What causes myositis ossificans and how is it managed?

Myositis Ossificans: Causes and Management

Primary Causes

Myositis ossificans is primarily caused by trauma to muscle tissue, including severe contusions, strains, repeated microtrauma, burns, or surgical procedures, with the masseter muscle being most commonly affected in the head and neck region. 1, 2

Traumatic Myositis Ossificans (Most Common)

• Acute or repetitive trauma is the predominant cause, resulting in hematoma formation within muscle tissue that subsequently calcifies 1, 2
• Severe contusions or strains to skeletal muscle, particularly in the extremities, trigger the ossification process 1
• Surgical procedures and burns can precipitate heterotopic bone formation in affected muscle tissue 2, 3
• Excessive rehabilitation exercises following orthopedic procedures have been documented as a causative factor, particularly in pediatric cases 4

Non-Traumatic Forms (Rare)

• Non-traumatic myositis ossificans can occur without identifiable injury, though this represents a rare variant with similar radiological and histopathological characteristics 2, 5
• Fibrodysplasia ossificans progressiva (FOP) is a distinct genetic condition caused by ACVR1/ALK2 mutations (c.617G>A; p.R206H), characterized by progressive heterotopic ossification that is spontaneous or triggered by minor trauma 6

Critical distinction: Standard myositis ossificans is a localized, benign process fundamentally different from FOP, which is a progressive, systemic genetic disorder 6, 3

Pathophysiology

• The process involves calcification of a hematoma that develops after muscle injury, creating a benign ossifying lesion with characteristic zonal histological appearance 1, 3
• The lesion displays progressive maturation from immature to mature bone, which is critical for determining appropriate timing of intervention 3

Diagnostic Approach

Clinical Presentation

• Palpable bony mass developing weeks to months after documented or suspected trauma to the affected area 1, 4
• History of recent trauma is the key diagnostic feature distinguishing this from other conditions 1

Imaging Studies

• Radiographic evidence of calcified mass within muscle tissue confirms the diagnosis 1
• Imaging is essential to differentiate myositis ossificans from sarcomatous change and to determine lesion maturity before any surgical consideration 3

Management Strategy

Initial Conservative Treatment (First-Line)

Management should prioritize minimizing extension of the original injury through conservative measures, as premature surgical intervention on immature lesions inevitably results in recurrence. 1, 3

• Rest, ice, compression, and elevation (RICE) is recommended as initial therapy for acute presentations 1
• Gentle, painless range-of-motion exercises may be prescribed to restore mobility once acute inflammation subsides 1
• Protective padding should be used to prevent additional trauma to the affected area 1

Surgical Considerations

• Surgical resection should only be considered after the lesion has fully matured, as determined by imaging studies 3
• Suboptimal operative intervention on immature lesions carries a high postoperative recurrence rate and should be avoided 2, 3
• Surgery is reserved for cases where the ossified mass significantly impairs function after conservative management has failed and the lesion has matured 3

Key Clinical Pitfalls

• Do not operate on immature lesions: This is the most critical error, as premature surgery guarantees recurrence 3
• Do not confuse with malignancy: Imaging characteristics help differentiate benign myositis ossificans from sarcomatous lesions 3
• Do not confuse with FOP: Standard traumatic myositis ossificans is localized and benign, whereas FOP is progressive and systemic, requiring entirely different management 6
• Avoid aggressive rehabilitation: Excessive post-injury or post-surgical exercise can precipitate myositis ossificans formation 4