Avascular necrosis of the hip 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 a pain in the region of 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. In non-traumatic cases, it is bilateral in 40%.
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Specific staging system (Ficat staging) exists for the hip which includes X-ray, MRI and bone scan appearance, 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 and effect on prognosis and treatment:
- 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
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 intensities represent oedema, which can be bordered by a hyper-intense line which represents blood products
- T2: it may show a second hyper-intense inner line between normal marrow and ischaemic marrow. This appearance is highly specific for AVN hip and known as "double line sign"
General imaging differential considerations include:
- haematopoietic marrow (see bone marrow)
- Pitt's pit
- fovea centralis
idiopathic transient osteoporosis of the hip (ITOH)
- hyperaemia with diffuse increased uptake of radiotracer by the femoral head, neck, and intertrochanteric region
- pain and fever
- usually involves both sides of the joint
- 1. Glickstein MF, Burk DL, Schiebler ML et-al. Avascular necrosis versus other diseases of the hip: sensitivity of MR imaging. Radiology. 1988;169 (1): 213-5. Radiology (abstract) - Pubmed citation
- 2. Ombregt L, Bisschop P, Veer HJ. A system of orthopaedic medicine. Elsevier Health Sciences. (2003) ISBN:0443073708. Read it at Google Books - Find it at Amazon
- 3. Armstrong P, Wastie ML. Diagnostic imaging. Wiley-Blackwell. (1998) ISBN:0632048468. Read it at Google Books - Find it at Amazon
- 4. Sugimoto H, Okubo RS, Ohsawa T. Chemical shift and the double-line sign in MRI of early femoral avascular necrosis. J Comput Assist Tomogr. 1992;16 (5): 727-30. Pubmed citation