We operated on five men and seven women, aged 17 to 48 years, for avascular necrosis of the femoral head. Eleven had subchondral collapse and one Calvé-Legg Perthes’ disease. The hip was dislocated through an anterolateral approach. The cartilage over the necrotic area was elevated as a flap with the base towards fovea capitis femoris. The necrotic/cystic area was debrided and channels were drilled into well-perfused bone. Autologous bone from the iliac crest was transplanted, slightly overcorrecting the defect. The cartilage flap was sutured back and the hip relocated.

Postoperatively patients were limited to 15 kg of weight-bearing for 12 weeks and then gradually resumed full weight-bearing over six weeks. Follow-up ranged from three months to three years. No patients have been operated on again and no major complication has occurred. Preoperatively the mean joint space was 4.3 mm (3 to 5 mm); at the last follow-up, it was 3.9 mm (2.3 to 5 mm). The roundness of the femoral head was judged better postoperatively than preoperatively. No patient has so far been scheduled for arthroplasty, but two patients have had relapses of more severe pain.

The Trap Door procedure may postpone the need for arthroplasty in patients with avascular necrosis of the femoral head. Our initial results have been encouraging, but further follow-up is required.