ABSTRACT
PURPOSE: To evaluate the patterns and the treatment of instability after primary TKA. MATERIAL & METHOD: We studied 8 patients (9 cases) who had instability after TKA. We analyze the onset of symptom, patterns and main causes of instability, method of treatment, and results. The average follow-up period was 31 months. RESULT: Average onset of symptom after TKA was 10.1 month (8 day -4 years 4 month). The patterns of instability included anterior/posterior instability in 2, valgus/varus instability in 5 and global instability in 2. The treatments were thicker polyethylene exchange in 1, repair or reconstruction of collateral ligament with polyethylene exchange in 5, and revision with constrained or hinged implant in 3 when it was impossible to correct the imbalance of flexion-extension gap. All patients got stable knees and KSS functional and knee scores improved from average 55 and 56 points to 88.8 and 91 points respectively. CONCLUSION: Active repair or reconstruction of the ligament with polyethylene exchange wasone of the good options for treating instability after TKA. In cases of severe instability that could not be corrected by polyethylene exchange and repair or reconstruction of the ligament, revision with constrained or hinged implant was necessary.