INTRODUCTION. Thorough understanding and feedback of the post-operative implant position relative to the pre-operative anatomy is missing in today's clinical practice. However, three dimensional insights in the local under or oversizing of the implant can provide important feedback to the surgeon. For the knee for instance, to identify a shift in the sagittal joint line that potentially links to mid-flexion instability or to identify zones at risk for soft tissue impingement. Despite a proven inferior outcome, clinical post-operative implant evaluation remains primarily based on bi-planar, static 2D x-rays rather than 3D imaging. Along with the cost, a possible reason is the increased radiation dose and/or metal artifact scatter in computed tomography (CT) and/or magnetic resonance imaging (MRI). These detrimental effects are now avoided by using recently released x-ray processing software. This technique uses standard-of-care post-operative x-rays in combination with a pre-operative CT and 3D file of the implant to determine the implant position relative to the pre-operative situation. The accuracy of this new technique is evaluated in this paper using patient cases. Therefore, the obtained implant position is benchmarked against post-operative CT scans. MATERIALS & METHODS. Retrospectively, 19 patients were selected who underwent total knee arthroplasty and received pre- and post-operative CT of their diseased knee. The CT scans were performed with a pixel size of 0.39 mm and slice spacing of 0.60 mm (Somatom, Siemens, München, Germany). All patients underwent TKA surgery using the same bi-cruciate substituting total knee (Journey II, Smith&Nephew, Memphis, USA). Following surgery, standard bi-planar standing x-rays of the operated knee was additionally performed as standard of care. To evaluate the implant position relative to the pre-operative situation, the 3D implants are first positioned on the post-operative CT slices. Using Mimics (Materialise NV, Leuven, Belgium), the pre-operative bone was subsequently automatically matched onto the post-operative scan to identify the implant location relative to the reconstructed pre-operative bone. This has been independently repeated by three observers to assess the inter-observer variability. Second, the post-operative bi-planar x-rays are combined with the reconstructed pre-operative bone and 3D file of the implant. This combination is performed using the 2D-to-3D conversion integrated in the recently launched X-ray module of Mimics. This module uses a contour based registration method to determine the implant and bone position using the post-operative x-rays. For both reconstruction methods, the implant position has been evaluated in six degrees of freedom using an automated Matlab routine; resulting in three translations and three rotations. RESULTS. From the evaluated implant positions, the root mean square error was derived between subsequent measurements. For the CT reconstruction based inter-observer evaluation, the median RMS error for all degrees of freedom is below 1 mm and 1 degree for both the femoral and tibial implant. Comparing the reconstructed CT implant position with the 2D-to-3D reconstruction, the median RMS difference between the implant positions remains below 1 mm and 1 degree except for the distraction/compression component and the internal/external rotation of the component. DISCUSSION. On average, the RMS difference between the 2D-to-3D conversion and the reconstructed post-operative CT exceeds the inter-observer RMS difference obtained using reconstructed post-operative CT. The differences are in line with previous cadaveric studies using the same reconstruction technique. The largest differences are seen for the femoral and tibial internal/external rotation. However, the obtained values are still within reasonable limits according to a recent review by De Valk et al., who reported an inter-observer variation of 3° for the femur and 2° for the tibia. In addition, the 2D-to-3D conversion displays a larger difference for the distraction/compression component. Since a true, golden standard measurement is lacking in our tests, it is not clear whether this error is attributed to the CT imaging or the 2D-to-3D conversion. Given the low inter-observer variation for this degree of freedom, it is hypothesized that this discrepancy is linked to the finite slice spacing for the CT scans. Apart from the obtained accuracy, the use of the 2D-to-3D module has the advantage of significantly reducing the radiation dose with approx. a factor 20. In addition, the imaging procedure needs no more than the standard imaging required by clinical practice

Three-dimensional (3D) weight-bearing alignment of the lower extremity is crucial for understanding biomechanics of the normal and pathological functions at the hip, knee, and ankle joints. In addition, implant position with reference to bone is a critical factor affecting the long-term survival of artificial joints. The purpose of this study was to develop a biplanar system using a slot-scan radiography (SSR) for assessing weight-bearing alignment of the lower extremity and for assessing implant positioning with respect to bone. A SSR system (Sonial Vision Safire 17, Shimadzu, Kyoto, Japan) with a custom-made rotation table was used to capture x-ray images at 0 deg and 60 deg relative to the optical axis of an x-ray source [Fig.1]. The SSR system uses collimated fan beam x-rays synchronized with the movement of a flat-panel detector. This system allows to obtain a full length x-ray image of the body with reduced dose and small image distortion compared with conventional x-ray systems. Camera calibration was performed beforehand using an acrylic reference frame with 72 radiopaque markers to determine the 3D positions of the x-ray source and the image plane in the coordinate system embedded in the reference frame. Sawbone femur and tibia and femoral components of the Advance total knee system (Wright Medical Technology, Arlington, TN, USA) were used. Computed tomography of the sawbone femur and tibia was performed to allow the reconstruction of the 3D surface models. For the component, the computer aided design (CAD) model provided by the manufacturer was used. Local coordinate system of each surface model was defined based on central coordinates of 3 reference markers attached to each model. The sawbone femur and tibia were immobilized at extension, axial rotation, and varus deformity and were imaged using the biplanar SSR system. The 3D positions of the femur and tibia were recovered using an interactive 2D to 3D image registration method [Fig.2]. Then, the femoral component was installed to the sawbone femur. The 3D positions of the femur and femoral component were recovered using the above-mentioned image registration method. Overall, the largest estimation errors were 1.1 mm in translation and 0.9 deg in rotation for assessing the alignment, and within 1 mm in translation and 1 deg in rotation for assessing the implant position, demonstrating that this method has an adequate accuracy for the clinical usage

