Stage 0 Theoretical stage: Assymptomatic. All diagnostic tests are normal. Biopsy from histology - is the only abnormality. Nil Required : Theoretical stage only Not a clinical problem.

Stage 1 X-Rays and CT-scan are normal MRI and Tc99 and histology are abnormal. Symptoms may or may not be present. Surgery is possible / desirable. Core - decompression possible, free vascularized fibula grafting.

Stage 2 X-Rays are abnormal - With linear sclerosis or cysts. There is no Subchondral lucency Head of the femur is still spherical. Surgery - free vascularized fibula grafting.

Stage 3 The femoral head starts to fail mechanically - With Trabecular collapse. The radioluscent crescent sign is visible at the Subchondral endplate. The femoral head itself is still spherical.Surgery - free vascularized fibula grafting. Success depends on degree of changes.

Stage 3a. Crescent < 15% Surgery still possible. Stage 3b Crescent 15-30% Increasing risk of failure of preventitive surgery.

Stage 3c Crescent>30% Increasing risk of failure of preventitive surgery.

Stage 4 Flattening of the femoral head is now seen NO HELP Medical Management. Surgery: total Hip Replacement, free vascularized fibula grafting.

Stage 4a <15% of the surface is collapsed Depression <2mm NO HELP Medical Management. Free vascularized fibula grafting, total hip replacement.

Stage 4b 15-30% collapse or 2-4mm depression Preventitive surgery NO HELP Medical Management. Total Hip Replacement Required.

Stage 4c >30% Collapse or >4mm depression. Preventitive surgery NO HELP Medical Management. Total Hip Replacement Required.

Stage 5 Any or all Xray features may be present There is a decrease in joint space. Secondary Osteoarthritis is present with: Sclerosis / Cysts / Osteophytes Preventitive surgery NO HELP Medical Management. Hip Replacement Required.

Stage 6 Extensive destruction Total Hip Replacement - Where available / Possible.