In 20 patients with patellar “clunks” after posterior stabilized total knee arthroplasty, the average time to presentation was 10.7 months postarthroplasty. All patients demonstrated an audible and often painful “clunk” during extension. Fourteen procedures (11 arthroscopic debridements and three patellar component revisions) were performed in 12 patients. At reoperation, a suprapatellar fibrous nodule was seen to wedge into the intercondylar notch during flexion and dislodge during extension, generating the symptoms. The disorder resolved after nodule excision. Although four recurrences arose after arthroscopic debridements, none developed after arthrotoray and patellar button revision. Femoral component design, postsurgical inflammation, and altered extensor mechanics are potential etiologic agents of this complication.