Robotic-assisted technology in total knee arthroplasty (TKA) aims to increase implantation accuracy, with real-time data being used to estimate intraoperative component alignment. Postoperatively, Perth computed tomography (CT) protocol is a valid measurement technique in determining both femoral and tibial component alignments. The aim of this study was to evaluate the accuracy of intraoperative component alignment by robotic-assisted TKA through CT validation. A total of 33 patients underwent TKA using the MAKO robotic-assisted TKA system. Intraoperative measurements of both femoral and tibial component placements, as well as limb alignment as determined by the MAKO software were recorded. Independent postoperative Perth CT protocol was obtained (n.29) and compared with intraoperative values. Mean absolute difference between intraoperative and postoperative measurements for the femoral component were 1.17 degrees (1.10) in the coronal plane, 1.79 degrees (1.12) in the sagittal plane, and 1.90 degrees (1.88) in the transverse plane. Mean absolute difference between intraoperative and postoperative measurements for the tibial component were 1.03 degrees (0.76) in the coronal plane and 1.78 degrees (1.20) in the sagittal plane. Mean absolute difference of limb alignment was 1.29 degrees (1.25), with 93.10% of measurements within 3 degrees of postoperative CT measurements. Overall, intraoperatively measured component alignment as estimated by the MAKO robotic-assisted TKA system is comparable to CT-based measurements.

Accurate implant alignment, prolonged operative times, array pin site infection and intra-operative fracture risk with computer assisted knee arthroplasty is well documented. This study compares the accuracy and cost-effectiveness of the pre- operative MRI based Signature custom made guides (Biomet) to intra-operative computer navigation (BrainLab Knee Unlimited). Twenty patients from a single surgeon's orthopaedic waiting list awaiting primary knee arthroplasty were identified. Patients were contacted and consented for the study and their suitability for MRI examination assessed. An MRI scan of the hip, knee and ankle was performed of the operative side following a set scanning protocol. Following MRI, patient specific femoral and tibial positioning cutting guides were manufactured. Patients then underwent arthroplasty and intra-operative computer navigation was used to measure the accuracy of the custom made, patient specific cutting guides. A cost analysis of the signature system compared with computer navigation was made. Our provisional results show that the accuracy of the pre-operative MRI patient specific femoral and tibial positioning guides was comparable to computer navigation. Pre-operative, patient specific implant positioning cutting guides were as accurate as computer navigation from analysis of our preliminary results. The potential advantages of the MRI based system are accurate pre-operative planning, reduced operating times and avoidance of pin site sepsis. However, further larger studies are required to examine this technique

Total shoulder arthroplasty (TSA) is an effective treatment for end-stage glenohumeral arthritis. The use of high modulus uncemented stems causes stress shielding and induces bone resorption of up to 63% of patients following TSA. Shorter length stems with smaller overall dimensions have been studied to reduce stress shielding, however the effect of humeral short stem varus-valgus positioning on bone stress is not known. The purpose of this study was to quantify the effect of humeral short stem varus-valgus angulation on bone stresses after TSA. Three dimensional models of eight male cadaveric humeri (mean±SD age:68±6 years) were created from computed tomography data using MIMICS (Materialise, Belgium). Separate cortical and trabecular bone sections were created, and the resulting bone models were virtually reconstructed three times by an orthopaedic surgeon using an optimally sized short stem humeral implant (Exactech Preserve) that was placed directly in the center of the humeral canal (STD), as well as rotated varus (VAR) or valgus (VAL) until it was contacting the cortex. Bone was meshed using a custom technique which produced identical bone meshes permitting the direct element-to-element comparison of bone stress. Cortical bone was assigned an elastic modulus of 20 GPa and a Poisson's ratio of 0.3. Trabecular bone was assigned varying stiffness based on CT attenuation. A joint reaction force was then applied to the intact and reconstructed humeri representing 45˚ and 75˚ of abduction. Changes in bone stress, as well as the expected bone response based on change in strain energy density was then compared between the intact and reconstructed states for all implant positions. Both varus and valgus positioning of the humeral stem altered both the cortical and trabecular bone stresses from the intact states. Valgus positioning had the greatest negative effect in the lateral quadrant for both cortical and trabecular bone, producing greater stress shielding than both the standard and varus positioned implant. Overall, the varus and standard positions produced values that most closely mimicked the intact state. Surprisingly, valgus positioning produced large amounts of stress shielding in the lateral cortex at both 45˚ and 75˚ of abduction but resulted in a slight decrease in stress shielding in the medial quadrant directly beneath the humeral resection plane. This might have been a result of direct contact between the distal end of the implant and the medial cortex under loading which permitted load transfer, and therefore load-reduction of the lateral cortex during abduction. Conversely, when the implant was placed in the varus angulation, noticeable departures in stress shielding and changes in bones stress were not observed when compared to the optimal STD position. Interestingly, for the varus positioned implant, the deflection of the humerus under load eliminated the distal stem-cortex contact, hence preventing distal load transfer thus precluding the transfer of load

