Myositis Ossificans

Myositis ossificans is heterotopic bone formation within muscle, typically occurring after trauma or in association with neurological conditions. The term "myositis" is a misnomer - there is no inflammation, and the bone forms in muscle, not from muscle.

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Key Pathophysiological Concept:

• Bone forms from outside in (periphery first)
• This is opposite to osteosarcoma (center first)
• Maturation takes 6-12 months
• Early excision disrupts this process and causes recurrence

The radiographic zoning phenomenon has a microscopic counterpart, and understanding it is what makes the "sarcoma trap" this topic repeatedly warns about comprehensible. The lesion is organised into three concentric zones, and the diagnostic danger lies entirely in the centre.

After the quadriceps, the elbow is the classic site this topic names - and it carries a distinct, heavily examinable iatrogenic risk. Myositis ossificans of the elbow follows posterior elbow dislocation, terrible-triad injuries, and paediatric supracondylar/forearm fractures, and characteristically forms anteriorly within the brachialis, which lies directly on the anterior capsule and distal humerus. Haematoma from the injury organises within the muscle and ossifies, blocking the flexion-extension arc.

The single greatest avoidable risk is forced passive stretching or manipulation of the stiff, freshly injured elbow. Vigorous passive mobilisation re-injures muscle, enlarges the haematoma, and converts it into heterotopic bone - which is exactly why the old teaching of aggressive passive stretching of a stiff post-traumatic elbow (and passive manipulation under anaesthesia in the acute or subacute phase) has been abandoned.

Principles specific to the elbow:

• Favour early active and active-assisted range of motion within a pain-free arc; avoid forced passive stretch and avoid early manipulation under anaesthesia.
• Consider NSAID/indomethacin prophylaxis after high-risk elbow trauma or surgery in at-risk patients.
• Neurogenic elbow ossification (after head injury) matures more slowly and recurs more often than the traumatic form.
• Once mature (cold scan, normal ALP, corticated margins), a symptomatic anterior lesion restricting the arc can be excised, applying the same maturity rule and post-excision prophylaxis used elsewhere.

History:

• Recent trauma or contusion (weeks to months)
• Quadriceps contusion (most common)
• Elbow trauma
• Hip trauma
• Head injury or spinal cord injury (neurogenic)

Physical Examination:

Key Clinical Signs:

• Palpable mass: Firm, fixed within muscle
• ROM limitation: Out of proportion to injury
• Pain with stretch: Aggravated by passive stretch
• Functional impairment: May limit activities

Differential Diagnosis

Note: Surgical excision is only performed when the lesion is mature and symptomatic. This section describes the technique for excising mature myositis ossificans.

After Excision:

Prophylaxis:

• Indomethacin: 75mg daily for 6 weeks (start post-op day 1)
• OR Radiation: 700-800 cGy single fraction within 72 hours
• Both equally effective
• Mandatory - reduces recurrence from 50%+ to 10-20%

Recurrence Rates:

Global epidemiology:

• Traumatic myositis ossificans is the dominant form worldwide and is closely tied to contact-sport participation and high-energy trauma, so reported frequency tracks local sporting culture and trauma burden rather than geography.
• Significant quadriceps contusions carry roughly a 9% risk (athlete cohorts); the elbow is the next most common site, particularly after paediatric supracondylar/forearm injuries and forceful reduction.
• Neurogenic heterotopic ossification (after traumatic brain or spinal cord injury) is a distinct, related entity that is more common in regions with high road-trauma and conflict-injury volumes.

Side-by-side guideline themes:

• The "50% recurrence if excised immature" figure comes from older surgical case series, not modern controlled data. The principle - wait for maturity - is sound, but the precise recurrence rate is uncertain and likely site- and technique-dependent.
• Bone scan vs serial imaging for maturity: historic teaching mandates a cold three-phase bone scan before excision, but many units now rely on stable, fully corticated lesions on serial radiographs/CT plus normalised ALP. There is no high-level trial defining the single best maturity test.
• Is excision even necessary? Conservative series (e.g. Simon et al. 2016) show most athletes return to full activity despite persisting ossification, challenging routine excision. Surgery is increasingly reserved for genuinely mechanical, function-limiting lesions.
• Prophylaxis after excision of traumatic MO: the RCT evidence for NSAID/radiotherapy equivalence derives from acetabular-fracture and arthroplasty HO, then extrapolated to MO excision. Direct trial data in traumatic myositis ossificans are lacking.
• NSAID vs radiotherapy choice: efficacy is equivalent; the real debate is NSAID gastrointestinal/renal risk and effect on fracture/soft-tissue healing versus radiotherapy cost, access, and theoretical malignancy concern in young patients - favouring NSAIDs in most healthy young trauma patients.