According to the 2026 clinical practice guideline, how should I evaluate and manage suspected osteomyelitis in an adult diabetic patient with peripheral arterial disease and recent lower‑extremity cellulitis, especially when a chronic ulcer, exposed bone, or persistent pain is present?

Evaluation and Management of Suspected Osteomyelitis in Adult Diabetic Patients with Peripheral Arterial Disease

In an adult diabetic patient with peripheral arterial disease and a chronic lower-extremity ulcer, you should suspect osteomyelitis if the ulcer fails to heal after 6 weeks of appropriate wound care and off-loading, then confirm with probe-to-bone testing, plain radiographs, and MRI if needed, followed by bone biopsy for culture-directed antibiotic therapy when diagnosis remains uncertain or surgical planning is required. 1, 2

Initial Clinical Assessment

When to Suspect Osteomyelitis

• Suspect osteomyelitis when an ulcer fails to heal after at least 6 weeks of appropriate wound care and off-loading, particularly in patients with adequate blood supply to the affected foot 3, 1, 2

• High-risk clinical features include:

  • Ulcer area larger than 2 cm² (positive likelihood ratio 7.2) 3
  • Ulcer depth >3 mm combined with CRP >3.2 mg/dL or ESR >60 mm/hour 3
  • Exposed bone visible in the wound (positive likelihood ratio 9.2) 3
  • "Sausage toe" appearance (swollen, erythematous, lacking normal contours) 3
  • Ulcer overlying a bony prominence 3, 2
  • History of recurrent or multiple wounds 3

• Important caveat: Neither the presence of wound infection signs nor elevated white blood cell count influences the likelihood of osteomyelitis 3

Probe-to-Bone Test

• Perform probe-to-bone (PTB) testing at every consultation using a sterile blunt metal probe gently inserted through the wound 3, 1, 2

• If bone is palpable (hard, gritty feel) or visible, osteomyelitis is highly likely (positive likelihood ratio 7.2) 3, 1

• Test interpretation depends on pretest probability:

  • In clinically infected wounds with high prevalence (>60%), a positive PTB test is highly suggestive of osteomyelitis 3
  • A negative PTB test in low-risk patients (≤20% prevalence) essentially rules out osteomyelitis (negative likelihood ratio 0.48) 3
  • In apparently uninfected wounds, a positive PTB test is not specific for osteomyelitis 3

Laboratory Evaluation

Inflammatory Markers

• Obtain erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels 3, 2

• ESR ≥70 mm/hour substantially increases the likelihood of osteomyelitis (positive likelihood ratio 11) and has sensitivity of 0.81 and specificity of 0.8 3, 2

• Lower ESR levels reduce the likelihood (negative likelihood ratio 0.34) 3

• Combining ulcer depth >3 mm with either CRP >3.2 mg/dL or ESR >60 mm/hour helps differentiate osteomyelitis from cellulitis 3

Imaging Studies

Plain Radiographs

• Obtain baseline plain radiographs as the initial imaging study to look for bony abnormalities, soft tissue gas, and foreign bodies 1, 2

• Plain radiographs have limited sensitivity (54%) and specificity (68%) for osteomyelitis, especially in early infection 1, 2

• A negative X-ray does not exclude the diagnosis; repeat in 2-3 weeks if clinical suspicion remains high 2

• Combining PTB test results with plain radiography improves overall diagnostic accuracy 3

MRI

• MRI is the imaging study of choice when osteomyelitis diagnosis remains uncertain after clinical assessment and plain radiographs, with 98% sensitivity and 89% specificity 3, 2

• MRI has a 100% negative predictive value for excluding infection—a negative MRI definitively rules out osteomyelitis and biopsy can be averted 3, 2

• Specific indications for MRI include:

  • Diagnostic uncertainty after initial evaluation with PTB and plain radiographs 3, 1, 2
  • Failure to respond to empiric antibiotic therapy 1
  • Need to define extent of bone and soft tissue involvement before surgical planning 1
  • Detection of septic joint or fluid collections 3

• MRI findings revealing a septic joint require immediate surgical debridement and intraoperative cultures due to high risk of bacteremia (approximately 70% of cases) 3

