An unusual cause of pain in both hips

In August 2001, a 55 year old renal physician presented with a three week history of a painful right hip. There was no obvious precipitating factor. The pain was situated over the outer aspect of the right hip as well as the groin, with intermittent radiation down to the right knee. At times, he needed to place a pillow between his knees to feel comfortable when lying down. Despite these symptoms, he was able to walk freely around Vienna on holiday. On examination, there was pain on external rotation of the right hip as well as discomfort at the extremes of abduction and adduction. There was no tenderness over the greater trochanter. An x ray examination of the right hip was normal. Magnetic resonance imaging (MRI) disclosed a bilobed 2 cm “collar-stud” cystic lesion, with one lobe intracapsular and the other extracapsular, just inferior to the lateral edge of the right acetabulum (fig 1). …