- Death of bone tissue due to loss of blood supply
- Advanced disease can result in bone collapse
Epidemiology
- Most common in 30-50 year olds
- Most commonly affects the femoral head in children – AKA Perthes disease
- Can also affect the humerus, knee, and rarely the small bones of the wrist
Etiology
Traumatic
- Dislocated joint – which damages nearby blood vessels
- Fracture
- Radiotherapy for cancer
Non-traumatic
- Alcoholism
- High dose steroids
- Cigarette smoking
- Obesity
- Systemic illnesses – e.g. sickle cell anaemia, SLE
Pathophysiology
- Cessation of blood supply to a section of the bone, can be due to
- Vascular occlusion – most common in traumatic etiology
- Hyperlipidemia – lipid deposition in femoral head, causing intraosseous hypertension and ischaemia
- Intravascular coagulation – triggered by a secondary event such as familial thrombophilia, infection, malignancy, pregnancy etc
- Healing process – necrotic bone triggers a process of repair (with osteoclasts, osteoblasts, histiocytes)
- Osteoblasts build new bone on top of the dead bone, leading to scarring that prevents revascularisation of the necrotic bone
- Earliest pathologic characteristics
- Necrosis of hematopoietic cells and adipocytes
- Interstitial marrow oedema
Classification – ARCO classification
- Stage 0 – normal XR, MRI and no symptoms
- Stage 1 – normal XR, no symptoms, however changes shown on MRI scan
- Stage 2 – symptoms present
- XR – trabecular bone changes, but no changes in subchondral bone and preserved joint space
- MRI – abnormal
- Stage 3 – symptoms persistent
- XR – trabecular bone changes, subchondral fracture ( Crescent sign ), preserved joint space
- Stage 4 – symptoms persistent
- XR – features of osteoarthritis, distorted femoral head shape, acetabular changes, narrowed joint space
Clinical features
- Asymptomatic in the early stages
- Pain and decreased range of motion in affected joint
- Joint stiffness
Diagnosis
- History of risk factors and physical exam
- X-ray – usually appears normal in the early stages, so is more useful is advanced disease
- Patchy sclerosis, rim calcification, crescent sign , secondary degenerative changes
- MRI – most sensitive
- Double line sign – outer dark (sclerosis) and inner bright (granulation tissue) lines
- Diffuse oedema
- Secondary degenerative changes – osteoarthritis
- Bone scintigraphy
- Doughnut sign – a cold spot with surrounding high uptake ring
Treatment
Non operative
- Medications – anticoagulants, statins, anti-inflammatory, analgesia, bisphosphonates
- Physiotherapy
Operative
- Core decompression – creates a tract in the femoral head that decompresses the head
- Facilitates increases blood flow and promotes neo-vascularisation
- Osteotomy – for young patients without co-morbidities
- Total hip replacement – when other treatment modalities have failed