Avascular Necrosis/Osteonecrosis

Avascular necrosis (AVN), or more correctly “osteonecrosis”, is a generic term referring to an ischaemic death of the constituents of bone.

AVN has a wide variety of causes and can affect nearly any bone in the body. Most sites of involvement have an eponym associated with avascular necrosis of that area, and these sites are discussed individually as each site has unique clinical, etiologic and prognostic features.

The terms ischaemic and avascular necrosis are typically reserved for subchondral osteonecrosis, whereas bone infarct refers to medullary osteonecrosis.

Epidemiology

There is no single affected demographic as the underlying predisposing factors are varied.

Pathology

Infarction begins when the blood supply to a section of bone is interrupted. Once an infarct has become established, just as in other tissues, there is a central necrotic core, surrounded by an ischaemic zone, the inner portion being ‘almost dead’ and the outer portion being hyperaemic. Beyond this is normal viable marrow. Between the normal and the ischaemic zone that demarcation occurs with the development of viable granulation separating dead tissue. This leads to the double line sign on MRI.

When the infarct is subchondral, a wedge of tissue is typically affected, the apex of which points towards the centre of the bone.

Aetiology
•trauma (fracture or dislocation)
•Increased pressure inside the bone
• HIV
• Lupus
•Cancer
•Caissons disease
• Blood Clot disorders,haemoglobinopathies, e.g. sickle cell disease
•pregnancy-related AVN
•radiotherapy,chemo
•connective tissue disorders and vascular issues
•renal transplantation
•corticosteroid excess (both endogenous and exogenous)
•pancreatitis
•gout
•Gaucher disease
•alcohol and smoking

Mnemonics: STARS, PLASTIC RAGS

Eponymous names for specific sites of avascular necrosis
• Ahlback disease: medial femoral condyle, i.e. SONK
• Brailsford disease: head of radius
• Buchman disease: iliac crest
• Burns disease: distal ulna
• Caffey disease: entire carpus or intercondylar spines of tibia
• Dias disease: trochlea of the talus
• Dietrich disease: head of metacarpals
• Freiberg infraction: head of the second metatarsal
• Friedrich disease: medial clavicle
• Hass disease: humeral head
• Iselin disease: base of 5th metatarsal
• Kienbock disease: lunate
• Kohler disease: patella or navicular (children)
• Kummel disease: vertebral body
• Legg-Calvé-Perthes disease: femoral head
• Liffert-Arkin disease: distal tibia
• Mandl disease: greater trochanter
• Mauclaire disease: metacarpal heads
• Milch disease: ischial apophysis
• Mueller-Weiss disease: navicular (adult)
• Panner disease: capitellum of humerus
• Pierson disease: symphysis pubis
• Preiser disease: scaphoid
• Sever disease: calcaneal epiphysis
• Thiemann disease: base of phalanges
• Van Neck-Odelberg disease: ischiopubic synchondrosis

Location specific sub-articles for avascular necrosis:
•hip avascular necrosis
•scaphoid avascular necrosis

Radiographic features

Radiographic changes alter with the stage of AVN – see Ficat staging, Steinberg classification.

Radiograph

In general, there is initial minor osteopenia, followed by variable density. Gradually microfractures of the subchondral bone accumulate in the dead bone, which is unable to repair leading to the collapse of the articular surface and the crescent sign of AVN. Eventually the cortex collapses and fragments, with superimposed secondary degenerative change.

MRI

MRI is the most sensitive (~95%) modality and demonstrates changes well before plain films changes are visible.
•diffuse oedema: oedema is not an early sign; instead, studies showed that oedema occurs in advanced stages and is directly correlated with pain
• reactive interface line is a focal serpentine low signal line with fatty centre (most common appearance and first sign on MRI)
• double line sign: serpiginous peripheral/outer dark (sclerosis) and inner bright (granulation tissue) on T2WI is diagnostic
• rim sign: osteochondral fragmentation:
•secondary degenerative change

Nuclear medicine

Bone scintigraphy is also quite sensitive (~85%) and is the second option after MRI. It is a choice when multiple sites of involvement must be assessed in patients with risk factors, such as sickle cell disease. The findings are different accordingly to the time of the scan:
• early disease: often represented by a cold area likely representing the vascular interruption
• late disease: may show a “doughnut sign”: a cold spot with surrounding high uptake ring (surrounding hyperaemia and adjacent synovitis)

Treatment and prognosis

The goal of treatment is to reduce the load on the affected part and to promote revascularisation. Treatment varies with location and includes:
•conservative: anti-inflammatory, analgesia, and reduced/non-weight bearing
•core decompression
•joint replacement for end-stage disease

Practical points
• MRI and bone scintigraphy have high sensitivity, with MRI studies being the first line for AVN assessment

See also
•differential diagnosis of erosive arthritis
•monoarticular arthropathy

Monoarticular arthropathy can result from a number of causes:
•infectious arthritis
•gout
• HADD (hydroxyapatite deposition disease)
•traumatic arthritis
•secondary osteoarthritis
•avascular necrosis
•PVNS
•synovial osteochondromatosis
•osteochondritis dissecans

What Research Is Being Done to Help People With Osteonecrosis?Some goals of research are to learn more about:How many people have osteonecrosis

Risk factors for osteonecrosisWhy steroids cause osteonecrosisThe role of genesHow to diagnose the disease earlyBetter treatments for osteonecrosisWays to improve hip replacementHow mechanical factors such as the alignment of hips, knees, and ankles affect treatment success.For More Information About Osteonecrosis and Other Related Conditions:
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) Information ClearinghouseNational Institutes of Health1 AMS CircleBethesda, MD 20892–3675Phone: 301–495–4484Toll free: 877–22–NIAMS (226–4267) TTY: 301–565–2966Fax: 301–718–6366Email: NIAMSinfo@mail.nih.gov Website: http://www.niams.nih.gov

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