What is the next step if osteomyelitis (infection of the bone) is suspected?

Next Steps When Osteomyelitis is Suspected

Obtain plain radiographs of the affected bone as the initial imaging study, followed by MRI if radiographs are negative or equivocal, and consider bone biopsy for culture and histology when the diagnosis remains uncertain or to guide antibiotic selection. 1

Initial Imaging Approach

Start with plain radiographs as they are widely available and inexpensive, though sensitivity is low in early disease (may take weeks to show changes). 1, 2, 3

• Look for cortical erosion, periosteal reaction, mixed lucency and sclerosis, sequestrum, or involucrum on plain films 1
• If initial radiographs show classic changes suggestive of osteomyelitis, treat for presumptive osteomyelitis after obtaining appropriate specimens for culture 1
• If radiographs show no evidence of bone pathology, treat for soft-tissue infection for approximately 2 weeks, then repeat radiographs 2-4 weeks later if suspicion persists 1

Advanced Imaging When Needed

MRI is the most accurate imaging study for defining bone infection and should be obtained when plain radiographs are negative or equivocal but clinical suspicion remains high. 1, 4

• MRI findings of low signal intensity on T1 images and high signal intensity on fluid-sensitive images indicate osteomyelitis 1
• Negative MRI effectively rules out osteomyelitis (maintained intramedullary fat signal and intact cortical signal) 1
• If MRI is unavailable or contraindicated, consider white blood cell-labeled radionuclide scans or PET scans as second-line options 1

When to Obtain Bone Biopsy

Bone biopsy with culture and histology is the gold standard for diagnosis and should be pursued in specific situations: 1, 4, 5

• Diagnosis remains uncertain after clinical and imaging evaluations 1
• Soft-tissue cultures are inconclusive or absent (no ulcer/sinus tract present) 1
• Infection has failed to respond to initial empirical antibiotic therapy 1
• Need to identify the causative organism or antibiotic susceptibilities when not predictable 1
• Mid- or hind-foot lesions that are more difficult to treat and may lead to high-level amputation 1

Biopsy Technique

• Percutaneous biopsy should be performed under fluoroscopic or CT guidance by a properly trained physician (orthopedic surgeon, podiatrist, interventional radiologist) 1, 5
• Obtain 2-3 specimens if possible: at least one for culture and another for histological analysis 1
• Preferably stop antibiotics 1-2 weeks before biopsy if safe to do so 1
• Bone cultures provide more accurate microbiologic data than soft-tissue specimens 1, 4, 5

Special Considerations for Diabetic Foot

In diabetic foot infections with suspected osteomyelitis, follow this algorithm: 1

• Perform probe-to-bone test: negative test in low-risk patients largely rules out osteomyelitis; positive test in high-risk patients is largely diagnostic 1
• Check for elevated inflammatory markers (especially ESR), which are suggestive of osteomyelitis 1
• If ulcer or sinus tract is present with positive MRI, obtain wound tissue cultures from tissues closest to bone (avoid superficial swabs due to contamination risk) 1
• If no ulcer or sinus tract with positive MRI, consider percutaneous image-guided bone biopsy after multidisciplinary discussion 1

Critical Pitfall to Avoid

Do not rely on soft-tissue or sinus tract cultures to guide antibiotic therapy for osteomyelitis, as they do not accurately reflect bone culture results and may lead to inappropriate treatment. 1, 4, 5 Bone biopsy changed antibiotic management in approximately 45% of cases in one study when compared to wound cultures alone. 6

When Immediate Surgical Intervention is Required

If MRI reveals a septic joint, proceed immediately to surgical debridement and intraoperative cultures, as the risk of bacteremia is approximately 70% due to absence of protective basement membrane. 1