Abstract. Optimal acetabular component position in Total Hip Arthroplasty is vital for avoiding complications such as dislocation and impingement, Transverse acetabular ligament (TAL) have been shown to be a reliable landmark to guide optimum acetabular cup position. Reports of iliopsoas impingement caused by acetabular components exist. The Psoas fossa (PF) is not a well-regarded landmark for Component positioning. Our aim was to assess the relationship of the TAL and PF in relation to Acetabular Component positioning. A total of 22 cadavers were implanted on 4 occasions with the an uncemented acetabular component. Measurements were taken between the inner edge of TAL and the base of the acetabular component and the distance between the lower end of the PF and the most medial end of TAL. The distance between the edge of the acetabular component and TAL was a mean of 1.6cm (range 1.4–18cm). The distance between the medial end of TAL and the lowest part of PF was a mean of 1.cm (range 1,3–1.8cm) It was evident that the edge of PF was not aligned with TAL. Optimal acetabular component position is vital to the longevity and outcome following THA. TAL provides a landmark to guide acetabular component position. However we feel the PF is a better landmark to allow appropriate positioning of the acetabular component inside edge of the acetabulum inside the bone without exposure of the component rim and thus preventing iliopsoas impingement at the psoas notch and resultant groin pain

Introduction. Roentgen stereophotogrammetric analysis (RSA) is currently the gold standard to measure early prosthetic migration which can predict aseptic loosening. However, RSA has some limitations such as the need for perioperative placed markers and exposure to X-radiation during follow up. Therefore, this study evaluates if low field MRI could be an alternative for RSA. Low field MRI was chosen because it is less hampered by metal artifacts of the prosthesis than high field MRI. Methods. 3D models of both the tibial component of a total knee prosthesis (Genesis II, Smith and Nephew) and the porcine tibia were made. The tibial component was implanted in the tibial bone. Consequently, 17 acquisitions with the low field MRI scanner (Esaote G-scan 0.25T) in transverse direction with a 2D PD weighted metal artifact reducing sequence PD-XMAR (TE/TR 10/1020ms, slice thickness 3mm, FOV 180×180×120 mm³, matrix size 224×224) were made. The first five acquisitions were made without repositioning the cadaver, the second twelve after slightly repositioning the cadaver within limits that are expected to be encountered in a clinical setting. Hence, in these 17 acquisitions no prosthetic-bone motions were induced. The scans were segmented and registered with Mimics. Virtual translation and rotation of the prosthesis with respect to the bone between two scans were calculated using a Procrustes algorithm. The first five scans without repositioning were used to calculate the measurement error, the following twelve to calculate the precision of low field MRI to measure prosthetic migration. Results were expressed as the maximum total point motion, mean error and 95% CI and expressed in boxplots. Results. The error of the method to measure the prosthetic position without repositioning has a mean translation between 0.09 and 0.22mm with a 95%CI between 0.30 and 0.46mm. The mean rotation was between 0.02° and 0.11° with a 95%CI between 0.18° and 0.32° with a MTPM of 0.45mm. The precision of low field MRI to measure migration with repositioning has a mean translation between 0.02 and 0.12mm with a 95%CI between 1.16mm and 1.86mm. The mean rotation was between 0.01° and 0.15° with a 95%CI between 1.78° and 3.26° with a MTPM of 2.35mm. The overall registration error was largest in the distal-proximal direction. Discussion. At the moment the low field MRI technique is not as accurate as this gold standard RSA. The accuracy of RSA varies between 0.05 and 0.5 mm for translation and 0.15 ° to 1.15 ° for rotation (95% confidence intervals). However, results are comparable with markerless RSA studies. The largest measurement error was found in the distal-proximal direction, which can be explained by the through-plane resolution of 3 mm, which is larger than the in-plane resolution of 0.8×0.8 mm². Future research should focus on improving resolution in the distal-proximal direction which would improve the precision. Moreover, an actual migration study should be performed to proof the true value of this low field MRI base markerless and X-radiation free alternative to measure prosthetic migration

Osteoarthritic (OA) changes to the bone morphology of the proximal tibia may exhibit load transfer patterns during total knee arthroplasty not predicted in models based on normal tibias. Prior work highlighted increased bone density in transverse sections of OA knees in the proximal-most 10mm tibial cancellous bone. Little is known about coronal plane differences, which could help inform load transfer from the tibial plateau to the tibial metaphysis. Therefore, we compared the cancellous bone density in OA and cadaveric (non-OA) subjects along a common coronal plane. This study included nine OA patients (five women, average age 59.1 ± 9.4 years) and 18 cadaver subjects (four women, average age 39.5 ± 14.4 years). Patients (eight with medial OA and one with lateral OA) received pre-operative CT scans as standard-of-care for a unicompartmental knee replacement. Cadavers were scanned at our institution and had no history of OA which was confirmed by gross inspection during dissection. 3D reconstructions of each proximal tibia were made and an ellipse was drawn on the medial and lateral plateau using a previously published method. A coronal section (Figure 1) to standardize the cohort was created using the medial ellipse center, lateral ellipse center, and the tibial shaft center 71.5mm from the tibial spine. On this section, profile lines were drawn from the medial and lateral ellipse centers, with data collected from the first subchondral bone pixel to a length of 20mm. The Hounsfield Units (HU) along each profile line was recorded for each tibia; a representative graphical distribution is shown in Figure 2. The Area Under the Curve (AUC) was calculated for the medial and lateral sides, which loosely described the stiffness profile through the region of interest. To determine differences between the medial and lateral subchondral bone density, the ratio AUC[medial] / AUC[lateral] was compared between the OA and cadaver cohorts using a two-sample t-test. Data from the sole lateral OA patient was mirror-imaged to be included in the OA cohort. The majority of the OA patients appeared to have higher subchondral bone density on the affected side. Figure 3 compares the medial and laterals sides of each group using the AUC ratio method described above. For the cadaver group the AUC was 1.2 +/− 0.22, with a median of 1.1 [0.9 1.6], smaller than the mean AUC for the OA group, which was 1.4 +/− 0.39, with a median of 1.6 [0.93 2.1]. The p-value was 0.06. The increased density observed in OA patients is consistent with asymmetric loading towards the affected plateau, resulting in localized remodeling of cancellous bone from the epiphysis to metaphysis. From the coronal plane, bone was often observed in OA patients bridging the medial plateau to the metaphyseal cortex. Although the cadaver subjects were normal from history and gross inspection, some subjects exhibited early bone density changes consistent with OA. Future work looks to review more OA scans, extend the work to the distal femur, and convert the HU values to bone elastic moduli for use in finite element modelling

