Keratotic Disorders of the Plantar Skin (Corns, Calluses, IPK)

Where the metatarsal pad goes - the detail that decides whether it works

An offloading pad only works if it is positioned correctly, and the commonest reason one fails is that it has been put in the wrong place.

The pad sits just PROXIMAL to the metatarsal heads, not under them. Its purpose is to support the metatarsal necks and shafts so that load is taken behind the heads and the transverse arch is lifted, which lowers the pressure at the head itself. A pad placed directly beneath the painful head does the opposite - it raises the very prominence that is causing the keratosis and makes the symptoms worse. Verify the position on the patient rather than trusting the pad's printed outline: with the pad in place, the palpable metatarsal heads should sit just distal to its leading edge.

The rest of the offloading prescription:

• A stiff or rocker sole limits dorsiflexion at the metatarsophalangeal joints and shortens the time the forefoot spends loaded at push-off - often more effective than anything placed inside the shoe.
• A wide, deep toe box for a clawed or hammered toe with a dorsal corn, so the shoe stops rubbing the prominence; a soft silicone sleeve or interdigital spacer for a soft corn, alongside keeping the web dry.
• Accommodative rather than corrective materials in the insensate foot - the aim is to spread load and cushion, not to hold a rigid correction against skin that cannot report pain.
• Full detail of the devices is in Foot & Ankle Orthotics.

Testing for the equinus you are being asked to treat

Equinus drives global forefoot overload and gastrocnemius recession is the operation that addresses it - but the contracture has to be demonstrated first, and distinguished from a tight whole triceps surae.

The Silfverskiöld test does this. Measure passive ankle dorsiflexion with the knee extended, then repeat with the knee flexed to 90 degrees, keeping the hindfoot in slight inversion so that the movement is true ankle dorsiflexion rather than midfoot break. Because gastrocnemius crosses the knee and soleus does not, flexing the knee slackens gastrocnemius alone:

• Dorsiflexion improves markedly with the knee flexed - an isolated gastrocnemius contracture, treated by a gastrocnemius recession.
• Dorsiflexion stays limited in both positions - the whole gastrocsoleus complex is tight, and a gastrocnemius recession alone will not correct it; a tendo-Achilles lengthening is the corresponding procedure, with a higher risk of over-lengthening and calcaneus gait.

The contracture and its management are developed in Gastrocnemius Equinus Contracture.

Approach from the dorsum, not through the sole

Every one of these operations is reached through a dorsal incision, and the reason is worth stating plainly: a scar on weight-bearing plantar skin can be more painful and more disabling than the keratosis it was meant to cure. Plantar skin is thick and tethered by fibrous septa to the fat pad beneath it, and it takes load with every step, so an incision there heals into a firm, tender scar that becomes a focal prominence in its own right - the patient trades a callus for something that cannot be offloaded.

• Perform the condylectomy or osteotomy through a dorsal or dorsolateral incision over the relevant metatarsal or web space, working down to the plantar condyle from above.
• Do not excise the keratosis. The skin is the symptom; removing it leaves a wound in a high-pressure area and the lesion returns unchanged once the bone beneath it is untouched.
• If a plantar incision is genuinely unavoidable, place it longitudinally and away from the loaded metatarsal heads and heel, in the relatively unloaded arch.
• The same logic is sharper in the diabetic foot, where a plantar wound in an insensate, poorly perfused ray is how an elective procedure becomes an ulcer.