Anatomy of the deep fascia of the upper limb. Second part: study of innervation.

Analysis of specimens taken from different areas of the deep fascia in 20 upper limbs was made in order to establish which kind of nerve fibres and endings are present in the deep muscular fascia. The flexor retinaculum and the lacertus fibrosus were also evaluated because they are anatomically hardly separable from the deep muscular fascia, although they have different functions. In particular, specimens were taken at the level of: (a) the expansion of pectoralis major onto the bicipital fascia, (b) the middle third of the brachial fascia, (c) the lacertus fibrosus, (d) the middle third of the antebrachial fascia, (e) the flexor retinaculum. This study demonstrated an abundant innervation of the fascia consisting in both free nerve endings and encapsulated receptors, in particular, Ruffini and Pacini corpuscles. However, differences in innervation were verified: the flexor retinaculum was resulted the more innervated element whilst lacertus fibrosus and the pectoralis major expansion the less innervated. These results suggest that the retinaculum has more a perceptive function whereas the tendinous expansions onto the fascia have mostly a mechanical role in the transmission of tension. The hypothesis that the fascia plays an important role in proprioception, especially dynamic proprioception, is therefore advanced. In fact, the fascia is a membrane that extends throughout the whole body and numerous muscular expansions maintain it in a basal tension. During a muscular contraction these expansions could also transmit the effect of the stretch to a specific area of the fascia, stimulating the proprioceptors in that area.