Aims. Accurate placement of acetabular and femoral stem components in total hip arthroplasty (THA) is an important factor in the success of the procedure. A variety of free hand or navigated techniques is reported. Survivorship and complications have been shown to be directly related to implant position during THA. The aim of this cadaver study was to assess the accuracy of the placement of the components in THA using patient specific instruments (PSI) in combination with a 3D planning software and the direct anterior approach. Method. Patient specific instruments (PSI) were developed to guide the surgeon during THA that were 3D printed with their bone models following a 3D software planning protocol (LPH software V2.5.1, Onefit-Medical, Eos Imaging Company, Besancon, France). Acetabular guides: cup, offset and straight reamer handle and impactor, femoral- and chisel guides were used in each THA (Fig. 1). To define anatomic bone landmarks and to generate a 3D model of each hip joint CT scans were performed preoperatively. The planning of component position was done by one surgeon (AZ) preop. Surgery was performed by two experienced surgeons (AZ, SD) on cadaver specimen with 4 hips in two separate series. A total of 8 hip replacements were evaluated pre- and postoperatively using CT-scans of each hip joint to compare planned to achieved results. Mechanical simulations of the guides were carried out to verify that there were no conflicts between the different instruments. To meet the ISO standard 16061: 2015 the compatibility of the instruments with the guides has been checked. Parameters were evaluated in 3D pelvic and femoral planes: center cup position, inclination angle, anteversion angle, cutting height and plan orientation, anteversion angle, flexion/extension angle, varus/valgus angle, anatomical and functional leg length, offset. Acceptance criteria: postop. parameters evaluated must not have a deviation of more than 5 degrees, 2,5 mm according to preop. planning. For every THA the test protocol has been completely realized. Results. The difference between the preop. and postop. measures in the first series of 4 hips revealed 2 outliers because of fractures of the acetabulum in 2 cases, related to bad cadaver quality. In the second series we found satisfactory results comparing the planned preop and postop component position (Fig. 2). For example difference of leg length showed a mean absolute of 1,58 mm, standard deviation 1,21 mm (min 0,62; max 3,34 mm). Offset revealed a mean absolute of 1,62 mm, standard deviation 0,57 mm (min 1,06; max 2,14 mm) concerning the difference between preop. planning and result postop. Conclusion. Accurate and safe placement of total hip components in THA, both acetabular cup and stem, performing the direct anterior approach can be achieved using a 3D preoperative planning along with patient specific instruments. The results of the cadaver study tests are promising and that is to be proven in the clinical setting and by application in the future

We introduce a novel active tensioning system that can be used for dynamic gap-based implant planning as well as for assessment of final soft tissue balance during implant trialing. We report on the concept development and preliminary findings observed during early feasibility testing in cadavers with two prototype systems. System description. The active spacer (fig 1) consists of a motorized actuator unit with integrated force sensors, independently actuated medial and lateral upper arms, and a set of modular attachments for replicating the range of tibial baseplate and insert trial sizes. The spacer can be controlled in either force or position (gap) control and is integrated into the OMNIBotics. TM. Robotic-assisted TKA platform (OMNI, MA, USA). Cadaver Study. Two design iterations were evaluated on eleven cadaver specimens by seven orthopaedic surgeons in three separate cadaver labs. The active spacer was used in a tibial-first technique to apply loads and measure gaps prior to and after femoral resections. To determine the range of forces applied on the spacer during a varus/valgus assessment procedure, each surgeon performed a varus/valgus stress test and peak medial and lateral forces were measured. Surgeons also rated the feel of the stability of the knee at 50N and 80N of preload using the following scale: 1 – too loose; 2 – slightly loose; 3 – ideal; 4 slightly tight; 5 – too tight. Final balanced was assessed with the spacer and with manual trial components. Results. Overall the prototype system successfully met the functional requirements for applying controlled tension during ligament balancing, and user feedback on usability and feasibility for use in TKA was highly positive. Peak forces measured during blinded stability assessments were significantly imbalanced from medial to lateral and exhibited a wide range across users (range: 70N – 310N, table 1). Each surgeon rated 50N of tension as feeling “slightly loose” and 80N as feeling “ideal” in extension. “Ideal” soft tissue balance was achieved in the last three knees tested using the second design iteration, as rated by the surgeons with final trial components in place. Discussion. Our preliminary cadaver results have established the initial feasibility of the active spacer concept for applying tension during ligament balancing and implant planning. Our initial results also suggest that performing a varus/valgus assessment without force readings can lead to imbalanced mediolateral load application. This may be due to factors such as hand dominance and pulling in varus versus pushing in valgus. There was also considerable inter-surgeon variability in the peak forces applied. An advantage of computer-controlled ligament tensioning and force sensing is ability to standardize applied mediolateral forces across patients and surgeons. In the assessment of the ‘ideal' static ligament tension in extension a force of 80N was preferred over 50N, which is in the range of forces applied by others during ligament balancing. What is the ideal patient specific force to apply remains a topic of future research. Our next steps will be to further evaluate use of the system in the context of virtual trialing

