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Textbook/Rheumatology/Avascular necrosis/Rapid
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Avascular necrosis

Essential points for quick revision.

2 min synopsisUK scopeSources checked 27 Aug 2026Clinical review pending
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Fracture, dislocation or septic mimic

Severe acute hip pain after trauma, deformity, inability to bear weight, a hot joint with systemic illness or neurovascular compromise may represent fracture, dislocation or infection rather than chronic osteonecrosis.

Action: Give analgesia, minimise movement, document distal neurovascular status and arrange urgent radiography and orthopaedic assessment; use the septic-joint pathway when infection is plausible and never delay dislocation reduction for elective MRI.

Synopsis

Recognise osteonecrosis before subchondral collapse, identify traumatic and systemic causes, use MRI when radiographs are unrevealing, protect the joint while staging is completed, and refer while joint-preserving options remain possible.

  • Suspect femoral-head osteonecrosis in progressive groin or buttock pain with painful internal rotation, especially after glucocorticoids, heavy alcohol, trauma, sickle-cell disease, lupus or transplantation.
  • Obtain anteroposterior pelvis and lateral hip radiographs first, while recognising that early osteonecrosis can be radiographically invisible.
  • MRI without contrast is the preferred confirmatory test when suspicion persists and sensitively defines lesion location, size, bilateral disease and early subchondral fracture.

Key red flags

A shortened or rotated limb, major trauma or sudden inability to bear weight requires urgent exclusion of femoral-neck fracture or hip dislocation.

Investigation priorities

01
First-line AP pelvis and lateral hipFirst stepFirst line

Exclude fracture, advanced osteoarthritis and destruction while identifying sclerosis, cysts, crescent fracture or flattening.

02
Preferred confirmatory MRIPreferred

Detect early necrotic bone, define lesion size and weight-bearing location, assess subchondral integrity and examine both hips.

Management branches

First-line recognitionImage risk-associated mechanical pain

Groin or joint pain and restricted movement occur after a recognised vascular insult or systemic exposure.

  1. Exclude fracture, dislocation and septic arthritis from acuity, observations and examination, then document glucocorticoid, alcohol, trauma, haematological and systemic risks.
  2. Obtain orthogonal radiographs and proceed to MRI of both hips when films are normal or equivocal but clinical probability remains meaningful.

Key medicines

NaproxenUse 250–500 mg orally twice daily with food for the shortest period needed while definitive assessment proceeds; add gastroprotection when indicated and stop without functional benefit.
ParacetamolTake 500–1,000 mg orally when needed at intervals of at least four hours, never exceeding 4,000 mg in 24 hours in a suitable adult; lower the ceiling for low weight, malnutrition, frailty or liver disease.
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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

Authoring stateRapid draftClinical stateAwaiting reviewJurisdictionUnited Kingdom