A chronically dislocating prosthetic patella. A case report.

A 63-year-old white woman was evaluated for a chronically dislocating right patella 6 months following total knee arthroplasty. At the time of our initial evaluation, her knee would not extend beyond 35 degrees and her patella was dislocated and irreducible. At arthrotomy, when the patella was everted, the patellar component was oriented with the facet ridge rotated 90 degrees to the trochlear groove of the femoral component. The patellar template guide indicated that the fixation pegs had been drilled properly, and thus, the patellar component had been assembled improperly during manufacturing. After dome-type patellar prosthesis replacement and proximal and distal extensor realignments were performed, 2 months post-revision the patient had a range of motion from 5 degrees to 95 degrees and ambulated with no patellar instability or pain.