Osteomyelitis

OSTEOMYELITIS

Pyogenic osteomyelitis is bone inflammation due to bacterial infection. The most common route of infection is hematogenous spread (leading to seeding of bone after bacteremia); this type of spread often affects the metaphysis. Other routes of spread include direct inoculation (e.g., trauma) and spread from an adjacent site of infection (e.g., prosthetic joint).

The most common infecting organism is S. aureus ; other important pathogens include E. coli, streptococci, gonococci, H. influenzae, Salmonella (common in sickle cell disease), and Pseudomonas (common in IV drug abusers and diabetics).

Clinically, osteomyelitis is characterized by fever and leukocytosis; and localized pain, erythema, and swelling. X-ray studies may be normal for up to 2 weeks, and then initially show periosteal elevation followed by a possible lytic focus with sur-rounding sclerosis. MRI and nuclear medicine studies are more sensitive and specific.

Microscopic examination shows suppurative inflammation. Vascular insufficiency can lead to ischemic necrosis of bone; a sequestrum is an area of necrotic bone, while an involucrum is the new bone formation that surrounds the sequestrum. The diagnosis is established with blood cultures or with bone biopsy and culture.

Patients are treated with antibiotics and some may require surgical drainage. Com-plications include fracture, intraosseous (Brodie) abscess, secondary amyloidosis, sinus tract formation, squamous cell carcinoma of the skin at the site of a persistent draining sinus tract, and, rarely, osteogenic sarcoma.

Tuberculous osteomyelitis is seen in 1% of cases of TB. It presents with pain or tenderness, fever, night sweats, and weight loss. Biopsy shows caseating granulo-mas with extensive destruction of the bones. Common sites of involvement include thoracic and lumbar vertebrae (“Pott disease”). Complications include vertebral compression fracture, psoas abscesses, and secondary amyloidosis.