Patellar clunk syndrome in fixed-bearing posterior-stabilised versus cruciate-substituting prostheses.

PURPOSE To compare the outcome of fixed-bearing posterior-stabilised versus cruciate-substituting prostheses in 46 patients who underwent primary bilateral total knee replacement (TKR). METHODS Records of 35 women and 11 men aged 54 to 78 (mean, 67) years who underwent primary bilateral TKR for osteoarthritis (n=44) and rheumatoid arthritis (n=2) were retrospectively reviewed. A fixed-bearing posterior-stabilised prosthesis (Zimmer NexGen Legacy flex [LPS-Flex]) was used in one knee, and a fixed-bearing cruciate-substituting prosthesis (Depuy Press Fit Condylar Sigma CS [PFC CS]) was used in the contralateral knee. The mean time interval between the 2 operations was 34 (range, 4-60) months. All operations were performed by the same group of surgeons using standardised techniques. The medial parapatellar approach was used, and the patella was resurfaced. Rehabilitation was also standardised. Outcome measures included the pre- and post-operative active range of movement and the American Knee Society Score. Postoperative complications were documented. RESULTS At one year, the mean fixed flexion contracture, maximum flexion, and American Knee Society scores in knees with PFC CS and LPS-Flex prostheses were comparable. Three knees with the PFC CS prosthesis developed the patellar clunk syndrome, compared to none with the LPS-Flex prosthesis (p=0.24). The onset of the patellar clunk syndrome was around one year after surgery. Despite this, the axial alignment and rotation of the femoral and tibial components were good. CONCLUSION Both prostheses produce good clinical outcome. The PFC CS prosthesis is more likely to be associated with the patellar clunk syndrome.