Myositis ossificans progressiva

Nature

Myositis ossificans comprises two syndromes characterized by heterotopic ossification (calcification) of muscle. The World Health Organization, 2020, has grouped myositis ossificans together with fibro-osseous pseudotumor of digits as a single specific entity in the category of fibroblastic and myofibroblastic tumors.

Source: Wikipedia

Broader 
Type 
(G) Very specific problems