X-ray - hips

Role

Hip X-ray remains first-line imaging for hip pain - assessing joint space, femoral head/acetabular morphology, and specific patterns of osteoarthritis, avascular necrosis, and inflammatory/spondyloarthritic involvement
One of the most commonly imaged large joints, particularly relevant in older adults (osteoarthritis) and in axial spondyloarthritis (hip involvement occurs in a meaningful subset and carries prognostic significance)

Osteoarthritis: superior/superolateral joint space narrowing (the classic weight-bearing pattern), osteophytes, subchondral sclerosis and cyst formation
Avascular necrosis (osteonecrosis): early changes can be subtle/normal on X-ray (MRI far more sensitive early) - later stages show subchondral lucency ("crescent sign"), femoral head flattening/collapse, and eventual secondary osteoarthritic change
Axial spondyloarthritis: hip involvement (when present) tends to show concentric joint space loss (distinct from osteoarthritis's typically superior-predominant pattern) reflecting the inflammatory rather than purely mechanical process

Hip involvement in axial spondyloarthritis is a recognised marker of more severe disease and worse functional prognosis, relevant to treatment intensity decisions and to counselling about the expected disease course
Early avascular necrosis (before X-ray changes develop) requires MRI for reliable detection - a normal hip X-ray does not exclude early AVN in a patient with risk factors (corticosteroid use, alcohol excess, sickle cell disease) and a compatible clinical picture

Total hip replacement is definitive treatment for end-stage osteoarthritis or advanced AVN with joint destruction; earlier AVN stages may be managed with core decompression or other joint-preserving procedures depending on stage and extent

Osteoarthritis, avascular necrosis (corticosteroid use, alcohol excess, sickle cell disease as risk factors), axial spondyloarthritis with hip involvement, femoroacetabular impingement

The joint space narrowing pattern (superior/weight-bearing predominant in osteoarthritis vs concentric in inflammatory disease) is a useful discriminator, but early AVN specifically requires a high index of suspicion and MRI, since X-ray can appear deceptively normal in the earliest, most treatable stage

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