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Management of Osteomyelitis

Classification

The key therapeutic decision is whether bone necrosis (sequestrum) is present: acute osteomyelitis without bone necrosis can generally be treated with antibiotics alone; chronic osteomyelitis requires combined antibiotic therapy + debridement surgery. — Harrison's, 22e

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Cierny-Mader Staging (Chronic Osteomyelitis)

• Type I — Medullary
• Type II — Superficial
• Type III — Localized
• Type IV — Diffuse

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General Principles of Treatment

1. Adequate IV access and fluid resuscitation if septic
2. Blood cultures × 2 before starting antibiotics (in clinically stable patients)
3. Tissue/bone culture before committing to a prolonged antibiotic course
4. Multidisciplinary involvement: Infectious disease + Orthopaedic/Surgical team

• Must penetrate bone/synovial membrane — most antibiotics do, but penicillin and metronidazole penetrate bone poorly
• Must be bactericidal against the offending organism
• Chemical stability at low pH of infected tissue is important — cephalosporins are stable; aminoglycosides lose bactericidal activity in acidic environments
• Target serum level ≥ 8× MIC

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Acute Osteomyelitis

Medical Management (Antibiotics)

• Asymptomatic osteomyelitis incidentally discovered
• Hematogenous infection by sensitive organisms or fungi
• Vertebral osteomyelitis caused by sensitive pathogens

• Oxacillin or Nafcillin (penicillinase-resistant penicillin) — first-line for MSSA
• First-generation cephalosporin (e.g., cefazolin) — alternative for MSSA
• Vancomycin — for penicillin allergy (type I), suspected or confirmed MRSA, or immunocompromised patients
  • Note: Retrospective studies show higher relapse rates with vancomycin vs. β-lactam for non-MRSA infections; reserve vancomycin for true indications
• Ceftriaxone or third-generation cephalosporins — for gram-negative organisms (Enterobacteriaceae, Proteus, Serratia)
• Cefepime/ceftazidime + aminoglycoside or piperacillin-tazobactam + aminoglycoside × 2–4 weeks → then ciprofloxacin 750 mg PO q12h — for Pseudomonas aeruginosa

Surgical Management — Acute

• Failure to improve after 48–72 hours of antibiotics
• Draining an abscess or subperiosteal collection
• Decompression to prevent avascular necrosis of cortical bone

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Subacute Osteomyelitis (Brodie's Abscess)

• Localized radiolucency with sclerotic rim at the metaphysis of long bones
• Almost exclusively S. aureus (lower virulence)
• Treatment: Surgical debridement + 6 weeks IV antibiotics
• Important: Rule out chondroblastoma — "biopsy all infections, culture all tumors" — Miller's Review of Orthopaedics, 9e

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Chronic Osteomyelitis

Surgical Principles

1. Multiple/repeat procedures are frequently necessary
2. Remove all infected hardware
3. Remove dead bone (sequestrum) — acts as a foreign body
4. Debridement until punctate bleeding is restored ("paprika sign")
5. Debridement of compromised or necrotic soft tissue
6. Preoperative sinus tract injection with methylene blue (to define extent)
7. Consider antibiotic spacers: PMMA (polymethylmethacrylate) cement impregnated with antibiotics, or biologic spacers
8. Restore vascularity and soft tissue/muscle coverage (plastic surgery input often required)

Medical Management — Chronic

• 6 weeks antibiotics directed at specific cultures (open bone biopsy is the best diagnostic test — sinus tract cultures are unreliable)
• Ensure adequate drug levels at the site of infection
• Treat underlying conditions: diabetes, malnutrition, vascular insufficiency, sickle cell disease

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Vertebral Osteomyelitis (Spondylodiscitis)

• Also called: disk-space infection, septic diskitis, spondylodiskitis
• Most common form of hematogenous osteomyelitis in adults
• Primary foci: urinary tract, skin/soft tissue, IV catheter sites, endocardium
• MRI with gadolinium is the investigation of choice (shows decreased T1, increased STIR signal in vertebral bodies + disk space loss)

• IV antibiotics (organism-directed, 6 weeks)
• Image-guided CT aspiration/biopsy for organism identification
• CT/ultrasound-guided drainage of paraspinal/psoas abscesses
• Surgery is indicated for:
  • Spinal instability
  • Neurological deficits / spinal cord compression
  • Failure to respond to antibiotics
  • Epidural abscess requiring decompression

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Osteomyelitis in Specific Populations

Children (Acute Hematogenous)

• Most common organism: S. aureus (MRSA is now most common in AHO)
• Male predominance (2:1 to 3:1); long bones ~80%
• Distal metaphysis is the predilection site (high vascularity)
• Blood cultures positive in ~40%; tissue cultures positive ~86%
• Often treatable with antibiotics alone — early IV then oral step-down
• Surgical drainage if abscess or failure to improve

Neonates

• Group B Streptococcus most common, followed by staphylococci
• Multiple sites involved in ~50%
• Radiographs often abnormal early; MRI if normal X-ray with high suspicion
• High risk of concurrent septic arthritis (vascular channels cross the physis)

Diabetic Foot Osteomyelitis

• Polymicrobial infection (gram-positive + gram-negative + anaerobes)
• Definitive care is usually surgical (debridement, revascularization, or amputation)
• Probe-to-bone test is a useful bedside test
• Prolonged oral fluoroquinolone therapy with anaerobic coverage is often used after surgery

Implant-Associated Osteomyelitis

• Even acute implant infection requires prolonged antimicrobial therapy
• Biofilm formation renders standard antibiotic courses insufficient
• Rifampin-based combinations are the cornerstone for staphylococcal implant infections
• Options: retain implant (DAIR — debridement, antibiotics, implant retention) vs. two-stage exchange

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Supportive Measures

• Rest and splintage of the affected limb
• Adequate analgesia
• Nutritional support
• Optimise glycaemic control in diabetics
• Treat underlying conditions (sickle cell, immunodeficiency, malnutrition)

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Complications

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• Harrison's Principles of Internal Medicine, 22e — Classification & Antibiotic Therapy Table
• Rosen's Emergency Medicine, 9e — Clinical Features, Management, Antibiotic Regimens
• Bailey & Love's Short Practice of Surgery, 28e — Pathophysiology, Surgical Principles
• Miller's Review of Orthopaedics, 9e — Cierny-Mader Staging, Chronic OM Treatment
• Grainger & Allison's Diagnostic Radiology — Vertebral Osteomyelitis, Imaging-guided Treatment