Introduction. Knee instability, stiffness, and soft-tissue imbalance are causes of aseptic revision and patient dissatisfaction following total knee arthroplasty (TKA). Surgical techniques that ensure optimal ligament balance throughout the range of motion may help reduce TKA revision for instability and improve outcomes. We evaluated a novel tibial-cut first gap balancing technique where a computer-controlled tensioner is used to dynamically apply a varying degree of distraction force in real-time as the knee is taken through a range of motion. Femoral bone cuts can then be planned while visualizing the predicted knee implant laxity throughout the arc of flexion. Surgical Technique Description. After registering the mechanical axes and morphology of the tibia and femur using computer navigation, the tibial resection was performed and a robotic tensioning tool was inserted into the knee prior to cutting the femur. The tool was programmed to apply equal loads in the medial and lateral compartments of the knee, but to dynamically vary the distraction force in each compartment as the knee is flexed with a higher force being applied in extension and a progressively lower force applied though mid-flexion up to 90° of flexion. The tension and predictive femoral gaps between the tibial cut and the femoral component in real-time was determined based on the planned 3D position and size of the femoral implant and the acquired pre-resection gaps (figure 1). Femoral resections were then performed using a robotic cutting guide and the trial components were inserted. Methods. The technique was evaluated by three experienced knee arthroplasty surgeons on 4 cadaver knees (3 torso-to-toe specimens, Pre-operative deformity range: 4° varus − 6° valgus; Extension lag: 0° – 13°; BMI 23.4 – 32.6; Age 68 – 85yr). An applied targeted load of 80N in extension and 50N in flexion was used in each of the four knees. These force values were determined in a prior cadaver study aimed at determining what magnitude of applied load corresponded to an optimally rated knee tension and stability. The femoral component was planned in each of the four knees to have symmetric gaps at 0° and 90° of flexion. The overall balance of the knee was assessed clinically by each surgeon using a varus/valgus stress test with the trial components inserted. No soft-tissue releases were performed other than a standard medial release during initial exposure of the knee. The following scale was used to rate the final knee stability achieved: 1 – too loose; 2 – slightly loose; 3 – ideal; 4 slightly tight; 5 – too tight. Results. ‘Ideal' balance was achieved in three out of the four knees tested (table 1). In two of the four knees the final inserted thickness selected was 1mm thicker than the planned insert thickness. Conclusions. Our preliminary cadaver results suggest that it is possible to achieve a balanced knee by incorporating dynamic ligament tensioning and gap data throughout flexion into the femoral planning process using a robotic tensioning tool. For figures/tables, please contact authors directly.

Introduction. The large diameter mobile polyethylene liner of the dual mobility implant provides increased resistance to hip dislocation. However, a problem specific to the dual mobility system is intra-prosthetic dislocation (IPD), secondary to loss of the retentive rim, causing the inner head to dissociate from the polyethylene liner. We hypothesized that impingement of the polyethylene liner with the surrounding soft-tissue inhibits liner motion, thereby facilitating load transfer from the femoral neck to the liner and leading to loss of retentive rim over time. This mechanism of soft-tissue impingement with the liner was evaluated via cadaver experiments, and retrievals were used to assess polyethylene rim damage. Methods. Total hip arthroplasty was performed on 10 cadaver hips using 3D printed dual mobility components. A metal wire was sutured to the posterior surface (underside) of the iliopsoas, and metal wires were embedded into grooves on the outer surface of the liner and inner head to identify these structures under fluoroscopy. Tension was applied to the iliopsoas to move the femur from maximum hyperextension to 90° of flexion for the purpose of visualizing the iliopsoas and capsule interaction with the mobile liner. The interaction of the mobile liner with the iliopsoas was studied using fluoroscopy and direct visual observation. Fifteen retrieved dual mobility liners were assessed for rim edge and rim chamfer damage. Rim edge damage was defined as any evidence of contact, and rim chamfer damage was classified into six categories: impact ribs on the chamfer surface, loss of machining marks, scratching or pitting, rim deformation causing a raised lip, a rounded rim edge, or embedded metal debris. Results. Manipulation of the cadaver specimens through full range of motion showed liner impingement with the iliopsoas tendon in low flexion angles, which impeded liner motion. At high flexion angles (beyond 30°), the iliopsoas tendon moved away from the liner and impingement was not observed. The fluoroscopy tests using the embedded metal wires confirmed what was observed during manual manipulation of the specimen. When observing the hip during maximum hyperextension, 0°, 15°, and 30° of flexion, there was obvious tenting of the iliopsoas. All retrieved components showed damage on the rim and the chamfer surface. The most common damage seen was scratching/ pitting. There was no association between presence of damage and time in vivo controlling for age and Body Mass Index (p≥0.255). Discussion. The cadaver studies showed that the mobile liner motion could be impeded by impingement with the iliopsoas tendon and hip capsule. Visual and fluoroscopic observation showed impingement of iliopsoas and hip capsule with the distal portion of the mobile liner, particularly during low flexion angles. All retrieved liners showed damage despite their limited time in vivo and despite being retrieved for reasons other than IPD. This suggests that soft-tissue impingement may inhibit liner motion routinely in vivo, resulting in load transfer from the femoral neck on to the rim of the liner. This may be an important mechanism for IPD

