A case of intra-articular snapping hip caused by articular cartilage detachment from the deformed femoral head consequent to Perthes disease.

We treated a relatively rare case of intra-articular snapping hip caused by an articular cartilage fragment detached from the deformed femoral head consequent to Perthes disease. We report the pathology as well as diagnosis and treatment of this case. A 24-year-old man presented with right coxalgia. He was diagnosed with Perthes disease at a young age and was treated conservatively. Six months before the patient visited our department, he started having intense pain accompanied by a clicking sound when he extended and at the same time externally rotated the right hip joint from a flexed position. Although a radiogram showed Stulberg class 3 deformity of the femoral head, the joint space was well preserved and no bone cyst or bone spur formation was seen. Computed tomography (CT) and magnetic resonance imaging (MRI) showed no abnormal findings inside the femoral head and in the hip joint. However, when 5 mL of 2% lidocaine hydrochloride was injected into the hip joint, the snapping phenomenon persisted but the sharp pain was temporarily resolved. Arthroscopic finding showed a valve-shaped detachment of articular cartilage in the anteromedial side of the femoral head. Arthroscopic shaving of the detached fragment was conducted. The pain and clicking sound accompanying hip joint movement disappeared postoperatively. Hip joint arthroscopy is useful for the diagnosis and treatment of intra-articular type snapping hip when the cause of snapping is inside the joint cavity.