Histological study of the antebrachial fascia and flexor retinaculum carpi.

Despite growing interest in retinacular structure and function, a comprehensive analysis is still lacking. For some authors, they are simple reinforcements of the fascia, while for others they are distinct structures. Postmortem specimens taken from the antebrachial fascia (AF) and flexor retinaculum carpi (FR) of 20 upper limbs were analyzed with histological (H.E., Weigert-van Gieson, azan-Mallory) and immunohistochemical (anti-S100) stains. The study demonstrated that the AF is formed by numerous layers of collagen fiber bundles and some elastic fibers. In each layer, the bundles are parallel to each other, whereas adjacent layers show different orientations. Each layer is separated from the adjacent one by a thin layer of loose connective tissue. The FR is not separable from the AF by dissection but presents different histological characteristics: the collagen fiber bundles are thicker, while the elastic fibers are almost absent. Muscular fibers from thenar and hypothenar eminences inserted into the FR. Both the AF and the FR showed an abundant innervation, mainly constituted by free nerve endings in the AF and by Ruffini and Pacini corpuscles in the FR. Thus, the FR, although in continuity with AF, may be considered for its peculiar structure and type of innervation as a specific anatomical entity.