Original Research
Incidence of Patellar Clunk With a Modern Posterior-Stabilized Knee Design
Am J Orthop. 2007 October;36(10):550-553
Author and Disclosure Information
Jess H. Lonner, MD, Jeff G. Jasko, MS, Hari P. Bezwada, MD, David G. Nazarian, MD, and Robert E. Booth, Jr, MD
Dr. Lonner is Director, Knee Replacement Surgery; Mr. Jasko is Research Associate; Dr. Bezwada is Orthopaedic Surgeon; Dr. Nazarian is Orthopaedic Surgeon; and Dr. Booth is Chief, Orthopaedic Surgery; all at Pennsylvania Hospital, Philadelphia, Pennsylvania.
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.