Myositis Ossificans : Pathogenesis

Comments:
Pathogenesis: The pathogenesis of myositis ossificans (MO) is incompletely understood. Most cases are related to trauma, which may be a recent episode of soft tissue trauma, repetitive minor trauma, or even unusual muscle exertion.

The initial reparative fibroblastic/myofibroblastic response is followed by ossification. This is due to dysregulation of local stem cells at the site of injury which causes inappropriate differentiation of fibroblasts into osteoblasts.

The mechanisms at play in nontraumatic cases are also unknown. MO has been seen in association with burns, paraplegia, and certain infections. Some cases with classic features of myositis ossificans harbor rearrangements of USP6 - a finding also seen in nodular fasciitis and soft tissue aneurysmal bone cyst.

About this image: Low-magnification view of myositis ossificans. The peripheral portion (top) shows mature lamellar bone. The center shows spindle cell stroma as well as foci of immature woven bone.