Avascular necrosis of the hip

Last revised by Dr MT Niknejad on 16 May 2022

Avascular necrosis of the hip (AVN) is more common than other sites, presumably due to a combination of precarious blood supply and high loading when standing. 

The most common presenting symptom is pain in the region of the affected hip, thigh, groin, and buttock. Although few patients may remain asymptomatic until late stages.

Typically it affects the superior articular surface (between 10-2 o'clock) and begins in the most anterior part of the hip.

It can be thought of as traumatic (secondary to the neck of femur fractures) or non-traumatic. Traumatic AVN is usually unilateral10. In non-traumatic cases, it is mostly bilateral in 70-80% 10.

A specific staging system (Ficat staging) exists for the hip which includes x-ray, MRI and bone scan appearances, and covers much of the imaging appearances, thus please refer to that article. 

Other than describing the general appearance of the affected region, the following are necessary to include in the report as they have a bearing on prognosis and treatment:

  • position 
  • estimating percentage volume of the head involved (axial) and percentage weight-bearing surface involved (coronal)
  • coexisting osteoarthritis or secondary degenerative change
  • joint effusion
  • presence of a potentially unstable osteochondral fragment: rim sign
  • subchondral fractures

Often more sensitive than plain film in showing subchondral fractures.

MRI is the most sensitive modality, with a sensitivity of 71-100% and specificity of 94-100%1. As there is a high rate of bilateral involvement, both hips should be included in the field of view of at least some sequences.

  • T1: usually the initial specific findings are areas of low signal intensity representing edema, which can be bordered by a hyperintense line that represents blood products
  • T2: may show a second hyperintense inner line between normal marrow and ischemic marrow. This appearance is highly specific for AVN hip and is known as "double line sign".

The Mitchell classification is commonly used to classify AVN based on MR-images.

In some situations consider

General imaging differential considerations include:

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Cases and figures

  • Figure 1: blood supply to the femoral head
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  • Case 1
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  • Case 2
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  • Case 3
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  • Case 4
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  • Case 5
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  • Case 6: bilateral
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  • Case 7
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  • Case 8
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  • Case 9: bilateral metachronous
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  • Case 10
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  • Case 11
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  • Case 12
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  • Case 13: with sickle cell disease
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  • Case 14: post sub capital NOF
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  • Case 15
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  • Case 16
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  • Case 17
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  • Case 18: steroid induced
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  • Case 19: with treated aplastic anemia
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  • Case 20
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  • Case 21
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  • Case 22
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  • Case 23
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  • Case 24: bilateral humeral and femoral heads
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  • Case 25
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  • Case 26
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  • Case 27
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  • Case 28
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  • Case 29
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  • Case 30
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