Define Chronic Osteomyelitis. Describe its clinical features, investigations, management and complications.

Definition

Chronic osteomyelitis is long-standing bone infection, usually following inadequately treated acute haematogenous osteomyelitis, an open fracture, or surgery/internal fixation. Its hallmark is the presence of dead, infected bone (a sequestrum) that harbours organisms protected from antibiotics and host defences, so the infection persists and relapses.

Key Pathological Terms

• Sequestrum — a piece of dead, avascular bone separated from living bone
• it acts as a reservoir of infection.
• Involucrum — a sheath of new living bone laid down by the periosteum around the sequestrum.
• Cloaca — an opening in the involucrum through which pus discharges.
• Sinus — a track from the cloaca to the skin surface discharging pus.
• Brodie’s abscess — a localised, walled-off chronic metaphyseal abscess.

Chronic osteomyelitis: dead bone (sequestrum) surrounded by new bone (involucrum), which is perforated by a cloaca that drains through a sinus.

Clinical Features

A history of previous acute infection or open injury, with recurrent pain, swelling and discharging sinuses punctuated by quiescent periods. The skin around the sinus is adherent, puckered and pigmented; there may be seropurulent discharge and occasionally a discharged sequestrum. Systemic upset is usually mild between flares.

Investigations

• Radiographs show a mix of bone destruction and sclerosis, cavities, sequestra (dense fragments) and involucrum.
• CT best demonstrates a sequestrum and its position
• MRI defines the extent of active infection and soft-tissue involvement
• a sinogram may map the track. Inflammatory markers (CRP/ESR) are raised in flares.
• Culture of deep tissue (not superficial swabs) guides antibiotics.

Management

The principle is eradication of infection by removing all dead and infected tissue, combined with prolonged antibiotics. Surgery: sequestrectomy and thorough debridement/saucerisation of the cavity, with dead-space management (muscle flap, antibiotic beads/cement, bone graft). Culture-directed antibiotics are given for a prolonged course (weeks). Adequate soft-tissue cover and skeletal stabilisation are essential; segmental defects may need bone transport (Ilizarov). Recurrence is common, so long follow-up is needed.

Complications

Recurrent flares and sinus formation, pathological fracture, growth disturbance and deformity, joint stiffness, secondary amyloidosis, and Marjolin’s ulcer in a long-standing sinus.

• Follows untreated acute infection, open fracture or surgery; hallmark = infected dead bone.
• Sequestrum (dead bone), involucrum (new bone), cloaca (opening), sinus (skin track).
• X-ray/CT show sequestrum; culture deep tissue, not superficial swabs.
• Cure = surgical debridement + sequestrectomy + dead-space/soft-tissue management + antibiotics.
• Beware Marjolin’s ulcer (SCC) in a chronic sinus.