Dissecting popliteal cyst resulting from a fragmented, dislodged metal part of the patellar component after total knee arthroplasty.

Dissecting popliteal cyst is an uncommon complication after total knee arthroplasty, occurring mainly as a result of either rheumatoid arthritis or a malfunctioning knee prosthesis. Its association with a failed metal-backed patellar component has not been reported since the introduction of the resurfacing of the patella with this kind of design in 1980. We present a case of a late fracture-dislocation of the metal part of the patellar component that migrated to the posterior popliteal fossa, resulting in a cystic mass formation caused by a foreign body granuloma. The patient was treated successfully with a 2-stage operation: first, revision of the total knee arthroplasty and, second, excision of the cyst. The patient had a pain-free functional knee 7 years after surgery, with no recurrence of the symptoms or the popliteal cyst.