OBJECTIVETo find out the reasons of extensor weakness after total knee arthroplasty for severe flexion deformity knees, and the rehabilitation method.

METHODSFrom January 2001 to January 2004, 30 knees (20 cases) with severe flexion deformity were performed total knee arthroplasty with PS prosthesis, and the follow up were at least 6 months (6 to 40 months, average 18 months). All cases in this group were classified with the extensor force grade and were given certain exercises according to the grade. The HSS scores, extensor force, residual flexion deformity, satisfaction scores and rang of motion were recorded pre-operation and 3 days, 2 weeks, 4 weeks, 8 weeks, 12 weeks, 6 months and then every year when follow up.

RESULTSAt the end point of the 6 months follow up, all items increased significantly, the average HSS score was 75.9 degrees, the average extensor force was 4.1, 8 knees among the group remained an average flexion deformity with 7.4 degrees, all patients were satisfied with the operation, and the average range of motion was 87.7 degrees.

CONCLUSIONSQuadriceps atrophy for disuse and the relative extensor mechanism excess are the main cause of extensor deficit, correct strength evaluation and individual exercise project are critical principle for successful rehabilitation.