Pigmented villonodular synovitis of the hip joint.

Diffuse pigmented villonodular synovitis of the hip joint is uncommon. The disease is usually slowly progressive with accompanying pain and limitation of movement. Radiographs often show cystic radiolucent defects in the acetabulum and femoral head, but the joint space remains preserved until late. Two cases are reported, both with a primary diagnosis of coxarthrosis which had been treated unsuccessfully by intertrochanteric osteotomy. A correct diagnosis was not reached until the hip joint was explored. The progress of radiographic changes over a period of eight years is demonstrated in one case. Arthroscopy and synovial biopsy should be considered in young adults with hip pain of unknown origin.