O1242 COMPONENT SIZE SELECTION IN TOTAL KNEE REPLACEMENT: IMPLICATIONS FOR IMPINGEMENT AND ABRASIVE POLYETHYLENE WEAR

Abstract

Aims: During total knee replacement (TKR), bone dimensions are sometimes between implant sizes. Many surgeons select the smaller tibial component size to avoid overhanging the cortex and the smaller femoral component size to avoid overstuffing the joint space. However, the larger femoral component size is sometimes selected to ensure adequate bone coverage. This study was initiated after contact between the polyethylene insert and posterior femoral osteophytes was observed at autopsy even though radiographs showed adequate osteophyte removal at index TKR. It was hypothesized that knees implanted with the same sized femoral and tibial components would have a higher incidence of contact and abrasive wear than knees with larger femoral components. Methods: Thirty five polyethylene inserts were retrieved at autopsy (34%) and at revision TKR for reasons of infection (20%), patellar complications (17%), loosening (11%), patellar resurfacing (14%), and supracondylar fracture (3%). Mean implantation time was 32(1–74) months. Articular damage was evaluated using light microscopy. Results: Nineteen knees had smaller femoral components and 13 (68%) had abrasive wear on the polyethylene rim. Sixteen knees had larger femoral components and 4 (25%) had the abrasive wear pattern. The incidence of abrasive wear was significantly lower in knees with larger sized femoral components (Fisher’s Exact, p< 0.05). Conclusions: Surgeons are encouraged to remove all osteophytes that might impinge and avoid sizing the components such that the polyethylene insert overhangs the femoral component. Selecting the larger femoral component size may lessen impingement and provide some benefit for increasing knee flexion and decreasing abrasive wear.