The Trap Door procedure for avascular necrosis of the femoral head has been reported to give acceptable result (1). All patients reported here were clinically approaching indication for total hip replacement (THR), and short-term results may therefore be of interest.

Material and Method: Thirteen patients (5 men) age 14–48 were operated for avascular necrosis with subchondral collapse (n = 12) or sequel CalvŽ-Legg Perthes disease (n = 1). The hip was dislocated through the anterolateral. The cartilage over the necrotic area was elevated as a ßap with the base towards fovea capitis femoris. The necrotic area was debrided and channels were drilled into well-perfused bone. Autologue bone from the iliac crest was transplanted, overcorrecting the defect slightly. The cartilage ßap was sutured back and the hip relocated. Postoperatively the patients have loaded 15 kg 12 weeks, and then gradually resuming full weight bearing in additionally 6 weeks.

Results: Follow up ranges from 3 months to 3.3 years. Postoperative recovery was uneventful. No patient has been reoperated, but two patient are scheduled for THR 19 and 13 months postoperatively. Preoperatively the joint space was mean 4.3 mm (3–5,) at the last follow-up it was 3.9 mm (2,3 Ð 5). The roundness of the femoral head was judged as being better postoperatively than preoperatively Discussion: The TrapDoor procedure may delay or postpone the need for arthroplasty in patients with avascular necrosis of the femoral head. The two patients who will be converted to THR did both have pain and poor range of motion after the procedure, probably indicating that the cartilage/transplanted bone were degenerating.