Diagnosis and Treatment of Osteomyelitis
Diagnostic Workup
Begin with plain radiographs of the affected area in all suspected cases, though recognize they will be normal in the first 7-10 days and require >30% bone destruction to show abnormalities. 1, 2 This initial imaging excludes alternative diagnoses like fracture, tumor, or degenerative changes and identifies radiodense foreign bodies or soft tissue gas. 1
Clinical Assessment
Perform a probe-to-bone (PTB) test on any ulcer using a sterile blunt metal probe at every wound assessment. 1, 3 A positive test (palpable hard, gritty bone) has a positive likelihood ratio of 9.2 in high-risk patients with clinically infected wounds, making it highly suggestive of osteomyelitis. 1, 3 However, a negative PTB does not exclude the diagnosis and should not prevent further workup. 1, 3
Key clinical findings that increase likelihood of osteomyelitis:
- Visible or palpable bone through a wound (positive likelihood ratio 9.2) 3
- Ulcer area >2 cm² (positive likelihood ratio 7.2) 1, 3
- Non-healing ulcer after ≥6 weeks of appropriate wound care and off-loading 1, 3
- "Sausage toe" appearance (swollen, erythematous digit lacking normal contours) 1, 3
- Deep ulcers over bony prominences (metatarsal heads, calcaneus, malleoli) 3
Important caveat: Neither wound infection signs (erythema, warmth) nor elevated white blood cell count influences the likelihood of osteomyelitis. 1, 3 However, markedly elevated ESR (>60 mm/hour) or CRP (>3.2 mg/dL) combined with ulcer depth >3 mm helps differentiate osteomyelitis from cellulitis. 1
Advanced Imaging
Order MRI (with IV contrast when hardware is present) as the next diagnostic step when osteomyelitis is suspected after initial radiographs. 1, 4, 2 MRI is superior for detecting bone marrow edema, cortical disruption, soft tissue inflammation, sinus tracts, and abscess formation. 1, 4, 2 A negative MRI (maintained intramedullary fat signal and intact cortical signal) effectively rules out osteomyelitis. 2
When MRI is unavailable or contraindicated, use FDG-PET/CT if surgery occurred >6 months ago (sensitivity 83-100%, specificity 76-100% for post-traumatic osteomyelitis with hardware). 1, 4 Alternatively, consider white blood cell-labeled radionuclide scan combined with bone marrow imaging. 1
Avoid three-phase bone scans alone (specificity only 25% in chronic osteomyelitis) and leukocyte scans alone (sensitivity 21-74% depending on location). 1, 4
CT plays a limited role but excels at detecting sequestra, cortical destruction, sinus tracts, soft tissue gas, and foreign bodies—findings superior to MRI for these specific features. 1
Definitive Diagnosis
The gold standard requires both positive bone culture and histology showing inflammatory cells and osteonecrosis from an aseptically obtained bone sample. 1, 2
Obtain bone biopsy in these specific situations: 1
- Diagnostic uncertainty exists
- Soft tissue cultures suggest antibiotic-resistant organisms
- Progressive bony deterioration or persistently elevated inflammatory markers during therapy
- Failure to respond to empiric antibiotics
- Planning to use high-resistance-risk antibiotics (rifampin, fluoroquinolones)
- Bone is a planned target for orthopedic hardware insertion
Critical pitfall: Never use soft tissue or sinus tract cultures to guide antibiotic selection for osteomyelitis—they do not accurately reflect bone pathogens. 1, 5 Bone biopsy should ideally be obtained before starting antibiotics to maximize culture yield. 1
Treatment Plan
Surgical Management
Osteomyelitis is fundamentally a surgical disease requiring débridement of infected and necrotic bone in chronic cases. 6, 7, 8 Acute hematogenous osteomyelitis can be treated with antibiotics alone, but chronic osteomyelitis with necrotic bone requires surgical intervention. 7, 8
For chronic osteomyelitis with hardware and sinus tracts, plan for hardware removal, extensive débridement, and possible staged reconstruction. 4 Obtain tissue cultures intraoperatively to guide culture-directed antibiotic therapy. 4
Antibiotic Therapy
Without surgical resection, antibiotic treatment must be prolonged (≥4-6 weeks). 6, 7, 8 After adequate surgical débridement, antibiotic duration can be shortened considerably. 6
For acute hematogenous osteomyelitis in children, treat with 4 weeks of antibiotics. 8 In adults with chronic osteomyelitis, antibiotic duration is typically several weeks longer than pediatric cases. 8
Empiric coverage must target Staphylococcus aureus (found in ~50% of cases), the most common pathogen. 1, 8 However, recognize that 30-40% of cases involve other organisms including coagulase-negative staphylococci (25%), aerobic streptococci (30%), and Enterobacteriaceae (~40%). 1, 5 Diabetic foot infections are often polymicrobial with 3-6 organisms. 6
The increasing prevalence of methicillin-resistant S. aureus complicates antibiotic selection and must be considered in empiric regimens. 7, 8
Special Populations
For diabetic foot osteomyelitis (found in 50-60% of hospitalized diabetic foot infections): 1
- Suspect osteomyelitis when deep ulcers fail to heal after ≥6 weeks despite adequate blood supply, wound care, and off-loading 1
- Bone infection typically involves the forefoot through contiguous spread 1
- Consider 2-3 weeks of antibiotics for moderate-to-severe infections 2
When surgery is not an option due to severe peripheral vascular disease, end-stage renal disease, or other prohibitive medical conditions, use long-term suppressive antibiotic therapy with adjunctive local treatments. 6
Multidisciplinary Approach
Optimal management requires coordination between infectious disease, orthopedic surgery, and wound care specialists. 7 The subtle balance between medical and surgical therapy determines whether a potentially curative outcome can be achieved. 6
Key caveat: Even with optimal treatment, recurrence rates remain high, so "remission" is a more appropriate term than "cure." 7, 8 Chronic osteomyelitis with hardware and sinus tracts carries significant morbidity and risk of recurrence. 4