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Male recruit who 1 month previously was negotiating a vertical wall on the obstacle course when he fell several feet, landing on his buttocks. His "gunny" recommended a series of stretching exercises for his resulting "stiffness"; these were not helpful. He was referred for a bone scan.
A 12 x 8 cm hematoma had deveoped in the left buttocks area. This had decreased in size by the time of the bone scan. He walked with a limp and had buttocks and anterior left groin pain and tenderness.
Alkaline phosphatase was elevated at 151 (nl. range 38-126) ESR was normal at 4.
Anterior and Posterior bone scan images 1 month post injury show a 4+ intense accumulation of MDP in the left buttock region. This has a horizontal orientation and does not conform to the femur or other, normal bony structures.
CT scan images a few days after the bone scan demonstrate circular/lamellar calcification in the left glueus maximus muscle. The calcification is well separated from the femur.
Differential diagnosis includes an ossifying soft tissue sarcoma as well as myositis ossificans. With the clear history of trauma and resulting hematoma the diagnosis of post-traumatic myositis ossificans is far more likely.
Dx: Myositis Ossificans (Post-Traumatic)
Dx Confirmed by:
Heterotopic ossification is a synonym for myositis ossificans. Myositis ossificans(MO) is a benign, extra-osseous area of active bone formation. It often follows trauma but the trauma may not be severe and may not be associated with an obvious hematoma. During the period of active calcification, the bone scan is nearly always 4+ intense. After several months(12-24 in our experience) the intensity of the bone scan decreases. If surgical therapy is considered, it is usually delayed until the bone scan intensity subsides in order to minimize the chances of recurring bone formation. Calcification also may spontaneously subside with time.
Several theories exist as to the cause of MO. It may be the result of a hematoma, or may be due to a disrupted periosteum that has been pushed into muscle tissue. Pleuri-potential soft tissue stem cells also seem to play a role in the bone formation.
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