Most techniques described for the correction of hallux valgus require exposure of the distal aspect of the first metatarsal. A dorsomedial incision is often recommended. Texts counsel against damaging the dorsal digital nerve, as a painful neuroma is an unwelcome surgical complication. Our study on cadavers aimed to investigate the anatomy of the dorsomedial cutaneous nerve in the metatarsophalangeal region, with special reference to surgical incisions. A constant, previously unrecognised branch of the nerve was identified. This branch is likely to be damaged if a dorsomedial approach is used. It is recommended that a mid-medial incision be used instead, i.e. at the junction of the plantar and dorsal skin

Damage to the dorsomedial branch of the medial dorsal cutaneous nerve is not uncommon in surgery of the hallux. The resultant morbidity can be disabling. In the light of the senior author’s operative observation of a sentinel vein, we undertook a cadaver study to investigate the anatomical relationships of the dorsomedial branch of the medial dorsal cutaneous nerve. This established that in 14 of 16 cadaver great toes exposed via a modified medial incision, there is an easily identified vein which runs transversely superficial and proximal to the nerve. In a prospective clinical study of 171 operations on the great toe using this approach, we confirmed this anatomical relationship in 142 procedures (83%), with no complaint of numbness or pain in the scar at follow-up. We attribute this to careful identification of the ‘sentinel’ vein and the subjacent sensory nerve, which had been successfully protected from damage. We recommend this technique when operating on the great toe.

Injury to the dorsomedial cutaneous nerve in the foot may occur after operations for hallux valgus. Pressure neuropathy before operation is also described but remains largely unexplored. We have investigated the incidence of sensory deficit in the great toe before operating for hallux valgus and examined to what extent any deficit was related to the degree of angulation of the joint. Forty-three patients with a total of 61 great toes with hallux valgus presenting for consideration of surgical correction had their sensation tested in pre-designated zones using a five-filament set of Semmes-Weinstein monofilaments. These allowed good inter-observer reliability with an intra-class correlation coefficient of 0.84. Sensory symptoms were noted by only 21% of the patients, a measurable reduction in sensation by one monofilament grade or more was found in an additional 44%. No relationship was found between the degree of sensory loss and the degree of angulation. Patients with symptomatic hallux valgus may have sensory loss in the toe without being aware of it. Normal subjective sensation does not reliably predict normal sensory function. Given the potentially high rates of nerve damage following operations for hallux valgus, we recommend objective sensory testing as part of routine assessment before surgery