Osteomyelitis and Septic Arthritis
Kelly Keogh
Andrew Mason
Osteomyelitis
Osteomyelitis results from hematogenous dissemination of an organism into the metaphysis of a long bone
Occasionally direct inoculation into bone from trauma
Bacterial proliferation evokes an inflammatory exudate leading to destruction of bone, necrosis of cortex, and elevation, then rupture of periosteum
Causes pain in affected limb
Lower limbs most often affected
Pathophysiology
Often associated with septic arthritis in children < 1 year and in joints with intracapsular metaphyses (proximal radius, humerus, and femur)
Children < 1 year:
Called septic osteomyelitis of infancy
Epiphysis contains capillaries that facilitate spread of osteomyelitis to contiguous joint space
Children > 1 year:
Hematogenously spread infection starts in metaphyseal sinusoidal veins
Infection contained within metaphysis and diaphysis by avascular epiphysis, which acts as a barrier
Infection spreads laterally to break through cortex and lifts the loose periosteum, creating a subperiosteal abscess
Clinical Presentation
Very similar to septic arthritis; clinical differentiation may be difficult
Sudden onset of bone pain, often with high fever
Bone pain is manifested according to age:
Infants: pseudoparalysis (voluntary immobilization of affected limb), crying with movement of limb
Child: pseudoparalysis, refusal to weight bear, limp
Examination: look unwell, may hold affected limb immobile, point tenderness at site of infection: difficult to assess in struggling toddler
Local erythema and edema if purulent material has ruptured through the cortex
Often an effusion is detectable
Investigations
CBC (WBC normal in > 50%)
Blood culture (causative organism 50-70%)
ESR (acute phase reactant; insensitive, nonspecific), CRP
Elevated in 90% and 98% of cases, respectively
Useful for monitoring effectiveness of therapy
ESR peaks 3-5 days after initiation of therapy and normalizes in ˜ 3 weeks
CRP peaks at day 2 and normalizes within 1 week in uncomplicated cases
X-ray: to exclude fracture
Initially, films will be normal
At 10-12 days: osseous destruction visible, reflecting 40% bone loss
Ultrasound: to rule out joint effusion if necessary to differentiate osteomyelitis from septic arthritis and to exclude concomitant septic arthritis
Bone radionuclide scan:
Technetium scan-tracer = Tc99m bound to phosphorus
Accumulates in areas of increased osteoblast activity with increased blood flow and new bone formation
Test of choice; sensitivity and specificity 95%
Usually positive within 2-3 days of onset of infection
Gallium citrate scan:
Radioactive gallium citrate acts as an analog of calcium and iron and attaches to transferrin to accumulate at sites of inflammation
Most sensitive and specific for vertebral osteomyelitis
Bone biopsy: definitive diagnosis based on positive bone or blood cultures or histopathologic changes consistent with osteomyelitis
If cultures are negative, needle biopsy may be necessary to provide tissue for histopathologic analysis
CT scan/MRI useful in select cases (sequestra, abscess)
Treatment
Medical Management
Antibiotics: empiric parenteral antibiotics based on most likely organism (see Table 42.1)
Directed antibiotics according to culture and sensitivities
If child not vaccinated for H. influenzae b, add coverage for ampicillin-resistant strainsRelated posts:
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