Avascular necrosis

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, aetiologic and prognostic features. 

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

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

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

Mnemonics: STARSPLASTIC RAGS

Eponymous names for specific sites of avascular necrosis
Location specific sub-articles for avascular necrosis:

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 show 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)

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

rID: 950
Section: Pathology
Synonyms or Alternate Spellings:
  • Avascular necrosis (AVN)
  • AVN
  • Osteonecrosis

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Cases and figures

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    Case 1: involving humeral head
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    Case 2
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    Case 3
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    Case 4
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Avascular ...
    Case 5
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    Scaphoid AVN STIR
    Case 6: scaphoid (Preiser disease)
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    Scaphoid fracture...
    Case 7: scaphoid fracture with early AVN
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    Case 8
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    Dietrich disease
    Case 9: Dietrich disease
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    Case 10: hip
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    Case 10
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    AVN
    Case 11: background sickle cell disease
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    Case 12: knee (STIR)
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    Fourth metatarsal...
    Case 13: fourth metatarsal - abnormal signal
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    left foot
    Case 14: Mueller-Weiss disease
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    Case 15: Kummel disease
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    Case 17: lunate
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    Case 18: double line sign of talar AVN
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    Case 19: van Neck-Odelberg disease
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    Case 21
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    Case 22: bilateral femoral head
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    Case 23: navicular
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