Introduction. Although total knee arthroplasty (TKA) is generally considered successful, 16–30% of patients are dissatisfied. There are multiple reasons for this, but some of the most frequent reasons for revision are instability and joint stiffness. A possible explanation for this is that the implant alignment is not optimized to ensure joint stability in the individual patient. In this work, we used an artificial neural network (ANN) to learn the relation between a given standard cruciate-retaining (CR) implant position and model-predicted post-operative knee kinematics. The final aim was to find a patient-specific implant alignment that will result in the estimated post-operative knee kinematics closest to the native knee. Methods. We developed subject-specific musculoskeletal models (MSM) based on magnetic resonance images (MRI) of four ex vivo left legs. The MSM allowed for the estimation of secondary knee kinematics (e.g. varus-valgus rotation) as a function of contact, ligament, and muscle forces in a native and post-TKA knee. We then used this model to train an ANN with 1800 simulations of knee flexion with random implant position variations in the ±3 mm and ±3° range from mechanical alignment. The trained ANN was used to find the implant alignment that resulted in the smallest mean-square-error (MSE) between native and post-TKA tibiofemoral kinematics, which we term the dynamic alignment. Results. Dynamic alignment average MSE kinematic differences to the native knees were 1.47 mm (± 0.89 mm) for translations and 2.89° (± 2.83°) for rotations. The implant variations required were in the range of ±3 mm and ±3° from the starting mechanical alignment. Discussion. In this study we showed that the developed tool has the potential to find an implant position that will restore native tibiofemoral kinematics in TKA. The proposed method might also be used with other alignment strategies, such as to optimize implant position towards native ligament strains. If native knee kinematics are restored, a more normal gait pattern can be achieved, which might result in improved patient satisfaction. The small changes required to achieve the dynamic alignment do not represent large modifications that might compromise implant survivorship. Conclusion. Patient-specific implant position predicted with MSM and ANN can restore native knee function in a post-TKA knee with a standard CR implant

Introduction. Recent technological advancements have led to the introduction of robotic-assisted total knee arthroplasty to improve the accuracy and precision of bony resections and implant position. However, the in vivo accuracy is not widely reported. The primary objective of this study is to determine the accuracy and precision of a cut block positioning robotic arm. Method. Seventy-seven patients underwent total knee arthroplasty with various workflows and alignment targets by three arthroplasty-trained surgeons with previous experience using the ROSA® Knee System. Accuracy and precision were determined by measuring the difference between various workflow time points, including the final pre-operative plan, validated resection angle, and post-operative radiographs. The mean difference between the measurements determined accuracy, and the standard deviation represented precision. Results. The accuracy and precision for all angles comparing the final planned resection and validated resection angles was 0.90° ± 0.76°. The proportion within 3° ranged from 97.9% to 100%. The accuracy and precision for all angles comparing the final intra- operative plan and post-operative radiographs was 1.95 ± 1.48°. The proportion of patients within 3° was 93.2%, 95.3%, 96.6%, and 71.4% for the distal femur, proximal tibia, femoral flexion, and tibial slope angles when the final intra-operative plan was compared to post-operative radiographs. No patients had a postoperative complication requiring revision at the final follow-up. Conclusions. This study demonstrates that the ROSA Knee System has accurate and precise coronal plane resections with few outliers. However, the tibial slope demonstrated decreased accuracy and precision were measured on post-operative short-leg lateral radiographs with this platform

