Contemporary total knee systems accommodate for differential sizing between femoral and tibial components to allow surgeons to control soft tissue balancing and optimize rotation. One method some manufacturers use to allow differential sizing involves maintaining coronal articular congruency with a single radius of curvature throughout sizes while clipping the medial-lateral width, called a single coronal geometry system. Registry data show a 20% higher revision rate when the tibial component is smaller than the femur (downsizing) in the DePuy PFC system, a single coronal system, possibly from increased stresses from edge loading or varying articular congruency. We examined a different single coronal geometry knee system, Smith & Nephew Genesis II, to determine if edge loading is present in downsized tibial components by measuring area and location of deviation of the polyethylene articular surface damage. 45 Genesis II posterior-stabilized polyethylene inserts (12 matched and 33 downsized tibial components) were CT scanned. 3D reconstructions were registered to corresponding pristine component reconstructions, and 3D deviation maps of the retrieved articular surfaces relative to the pristine surfaces were created. Each map was exported as a point cloud to a custom MATLAB code to calculate the area and weighted center of deviation of the articular surfaces. An iterative k-means clustering algorithm was used to isolate regions of deviation, and a shrink-wrap algorithm was applied to calculate their areas. The area of deviation was calculated as the sum of all regions of deviation and was normalized to the area of the articular surface. The location of deviation was described using the weighted center of deviation and the location of maximum deviation on the articular surfaces relative to the center of the post (Fig. 1). Pearson product moment correlations were conducted to examine the correlation between length of implantation (LOI) and the medial and lateral areas of deviation for all specimens, matched components, and downsized components.Introduction
Methods
Robotically-assisted unicondylar knee arthroplasty (UKA) is intended to improve the precision with which the components are implanted, but the impact of alignment using this technique on subsequent polyethylene surface damage has not been determined. Therefore, we examined retrieved ultra-high-molecular-weight polyethylene UKA tibial inserts from patients who had either robotic-assisted UKA or UKA performed using conventional manual techniques and compared differences in polyethylene damage with differences in implant component alignment between the two groups. We aimed to answer the following questions: (1) Does robotic guidance improve UKA component position compared to manually implanted UKA? (2) Is polyethylene damage or edge loading less severe in patients who had robotically aligned UKA components? (3) Is polyethylene damage or edge loading less severe in patients with properly aligned UKA components? We collected 13 medial compartment, non-conforming, fixed bearing, polyethylene tibial inserts that had been implanted using a passive robotic-arm system and 21 similarly designed medial inserts that had been manually implanted using a conventional surgical technique. Pre-revision radiographs were used to determine the coronal and sagittal alignment of the tibial components. Retrieval analysis of the tibial articular surfaces included damage mapping and 3D laser scanning to determine the extent of polyethylene damage and whether damage was consistent with edge loading of the surface by the opposing femoral component.Introduction
Methods
Adverse local tissue reactions (ALTR) and elevated serum metal ion levels secondary to fretting and corrosion at head-neck junctions in modular total hip arthroplasty (THA) designs have raised concern in recent years. Factors implicated in these processes include trunnion geometry, head-trunnion material couple, femoral head diameter, head length, force of head impaction at the time of surgery, and length of implantation. Our understanding of fretting and corrosion Ten cobalt-chromium femoral stems and engaged cobalt-chromium femoral heads were retrieved at autopsy from 9 patients, after a mean length of implantation (LOI) of 11.3 ± 8 years (range 1.9–28.5). Trunnion design and material, femoral head material, size, and length, LOI, and patient sex were recorded (Table 1). Femoral heads were pulled off on a uniaxial load frame according to ASTM standards under displacement control at a rate of 0.05mm/s until the femoral head was fully disengaged from the trunnion. Mating surfaces were gently cleaned with 41% isopropyl alcohol to remove any extraneous debris. Femoral trunnions and head tapers were examined under a stereomicroscope by two independent graders to assess presence and severity of fretting and corrosion (method previously established). Trunnions and tapers were divided into 8 regions: anterior, medial, posterior, and lateral in both proximal and distal zones. Minimum possible damage score per hip was 32 (indicating pristine surfaces). The total possible score per hip was 128 (2 damage modes × 2 mating surfaces × 8 regions × max score of 4 per region).INTRODUCTION
METHODS
