Diabetic Leg Ulcer and Osteomyelitis

• Most common cause of nontraumatic amputations = diabetic foot problems

Osteomyelitis:

• 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

Note:

• 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

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

References

• 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]