Compressive intrapelvic synovial cysts: an early complication of an HA-coated cup.

Synovial cysts arising from the hip are not common but can develop in response to intraarticular derangement and increased intraarticular pressures. We present a case of a compressive intrapelvic synovial cyst 3 years after a total hip replacement with a hydroxyapatite-coated acetabular component. At surgery, cracking of the coating of the acetabular component was observed in the areas where the cup was not covered by host bone. The cyst was excised and the bearing surface was replaced. Three years after surgery there has been no recurrence. Migration of hydroxyapatite granules from uncovered portions of hydroxyapatite-coated cups may be a source of third-body wear and could accelerate synovial cyst formation.