Why Diabetic Foot Ulcers Predominantly Affect the Plantar Surface
Diabetic foot ulcers occur primarily on the plantar surface because diabetic neuropathy causes insensitivity to repetitive moderate pressure during walking, while simultaneously creating foot deformities that dramatically increase plantar pressures—making the weight-bearing sole vulnerable to unrecognized trauma.
Biomechanical Mechanism
The plantar surface bears the brunt of mechanical loading during ambulation, and this becomes pathological in diabetes through a specific cascade:
Repetitive moderate pressure applied to the plantar aspect during walking is the primary mechanical cause of ulceration 1. Unlike acute trauma, this chronic loading goes unnoticed due to sensory loss.
Diabetic peripheral neuropathy alters foot structure, which directly increases plantar foot pressure—a predictive risk factor for ulcer development 1. The neuropathy doesn't just remove protective sensation; it actively deforms the foot architecture.
High plantar pressures combined with foot deformity create focal areas of excessive loading 2, 3. These pressure points concentrate forces that would normally distribute across the entire foot.
The Neuropathy-Deformity-Pressure Triad
The pathophysiology operates through three interconnected mechanisms:
Neuropathy leads sequentially to foot deformity, callus formation, and insensitivity to trauma or pressure 4. Each element compounds the next—deformity increases pressure, pressure causes callus, and insensitivity prevents recognition of tissue damage.
Ankle equinus contracture specifically increases plantar surface pressure during ambulation 5. This contracture shifts the center of pressure forward onto the forefoot, creating a vicious cycle where ulcers lead to immobilization, which worsens contracture.
The insensate foot cannot detect the repetitive trauma occurring with each step, allowing tissue breakdown to progress from callus to pre-ulcer to full-thickness wound 2, 1.
Clinical Pitfall to Avoid
The most critical error is assuming ulcers result from a single traumatic event. The plantar location reflects chronic biomechanical overload during normal walking, not acute injury 1. This distinction matters because treatment requires pressure redistribution (off-loading with total contact casts or removable cast walkers), not just wound care 2, 1.
Early identification of the insensitive foot as "at risk" enables prevention by protecting against abnormal biomechanical loading before ulceration occurs 1. The plantar surface is where prevention efforts must focus, as this is where pathological pressures concentrate during the gait cycle.