Femoroacetabular impingement caused by a femoral osseous head-neck bump deformity: clinical, radiological, and experimental results.

Femoroacetabular impingement is often associated with reduced femoral anteversion or an osseous bump deformity on the femoral head-neck junction. We report prospectively on 17 patients showing an osseous bump at the anterolateral head-neck junction on radiography (22 hips) and typical signs of femoroacetabular impingement on clinical examination. Following three plans of treatment, nine patients (10 hips) underwent nonoperative treatment, and eight patients (12 hips) had surgery. In eight hips with labral defects but minor cartilage damage, the bump was surgically removed via trochanter flip osteotomy. Two hips were treated surgically through an anterior surgical approach without hip dislocation. Four hips with severe signs of osteoarthritis and significantly reduced range of motion underwent total replacement. To elucidate a local osteogenic differential potential, tissue specimens of the perilesional capsule were investigated immunohistochemically. Various antigens and protein synthesis products served to identify osteoblastic and progenitor cells. There was a significant improvement in internal rotation and pain relief in patients who underwent surgical resection of the osseous bump. No avascular osteonecrosis or other significant severe side effects were observed during follow-up. In contrast, no nonoperatively treated patients improved. Furthermore, immunohistochemical studies showed perilesional recruitment of osteoprogenitor cells.