Anatomical bases of surgical approaches to the nerves of the flexor digitorum brevis, quadratus plantaris, and interossei of the foot in the spastic foot surgery

Objective The majority of toe claws in spastic patients are of extrinsic origin, by hypertonia and/or retraction of the long flexor muscles; they are treated by a partial neurotomy (hyponeurotization) of the branches of the tibial nerve [1] or by lengthening their tendon. A minority is related to a hypertonia and/or retraction of the intrinsic muscles: interossei, flexor digitorum brevis (FDB) or quadratus plantaris (QP). When the deformity is related to spasticity, without associated retraction, it could respond to a hyponeurotization of their nerves. The aim of this work was to identify reliable clinical landmarks to approach them surgically. Material/patients and methods Five preserved feet were dissected. The course of the medial and lateral plantar nerves, the origin of branches to the FDB and QP and the deep branch of the lateral plantar nerve were compared with 7 clinical landmarks and 4 lines connecting them, including tubercle of the navicular (TN), the tuberosity of the fifth metatarsal (M5), the tip of the hallux (H), the tip of the 5th toe (5), the tuberosity of calcaneus (TC). Results Incisions, crossed plans and tracking of target branches are presented: – for the nerve to FDB: 4cm long incision parallel to the medial edge of the plantar fascia, 1 cm medially to line H-TC, starting just 3 cm downstream line TN-M5; – for the nerve to CQ: 4cm long incision parallel to the medial edge of the plantar fascia, 1 cm medially to line H-TC, starting 3 cm upstream line TN-M5; – for the lateral plantar nerve deep branch: 4cm long incision parallel to the lateral edge of the plantar fascia on the line 5-TC, 3 cm upstream and 1 cm below the line TN-M5. Discussion–conclusion Such a hyponeurotization could help in the rare cases of isolated spasticity of the intrinsic muscles of the toes, easily diagnosed through retromalleolar tibial nerve block.