Thoracic hyperkyphosis (TH – Cobb angle >40°) is correlated with rotator cuff arthropathy and associated with anterior tilting and protraction of scapula, impacting the glenoid orientation and the surrounding musculature. Reverse total shoulder arthroplasty (RTSA) is a reliable surgical treatment for patients with rotator cuff arthropathy and recent literature suggests that patients with TH may have comparable range of motion after RTSA. However, there exists no study reporting the possible link between patient-reported outcomes, humeral retroversion and TH after RTSA. While the risk of post-operative complications such as instability, hardware loosening, scapular notching, and prosthetic infection are low, we hypothesize that it is critical to optimize the biomechanical parameters through proper implant positioning and understanding patient-specific scapular and thoracic anatomy to improve surgical outcomes in this subset of patients with TH. Patients treated with primary RTSA at an academic hospital in 2018 were reviewed for a two-year follow-up. Exclusion criteria were as follows: no pre-existing chest radiographs for Cobb angle measurement, change in post-operative functional status as a result of trauma or medical comorbidities, and missing component placement and parameter information in the operative note. As most patients did not have a pre-operative chest radiograph, only seven patients with a Cobb angle equal to or greater than 40° were eligible. Chart reviews were completed to determine indications for RTSA, hardware positioning parameters such as inferior tilting, humeral stem retroversion, glenosphere size/location, and baseplate size. Clinical data following surgery included review of radiographs and complications. Follow-up in all patients were to a period of two years. The American Shoulder and Elbow Surgeons (ASES) Shoulder Score was used for patient-reported functional and pain outcomes. The average age of the patients at the time of RTSA was 71 years old, with six female patients and one male patient. The indication for RTSA was primarily rotator cuff arthropathy. Possible correlation between Cobb angle and humeral retroversion was noted, whereby, Cobb angle greater than 40° matched with humeral retroversion greater than 30°, and resulted in significantly higher ASES scores. Two patients with mean Cobb angle of 50° and mean humeral retroversion 37.5° had mean ASES scores of 92.5. Five patients who received mean humeral retroversion of 30° had mean lower ASES scores of 63.7 (p < 0 .05). There was no significant correlation with glenosphere size or position, baseplate size, degree of inferior tilting or lateralization. Patient-reported outcomes have not been reported in RTSA patients with TH. In this case series, we observed that humeral stem retroversion greater than 30° may be correlated with less post-operative pain and greater patient satisfaction in patients with TH. Further clinical studies are needed to understanding the biomechanical relationship between RTSA, humeral retroversion and TH to optimize patient outcomes

Aim. The primary endpoint of this study is to characterize the progression of bone defects at the femoral and tibial side in patients who sustained PJI of the knee that underwent two-stage revision with spacer implantation. In addition, we want to analyze the differences between functional moulded and hand-made spacers. Methods. A retrospective analysis of patients that underwent two-stage revision due to PJI of the knee between January 2014 and December 2021 at our institution. Diagnosis of infection was based on the criteria of the Muscoloskeletal Infection Society. The bone defect evaluation was performed intraoperatively based on the AORI classification. The basal evaluation was performed at the time the resection arthroplasty and spacer implantation surgery. The final evaluation was performed at the second-stage surgery, at the time of spacer removal and revision implant positioning. The differences between groups were characterized by using T-test student for continuous variables, and by using chi-square for categorical variables. A p-value < 0.05 was defined as significant. Results. Complete data of 37 two-stage TKAs revision were included in the study. An articulating moulded functional spacer was used in 14 (35.9%) cases, while a hand-made spacer was used in 23 (58.9%) cases. The average length of interval period (excluding the time for patients that retained the spacer) was 146.6 days. A bone defects progression based on the AORI classification was documented in 24 cases at the femoral side (61.6%), a bone defect progression was documented in 17 cases at the tibial side (43.6%), and a bone defect at both sides was documented in 13 cases (33.3%). A statistically significant greater bone defect progression at the tibial side was observed when hand-made spacers were used. A complication during the interval period was reported in five cases (12.8%) and postoperative complication was reported in 9 cases (23.1%). Conclusions. When comparing patients in which a functional articulating spacer was used, with patients in which static spacer was used, we reported a statistically significant reduced bone defect progression during the interval period at the femoral side only when moulded spacers were used. We observed a higher incidence of bone defect progression also at the tibial and both sides when hand-made spacers were used. This is the first study that documented the bone defect progression during two-stage revision of the knee, the results observed in this study are very encouraging

Background. Conventional instrumented total knee arthroplasty uses fixed angles for bony cuts followed by soft tissue releases to achieve balance. Robotic-assisted surgery allows for soft tissue balancing first then bony resection. The changes to the implant position from conventional instrumented surgery were measured and recorded. Methods. A single center, retrospective study reviewed consecutive total knee replacement surgeries over a 12 month period utilizing robotic pre-planning and balancing techniques. Changes to femoral and tibial varus/valgus and femoral rotation from traditional instrumented surgery positions were analyzed. Results. There were 145 knees which were grouped by preoperative deformity and the changes were frequent (94%), variable for any given deformity, and often unpredictable. Staged bilateral total knee arthroplasty patients also showed variability between knees. Conclusion. Robotic-assisted knee replacement technology not only has the advantage of navigation with regard to accurate implant positioning but also provides real-time, actionable data to better position the implant prior to bone resection and minimize soft tissue damage

