Incidence of patellar clunk with a modern posterior-stabilized knee design

Patellar clunk is an uncommon complication of posterior-stabilized total knee arthroplasty (TKA), though the incidence has been reported to be as high as 7.5% with some posterior-stabilized implants, and the etiology is multifactorial. Femoral component design has been implicated as a major cause of this complication. This series compares the incidence of patellar clunk with 2 different knee prostheses, the Insall-Burstein II (IB) and the NexGen Legacy PS (NG), both manufactured by Zimmer (Warsaw, Ind). One-hundred fifty consecutive posterior-stabilized TKAs were in each group, and the groups were similar in surgical approaches and techniques. Insall-Salvati (IS) ratios and joint-line positions were measured on preoperative and postoperative x-rays. Knee Society Clinical and Functional scores were calculated. Incidence of patellar clunk was reduced from 4% with the IB design to 0% with the NG design. IS ratios, joint-line positions, and clinical outcomes were no different between the groups. It appears that femoral component design may play a substantial role in development of patellar clunk after posterior-stabilized TKA.