Bone Sampling and Culture

When to Obtain Bone Biopsy

According to the International Working Group on the Diabetic Foot and IDSA guidelines, bone cultures are not always needed but should be strongly considered in the following situations: 3

• When clinical and imaging evaluations result in uncertain diagnosis 3
• When soft-tissue cultures are inconclusive 3
• When infection has failed to respond to initial empirical antibiotic therapy 3, 1
• When considering antibiotic regimens with higher potential for selecting resistant organisms (e.g., rifampin, fluoroquinolones) 3
• For midfoot or hindfoot lesions, which are more difficult to treat and more often lead to high-level amputation 3

Bone Biopsy Technique

• Obtain deep tissue and bone specimens at the time of surgical debridement or biopsy for both culture and histopathologic examination 3

• Bone biopsy for histopathologic examination definitively confirms the diagnosis (showing acute or chronic inflammatory cells, necrosis) and is most useful in guiding antimicrobial therapy 3

• Withhold systemic antibiotic therapy before obtaining bone specimens when possible, though recent data suggest at least half of bone cultures will be positive even with antimicrobial pretreatment 3

• Important caveat: In pressure ulcers with exposed bone, histopathology yields positive results in only <20% of cases, possibly due to sampling error 3

Alternative Sampling Strategies

• Wound tissue cultures can be obtained by probing communicating ulcers or after careful debridement when managing diabetic foot wounds 3

• Some evidence suggests microorganisms isolated from nonbone specimens (sinus tracts, superficial wounds) are generally concordant with bone specimens, though this remains debated 3

• Superficial swabs of pressure ulcers cannot differentiate colonization from infection and should be avoided 3

Management Algorithm

For Chronic Ulcers with Suspected Osteomyelitis

1. Perform PTB test and obtain plain radiographs 1, 2

2. If bone is visible/palpable or radiographs show bony destruction:

   • Obtain MRI to confirm diagnosis and define extent 3, 1, 2
   • If MRI positive and surgery is planned, obtain intraoperative cultures and histopathology 3
   • If MRI positive but surgery not immediately needed, consider percutaneous bone biopsy based on criteria above 3

3. If PTB negative and radiographs negative but clinical suspicion remains high (ESR ≥70, large ulcer, failed 6-week healing):

   • Obtain MRI 3, 1, 2
   • If MRI negative, osteomyelitis is ruled out 3, 2
   • If MRI positive, proceed with bone biopsy or empiric therapy based on clinical context 3

For Decubitus Ulcers

• If wound is visibly necrotic and extends to bone, refer to surgeon for surgical debridement and intraoperative cultures 3

• If extension into bone is unclear, obtain MRI first 3

• Debridement and intraoperative cultures should only be performed if surgery is deemed necessary 3

Monitoring During Treatment

• Reassess clinically at 6 weeks if ulcer is not healing despite appropriate wound care and off-loading 1

• At the 6-week checkpoint, repeat PTB testing and consider plain radiographs if clinical suspicion has increased 1

• Monitor clinical response during antibiotic therapy (typically 4-6 weeks for osteomyelitis) 1

• Consider repeat MRI if there is progressive bony deterioration or persistently elevated inflammatory markers during treatment 1

• Do not continue antibiotics until complete wound healing—discontinue once clinical signs of infection resolve, not when the wound fully closes 1

Common Pitfalls

• Do not rely on superficial wound swabs for culture—they cannot distinguish colonization from infection 3

• Do not assume exposed bone in pressure ulcers is diagnostic of osteomyelitis—histopathology confirms in only <20% of cases 3

• Do not skip MRI when diagnosis is uncertain—it has 100% negative predictive value and can definitively rule out osteomyelitis 3, 2

• Do not obtain bone biopsy routinely in all diabetic foot cases—only 20% of clinicians use percutaneous biopsies, instead opting for empirical or delayed tailored strategies 3

• In patients with peripheral arterial disease, recognize that vascular insufficiency may complicate both diagnosis and healing, requiring vascular assessment and possible revascularization 3