Explanation:
The correct option is c. Patellar clunk syndrome is a classic, design-specific complication seen almost exclusively in posterior-stabilized (PS) total knee arthroplasty. It is caused by the formation of a fibrosynovial nodule on the undersurface of the distal quadriceps tendon just proximal to the patella. As the knee moves from deep flexion into extension, this nodule becomes trapped within the intercondylar box of the PS femoral component. As the knee forces its way into full extension, the nodule violently dislodges over the superior rim of the box, producing a painful, audible, and palpable 'clunk'. Modern PS designs have drastically reduced this incidence by smoothing the trochlear transition and rounding the superior edge of the box. Reference: Hozack WJ et al. Patellar clunk syndrome. Clin Orthop Relat Res.