The Diabetic Foot With a Deep Ulcer and Osteomyelitis

Diagnosis:

• Clinical: probe-to-bone in a diabetic with a plantar ulcer has a high positive predictive value for osteomyelitis. Combined with cortical erosion on plain film, the diagnosis is likely.
• Imaging: MRI with contrast is the modality of choice for marrow involvement and soft-tissue extension. Plain films are insensitive early but specific when erosion is present. Avoid relying on a single test.
• Microbiology: obtain deep tissue samples (not superficial swabs) at debridement for culture and sensitivity. Bone culture is the gold standard.

Extent of debridement:

• Debride all necrotic and infected tissue, including infected bone, until healthy bleeding bone and soft tissue are reached. Preserve as much of the weight-bearing metatarsal head as possible if it is not frankly infected; if the metatarsal head is destroyed, a ray amputation may be required.
• The goal is source control with a plantigrade, sensate foot - not necessarily a 'clean' wound at the expense of a non-functional foot.
• Plan for staged debridement and reassess at 48–72 hours.

Exam point: distinguish osteomyelitis (needs bone resection) from soft-tissue infection (debridement + antibiotics), and avoid unnecessary major amputation.

Vascular assessment:

• ABPI 0.75 with an absent posterior tibial pulse suggests peripheral arterial disease, though ABPI can be falsely elevated in diabetes due to medial calcinosis. Obtain toe pressures, TBI, or duplex/CT angiography to assess distal runoff.
• Healing of a forefoot amputation requires adequate perfusion; poor inflow predicts failure of local debridement.

Role of revascularization:

• If perfusion is inadequate for healing (e.g., toe pressure <30–40 mmHg, or non-healing after debridement), refer for revascularization (angioplasty or bypass) before or alongside debridement. Revascularization improves limb salvage and wound healing.
• Sequencing: in a patient with spreading infection, urgent debridement first to control sepsis, with revascularization as soon as feasible - do not delay source control for a full vascular work-up if the limb is threatened.

Exam point: a 'pink, warm' foot does not exclude PAD, and revascularization is a limb-salvage procedure, not an elective add-on.

Offloading:

• Total contact cast or a removable cast walker (with adherence) is the gold standard for plantar neuropathic ulcers. Non-removable devices have better healing rates but require monitoring.
• Custom insoles and rocker-bottom shoes after healing to redistribute pressure away from the metatarsal heads.
• Avoid weight-bearing on the affected foot until the wound is healed.

Long-term strategy:

• Glycaemic control (target HbA1c <7–8% individualized), smoking cessation, and renal protection (SGLT2 inhibitors with eGFR caution, ACE inhibitor).
• Foot care education, regular podiatry review, and screening for the contralateral foot.
• Vascular surveillance and management of PAD.

Risks of alternatives:

• Primary closure or skin grafting over an infected bed risks abscess and recurrence.
• Early major amputation without attempting limb salvage may be appropriate if the foot is non-functional, but should be a shared decision after vascular and infection control.
• Prolonged antibiotics alone without debridement fails to eradicate infected bone.

Exam point: the exam tests whether you integrate offloading, vascular assessment, and infection control rather than treating the ulcer as a purely surgical problem.