Unrecognized acetabular component rotation with formation of a pseudoarticulation after total hip arthroplasty

We report an unusual case of an 82-year-old woman who presented with bilateral knee pain and advanced tibial-femoral and patellofemoral arthrosis. A preoperative total lower extremity film revealed an unrecognized, asymptomatic, dislocated right total hip arthroplasty with a rotated acetabular component that likely occurred 12 years earlier. The dislocated prosthetic femoral head appeared to be articulating with a pseudoacetabulum that had formed superiorly and laterally to the acetabular cup. The patient was unaware of any incident where she noticed an acute change after her hip arthroplasty surgery. We believed the patient to have a chronically dislocated hip that was pain free and quite functional for many years, an unusual condition that has not been reported previously in the literature.