Musculoskeletal & Integumentary · Topic 3 of 11
Osteomyelitis & Diabetic Foot Infection
Musculoskeletal · bone and foot infection
Osteomyelitis & Diabetic Foot Infection
In a diabetic foot ulcer, probe to bone, get MRI when unsure, culture bone rather than swabs, and treat osteomyelitis for about 6 weeks.
Key numbers
Positive probe-to-bone test suggests osteomyelitisPTB sens 87% · spec 83%
Treat osteomyelitis 6 weeks without bone resection6 weeks
01 · Defined byPositive probe-to-bone test suggests osteomyelitis
Start with a probe-to-bone test (hard, gritty bone felt with a sterile blunt probe), plain foot x-rays and ESR, CRP or procalcitonin; probe-to-bone has about 87% sensitivity and 83% specificity for diabetic foot osteomyelitis.
02 · DoCulture bone, not swabs or sinus drainage
Obtain bone for culture (percutaneous or intraoperative biopsy) to guide therapy; swabs and sinus-tract drainage do not reliably show the bone pathogen. Biopsy before antibiotics unless the patient is in shock or has neurologic compromise.
03 · GiveTreat osteomyelitis 6 weeks without bone resection
Give about 6 weeks of antibiotics for diabetic foot osteomyelitis treated without bone resection or amputation, and up to 3 weeks after a minor amputation when the bone margin culture is positive.
01
Causes & risk factors
Why it happensContiguous spread, often polymicrobial with S. aureusAbout 80% of osteomyelitis spreads from adjacent infected tissue or open wounds (diabetic foot ulcers, pressure injuries, open fractures) and is often polymicrobial; S. aureus is present in at least half.
02
Presentation
What you'll seeLarge, deep ulcer or sausage toe suggests osteomyelitisOsteomyelitis is likely under an ulcer larger than 2 cm² or deeper than 3 mm, with exposed bone, or with a red swollen 'sausage toe'; patients are often afebrile with little local inflammation.
03
Diagnosis & monitoring
Work-upIWGDF/IDSA grades infection mild, moderate, severeInfected = 2 or more of swelling, erythema, tenderness, warmth, pus. Mild: erythema up to 2 cm; moderate: erythema over 2 cm or deeper tissue; severe: 2 or more SIRS signs. Add (O) for osteomyelitis.
04
Do right now
In this orderFirst moves
1
→IWGDF/IDSA grades infection mild, moderate, severe
2
→Urgent surgery for severe or necrotizing foot infection
3
→Positive probe-to-bone test suggests osteomyelitisPTB sens 87% · spec 83%
4
→Culture bone, not swabs or sinus drainage
5
Vascular consult when infection meets PAD
Why each step
IWGDF/IDSA grades infection mild, moderate, severeInfected = 2 or more of swelling, erythema, tenderness, warmth, pus. Mild: erythema up to 2 cm; moderate: erythema over 2 cm or deeper tissue; severe: 2 or more SIRS signs. Add (O) for osteomyelitis.
Urgent surgery for severe or necrotizing foot infectionGet urgent surgical consultation for severe infection, or moderate infection with extensive gangrene, necrotizing infection, deep abscess, compartment syndrome or severe limb ischemia; early surgery (within 24–48 hours) plus antibiotics for moderate and severe infections.
Positive probe-to-bone test suggests osteomyelitisStart with a probe-to-bone test (hard, gritty bone felt with a sterile blunt probe), plain foot x-rays and ESR, CRP or procalcitonin; probe-to-bone has about 87% sensitivity and 83% specificity for diabetic foot osteomyelitis.
Culture bone, not swabs or sinus drainageObtain bone for culture (percutaneous or intraoperative biopsy) to guide therapy; swabs and sinus-tract drainage do not reliably show the bone pathogen. Biopsy before antibiotics unless the patient is in shock or has neurologic compromise.
Vascular consult when infection meets PADWith peripheral artery disease and an infected ulcer or gangrene, get urgent surgical and vascular consultation to time drainage and revascularization; PAD raises the infection risk and worsens outcomes.