NavioPFS™ is a hand-held robotic technology for bone shaping that employs computer control of a high-speed bone drill. There are two control modes – one based on control of exposure of the cutting bur and another based on the control of the speed of the cutting bur. The unicondylar knee replacement (UKR) application uses the image-free approach in which a mix of direct and kinematic referencing is used to define all parameters relevant for planning. After the bone cutting plan is generated, the user freely moves the NavioPFS handpiece over the bone surface, and carves out the parts of the bone targeted for removal. The real-time control loop controls the depth or speed of cut, thus resulting in the planned bone preparation. This experiment evaluates the accuracy of bone preparation and implant placement on cadaveric knees in a simulated clinical setting. Three operators performed medial UKR on two cadaver specimens (4 knees) using a proprietary implant design that takes advantage of the NavioPFS approach. In order to measure the placement of components, each component included a set of 8 conical divots in predetermined locations. To establish a shared reference frame, a set of four fiducial screws is inserted in each bone. All bones were cut using a 5 mm spherical bur. Exposure Control was the primary mode of operation for both condylar cuts – although the users utilised Speed Control to perform some of the more posterior burring activities and to prepare the peg holes. Postoperatively, positions of conical divots on the femoral and tibial implants and on the respective four fiducial screws were measured using a Microscribe digitising arm in order to compare the final and the planned implant position. All implants were placed within 1.5 mm of target position in any particular direction. Maximum translation error was 1.31 mm. Maximum rotational error was 1.90 degrees on a femoral and 3.26 degrees on a tibial component. RMS error over all components was 0.69mm/1.23 degrees. This is the first report of the performance of the NavioPFS system under clinical conditions. Although preliminary, the results are overall in accordance with previous sawbones studies and with the reports from comparable semi-active robotic systems that use real time control loop to control the cutting performance. The use of NavioPFS in UKR eliminates the need for conventional instrumentation and allows access to the bone through a reduced incision. By leveraging the surgeon's skill in manipulating soft tissues and actively optimising the tool's access to the bone, combined with the precision and reproducibility of the robotic control of bone cutting, we expect to make UKR surgery available to a wider patient population with isolated medial osteoarthritis that might otherwise receive a total knee replacement. In addition to accurate bone shaping with a handheld robotically controlled tool, NavioPFS system for UKR incorporates a CT-free planning system. This approach combines the practical advantages of not requiring pre-operative medical images, while still accurately gathering all key information, both geometric and kinematic, necessary for UKR planning

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

Sensitive and accurate measures of osteolysis around TKR are needed to enhance clinical management and assist in planning revision surgery. Therefore, our aim was to examine, in a cadaver model of osteolysis around TKR, the sensitivity of detection and the accuracy of measuring osteolysis using Xray, CT and MRI. Fifty-four simulated osteolytic lesions were created around six cadaver knees implanted with either a cemented or cementless TKR. Twenty-four lesions were created in the femur and thirty in the tibia ranging in size from 0.7 cm3 to 14 cm3. Standard anteroposterior and lateral fluoroscopically guided radiographs, CT and MRI scans with metal reduction protocols were taken of the knees prior to the creation of lesions and at every stage as the lesion sizes were enlarged. The location, number and size of the lesions from images obtained by each method were recorded. The sensitivity of osteolytic lesion detection was 44% for plain radiographs, 92% for CT and 94% for MRI. On plain radiographs, 54% of lesions in the femur and 37% of lesions in the tibia were detected. None of the six posterior lesions created in the tibia were detected on the AP radiographs; however, three of these six lesions were detected on the lateral radiographs. CT was able to detect lesions of all sizes, except for four lesions in the posterior tibia (mean volume of 1.2 cm3, range 1.06–1.47 cm3). Likewise, MRI was very sensitive in detecting lesions of all sizes, with the exception of three lesions, two of which were in the femur and one was in the medial condyle of the tibia (mean volume of 1.9 cm3, range 1.09–3.14 cm3). Notably, all six posterior tibial lesions, which could not be detected using AP radiographs, were detected by MRI. This study demonstrates the high sensitivity of both CT and MRI (which uses no ionising radiation) to detect simulated knee osteolysis and can therefore be used to detect and monitor progression of osteolysis around TKR. The study also shows the limitations of plain radiographs to assess osteolysis

