Injury to the dorsomedial cutaneous nerve has been identified as a potentially frequent occurrence after hallux valgus surgery. The existence of pre-operative pressure neuropathy is also described but remains largely unexplored. This study was performed to investigate the incidence of pre-operative sensory deficit in the hallux valgus toe, and to examine to what extent any deficit was related to the degree of joint angulation.

A cohort of 43 patients (61 hallux toes) presenting for consideration of surgical correction had their sensation tested in pre-designated sensory zones using a five-filament set of Semmes-Weinstein monofilaments. These allowed good inter-observer reliability with an ICC (intra-class correlation coefficient) of 0.84 overall.

Whilst sensory symptoms were self reported in only 21% of the feet, a measurable reduction in sensation by one monofilament grade or more was found in an additional 44% of the feet. No relationship was found between the degree of sensory loss and degree of angulation.

Patients with symptomatic hallux valgus may have sensory loss of the toe despite not being aware of the deficit. Normal subjective sensation does not reliably predict normal sensory function. Given the potentially high rates of intra-operative nerve damage in hallux surgery we recommend objective sensory testing as part of routine pre-operative assessment.