Glenoid replacement is a manual bone removal procedure that can be difficult for surgeons to perform. Surgical robotics have been utilized successfully in hip and knee orthopaedic procedures but there are no systems currently available in the shoulder. These robots tend to have low adoption rates by surgeons due to high costs, disruption of surgical workflow and added complexity. As well, these systems typically use optical tracking which needs a constant line-of-sight which is not conducive to a crowded operating room. The purpose of this work was developing and testing a surgical robotic system for glenoid replacement. The new surgical system utilizes flexible components that tether a Stewart Platform robot to the patient through a patient specific 3D printed mount. As the robot moves relative to the bone, reaction loads from the flexible components bending are measured by a load cell allowing the robot to “feel” its way around. As well, a small bone burring tool was attached to the robot to facilitate the necessary bone removal. The surgical system was tested against a fellowship-trained surgeon performing standard surgical techniques. Both the robot and the surgeon performed glenoid replacement on two different scapula analogs: standard anatomy and posterior glenoid edge wear referred to as a Walch B2. Six of each scapula model was tested by the robot and the surgeon. The surgeon created a pre-operative plan for both scapula analogs as a target for both methodologies. CT scans of the post-operative cemented implants were compared to the pre-operative target and implant position and orientation errors were measured. For the standard shoulder analogs the net implant position and orientation errors were 1.47 ± 0.48 mm and 2.57 ± 2.30° for the robot and 1.61 ± 0.29 mm and 5.04 ± 1.92° for the surgeon respectively. For the B2 shoulders, the net implant position and orientation errors were 2.16 ± 0.36 mm and 2.89 ± 0.88° for the robot and 3.01 ± 0.42 mm and 4.54 ± 1.49° for the surgeon respectively. The new tracking system was shown to be able to match or outperform the surgeon in most metrics. The surgeon tended to have difficulty gauging the depth needed as well as the face rotation of the implant. This was not surprising as the reaming tool used by the surgeon obscures the view of the anatomy and the spherical cutter hinders the ability to index the tool. The robot utilized only one surgical tool, the bone burr, precluding the need for multiple instruments used by the surgeon to prepare the glenoid bone bed. The force-space navigation method can be generalized to other joints, however, further work is needed to validate the system using cadaveric specimens

Background. Despite the success of total hip arthroplasty (THA), there are still challenges including restoration of leg length, offset, and femoral version. The Tsolution One combines preoperative planning with an active robotic system to assist in femoral canal preparation during a THA. Purpose of Study. To demonstrate the use of an active robotic system in femoral implant placement and determine the accuracy of femoral implant position. This was evaluated in a cadaveric study. Study Design and Methods. Four THA's were performed in fresh frozen cadaveric hips with assistance of the TSolution One System for preparation of the femoral canal. CT scans of the hip were used as input for TPLAN preoperative planning software to position the implants in three-dimensions (3D). The intraoperative process includes exposure of the joint using a posterolateral approach, fixation of the femur relative to the TCAT system, and registration of the femur. TCAT then actively milled the femoral canal in each of the cases after which Depuy Trilock implants were inserted by the surgeon. Only the femoral stem implants were considered in this study. Postoperative CT was used to compare actual implant position with preoperatively planned implant position in 3D. The translations between the centroids of the implant positions were compared. Findings of Study. All femoral stems were successfully implanted with no complications. Implant position very closely matched the preoperative plan. Compared to the preoperative plan, the mean (± SD) positions of the centroid of the implant were off by 0.6 (±0.6) mm in the medial-lateral direction, 0.8 (±0.3) mm in the anterior-posterior direction, and 2.0 (±1.3) mm in the superior-inferior direction. No intraoperative fractures occurred. A sample of the preoperative planned position (left) and actual postoperative position (right) as seen on TPLAN can be seen in Figure 1. An example of the final 3D implant position in blue as compared to the preoperative implant position in red can be seen in Figure 2. Conclusions. Overall, the post-operative stems positions were superior compared to the preoperative plan and it is believed that this is likely a result of not impacting the stems enough during the procedure. The medial-lateral and anterior-posterior stem positions were within 1 mm of what was planned. Active robotics can successfully be used to improve accuracy, precision, and reproducibility when considering final implant position in THA. These improvements can reduce unwanted human error and reduce complications. Further in vivo study is planned to demonstrate the clinical benefits of such improved precision

As Total Hip Replacement (THR) rates increase healthcare providers have sought to reduce costs, while at the same time improving patient safety and satisfaction. Up to 50% of patients may be appropriate for Day Case THR, and in appropriately selected patients’ studies show no increase in complication rate while affording a significant cost saving and maintaining a high rate of patient satisfaction. Despite the potential benefits, levels of adoption of Day Case THR vary. A common cause for this is the perception that doing so would require the adoption of new surgical techniques, implants, or theatre equipment. We report on a Day-Case THR pathway in centres with an established and well-functioning Enhanced Recovery pathway, utilising the posterior approach and standard implants and positioning. We prospectively collected the data on consecutive THRs performed by a single surgeon between June 2018 and July 2021. A standardised anaesthetic regimen using short acting spinal was used. Surgical data included approach, implants, operative time, and estimated blood loss. Outcome data included time of discharge from hospital, post operative complications, readmissions, and unscheduled health service attendance. Data was gathered on 120 consecutive DCTHRs in 114 patients. 93% of patients were successfully discharged on the day of surgery. Four patients required re-admission: one infection treated with DAIR, one dislocation, one wound ooze admitted for a day of monitoring, one gastric ulcer. One patient had a short ED attendance for hypertension. Our incidence of infection, dislocation and wound problems were similar to those seen in inpatient THR. Out data show that the widely used posterior approach using standard positioning and implants can be used effectively in a Day Case THR pathway, with no increase in failure of same-day discharge or re-admission to hospital

