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

Definition & Epidemiology

Acute haematogenous osteomyelitis is an acute pyogenic infection of bone reaching it through the bloodstream. It is chiefly a disease of children, affecting the metaphysis of a rapidly growing long bone (lower femur, upper tibia). The commonest organism at all ages is Staphylococcus aureus; in neonates group B streptococcus and Gram-negatives, and in sickle-cell disease Salmonella.

WHY the Metaphysis?

The metaphyseal ends of growing long bones have a rich but sluggish circulation — the afferent arterioles make sharp hairpin loops into wide venous sinusoids, where blood flow is slow and phagocytic defence is poor. Blood-borne bacteria therefore settle and multiply here.

Haematogenous osteomyelitis begins in the metaphysis, where sluggish venous sinusoids let blood-borne bacteria lodge; pus then spreads to strip the periosteum.

Pathology (sequence of Events)

Infection begins as inflammation and suppuration in the metaphysis. Rising intra-osseous pressure and pus spread through the Haversian and Volkmann canals to the surface, lifting the periosteum. Stripping of the periosteum cuts off the periosteal blood supply, and with the endosteal supply also thrombosed the cortex dies, forming a sequestrum (dead bone). New bone laid down by the stripped periosteum forms an involucrum around it. Untreated, the disease becomes chronic. In infants and adults (where metaphyseal vessels cross the physis or the physis is closed) infection may reach the joint, causing septic arthritis.

Clinical Features

A child presents with severe constant pain near a large joint, refusal to move or bear weight (pseudoparalysis in infants), and systemic toxicity — high fever, malaise, tachycardia. There is exquisite metaphyseal tenderness, warmth and later swelling; the child holds the limb still.

Investigations

Blood tests: raised WCC, CRP and ESR; blood cultures (positive in ~50%). Imaging: radiographs are normal early (soft-tissue swelling first, bony changes after 2 weeks); MRI is the most sensitive early investigation (marrow oedema); ultrasound detects a subperiosteal collection; bone scan is an alternative. Aspiration of the metaphysis / subperiosteal pus gives the organism and sensitivities.

Management

Prompt empirical intravenous antibiotics (after cultures) directed against Staph. Aureus — e.g. A penicillinase-resistant penicillin or first-generation cephalosporin, adjusted to sensitivities and local resistance (add MRSA cover where prevalent). Supportive care includes analgesia, rest/splintage of the limb and fluids. Surgical drainage is indicated if there is an abscess, if the child fails to improve within 24–48 hours of antibiotics, or if pus is aspirated — the bone is drilled/decompressed and pus evacuated. Antibiotics are continued (IV then oral) for several weeks guided by clinical and CRP response.

Complications

Chronic osteomyelitis (the most important), septic arthritis (especially in infants and where the metaphysis is intracapsular, e.g. The hip), pathological fracture, growth disturbance from physeal damage (limb shortening or deformity), metastatic infection/septicaemia, and (historically) amyloidosis.

• Children; metaphysis of long bones; commonest organism Staph. Aureus (Salmonella in sickle-cell).
• Metaphyseal sluggish venous sinusoids let bacteria settle; pus strips periosteum → sequestrum.
• Severe pain, fever, refusal to move; X-ray normal for 10–14 days — use MRI.
• Treat early with IV antistaphylococcal antibiotics; drain if abscess or no response in 24–48 h.
• Complications: chronic osteomyelitis, septic arthritis, growth arrest, pathological fracture.