NEUROANATOMY OF THE NAVICULAR

Participants: J. Femino, J. Baker, R. Taylor

Keywords: neuroarthropathy, foot, neurovascular

Introduction

A widespread and growing clinical problem facing the orthopaedic surgeon today is the diabetic neuroarthropathy. The pathways by which the polyneuropathy in diabetes leads to neuroarthropathy are not well understood. One of the current popular theories proposes that the loss of autonomic fibers leads to loss of vasomotor control. This in turn causes changes in bone metabolism leading to neuroarthropathy. A thorough understanding of neuroanatomy and its relation to the blood supply would be crucial to further understanding this process and formulating treatment alternatives. One may also formulate that the nerves innervating the bone, control bone metabolism and remodeling and thus, dysfunction of this control in diabetics leads to the disorganization of the bony architecture that is the hallmark of this disease.

We elected to study the navicular in the human foot since its small size and high ratio of articular to non-articular surface area makes it an ideal subject. The blood supply to the navicular has been investigated previously and this was included with all specimens. This allowed preservation of the nerve supply accompanying the vasculature and their relationship, which was followed through the bone. To our knowledge, the only report in the English literature of the neuroanatomy of the foot involves the study of navicular in the foal by Bowker et al, which did demonstrate occasional nerve fibers innervating the articular cartilage.

Materials and Methods

In this study, the navicular from ten cadaveric feet will be dissected free along with its blood supply which has been characterized previously by Torg et al. The neuroanatomy of the navicular will be investigated with H & E staining by the method described by Antonacci et al. The nerves will then be further characterized by immunohistochemical staining using antibodies against GABA, substance P, and CGRP. Whole mount labeling of the nerve supply will also be performed using diI labeling. These studies will then be repeated on five specimens with known degenerative changes involving the navicular and five specimens from charcot feet involving the navicular.