Background. Total knee arthroplasty (TKA) surgical techniques attempt to achieve equal flexion and extension gaps to produce a well-balanced knee, but unexplainable unhappy patients persist. Mid-flexion instability is one proposed cause of unhappy patients. There are multiple techniques to achieve equal flexion and extension gaps, but their effects in mid-flexion are largely unknown. Purpose of study. The purpose of the study is to determine the effects that changing femur implant size and/or adjusting the femur and tibia proximal -distal and femur anterior-posterior implant positions have on cruciate retaining (CR) TKA mid-flexion ligament balance when equal flexion and extension gaps are maintained. Methods. A computational analysis was performed simulating knee flexion of two CR TKA designs (JOURNEY II CR and LEGION HFCR; Smith & Nephew) using previously validated software (LifeMOD/KneeSim; LifeModeler). Deviations from the ideal implant position were simulated by adjusting tibiofemoral proximal-distal position and femur anterior-posterior position and size (Table 1). Positioning the femur more proximal was accompanied by equal anterior femur and proximal tibia shifts to maintain equal flexion and extension gaps. The forces in ligaments connecting the femur and tibia, which included superficial and posterior MCL, LCL, popliteal-fibular ligament complex, iliotibial band, and anterior-lateral and posterior-medial PCL, were collected. Total tibiofemoral ligament load and PCL load for 15–75° knee flexion were analyzed versus proximal-distal implant position, implant size, implant design, and knee flexion using a MANOVA in Minitab 16 (Minitab). Results. Total tibiofemoral ligament load was significantly reduced by a more proximal implant position (p<.001) (Figure 1) but was not affected by implant size (p>0.6). PCL load was not affected by implant proximal-distal position or size (p>0.9) (Figure 2). Therefore, the PCL did not contribute to changes in mid-flexion balance caused by proximal-distal implant position. Implant design and knee flexion significantly influenced total tibiofemoral ligament and PCL loads (p<.05), but the interactions with implant proximal-distal position and size were not significant (p>0.7) indicating that the effects of implant proximal-distal position applies across the studied implant designs and 15°–75° knee flexion range. Conclusions. Our results suggest that a CR TKA can be well balanced at 0° and 90° knee flexion and be too tight or loose in mid-flexion. Since placement of implant was the variable studied, when the knee is too tight in mid-flexion, our recommendation to loosen the knee is to resect more distal and posterior femur, downsizing if necessary, and increase the tibial insert thickness. The opposite could be done to guard against the knee being too loose in mid-flexion. Finally, it is recommended to gauge balance in more than simply 0° and 90° to determine overall knee balance

Longevity of total hip arthroplasty (THA) is dependent upon avoiding both short- and long-term problems. One of the most common short-term / early complications of THA is instability while longer term issues of wear remain a concern. Both of these concerns appear to be related to implant position: either static or functional. While achieving “ideal” implant position in primary THA for osteoarthritis is only successful in 50% of cases (Callanan et al.), it is even more difficult in complex primary disorders such as dysplasia and post-traumatic arthritis. Many theories exist as to why implant position and short-term complications appear to be higher in this “complex primary” cohort but certainly the ability to achieve desired implant position appears to be more challenging. The loss of usual anatomic landmarks, the presence of soft tissue contractures, and the recognition of both pelvic and femoral deformities play a role. Enabling technologies have emerged to help in achieving improved implant position. These technologies include both navigation (both imageless and image guided) as well as the newly adopted technology of robotic assistance. Robot-assisted THA is based upon a CT scan protocol. Three-dimensional pre-operative planning on both the femoral and acetabular side can be performed. Precision guided bone preparation and exacting implant delivery is achievable using robotic technology. Examples of use of this technology in complex primary THA will be demonstrated including planning, preparation and implantation

