Ans. B. A piece of dead bone surrounded by infected tissue (Ref. Maheshwari ortho 3rd/pg.l60)Maheshwari orthopaedics 3rd/pg. 160...."Sequestrum is a piece of dead bone, surrounded by infected granulation tissue trying to 'eat' the Sequestrum away"CHRONIC OSTEOMYELITISPresents in 3 forms:A. Chronic osteomyelitis secondary to acute osteomyelitisB. Garre's osteomyelitisC. Brodie's abscessA. Chronic osteomyelitis secondary to acute osteomyelitis# Key radiological feature is Sequestrum ( a feature of chronic osteomyelitis) which appears denser than surrounding normal bone because decalcification which occurs in normal bones does not occur here. The granulation tissue surrounding the sequestrum gives rise to a radiolucent zone around it. A sequestrum may be visible in soft-tissues.# Involucrum is the dense sclerotic bone overlying a sequestrum. There may be some holes in involucrum for the pus to drain out and these holes are called cloacae. The bony cavities are lined by infected granulation tissue. Involucrum and cloacae are often visible.- Chronic osteomyelitis is commonest complication of acute osteomyelitis.- A chronic discharging sinus is the commonest presenting symptom.- The lower end of femur is commonest site of chronic osteomyelitis.B. Garre's osteomyelitis# Sclerosing non-suppurative chronic osteomyelitis.0# Begins with acute local pain, swelling and pyrexia.# Fever subsides but fusiform osseous enlragment persists.# Tenderness on deep palpation.# No discharging sinus.# Shaft of femur or tibia are the commonest sites affected.# Importance lies in differentiating it from bone tumors which present with similar features e.g. Ewing's sarcoma and osteosarcoma.# Rx: Acute symptoms subside with rest and broad spectrum antibiotics and Some times making a gutter or holes in the affected bone brings relief in pain.C. Brodie's abscess# Special osteomyelitis in which body defense mechanism have been able to contain the infection so as to create a chronic bone abscess containing pus/jelly-like granulation tissue surrounded by a zone of sclerosis.# Age: 1 - 20 yrs.# A deep boring pain is predominant symptom, which may become worse at night & relived by rest.# Occasionally, there may be transient effusion in the adjacent joint during exacerbation.# Examination may reveal tenedemess and thickening of bone.# Common sites: Upper end of the tibia and Lower end of femur# Usually located at metaphysis# X-ray rCircular or oval translucent area surrounded by a zone of sclerosis.# Rx: Surgical evacuation and curettage under antibiotic cover and If the cavity is large it is packed with cancellous bone chips.