Rapid acetabular osteolysis secondary to subchondral insufficiency fracture

A 93-year-old man presented with a one-month history of persistent left hip pain of sudden onset. At first visit, radiographs revealed a fracture line at the medial portion of the acetabulum with no displacement. Magnetic resonance imaging revealed bone marrow edema in the corresponding medial portion of the acetabulum. Radiographs obtained 2 months later showed rapid acetabular osteolysis with associated prominent migration of the femoral head into the acetabulum. Histology obtained from the hip joint was consistent with a subchondral insufficiency fracture with no evidence of massive chondrolysis. Our case was considered as a subchondral insufficiency fracture of the left acetabulum resulting in rapid acetabular osteolysis (protrusio acetabuli).