Background. Total knee arthroplasty (TKA) surgical techniques attempt to achieve equal flexion and extension gaps to produce a well-balanced knee. Anterior knee pain, which is not addressed by flexion-extension balancing, is one of the more common complaints for TKA patients. The variation in patellofemoral balance resulting from the techniques to achieve equal flexion and extension gaps has not been widely studied. Purpose of study. The purpose of the study is to determine the effects on cruciate retaining (CR) TKA patellofemoral balance when equal flexion and extension gaps are maintained while changing femur implant size and/or adjusting the femur and tibia implant proximal -distal and femur anterior-posterior positions. Methods. A computational analysis was performed simulating knee flexion of two CR TKA designs (JOURNEY II CR and LEGION HFCR; Smith & Nephew) using previously validated software (LifeMOD/KneeSim; LifeModeler). Deviations from the ideal implant position were simulated by adjusting tibiofemoral proximal-distal position and femur anterior-posterior position and size (Table 1). Positioning the femur more proximal was accompanied by equal anterior femur and proximal tibia shifts to maintain equal flexion and extension gaps. The forces in the medial and lateral retinaculum were collected and summed at every 15° knee flexion up to 135° to determine the total patellofemoral retinaculum load which was analyzed versus proximal-distal implant position, implant size, implant design, and knee flexion using an ANOVA in Minitab 16 (Minitab). Results. Patellofemoral retinaculum load was significantly affected by proximal-distal implant position, implant size, and knee flexion angle (p<.001) but was not significantly affected by implant design (p>0.2). Interactions with knee flexion angle were significant for both proximal-distal implant position (p<.001) and implant size (p=.003) indicating that their effects change with knee flexion (Figures 1 and 2). For 15°–30° knee flexion, more proximal tibiofemoral positions corresponding to a more anterior femur increased patellofemoral retinaculum load. Implant position had little effect at 45° knee flexion. For 60°–135° knee flexion, more proximal implant positions decreased patellofemoral retinaculum load. Increased femoral size caused increased patellofemoral retinaculum load with a larger effect for 15–45° knee flexion. Conclusions. Our results indicate that patellofemoral balance should be considered when selecting implant size and position for flexion-extension balancing. The more common adjustment of positioning implants more proximal decreases patellofemoral retinaculum load in flexion, but the anterior femoral shift to balance the flexion space overstuffs the patella near extension. Downsizing the femoral implant is an option to mitigate increased patellofemoral retinaculum load when shifting the femoral anterior. For figures/tables, please contact authors directly.

Acetabular implant position is important for the stability, function, and long-term wear properties of a total hip arthroplasty (THA). Prior studies of acetabular implant positioning have demonstrated a high percentage of outliers, even in experienced hip surgeons, when conventional instruments are used. Computer navigation is an attractive tool for use in (THA, as it has been shown to improve the precision of acetabular component placement and reduce the incidence of outliers. However, computer navigation with imageless, large-console systems is costly and often interrupts the surgeon's workflow, and thus, has not been widely adopted. Another method to improve acetabular component positioning during THA is the use of fluoroscopy with the direct anterior approach. Studies have demonstrated that the supine position of the patient during surgery facilitates the use of fluoroscopic guidance, thus improving acetabular component position. A handheld, accelerometer based navigation unit for use in total hip replacement has recently become available to assist the surgeon in positioning the acetabular component during anterior approach THA, potentially reducing the need for intraoperative fluoroscopic studies. We sought to compare the radiographic results of direct anterior THA performed with conventional instrumentation vs. handheld navigation to determine the accuracy of the navigation unit, and to see whether or not there was a reduction in the fluoroscopic time used during surgery. Furthermore, we timed the use of the navigation unit to see whether or not it required a substantial addition to surgical time. Our results demonstrate that a handheld navigation unit used during anterior approach THA had no difference with regard to acetabular cup positioning when compared to fluoroscopically assisted THA, but led to a reduction in the use of intraoperative fluoroscopy time

Restoring native hip biomechanics is crucial to the success of THA. This is reflected both in terms of complications after surgery such as instability, leg length inequality, pain and limp; and in terms of patient satisfaction. The challenge that remains is that of achieving optimal implant sizing and positioning so as to restore, as closely as possible, the native hip biomechanics specific to the hip joint being replaced. This would optimise function and reduce complications, particularly, instability. (Mirza et al., 2010). Ideally, this skill should also be reproducible irrespective of the surgeon's experience, volume of surgery and learning curve. The general consensus is that the most substantial limiting factor in a THA is the surgeon's performance and as a result, human errors and unintended complications are not completely avoidable (Tarwala and Dorr, 2011). The more challenging aspects include acetabular component version, sizing and femoral component sizing, offset and position in the femoral canal. This variability has led to interest in technologies for planning THA, and technologies that help in the execution of the procedure. Advances in surgical technology have led to the development of computer navigation and robotic systems, which assist in pre-operative planning and optimise intra-operative implant positioning. The evolution of surgical technology in lower limb arthroplasty has led to the development of computer navigation and robotics, which are designed to minimise human error and improve implant positioning compared to pre-operative templating using plain radiographs. It is now possible to use pre-operative computerised tomography (image-based navigation) and/or anatomical landmarks (non-imaged-based navigation) to create three-dimensional images of each patient's unique anatomy. These reconstructions are then used to guide bone resection, implant positioning and lower limb alignment. The second-generation RIO Robotic Arm Interactive Orthopaedic system (MAKO Surgical) uses pre-operative computerised tomography to build a computer-aided design (CAD) model of the patient's hip. The surgeon can then plan and execute optimal sizing and positioning of the prostheses to achieve the required bone coverage, minimise bone resection, restore joint anatomy and restore lower limb biomechanics. The MAKO robotic software processes this information to calculate the volume of bone requiring resection and creates a three-dimensional haptic window for the RIO-robotic arm to resect. The RIO-robotic arm has tactile and audio feedback to resect bone to a high degree of accuracy and preserve as much bone stock as possible. We have used this technology in the hip to accurately reproduce the anteversion, closure and center of rotation that was planned for each hip. Whilst the precise safe target varies from patient to patient, the ability to reproduce native biomechanics, to gain fixation as planned and to get almost perfect length and offset are a great advantage. Complications such as instability and leg length inequality are thus dramatically reduced