05
Management
OrdersMRI when osteomyelitis is still in doubt must knowOrder MRI when the diagnosis remains uncertain after examination, plain x-rays and inflammatory markers; radiographs lag 2–4 weeks behind infection. PET, leukocyte scintigraphy or SPECT are alternatives when MRI is unavailable.
Mild infection: cover streptococci and S. aureusFor mild infection without recent antibiotics, target aerobic gram-positive cocci (streptococci, S. aureus, MRSA if risk factors). Do not empirically cover Pseudomonas in temperate climates; broaden for moderate or severe infection.
Soft-tissue foot infection: 1–2 weeks of antibioticsTreat skin and soft-tissue diabetic foot infection for 1–2 weeks, extending up to 3–4 weeks if it is extensive, resolving slowly, or accompanied by severe peripheral artery disease.
Diabetic foot osteomyelitis: cover anaerobes tooEmpiric therapy for contiguous diabetic foot osteomyelitis must cover gram-positive, gram-negative and anaerobic organisms (e.g. ampicillin-sulbactam or piperacillin-tazobactam), adding vancomycin for severe infection or MRSA risk; then tailor to bone culture.
06
The rules
Know theseNo antibiotics for clinically uninfected ulcersDo not treat a clinically uninfected foot ulcer with systemic or topical antibiotics to prevent infection or speed healing; diagnose infection clinically, not from wound cultures.
Forefoot osteomyelitis may be treated without surgeryAntibiotics alone are reasonable for forefoot osteomyelitis with no need for urgent drainage, no peripheral artery disease and no exposed bone; otherwise consider resection of infected bone plus antibiotics. Bioavailable oral agents are acceptable.
07
Diabetic foot osteomyelitis or acute Charcot foot?
Commonly confused| Usual site | Toes and forefoot |
|---|---|
| Skin | Ulcer over the bone, often probes to bone |
| Presentation | Chronic ulcer; often afebrile with little local inflammation |
| MRI | Focal marrow signal next to an ulcer or sinus tract |
| Treatment | Bone culture, antibiotics, resection if needed |
08
More detail
ReferenceShow 7 reference facts
An ESR above 43 mm/h combined with a positive probe-to-bone test correlates strongly with culture- or histology-proven osteomyelitis; an ESR above 70 mm/h without another cause also suggests it.
Remission of diabetic foot osteomyelitis is judged at least 6 months after antibiotics end; recurrence is common, so the term remission is preferred over cure.
Consider hospitalizing patients with severe diabetic foot infection, or moderate infection with key comorbidities; others, including many with osteomyelitis, can be managed as outpatients, using bioavailable oral antibiotics.
Hyperbaric or topical oxygen, G-CSF, topical antiseptics or antibiotics, silver, honey and negative-pressure wound therapy are not recommended to treat the infection itself.
Hematogenous osteomyelitis in adults usually involves the vertebrae: localized back pain and tenderness, often without fever; MRI or CT shows disk-space and end-plate destruction and paravertebral or epidural abscess.
Unusual pathogens: Pseudomonas and Serratia in people who inject drugs, Salmonella in sickle cell disease, and MRSA with gram-negative enterics in hemodialysis patients.
Diabetic foot osteomyelitis usually affects the toes and forefoot under an ulcer, with focal marrow signal on MRI; acute Charcot affects the midfoot with periarticular, subchondral marrow edema and joint deformity.
If the probe hits hard, gritty bone, assume osteomyelitis until the bone culture says otherwise.
Sources · Senneville É et al. IWGDF/IDSA Guidelines on the Diagnosis and Treatment of Diabetes-related Foot Infections (IWGDF/IDSA 2023). Clin Infect Dis 2023 (IWGDF full text) · Merck Manual Professional — Osteomyelitis · Ertugrul BM, Lipsky BA et al. Osteomyelitis or Charcot neuro-osteoarthropathy? Differentiating these disorders in diabetic patients with a foot problem. Diabet Foot Ankle 2013;4:21855 · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).