Introduction. Posterolateral tibial plateau fractures account for 7 % of all proximal tibial fractures. Their fixation often requires posterolateral buttress plating. Approaches for the posterolateral corner are not extensile beyond the perforation of the anterior tibial artery through the interosseous membrane. This study aims to provide accurate data about the inferior limit of dissection by providing measurements of the anterior tibial artery from the lateral joint line as it pierces the interosseous membrane. Materials and Methods. Forty unpaired adult lower limbs cadavers were used. The posterolateral approach to the proximal tibia was performed as described by Frosch et al. Perpendicular measurements were made from the posterior limit of the articular surface of the lateral tibial plateau and fibula head to the perforation of the anterior tibial artery through the interosseous membrane. Results. The anterior tibial artery coursed through the interosseous membrane at 46.3 +/− 9.0 mm (range 27–62 mm) distal to the lateral tibial plateau and 35.7 +/− 9.0 mm (range 17–50 mm) distal to the fibula head. There was no significant difference between right or left sided knees. Discussion. This cadaveric study demonstrates the safe zone (min 27 mm, mean 45mm) up to which distal exposure can be performed for fracture manipulation and safe application of a buttress plate for displaced posterorlateral tibial plateau fractures. Evidence demonstrates quality of reduction correlates with clinical outcome and the surgeon can expect to be able to use a small fragment buttress plate of up to 45mm as this is the mean

Introduction. Dual Mobility (DM) implants have gained popularity for the treatment and prevention of hip dislocation, with increased stability provided by a large diameter mobile insert. However, distal regions of the insert may impinge on soft tissues like the iliopsoas, leading to groin pain. Additionally, soft-tissue impingement may trap the mobile insert, leading to excessive loading of the insert rim from engagement with the femoral neck and subsequent intra-prosthetic dislocation. To address this, an Anatomically Contoured Dual Mobility (ACDM) insert with a soft-tissue friendly distal geometry was developed (Fig.1). Previously, the ACDM insert was shown to maintain the femoroacetabular contact area and joint stability of a conventional DM insert [Duffy et al. BJJ 2013, 95-B:34, p298; Zumbrunn et al. BJJ 2013, 95-B:34, p605]. The goal of this study was to utilize cadaver specimens to verify whether the ACDM insert could reduce soft-tissue impingement relative to a conventional DM insert. Methods. Fluoroscopic imaging was used to evaluate soft-tissue interaction with ACDM and conventional DM inserts in four cadaver hips (Fig. 2). A metal wire was sutured to the deep fibers of the iliopsoas muscle/tendon, and metal wires were embedded in the inner head and the mobile insert for fluoroscopic visualization. All soft tissue except the anterior hip capsule and iliopsoas were removed, and a rope was attached to the iliopsoas to apply tension along its native orientation. A femoral stem and a DM acetabular shell were implanted sothe ACDM or conventional DM inserts, together with the inner heads, could be inserted. Fluoroscopic images of the hip joint were taken at maximum hyperextension, 0°, 15° and 30° hip flexion with the insert positioned in neutral and anteverted orientations (Fig. 2). Neutral orientation corresponded to the insert axis parallel to the femoral neck, while anteverted orientation corresponded to a flexed insert that contacted the femoral neck posteriorly. Results. In all hips, fluoroscopic images revealed iliopsoas tenting with the conventional DM insert, and impingement of the iliopsoas occurred at low hip flexion angles (hyperextension, 0°, 15°) with the insert in neutral and anteverted orientations (Fig. 2 and 3). Further, at certain low flexion positions during dynamic motion, the movement of the conventional DM insert was blocked due to trapping of the insert by the anterior soft tissue and the femoral stem (Fig. 2B). At flexion angles above 30°, the iliopsoas moved away from the mobile insert and no impingement was seen. In all hips, the soft-tissue impingement and insert trapping was significantly reduced with the ACDM insert (Fig. 2 and 3). The reduction in impingement occurred with the insert in both neutral and anteverted orientations, although it was more evident for the latter. Conclusion. This study showed that conventional DM inserts impinge against the iliopsoas in low flexion, and their motion can be blocked by soft-tissue impingement. The Anatomically Contoured Dual Mobility (ACDM) insert significantly reduced this undesirable soft-tissue impingement. Thus, the ACDM insert may reduce the risk of groin pain and intra-prosthetic dislocation resulting from soft-tissue impingement and entrapment of the mobile insert

