An infection of the bone is termed osteomyelitis. A number of systemic infectious disease may spread to the bone such as enteric fever, tuberculosis etc. Two of the condition which produce pathologic leisons-
1. Pyogenic Osteomyelitis– caused by bacterial infection rarely by fungi. Most commonly in the long bone of infant & young children(5-15 years of age).
• Depending upon the duration it may be acute, subacute, chronic. Basic pathologic changes in any stage are suppuration, ischaemic necrosis, healing by fibrosis.
• The infection begins in the metaphyseal end of marrow cavity which is largely occupied by pus, microscopy reveals congestion, oedema & exudates of neutrophils.
• Tension in the marrow cavity is increased due to pus & result in spread of infection along the marrow cavity causing periostitis.
• The infection may reach the subperiosteal space forming subperiosteal abcesses.
• Combination of suppuration & impaired blood supply to the cortical bone results in erosion called sequestrum.
• With the passage of time, there is formation of new bone beneath the periosteum present over the infected bone is known as involucrum. It has irregular surface.
• In vertebral pyogenic osteomyelitis infection begins from the disc & spread to involve the vertebral bodies.
The tubercle bacilli M. tuberculosis reach the bone marrow & synovium most commonly by haematogenous dissemination from infection elsewhere, usually from the lungs & infrequently by direct extension. The disease affect adolescents & young adults more frequently.
The bone lesions in tuberculosis have the same general histological appearance as in tuberculosis elsewhere & consist of central caseation necrosis surrounded by tuberculous granulation tissues & fragments of necrotic bone. Tuberculosis of the spine ‘pott’s disease’ commences in the vertebral body & may be associated with compression fractures & destruction of intervertebral disc.