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Rectus femoris heterotopic ossification

Case contributed by Yahya Baba
Diagnosis almost certain

Presentation

Right groin pain after soccer trauma.

Patient Data

Age: 25 years
Gender: Male

There is a well-corticated bone fragment adjacent to the right anterior inferior iliac spine.

The bony fragment seems to develop along the tendon of the straight head of the rectus femoris.

Soft tissue edema adjacent to the bone fragment with mild edema in the iliac bone.

The ilium shows no cortical defect.

The following CT is 4 years prior, in a setting of acute right iliac pain.

4 years prior

ct

There is no preexisting bony calcification /exostosis adjacent to the right anterior inferior iliac spine.

Case Discussion

The differential diagnosis for this case is osteochondroma, pelvic digit, myositis ossificans, and

AIIS avulsion injury.

The pelvic digit is ruled out because it's a congenital anomaly, and should have been present in the CT performed 4 years prior. Same for osteochondroma, there is no medullary and cortical continuation, so the diagnosis is eliminated.

Anterior inferior iliac spine injury is also ruled out because the bone fragment is corticated from its inner and outer surfaces and the iliac bone shows no cortical defect.

As for myositis ossificans, the calcifications involve the muscle, rather than the tendon, which leaves us with the diagnosis of heterotopic ossification of the tendon of the straight head of rectus femoris, probably due to a past healing injury.

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