Introduction. Regarding TKA, patient specific cutting guides (PSCG), which have the same fitting surface with patient's bones or cartilages and uniquely specify the resection plane by fitting guides with bones, have been developed to assist easy, low cost and accurate surgery. They have already been used clinically in Europe and the USA. However little has been reported on clinical positioning accuracy of PSCG. Generally, the methods of making PSCG can be divided into 3 methods; construct 3D bone models with Magnetic Resonance (MR) images, construct 3D bone models with Computed Tomography (CT) images, and the last is to construct 3D bone models with both MR and CT images. In the present study, PSCG were made based on 3D bone models with CT images, examined the positioning accuracy with fresh-frozen cadavers. Materials and Methods. Two fresh-frozen cadavers with four knees were scanned by CT. Image processing software for 3D design (Mimics Ver. 14, Marialise Inc.) was used to construct 3D bone model by image thresholding. We designed femoral cutting guides and tibial cutting guides by CAD software (NX 5.0, Siemens PLM Software Co.). CT free navigation system (VectorVision Knee, BrainLab, Inc.) was used to measure positioning error. Average absolute value of positioning error for each PSCG was derived. Results. The average absolute value of positioning error in femoral PSCG was 1.5±0.8° for varus/valgus, 2.3±1.9° for extension/flexion, 1.2±1.8 mm for bone resection. The stability of femoral PSCG was satisfactory. The average absolute value of positioning error in tibial PSCG was 4.3±2.5° for varus/valgus, 5.2±3.3° for anterior slope/posterior slope, 2.6±1.1 mm for bone resection. The stability of tibial PSCG was not sufficient. Discussion. PSCG of the present study were made based on CT images, mainly designed to be fit with cortex, keeping away from cartilage or osteophytes. The fitting surfaces of distal femoral PSCG covered anterior femoral cortex. Also, the fitting surface of tibial PSCG fit to anterior medial cortex of horizontal tibial tuberosity. The average absolute value of positioning error by tibial PSCG varied widely. The main cause for this was their contacts with patellar tendon. Lateral sides of PSCG were contacted with patella tendon near the tibial tuberosity, they were pushed medially. Positioning accuracy of the femoral PSCG is thought to be enough for clinical application

Introduction. The number of total hip arthroplasties has been increasing worldwide, and it is expected that revision surgeries will increase significantly in the near future. Although reconstructing normal hip biomechanics with extensive bone loss in the revision surgery remains challenging. The custom−made acetabular component produced by additive manufacturing, which can be fitted to a patient's anatomy and bone defect, is expected to be a predominant reconstruction material. However, there have been few reports on the setting precision and molding precision of this type of material. The purpose of this study was to validate the custom−made acetabular component regarding postoperative three−dimensional positioning and alignment. Methods. Severe bone defects (Paprosky type 3A and 3B) were made in both four fresh cadaveric hip joints using an acetabular reamer mimicking clinical cases of acetabular component loosening or osteolysis in total hip arthroplasty. On the basis of computed tomography (CT) after making the bone defect, two types of custom−made acetabular components (augmented type and tri−flanged type) that adapted to the bone defect substantially were produced by an additive manufacturing machine. A confirmative CT scan was taken after implantation of the component, and then the data were installed in an analysis workstation to compare the postoperative component position and angle to those in the preoperative planning. Results. The mean absolute deviations of the center of the hip joint between preoperative planning and the actual component position in the augmented type were 0.7 ± 0.4 mm for the horizontal position, 0.2 ± 0.1 mm for the vertical position, and 0.5 ± 0.3 mm for the antero−posterior position. The mean absolute deviations of the center of the hip joint in the tri−flanged type in the horizontal, vertical, and antero−posterior positions were 1.0 ± 0.4 mm, 0.4 ± 0.2 mm, 0.3 ± 0.1 mm, respectively. The mean absolute deviations of the component angle were 3.5° ± 0.9° at inclination and 2.0° ± 1.7° at anteversion in the augmented type and 0.6° ± 0.5° at inclination and 0.9° ± 0.3° at anteversion in the tri−flanged type. Conclusion. Since custom−made orthopaedic implants produced by additive manufacturing can support individual anatomy and bone defect, this type of implant is expected to be applied to revision surgery and bone tumor surgery for severe bone defects. The present study demonstrated that preoperative planning of the center of the hip joint was successfully reproduced after the implantation of both types of custom−made acetabular components. In the tri−flanged type, better satisfactory results were provided in the component position and angle by comparing the past CAOS tools such as a surgical navigation system and a patient−specific guide. There is scope for further improvement, but the custom−made acetabular component produced by additive manufacturing may become very useful reconstruction material in hip revision surgeries. Problems to be addressed in the future include the improvement of the reproducibility of the preoperative planning and investigation of long−term clinical results

Hypothesis. Recurrent shoulder dislocation is associated with bony defect of the glenoid rim, commonly seen along with bankart tear - a soft tissue injury of glenoid labrum. This cadaveric study compares the bone block effect of coracoid transfer using using two common techniques, Classical Latarjet technique and the Congruent-Arc Latarjet. We hypothesized that the force needed to dislocate the shoulder would be greater in Congruent Arc technique than the Classical Latarjet, because of increased contact surface area as a result of greater linear dimensions. Material and methods. We dissected 14 cadaveric shoulders. A bony Bankart lesion was created in form of an inverted pear glenoid. The humeral head was attached to a pulley system that was sequentially loaded until the shoulder dislocated anteriorly. The force needed to dislocate was noted. This was repeated after coracoid transfer with two common techniques, Classical Latarjet technique and the Congruent-Arc Latarjet. Results. The mean force required to dislocate shoulder post-Classical Latarjet technique was 325.71N, compared to 123.57 N in uncorrected shoulder. Similarly, the mean force required to dislocate shoulder post Congruent-Arc Latarjet technique was 327.14 N compared to 123.57 N in uncorrected shoulder. The two-tailed P value in either case was less than 0.0001, thus statistically significant. Unpaired t-test was done to compare the force required to dislocate the shoulder post procedure. Mean force required to dislocate shoulder post-Classical Latarjet, was 325.7N compared to 327N in post-Congruent Arc. The two-tailed P value equals 0.9020 and the 95% confidence interval was from −25.05 to 22.19, thus the difference was not statistically significant. Conclusion. The results confirm that both (Classical and Congruent-Arc Latarjet) techniques are good for addressing the shoulder instability, however bone block effect provided by one is not superior to other

