Osteomyelitis

Risk factors

• Diabetes mellitus (foot osteomyelitis under ulcer)
• Peripheral vascular disease
• IV drug use (vertebral, sternoclavicular, sacroiliac)
• Recent orthopedic surgery, open fracture, prosthetic hardware
• Pressure ulcers, decubitus wounds
• Sickle cell disease (Salmonella in addition to S. aureus)
• Immunosuppression
• Endocarditis or persistent bacteremia
• Pediatric: recent infection, blunt trauma to bone

Pathophysiology

Bacteria reach bone via hematogenous seeding, contiguous spread, or direct inoculation. Bacterial proliferation triggers neutrophilic inflammation; rising intramedullary pressure compromises blood supply, producing devitalized bone (sequestrum) that harbors persistent infection. New reactive bone (involucrum) forms around the sequestrum. Biofilms on hardware and necrotic bone make chronic osteomyelitis difficult to eradicate without surgical debridement.

Clinical presentation

Differential diagnosis

• Charcot neuroarthropathy — Diabetic neuropathy with destructive midfoot arthropathy; warm swollen foot without ulcer; MRI can mimic osteomyelitis
• Soft tissue infection / cellulitis — No bone involvement; MRI normal marrow
• Bone tumor (Ewing sarcoma, osteosarcoma, metastasis) — Periosteal reaction, lytic/sclerotic lesions; biopsy if equivocal
• Stress fracture — Repetitive activity, focal pain; MRI shows fracture line
• Avascular necrosis — Risk factors (steroids, sickle, alcohol); MRI 'double-line' sign
• Septic arthritis with adjacent bone involvement — Joint effusion plus bony edema; treat both
• Gout / pseudogout — Crystals; can be confused with foot osteomyelitis on imaging

Diagnostic workup

Diagnostic algorithm

flowchart TD
  A[Suspected osteomyelitis] --> B[X-ray + ESR/CRP<br/>+ blood cultures x 2]
  B --> C[MRI with contrast<br/>most sensitive]
  C --> D{Stable patient?}
  D -->|Yes| E[Bone biopsy<br/>BEFORE antibiotics]
  D -->|No, sepsis| F[Empiric vanco + GN coverage<br/>cultures ASAP]
  E --> G[Targeted antibiotics<br/>4-6 weeks]
  F --> G
  G --> H{Necrotic bone,<br/>hardware, or abscess?}
  H -->|Yes| I[Surgical debridement /<br/>hardware management]
  H -->|No| J[Antibiotics alone<br/>track CRP response]

Complications

• Chronic osteomyelitis with sinus tracts (squamous cell carcinoma can arise — Marjolin ulcer)
• Pathologic fracture
• Growth plate damage with limb-length discrepancy (pediatric)
• Spinal cord compression from epidural abscess (vertebral osteomyelitis emergency)
• Sepsis, endocarditis, metastatic infection
• Amyloidosis (chronic suppurative osteomyelitis)

PANCE pearls

• Probe-to-bone test in a diabetic foot ulcer combined with elevated CRP/ESR is sufficient to start treatment.
• ESR >70 in diabetic foot ulcer is a sensitive marker for osteomyelitis.
• Hold antibiotics for bone biopsy whenever the patient is stable — empiric therapy without culture often produces inadequate treatment of chronic disease.
• Vertebral osteomyelitis with new neurologic deficit = epidural abscess until proven otherwise — emergent MRI and neurosurgical consult.
• Sickle cell + osteomyelitis = think Salmonella in addition to staph.

References

• IDSA 2015 — IDSA Clinical Practice Guideline for the Diagnosis and Treatment of Native Vertebral Osteomyelitis (Berbari et al., Clin Infect Dis 2015)
• IDSA 2012 — IDSA Clinical Practice Guideline for the Diagnosis and Treatment of Diabetic Foot Infections (Lipsky et al., Clin Infect Dis 2012)
• OVIVA Trial — Oral versus Intravenous Antibiotics for Bone and Joint Infection (Li et al., NEJM 2019)