Myositis Ossificans: Causes, Zoning Pattern & Rehab MCQs

Myositis Ossificans

Myositis Ossificans Traumatica is the heterotopic formation of non-neoplastic bone in muscle or soft tissue, usually following a contusion or hematoma.

1. Pathophysiology

• Cause: Blunt trauma (Hematoma) -> Metaplasia of fibroblasts into osteoblasts.
• Sites: Quadriceps (Thigh - "Charley Horse") and Brachialis (Elbow).
• Stages: Active (Painful, swelling) -> Mature (Painless, bony mass).

2. Diagnosis & The Zoning Pattern

Differentiating from Osteosarcoma:
- Myositis Ossificans: Peripheral Maturation (Bone is mature on the outside, immature in the center).
- Osteosarcoma: Central Maturation (Mature center, immature periphery).

3. Management

• Acute: RICE. AVOID aggressive massage or passive stretching (worsens it).
• Medical: Indomethacin (NSAID) to inhibit bone formation.
• Surgical: Excision ONLY after the bone is fully mature (6-12 months) and "Cold" on bone scan. Early excision leads to recurrence.

25 Practice MCQs

Q1. Myositis Ossificans is:

Answer: A). Metaplasia of soft tissue.

Q2. The most common site is:

Answer: A). Areas prone to direct blows.

Q3. The "Zoning Pattern" on histology/X-ray shows:

Answer: A). Key to distinguishing from Malignancy.

Q4. Osteosarcoma shows which pattern?

Answer: B). Center is most dense/mature.

Q5. Surgery should be performed:

Answer: A). Early excision causes massive recurrence.

Q6. Which drug helps prevent MO?

Answer: A). Inhibits osteogenic differentiation.

Q7. Passive stretching in the acute phase:

Answer: A). Aggressive massage/stretch increases hematoma and bone formation.

Q8. Alkaline Phosphatase (ALP) levels are:

Answer: A). Returns to normal when mature.

Q9. Is it malignant?

Answer: B). But mimics sarcoma on X-ray early on.

Q10. Radiotherapy is used for:

Answer: A). Single dose radiation prevents heterotopic ossification.

Q11. The "Dotted Veil" pattern on X-ray appears at:

Answer: A). Faint calcification.

Q12. Myositis Ossificans Progressiva is:

Answer: A). Fatal condition; distinct from traumatic type.

Q13. Bone scan activity in MO:

Answer: A). Surgery is delayed until it becomes "Cold".

Q14. Stiffness in the elbow after dislocation is often due to:

Answer: A). Massage is strictly banned in elbow dislocation rehab.

Q15. Does the bone formed in MO attach to the underlying skeleton?

Answer: A). Diagnostic clue.

Q16. Management of a hematoma to prevent MO includes:

Answer: A). Minimize bleeding.

Q17. "Eggshell" calcification is seen at:

Answer: A). Indicates zoning.

Q18. Neurological injury causes MO?

Answer: A). Common around hips in coma patients.

Q19. Main symptom in active phase is:

Answer: A). Inflammatory signs.

Q20. Mature MO is usually:

Answer: A).

Q21. Biopsy of early MO can be mistaken for:

Answer: A). Dangerous diagnostic pitfall. Rely on X-ray zoning.

Q22. "Rider's Bone" is MO in the:

Answer: A). Historical term.

Q23. "Clay Shoveler's" fracture can have MO in:

Answer: A).

Q24. Etidronate (Bisphosphonate) is:

Answer: A).

Q25. Range of motion should be:

Answer: A). Avoid trauma.