The effect of hallux valgus on the anatomy of the nerves around the first metatarsal bone: Does the valgus deviation affect the location of the nerves?

Objective: To identify the variations in the position and distribution of the nerves that may be at risk in surgical approaches to hallux valgus (HV), and to reveal whether these nerves are affected by the anatomical changes associated with HV. Method In the formalin fixed 46 lower extremities (19 female, 27 male), extensor hallucis longus tendon (EHL), deep plantar artery, medial dorsal cutaneous (MDCN), deep fibular (DFN), common plantar digital (CPDN) and proper plantar digital (PPDN) nerves were examined. The branches of MDCN extending to the medial side of foot were recorded in three segments. The positional topography of nerves according to EHL were analysed on 360° circle and clock models. Results Gender-related differences for some parameters in direct measurements were not found in comparisons on the clock model. In HV cases, DFN was closer to EHL in the distal part of the metatarsal bone, while there was no difference in the proximal and the intersection of the medial branch of the MDCN with the EHL was more proximal. The location of the nerves in the clock pattern did not change in HV cases. Of the nerve branches reaching the medial side of the foot, 65.2% were in Part I, 71.7% in Part II, and 4.3% in Part III. Conclusion It was revealed that the gender differences in the distance of the nerves to the EHL disappeared when the size effect of the cross-section of the first metatarsal bone region was eliminated with the clock model. No evidence was found that the location of the nerves around the proximal metatarsal is affected by HV. However, in advanced HV levels, the DFN was found distally closer to the EHL, and the intersection of the medial branch of the MDCN with the EHL was more proximal. The variations we revealed in the number of branches reaching the inside of the foot may explain the diversity of neuromas or nerve injuries associated with hallux valgus surgery.