In order to avoid complications of hip arthroplasty such as dislocation, impingement and eccentric liner wear accurate acetabular orientation is essential. The three-dimensional assessment of acetabular cup orientation using two-dimensional plain radiographs is inaccurate. The aim of this study was to develop a CT-based protocol to accurately measure postoperative acetabular cup inclination and anteversion establishing which bony reference points facilitate the most accurate estimation of these variables. An all-polyethylene acetabular liner was implanted into a cadaveric acetabulum. A conventional pelvic CT scan was performed and reformatted images created in both functional and anterior pelvic planes. CT images were transferred to a Freedom-Plus Graphics software package enabling an identical, virtual, three dimensional model of the cadaveric pelvis to be created. Using a computer interface this model could be ‘palpated’, bony landmarks accurately identified and definitive acetabular cup orientation established. Using original CT scans, acetabular cup inclination and anteversion were measured on five occasions by eight radiographers using differing predetermined bony landmarks as reference points. The intra- and inter-observer variation in measurement of acetabular cup orientation using varying bony reference points was assessed in comparison to the previously elucidated definitive cup position. Statistical analysis using appropriate ANOVA models was performed in order to assess the significance of the results obtained. Virtually derived definitive acetabular cup orientation was measured showing cup inclination and anteversion as 41.0 and 22.5 degrees respectively. Mean CT-based measurement of cup inclination and anteversion by eight radiographers were 43.1 and 20.8 degrees respectively. No statistically significant difference was found in intra- and inter-observer recorded results. No statistically significant differences were found when using different bony landmarks for the measurement of inclination and anteversion (p= 0.255 and 0.324 respectively). CT assessment of acetabular component inclination and anteversion is accurate, reliable and reproducible when measured using differing bony landmarks as reference points. We recommend measuring acetabular inclination and anteversion from the inferior acetabular wall/teardrop and posterior ischium respectively. The Perth CT hip protocol is easily reproducible in the clinical setting both in the routine assessment of hip arthroplasty patients and as research tool. In our unit its initial application will be to validate commercially available hip navigation systems

Implant alignment in knee arthroplasty has been identified as critical factor for a successful outcome. Human error during the registration process for imageless computer navigation knee arthroplasty directly affects component alignment. This cadaveric study aims to define the error in the registration of the landmarks and the resulting error in component alignment. Five fresh frozen cadaveric limbs including the hemipelvis were used for the study. Five surgeons performed the registration process via a medial parapatellar approach five times. In order to identify the gold standard point, the soft tissues were stripped and the registration was repeated by the senior author. Errors are presented as mm or degrees from the gold standard registration. The error range in the registration of the femoral centre in the coronal plane was 6.5mm laterally to 5.0mm medially (mean: −0.1, SD: 2.7). This resulted in a mechanical axis error of 5.2 degrees valgus to 2.9 degrees varus (mean: 0.1, SD: 1.1). In the sagittal plane this error was between −1.8 degrees (extension) and 2.7 degrees (flexion). The error in the calculation of the tibial mechanical axis ranged from −1.0 (valgus) to 2.3 (varus) degrees in the coronal plane and −3.2 degrees of extension to 1.3 degrees of flexion. Finally the error in calculating the transepicondylar axis was −11.2 to 6.3 degrees of internal rotation (mean: −3.2, SD: 3.9). The error in the registration process of the anatomical landmarks can result in significant malalignment of the components. The error range for the mechanical axis of the femur alone can exceed the 3 degree margin that has been previously been associated with implant longevity. The technique during the registration process is of paramount importance for image free computer navigation. Future research should be directed towards simplifying this process and minimizing the effect of human error

INTRODUCTION. In native knees the anterior cruciate ligament (ACL) plays a major role in joint stability and kinematics. Sacrificing the ACL in contemporary total knee arthroplasty (TKA) is known to cause abnormal knee motion, and reduced function. Hence, there is growing interest in the development of ACL retaining TKA implants. Accommodation of ACL insertion around the tibial eminence is a challenge with these designs. Therefore, a reproducible and practical test setup is necessary to characterize the strength of the ACL/bone construct in ACL retaining implants. Seminal work showed importance of loading the ACL along its anatomical orientation. However, prior setups designed for this purpose are complex and difficult to incorporate into a standardized test for wide adoption. The goal of this study was to develop a standardized and anatomically relevant test setup for repeatable strength assessment of ACL construct using basic force-displacement testing equipment. METHODS. Cadaver knees were positioned with the ACL oriented along the loading axis and being the only connection between femur and tibia. 15° knee flexion was selected based on highest ACL tensions reported in literature. Therefore, the fixtures were adjusted accordingly to retain 15° knee flexion when the ACL was tensioned. The test protocol included 10 cycles of preconditioning between 6N and 60N at 1mm/s, followed by continuous distraction at 1mm/s until failure (Fig. 1). Eleven cadaveric knees (4 male, 7 female; 70.9 yrs +/−13.9 yrs) were tested using this setup to characterize a baseline ACL pullout strength (peak load to failure) in native knees. RESULTS. The average ACL pullout strength was 935.6N +/−327.5N with the extremes ranging from a minimum of 346N to a maximum of 1425N. There were five failure modes observed: [1] ACL avulsion from the femur with bony attachment (one knee), [2] ACL pull-off from the femur w/o bony attachment (two knees), [3] ACL tear (three knees), [4] ACL pull-off from the tibia w/o bony attachment (one knee), [5] ACL avulsion from the tibia with bony attachment (three knees). One knee showed a combined failure mode of 2 & 4, meaning part of the ACL was pulled off the femur and part pulled off the tibia. CONCLUSION. There was a large variation in failure load between specimens. The knee with the minimum failure load had severe arthritis, osteophytes and signs of ACL deficiency. The average failure load (935.6N +/−327.5N) is in line with those published in literature for a comparable age group. This indicates that failure loads and modes obtained with more complex setups could be reproduced by using standard uniaxial load frames and simple fixtures. The failure modes in our experiment were evenly spread between mid-substance, and insertions (either femur or tibia). This test could be used as a standardized method to investigate the strength of the ACL complex following procedures such as ACL reconstruction, partial- and total knee arthroplasty. In particular, this setup provides a reliable mechanism for evaluation of the ACL-bone construct in bi-cruciate retaining (BCR) TKA, which is likely required for regulatory pathways