The goals of a total knee arthroplasty include approximation of the function of a normal knee and achievement of balance post-surgery. Accurate bone preparation and the preservation of natural ligaments along with a functional knee design, holds the potential to provide a method of restoring close to normal function. Although conventional knee arthroplasty is considered a successful intervention for end-stage osteoarthritis, some patients still experience reduced functionality and in some cases, require revision procedures. With conventional manual techniques, accurate alignment of the tibial component has been difficult to achieve. Even in the hands of skilled knee surgeons, outliers beyond 2 degrees of the desired alignment may occur in as many as 40%-60% of cases using conventional methods, and the range of component alignment varies considerably. Similarly, for total knee replacement outliers beyond 2 degrees of the desired alignment may occur in as many as 15% of cases in the coronal plane, going up to 40% of unsatisfactory alignment in the sagittal plane. Robotics-assisted arthroplasty has gained increasing popularity as orthopaedic surgeons aim to increase accuracy and precision of implant positioning. With advances in computer generated data, with image free data, surgeons have the ability to better predict and influence surgical outcomes. Based on planned implant position and soft tissue considerations, robotics-assisted systems can provide surgeons with virtual tools to make informed decisions for knee replacement, specific to the needs of the patient. Here, for the first time in a live surgical setting, we assess the accuracy and technique of a novel imageless semiautonomous handheld robotic surgical technique in bi-cruciate retaining total knee arthroplasty (Navio, Smith and Nephew). The system supports image-free anatomic data collection, intraoperative surgical planning and execution of the plan using a combination of robotic burring and saw cut guides

Introduction. Reverse shoulder Arthroplasty is a successful treatment for gleno-humeral osteoarthritis. However, components loosening and painful prostheses, related to components wrong positioning, are still a problem for those patients who underwent this kind of surgery. Several new technology has been developed the improve the implant positioning. CT-based intraoperative navigation system is a suitable technology that allow the surgeon to prepare the implant site exactly as planned with preoperative software. Method. Thirty reverse shoulder prostheses were performed at Modena Polyclinic using GPS CT-based intraoperative navigation system (Exactech, Gainsville, Florida). Walch classification was used to assess glenoid type. Planned version and inclination of the glenoid component, planned seating, final version and inclination of the reamer were recorded. Intraoperative and perioperative complication were recorded. Planned positioning was conducted aiming to the maximum seating, avoiding retroversion >10° and superior inclination. Results. Eight patients were male, 22 were female. Mean age was 75 years old (range 58–87). 4 glenoid were type B3, four were B2, 10 cases were B1, 12 case were A1/A2. Posterior or superior augment was used in 15 cases. Mean planned seating was 93%. Mean preoperative version was -7.5±6.9°; Mean planned version was -2±2.8°; Mean intraoperative measured version was -1.9±2.8°; no statistical difference was found between planned and intraoperative version (p=0.16). Mean preoperative inclination was 1.8±6.°; Mean planned inclination was -2.2±2.4°; Mean intraoperative measured inclination was -2.1.9±2.3°; no statistical difference was found between planned and intraoperative version or inclination (respectively p=0.16 and p=0.32). Mean surgical time was 71 minute (range 51–82). Three cases of coracoid ruptures were reported, 1 failure of the system occurred. Discussion. GPS navigation system allows the surgeon to prepare the implant site as planned on Preoperative software in Reverse shoulder arthroplasty, with no statistical difference between planned orientation and intraoperative measured orientation. That means that even in the most difficult cases the surgeon is able to find a good positioning (93% seating)and to replicate it in the operative room. Only one failure of the system occurred, because too much time was passed between CT scan and surgery (9 months). Three coracoid fractures occurred in the first 10 cases: these could be addressed to a lack of confidence with the double lateralization of this prosthesis which increase tensioning on the coracoid and a lack of confidence in tracker positioning, which should be made as proximal as it is possible. Finally, the system needs several improvements to be considered a breakthrough technology, such as humeral component positioning and final control of the implant, but by now is a useful way to improve our surgery, especially in difficult cases