Osteomyelitis

Classified by anatomical location (long bone or vertebral) and time course (acute or chronic). Long-bone osteomyelitis most commonly occurs in children; vertebral osteomyelitis (discitis/spondylodiscitis) primarily occurs in older adults, and often develops secondary spinal/paraspinal collections.

• Acute osteomyelitis: clinically a newly recognised bone infection, pathologically characterised by the absence of bone necrosis/sequestra. Symptoms present <14 days correlate with acute disease histopathologically.
• Chronic osteomyelitis: a relapsed or longstanding infection, possibly involving a sinus or compromised soft-tissue envelope; pathologically characterised by low-grade inflammation and sequestra/involucra (new bone formation adjacent to sequestra).

Osteomyelitis in adults

Staphylococcus aureus is the most common cause. Others: coagulase-negative staphylococci, beta-haemolytic streptococci, enterococci, Cutibacterium acnes (formerly Propionibacterium acnes); ~20% are Gram-negative (Enterobacteriaceae — E. coli, Klebsiella pneumoniae — and Pseudomonas). Rare: M. tuberculosis, Brucella, fungi (Candida).

Risk factors: injecting drug use; postoperative infection; current/ recent confirmed UTI, hepatobiliary or GI infection; healthcare-associated infection; immunocompromise; poor vascular supply; peripheral neuropathy; systemic conditions (diabetes, sickle cell disease).

Osteomyelitis in children

Almost always S. aureus. Haemophilus influenzae type b (Hib) can cause acute osteomyelitis in unvaccinated children <5 years. Kingella kingae is an increasingly recognised cause, primarily in infants and children <4 years.

Investigations

• Blood culture
• Bone biopsy culture (radiologically guided or open biopsy)
• X-ray commonly negative in the first 2 weeks, then shows erosion
• MRI is the best imaging modality for diagnosing early osteomyelitis and localising infection (CT/bone scan as alternatives)

Management

Refer to a specialist.

Adult long-bone OM / paediatric OM:

• Low MRSA risk: IV flucloxacillin/cefazolin/vancomycin
• High MRSA risk: IV vancomycin

Adult vertebral OM:

• Normal neurology: IV flucloxacillin/cefazolin/vancomycin
• Epidural abscess/neurological compromise: IV flucloxacillin + vancomycin + ceftriaxone/cefotaxime, OR IV vancomycin + ceftriaxone/cefotaxime, OR IV vancomycin + ciprofloxacin

Suggested antibiotic duration

	Patient age	IV duration	Total (IV + oral) duration
Acute osteomyelitis	Neonate	4 weeks	4 weeks (all IV)
	Child	3 days, or until cultures negative + afebrile + clinically improved + CRP/ESR falling	Minimum 3 weeks
	Adult	4 weeks	Minimum 6 weeks
Chronic osteomyelitis	Child	May not be necessary	Minimum 6 weeks
	Adult	2 weeks	Many months