Abstract
Seventy-four mobile bearing total knee arthroplasties (LCS) without patellar resurfacing were analysed in 54 patients who were followed for a minimum of one year. We examined the congruence angle on Merchant’s view, the component rotation to the epicondylar line of the femur on computed tomography(CT), the femorotibial angle on weight-bearing anteroposterior radiograph to assess the contributing factors for the patellofemoral malalignment. The statistical analysis was performed by ANOVA test, student t test, and chi sguare test.
The patellofemoral pain was noted in 17 knees(23%). The incidence of patellofemoral pain was significantly increased in the knee when its congruence angle was more than 16 degrees (p=0.034). But the pain did not correlate with the status of the articular cartilage of the patella on operation. The average congrunce angle was 4¢ªdegrees preoperatively and 24.2 degrees postoperatively. The congruence angle in 29 knees with lateral release was significantly lower than that in 45 knees without lateral release (p=0.037). All femoral components were internally rotated on CT scan with average of 6.7 degrees. More significant increase of the congruence angle was observed in 42 knees with femoral or tibial component rotation than in 15 knees with normal or minimal rotation of both components(p=0.017). Pre-operative congruence angle and postoperative femorotibial angle also affected the patellofemoral alignment, which increased postoperative congruence angle respectively.
Based on our findings, it seems that the excessive internal rotation of one component and excessive valgus of the femorotibial angle should be avoided to prevent the patellofemoral maltracking. We believe that “no thumb test” should be done carefully and the lateral release performed without hesitation if patellar tracking is a concern.
The abstracts were prepared by Professor Jegan Krishnan. Correspondence should be addressed to him at the Flinders Medical Centre, Bedford Park 5047, Australia.
