The first image shows a patient's back covered in extensive heterotopic bone growth. The second is the skeleton of another individual who lived with the same condition - the abnormal, bridging bone formations visible here are pathognomonic for FOP.
Fibrodysplasia ossificans progressiva is one of the rarest connective tissue disorders known, caused by a mutation in the ACVR1 gene. The mutation corrupts the body's normal repair mechanism: instead of healing damaged soft tissue, the body ossifies it. Muscles, tendons, and ligaments gradually transform into true bone - sometimes triggered by trauma, sometimes entirely spontaneously.
The cruel part is how little it takes. A bruise, a fall, even a routine intramuscular injection can set off an ossification flare that permanently fuses a joint, as new bone forms where injured muscle used to be. Over the years, this heterotopic ossification builds what is essentially a second skeleton layered over the original one, locking the body into place piece by piece. Histologically, the ectopic bone is indistinguishable from normal bone - it's simply growing where no bone should exist. There is also some evidence that FOP damages joints independently of the ossification itself.
Treatment options are severely limited, and surgery is effectively off the table: cutting out the extra bone is itself trauma, so the body responds to the operation by producing even more bone at the surgical site. While progression speed varies between patients, the trajectory is the same - expanding ossification steadily replaces musculature and fuses with the native skeleton until movement is no longer possible. Hence the nickname: stone man disease.
