17. Osteomyelitis

1. Definition

• Osteomyelitis → infection and inflammation of bone, including marrow, cortex and periosteum
• Acute → < 2 weeks
• Subacute → 2–6 weeks
• Chronic → > 6 weeks, with dead bone

2. Aetiology

Organisms

• Staphylococcus aureus → most common at all ages
• Streptococci, Haemophilus influenzae → children
• Group B streptococcus, Escherichia coli → neonates
• Salmonella → sickle cell disease
• Pseudomonas → puncture wounds of the foot, drug users
• Mycobacterium tuberculosis → spine (Pott's disease)

Routes of entry

1. Haematogenous → from a distant focus (skin, tonsils, teeth); mostly children
2. Contiguous → from adjacent soft tissue infection (diabetic foot, pressure ulcer)
3. Exogenous (post-traumatic) → open fractures, gunshot wounds, surgery, implants

3. Pathogenesis

Acute haematogenous osteomyelitis

• Site → metaphysis of long bones; distal femur, proximal tibia
• Slow flow in metaphyseal hairpin capillary loops → bacteria settle
• Few phagocytes in the metaphysis
• Evolution of the purulent process:
  1. Inflammation, oedema in the rigid bone → raised pressure
  2. Pus spreads through Haversian and Volkmann canals to the cortex
  3. Subperiosteal abscess → periosteum lifted
  4. Cortex loses blood supply from both sides → necrosis
  5. Sequestrum → dead bone separated from living bone
  6. Involucrum → new subperiosteal bone around the sequestrum
  7. Cloacae → openings in the involucrum through which pus drains
  8. Sinus → track to the skin
• Infants → transphyseal vessels allow spread into the joint (septic arthritis)
• Joints with intra-articular metaphysis → hip, shoulder, elbow, ankle → septic arthritis

Chronic osteomyelitis

• Sequestrum, dead space, biofilm → protect bacteria from antibiotics and immune cells
• Sclerotic, poorly perfused bone
• Brodie's abscess → localised subacute abscess in the metaphysis with sclerotic wall

4. Classification

• By route → haematogenous, contiguous, post-traumatic
• By course → acute, subacute, chronic
• Primary chronic forms:
  • Brodie's abscess
  • Garré's sclerosing osteomyelitis → dense sclerosis, no pus
  • Ollier's albuminous osteomyelitis
• Cierny-Mader (adults):
  1. Medullary
  2. Superficial
  3. Localised
  4. Diffuse
  5. Host type → A (healthy), B (compromised), C (treatment worse than disease)

5. Clinical picture

Acute haematogenous osteomyelitis

• Children, often boys
• Sudden high fever, rigors, toxaemia
• Severe bone pain, refusal to move or bear weight (pseudoparalysis)
• Local tenderness over the metaphysis
• Later → swelling, redness, heat (subperiosteal or soft tissue abscess)
• Sympathetic joint effusion
• Toxic form → septic shock

Chronic osteomyelitis

• History of acute infection, fracture or surgery
• Discharging sinus, periods of remission and flare
• Thickened, irregular bone, scars
• Pain, low-grade fever during flares
• Long-term → Marjolin's ulcer (squamous cell carcinoma in the sinus), amyloidosis

6. Diagnosis

Laboratory

• Leucocytosis, raised erythrocyte sedimentation rate (ESR) and CRP
• Blood cultures → positive in 50% of haematogenous cases
• Bone aspirate or biopsy culture → definitive
• Sinus swabs → unreliable

Imaging

• X-ray → normal for the first 10–14 days; then periosteal reaction, lytic areas, sequestrum, involucrum
• MRI → investigation of choice; marrow oedema within days
• Ultrasound → subperiosteal abscess, joint effusion
• Bone scan → early, multifocal disease
• CT → sequestra in chronic disease
• Fistulography → sinus track

7. Differential diagnosis

• Septic arthritis
• Cellulitis
• Ewing's sarcoma → fever, pain, onion-skin periosteal reaction
• Fracture, trauma
• Rheumatic fever, juvenile arthritis
• Bone infarction in sickle cell disease

8. Treatment

Acute osteomyelitis: conservative

• Blood cultures and aspirate before antibiotics
• Intravenous antibiotics → anti-staphylococcal (flucloxacillin), adjusted by culture
• Duration → 4–6 weeks total; switch to oral after clinical and CRP response
• Immobilisation → splint, rest
• Analgesia, fluids

Acute osteomyelitis: surgical

• Indications:
  • Abscess (subperiosteal, soft tissue)
  • No response to antibiotics in 48–72 h
• Drain the subperiosteal abscess
• Drill holes or a cortical window to decompress the medulla
• Drain coexistent septic arthritis

Chronic osteomyelitis

• Combined surgical and antibiotic treatment
• Sequestrectomy and radical debridement (saucerisation) of dead bone and sinus
• Dead space management → antibiotic-loaded beads or cement spacer, muscle flaps, bone graft
• Stabilise bone → external fixator (Ilizarov)
• Soft tissue cover → flaps
• Prolonged antibiotics, 6 weeks or more
• Remove infected implants
• Amputation → last resort

9. Complications

• Septic arthritis
• Sepsis, metastatic abscesses
• Pathological fracture
• Growth disturbance → limb shortening, deformity
• Chronic osteomyelitis
• Marjolin's ulcer
• Amyloidosis