Anatomy of the Dorsomedial Cutaneous Nerve to Hallux and Surgical Implications According to the Severity of Hallux Valgus Deformity: A Cadaveric Study.

Abstract The dorsomedial cutaneous nerve to hallux provides sensation to the dorsomedial aspect of the first metatarsophalangeal joint and hallux. Postoperative damage to the dorsomedial cutaneous nerve to hallux have been reported with the dorsomedial approach and symptoms can be very debilitating. The present study aims to understand how the distance between this nerve and the extensor hallucis longus tendon are affected by the severity of the hallux valgus deformity, at the level of the first metatarsophalangeal joint. We performed a cadaveric study using 35 cadaveric lower extremities (N=35). Each specimen was classified according to the hallux valgus severity through a 30 Kg partial weight-bearing antero-posterior radiograph. Before dissection, the lower extremities’ greater saphenous vein was injected with black latex to simplify the distinction between anatomical structures. We concluded that as the hallux valgus angle and the first intermetatarsal angle increase, the distance between the dorsomedial cutaneous nerve to hallux and the extensor hallucis longus tendon also increases, ranging from 12mm in normal feet to 19mm in severely deformed feet. Hallux valgus is a three-dimensional deformity that changes traditional surgical landmarks. To avoid harming this nerve, we established a danger zone ranging from 12mm to 19mm medial from the extensor hallucis longus tendon, at the level of the first metatarsophalangeal joint. The mid-medial approach to MTP should be preferred as it is out of the danger zone.