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Heterotopic ossification (HO)
Heterotopic ossification is the formation of true bone in soft tissues around joints — mainly the hip — after spinal cord injury, brain injury, hip replacement or burns; in the early stage it mimics venous thrombosis or inflammation, so thrombosis is excluded first.
Why it matters in the exam
In spinal cord injury HO appears below the level of injury, mainly at the hip (anterior and medial), usually in the first months. In brain injury it appears at the hip, elbow, shoulder and knee; in burns — the elbow is the common site. Risk factors: complete injury, spasticity, prolonged immobility, pressure injuries and thrombosis. Early presentation: swelling, local warmth, redness, reduced range of motion and sometimes fever — a picture that mimics venous thrombosis, cellulitis or arthritis, so venous Doppler is performed.
Diagnosis: alkaline phosphatase rises but is not specific; a three-phase bone scan is the early and sensitive test (positive in the first weeks, before X-ray); plain X-ray becomes positive only after several weeks; CT defines the extent before surgery. After hip replacement HO is graded by Brooker (grades I–IV, where IV is complete ankylosis of the joint).
Prevention: after hip replacement or acetabular surgery — NSAIDs (for example indomethacin) or a single dose of radiation around the operation; in spinal cord injury — NSAIDs in the early stage. Treatment: gentle range-of-motion exercises (not forceful), a bisphosphonate (etidronate) and NSAIDs. Surgical excision is kept for HO that limits function (sitting, hygiene, transfers) or causes pressure injuries or nerve compression, and is done when the bone is mature, with post-operative prevention to reduce recurrence. Complications: joint ankylosis, pressure injuries and nerve compression — for example of the ulnar nerve at the elbow.
Key points
- Bone in soft tissue; mainly at the hip.
- Mimics thrombosis — exclude by Doppler.
- Three-phase bone scan — the early test.
- Prevention: NSAIDs or radiation.
- Excision when the bone is mature and limits function.
Summary table
| Topic | Main point | Note |
|---|---|---|
| Common site | Hip in spinal cord injury; elbow in burns | In brain injury — hip, elbow, shoulder, knee |
| Early presentation | Swelling, warmth, reduced range | Exclude thrombosis by Doppler |
| Early test | Three-phase bone scan | X-ray positive only after weeks |
| Prevention | NSAIDs or radiation around surgery | After hip replacement and in spinal cord injury |
| Treatment | Gentle range of motion, etidronate, NSAIDs | Excision when the bone is mature and limits function |
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Sources
- Braddom's Physical Medicine and Rehabilitation, 6th edition (2021) — Heterotopic ossification in spinal cord and brain injury
- Brooker classification of heterotopic ossification after total hip arthroplasty, 1973 — Grades I–IV
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.