Diabetic Leg Ulcer and Osteomyelitis

Author: Michelle Lin, MD
Updated: 5/26/2013

Diabetic Leg Ulcer and Osteomyelitis

  • Most common cause of nontraumatic amputations = diabetic foot problems


  • Diagnostic gold standard for osteomyelitis = Bone biopsy and culture
  • If inadequately treated, increases risk of amputation
  • Starting pretest probability for osteomyelitis in DM patient with leg ulcer = 15%

Physical Exam of DM leg ulcer

Ulcer type: Difficult to distinguish ulcer secondary to diabetic vs vascular insufficiency

Classic ulcer location and appearance:

  • Venous ulcer: Above medial/lateral malleoli, irregular borders
  • Arterial ulcer: Affects toes or shins, pale/punched out borders, painful
  • Diabetic ulcer: Areas of increased pressure (plantar foot, shoe friction areas)

Probe-to-Bone test: Using a sterile, blunt, stainless steel probe, push against ulcerbase to see if can contact hard, gritty structure (bone)

Measure ulcer area: Multiply greatest width by greatest length of ulcer

Wagner grading scale of ulcers

  • Grade 0 – No open lesions; may have evidence of healed lesions/deformitities
  • Grade 1 – Superficial ulcer
  • Grade 2 – Deeper ulcer to tendon, bone, or joint capsule
  • Grade 3 – Deeper tissues involved, with abscess, osteomyelitis, or tendonitis
  • Grade 4 – Localized gangrene of toe or forefoot
  • Grade 5 – Gangrene of foot (partial or total)

Xray findings = loss of trabecular pattern, periosteal reaction, frank bone destruction

Bottom Line

Best positive predictors of osteomyelitis of diabetic leg ulcer are:

  1. Probe-to-bone test
  2. Ulcer area >2 cm2
  3. ESR >70 mm/hr

Best negative predictor is MRI foot

  • Sensitivity 90%
  • Specificity 83%
Finding (+) LR (-) LR
Erythema, swelling, purulence 1.5 0.84
Positive probe-to-bone test 6.4 0.39
Ulcer area (LxW) >2 cm2 7.2 0.48
Clinical gestalt+/- Wagner grade 5.5 0.54
ESR >70 mm/h 11 0.34
Plain film evidence of osteomyelitis 2.3 0.63
MRI foot 3.8 0.14


  • Serum WBC and soft tissue swab culture = not diagnostic
  • Soft tissue culture: Identified same pathogens as bone culture only 19-36% isolates. Not reliably predictive.

Fagan Nomogram

Fagan nomogram

Draw a connecting your pre-test probability and your likelihood ratio. This provides you with your post-test probability.


  • Butalia S, Palda VA, Sargeant RJ, Detsky AS, Mourad O. Does this patient with diabetes have osteomyelitis of the lower extremity? JAMA. 2008 Feb 20;299(7):806-13. doi: 10.1001/jama.299.7.806. [PubMed]