Involucrum

Involucrum is a layer of new bone growth outside existing bone seen in pyogenic osteomyelitis. It results from the stripping off of the periosteum by the accumulation of pus within the bone, and new bone growing from the periosteum.

It can be seen radiographically (e.g. with x-rays), but is extremely rare in developed countries as osteomyelitis is rarely left untreated.