Chronic osteomyelitis occurs when there is ongoing or relapsing infection resulting from encasement of infected dead bone during the healing of an acute osteomyelitis.
Previously, chronic osteomyelitis resulted from poorly treated acute osteomyelitis. It now occurs more frequently in post-traumatic osteomyelitis. Multiple organisms are often isolated from the pus.
Normally in an acute osteomyelitis, new bone is formed beneath the raised periosteum, which is termed involucrum. If the new bone formed encloses infected tissue and sequestrated bone fragments, pus discharges through perforations (cloacae) and sinuses. Bacteria in the bone may remain dormant for years giving rise to recurrent flares of acute infection.
The clinical course is typically ongoing chronic pain and low-grade fever following an episode of acute osteomyelitis. There may be pus discharging through a sinus. However, if the pus is retained within the bone or the sinus becomes obstructed, rising pressure leads to an acute flare of pain, redness, local tenderness and pyrexia (similar to an acute osteomyelitis).
There is often no leucocytosis; however, the ESR is normally raised. X-ray shows areas of decreased density (rarefaction) surrounded by sclerotic bone and sometimes sequestra. The periostium may be raised with underlying new bone formation. Bone scans may be used to reveal the focus of infection.
Discharging sinuses require dressing, and if an abscess persists despite antibiotic therapy it should be incised and drained. Prolonged combined parenteral antibiotics are required. Surgical intervention proves difficult but may involve debridement of necrotic tissue, dead space obliteration, provision of soft tissue coverage of the bone and stabilisation of bone.