Fact-sheet: Avascular necrosis of hip


Updated on 07/14/2016 at 10:24 AM

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Definition

Osteonecrosis may be of ischemic origin, due to impaired vascularization, post-traumatic, or idiopathic.
Other causes include: NSAIDs, Gaucher disease, osteomyelitis, sickle cell disease, alcoholism, coagulopathy, vasculitis, decompression sickness, Fabry disease, radiation therapy, corticosteroid therapy, Cushing syndrome, neurogenic arthropathies, gout, Langerhans cell histiocytosis, pancreatitis, hemophilia, infection.

Clinical features

Often bilateral and asymptomatic. Otherwise, mechanical-type hip pain (a turning point in the course occurs with the onset of a subchondral fracture)
Male predominance (3 to 8 M/1 F). 40-60 years

Radiography

Zone of osteosclerosis
or radiolucent image ringed by a thin rim of osteosclerosis
Collapse of the articular surface
Secondary osteoarthritis

CT

More sensitive than radiography for detecting a subchondral fracture
Superseded by MRI

MRI

More sensitive than scintigraphy
Defect in post-gadolinium enhancement
Subchondral area of T1 hypointensity rimmed by a T1 and T2 hypointense band
Occasionally, an internal T2 hyperintense and external T2 hypointense band is present: double-line sign
Subchondral fracture

Nuclear medicine

More sensitive than standard radiography, less sensitive than MRI

Classification

Ficat classification: - Stage I: normal radiographs, detected on MRI - Stage II: abnormalities of transparency or signal of the femoral head structure, without loss of sphericity - Stage III: loss of sphericity of the femoral head, with or without cortical step-off, due to collapse of the necrotic focus. Subchondral crescent sign (eggshell dissection) is a classic finding - Stage IV: secondary osteoarthritis Prognostic value of the ARCO classification +++ In the ARCO classification, stage III = subchondral fracture, stage IV = femoral head collapse, and MRI stages are subdivided into - A: Necrotic zone - B: Necrotic zone = 15-30% - C: Necrotic zone > 30%

Differential diagnosis

Mechanical osteonecrosis
Complex regional pain syndrome
Epiphyseal fracture
Spondyloarthropathy
Osteoarthritis