Fig. 1. Light micrograph showing chronic osteomyelitis. Note the presence of fibrosis of the marrow fields, with the absence of pre-existent haematopoiesis. Aggregates of lymphocytes and plasma cells are present. The surrounding bone trabeculae show marked remodelling

Elevation of the periosteal membrane triggers periosteal ossification, which arises from the cambium (inner) layer of the per-iosteum. The periosteal new bone formation is referred to as involucrum,which partially or fully surrounds the infected bone.