Osteomyelitis

Orthopedic Surgery

OverviewWhoPresentationMechanismWorkupManagementPivots

Illness script · Orthopedic Surgery

Osteomyelitis

Infection of bone, most commonly bacterial, causing bone destruction and marrow inflammation; classified as hematogenous, contiguous, or vascular insufficiency.

This illness script for Osteomyelitis covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.

Updated Jul 19, 2026All scripts

01

Predisposing factors

  • Children: hematogenous spread to metaphysis (rich slow-flow sinusoids)
  • Adults: contiguous spread from wound, surgery, or diabetic foot ulcer
  • Sickle cell disease → Salmonella spp. is classic pathogen
  • S. aureus is #1 overall pathogen across all ages
  • IVDU, immunosuppression, prosthetic joints increase risk
  • Vertebral osteomyelitis: hematogenous, peaks in adults >50

02

Presentation

  • Acute: fever, localized bone pain, erythema, swelling, point tenderness
  • Children: refusal to bear weight or move limb; pseudoparalysis
  • Vertebral: insidious back pain + fever; percussion tenderness over spine
  • Subacute (Brodie abscess): afebrile child with metaphyseal lucency, minimal systemic signs
  • Chronic: sinus tract draining purulent material, low-grade fever
  • Diabetic foot: ulcer overlying bone that can be probed to bone ('probe-to-bone' test)

03

Pathophysiology

  • Bacteria seed bone via bloodstream, direct inoculation, or contiguous spread
  • Metaphyseal sinusoids in children have sluggish flow and lack phagocytes — ideal nidus
  • Infection → inflammatory exudate → increased intraosseous pressure → vascular compromise → cortical necrosis (sequestrum)
  • Periosteum lifts → new bone laid down (involucrum); chronic infection with dead bone persists

04

Diagnostics

  • MRI is gold standard — earliest and most sensitive imaging (detects marrow edema)
  • Plain X-ray: lytic lesion + periosteal elevation (lag 10–21 days from onset)
  • ESR and CRP elevated; WBC may be normal
  • Blood cultures before antibiotics — positive ~50% hematogenous cases
  • Bone biopsy + culture is definitive — essential before targeted therapy
  • Probe-to-bone test in diabetic foot: high PPV for osteomyelitis

05

Management

  • Empiric IV antibiotics: nafcillin/oxacillin; MRSA coverage (vancomycin) if risk factors present
  • Sickle cell: cover Salmonella + S. aureus (ciprofloxacin or ceftriaxone + vancomycin)
  • Duration: 4–6 weeks total (IV then step-down to oral if good bioavailability)
  • Surgical debridement required for: abscess, sequestrum, failed medical therapy, or hardware infection
  • Chronic osteomyelitis: surgical removal of sequestrum + dead tissue is definitive

06

Clinical pivots

How to separate this script from the look-alikes that show up on exams and on the wards.

  • Septic Arthritis

    Pain localizes to joint with effusion and restricted ROM in all planes; osteomyelitis localizes to bone with point tenderness away from joint line

  • Ewing Sarcoma

    Onion-skin periosteal reaction on X-ray in adolescent; no fever response to antibiotics; biopsy shows small round blue cells

  • Cellulitis

    Skin/soft tissue erythema without bone tenderness; MRI shows no marrow signal change; normal plain films

  • Brodie Abscess vs. Bone Tumor

    Brodie abscess shows sclerotic rim around metaphyseal lucency; responds to antibiotics; biopsy differentiates definitively

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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.