compare the result for various implant positions and scapula geometries. 150 virtual shapes from a healthy scapula statistical shape model (SSM) were planned with a reverse glenoid implant in diverse positions. The IF-ROM was visualised on a 2D polar plot and quantified based on healthy kinematic motion data. The ROM score for a neutral implant position had a mean value of 0.85 +/- 0.04 for randomly selected scapula shapes. A lateral, inferior and posterior implant position and a negative shape coefficient in the first SSM mode improved the ROM score. The impact of implant position and scapula shape was also visible in the 2D polar plots. The plots showed that the inferior region of the kinematic motion domain was often not reachable. Hence, the resulting ROM score and ROM polar plot were both sensitive to implant position and scapula shape. A lateral, inferior and posterior implant position resulted in a better range-of-motion, which agrees with many studies in literature. Inferior impingement, or notching, is one of the major impingement occurrences and can be caused by the unreached kinematic motion domain in the inferior region of the 2D polar maps. We conclude that the ROM score and ROM polar plot proposed in this study agree well with what has been published in literature and are therefore considered as a suitable candidate to objectively evaluate and improve an implant plan during preoperative planning.