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Osteomyelitis

BASICS

Description

  • Acute or chronic bone infection with associated inflammation
  • Etiology: Hematogenous seeding, contiguous spread, or direct inoculation (trauma/surgery)
  • Classification:
  • Lew and Waldvogel: acute vs. chronic; hematogenous vs. contiguous
  • Cierny-Mader: bone location, host status, risk factors
  • Special situations:
  • Vertebral osteomyelitis: usually hematogenous, lumbar most common; presents with back pain
  • Prosthetic joint infections: x-ray, bone scan; MRI/CT less helpful due to artifact
  • Posttraumatic: tibia most common site

EPIDEMIOLOGY

  • More common in older adults; male > female
  • Children: hematogenous, long bones
  • Adults: vertebral (hematogenous), prosthetic, diabetic foot, trauma
  • TB: most common vertebral cause worldwide; thoracic spine, paraspinal abscess
  • Incidence: vertebral—2.4/100,000 (increases with age)
  • Prevalence: up to 66% of diabetics with foot ulcers

ETIOLOGY & PATHOPHYSIOLOGY

  • Acute: Suppurative infection → edema, vascular compromise, necrosis (sequestrum)
  • Chronic: Necrotic bone, sequestrum, or recurrent infection
  • Hematogenous: Monomicrobial (S. aureus most common; also coagulase-negative staph, gram-negative rods, Pseudomonas—IV drug use, Salmonella—sickle cell, TB/fungal—immunocompromised/endemic)
  • Contiguous: Polymicrobial (staph, strep, gram-negatives, anaerobes); common in diabetes, vascular insufficiency, trauma
  • Special situations: P. aeruginosa (puncture wound through shoe); prosthetic—coagulase-negative staph/S. aureus

RISK FACTORS

  • Diabetes mellitus (esp. foot ulcer)
  • Recent trauma or surgery
  • Prosthetic implants/foreign body
  • Neuropathy, vascular insufficiency
  • Immunosuppression (dialysis, etc.)
  • Sickle cell disease
  • Injection drug use
  • Prior osteomyelitis, bacteremia

GENERAL PREVENTION

  • Annual foot exam for diabetics; manage peripheral artery disease, optimize glycemic control
  • Antibiotic prophylaxis (perioperative for trauma/orthopedic surgery)
  • Closed fractures: cefazolin, cefuroxime, or clindamycin/vancomycin (if allergy/MRSA)
  • Open fractures: 1st-gen cephalosporin within 3h, ceftriaxone for type III, add metronidazole for gross contamination

DIAGNOSIS

History

  • Acute: fever, chills, pain, swelling, erythema
  • Chronic: draining sinus, history of prior infection, less systemic symptoms
  • Vertebral: back pain, fever, restricted ROM, neuro deficits (in ⅓)
  • Diabetics may have masked symptoms due to neuropathy/vascular disease

Physical Exam

  • Fever, localized tenderness, swelling, redness, reduced ROM
  • Motor/sensory loss (vertebral)
  • Exposed bone in DFI

Differential Diagnosis

  • Systemic infection, aseptic bone infarction, overlying skin/soft tissue infection (gout), Brodie abscess, Charcot joint, tumor

Diagnostic Tests

  • Labs:
  • WBC—may be normal
  • CRP/ESR—usually elevated (ESR >70 increases likelihood >10-fold)
  • Anemia (chronic)
  • Blood cultures (esp. vertebral/hematogenous)
  • Procalcitonin—may be elevated
  • Imaging:
  • X-ray (late findings: demineralization, periosteal reaction, destruction)
  • Bone scan (esp. prosthesis)
  • MRI—gold standard for spinal, DFI, and septic arthritis (sensitivity ~90%, specificity ~80%)
  • CT—bone fragments/sequestra
  • Procedures:
  • Probe-to-bone test: high sensitivity/specificity in DFI
  • Bone biopsy: definitive (culture/histology); avoid wound swabs in DFI
  • Pathology: necrosis, pyogenic bacteria

TREATMENT

General Measures

  • Nutrition, glycemic control, foot care, smoking/IV drug use cessation

Medication

  • Delay empiric antibiotics if stable until after biopsy/culture
  • Acute: 4–6 weeks antibiotics (longer for chronic/MRSA)
  • Vertebral/hematogenous: 6 weeks
  • Post-amputation/removal: 2 weeks may suffice if complete removal
  • Empiric (tailor to cultures):
  • MRSA/gram-negative coverage: IV vancomycin + 3rd/4th gen cephalosporin
  • DFI/contiguous: add metronidazole for anaerobes

First Line

  • MSSA: Nafcillin/oxacillin 2g IV q4h or cefazolin 1–2g IV q8h
  • MRSA: Vancomycin 15–20 mg/kg IV q8–12h (target trough 15–20)
  • Strep: Ceftriaxone 2g IV q24h or cefazolin 2g IV q8h
  • Pseudomonas: Cefepime 2g IV q8h or ciprofloxacin 750 mg PO q12h

Second Line

  • MSSA: Ceftriaxone 2g IV q24h
  • MRSA: Linezolid 600 mg PO/IV q12h, daptomycin 6 mg/kg IV q24h
  • Strep: Penicillin G 4 million U q4–6h
  • Pseudomonas: Piperacillin-tazobactam 3.375g IV q6h

ALERT: Vancomycin + piperacillin-tazobactam ↑ risk of acute renal failure (NNH = 11).

Additional Therapies

  • Hyperbaric oxygen therapy (chronic/refractory)
  • Monitor: Weekly labs (antimicrobial levels, CRP, ESR)

Surgery/Procedures

  • Surgical drainage, debridement to healthy bone, minimize dead space, restore blood supply, soft tissue coverage
  • Hardware: Remove if possible; if retained, prolonged antibiotics
  • Antibiotic cement beads: for dead space in vascular insufficiency

Admission/Inpatient

  • Off-load pressure, monitor clinical/lab resolution before discharge

ONGOING CARE

  • Follow-up: Monitor CRP/ESR, radiographs, antimicrobial levels as needed

DIET

  • Glycemic control in diabetics, nutrition for malnourished

PATIENT EDUCATION

  • Foot care in diabetics, IV drug use cessation

PROGNOSIS

  • Acute/superficial/medullary: Cure in 90–100% with appropriate management
  • Chronic/diabetics: Up to 36% recurrence; ↑ mortality after amputation

COMPLICATIONS

  • Abscess, bacteremia, fracture, nonunion, prosthetic loosening, sinus tract (can → Marjolin ulcer), post-op infection

ICD-10 Codes

  • M86.03: Acute hematogenous osteomyelitis, radius/ulna
  • M86.032: ...left radius/ulna
  • M86.01: ...shoulder

Clinical Pearls

  • Hematogenous osteomyelitis: usually monomicrobial; contiguous/direct is usually polymicrobial
  • Pain: typically gradual onset in acute cases
  • Chronic osteomyelitis: requires debridement + ≥6 weeks antibiotics
  • Probe-to-bone test: diagnostic in DFI; not diagnostic in stage IV sacral ulcers
  • MRI: not for follow-up if clinical improvement
  • No antibiotics for diabetic foot wounds without signs of infection