Introduction. Simulation is increasingly perceived as an important component of surgical training. Cadaveric simulation offers an experience that can closely simulate operating on a living patient. We have explored the feasibility of providing cadaveric training for the whole curriculum for trauma and orthopaedic surgery speciality trainees, before they perform those operations on living patients. Methods. An eight station surgical training centre was designed and built adjacent to the mortuary of a University Hospital. Seven two-day courses for foot and ankle, knee, hip, spine, shoulder and elbow, hand and wrist, and trauma surgery were designed and delivered. These courses, designed for 16 trainees, were delivered by eight consultant trainers and a course director. Each was structured to allow every trainee to perform each standard operation in the curriculum for that respective subspecialty. We designed the courses to maximise simulated operating time for the trainees and to minimise cost. We surveyed trainers and trainees after the courses to qualitatively assess their value. Results. We found that it was possible to create a state-of-the-art surgical training centre in a University Hospital with a business model that could be replicated. It was possible to deliver cadaveric surgical training to trainees, early in their experience in that subspecialty, such that they learn the principles of each operation in the curriculum in the course of two days. This required some very intense work: for example the foot and ankle course included 30 surgical procedures. Trainees and trainers rated this experience as very high quality training and judge that it will substantially affect the safety and value of future training with living patients. Conclusion. We suggest that our findings support the idea of cadaveric training for all trainees before operating on living patients. We are implementing this in our training programme

A functional total knee replacement has to be well aligned, which implies that it should lie along the mechanical axis and in the correct axial and rotational planes. Incorrect alignment will lead to abnormal wear, early mechanical loosening, and patellofemoral problems. There has been increased interest of late in total knee arthroplasty with robot assistance. This study was conducted to determine if robot-assisted total knee arthroplasty is superior to the conventional surgical method with regard to the precision of implant positioning. Twenty knee replacements of ten robot-assisted and another ten conventional operations were performed on ten cadavers. Two experienced surgeons performed the surgery. Both procedures were undertaken by one surgeon on each cadaver. The choice of which was to be done first was randomized. After the implantation of the prosthesis, the mechanical-axis deviation, femoral coronal angle, tibial coronal angle, femoral sagittal angle, tibial sagittal angle, and femoral rotational alignment were measured via three-dimensional CT scanning. These variants were then compared with the preoperative planned values. In the robot-assisted surgery, the mechanical-axis deviation ranged from −1.94 to 2.13° (mean: −0.21°), the femoral coronal angle ranged from 88.08 to 90.99° (mean: 89.81°), the tibial coronal angle ranged from 89.01 to 92.36° (mean: 90.42°), the tibial sagittal angle ranged from 81.72 to 86.24° (mean: 83.20°), and the femoral rotational alignment ranged from 0.02 to 1.15° (mean: 0.52°) in relation to the transepicondylar axis. In the conventional surgery, the mechanical-axis deviation ranged from −3.19 to 3.84°(mean: −0.48°), the femoral coronal angle ranged from 88.36 to 92.29° (mean: 90.50°), the tibial coronal angle ranged from 88.15 to 91.51° (mean: 89.83°), the tibial sagittal angle ranged from 80.06 to 87.34° (mean: 84.50°), and the femoral rotational alignment ranged from 0.32 to 4.13° (mean: 2.76°) in relation to the transepicondylar axis. In the conventional surgery, there were two cases of outlier outside the range of 3° varus or valgus of the mechanical-axis deviation. The robot-assisted surgery showed significantly superior femoral-rotational-alignment results compared with the conventional surgery (p=0.006). There was no statistically significant difference between robot-assisted and conventional total knee arthroplasty in the other variants. All the variants were measured with high intraobserver and interobserver reliability. In conclusion, Robot-assisted total knee arthroplasty showed excellent precision in the sagittal and coronal planes of the three-dimensional CT. Especially, better accuracy in femoral rotational alignment was shown in the robot-assisted surgery than in the conventional surgery despite the fact that the surgeons who performed the operation were more experienced and familiar with the conventional surgery than with robot-assisted surgery. It can thus be concluded that robot-assisted total knee arthroplasty is superior to the conventional total knee arthroplasty