Functional Anatomy of Palmar Musculature

The palmaris longus (PL) and palmaris brevis (PB) are upper limb muscles considered atavistic remnants of those found in animal species. Despite their use in surgical grafting and tendon transfer procedures, the functional role of the PL and PB have not been investigated comprehensively in vivo. Using a multi-modal experimental approach consisting of indwelling fine wire electromyography (EMG), ultrasonography and immunohistochemical muscle staining techniques, the function of the PL and PB in the hand was evaluated both in in vivo and in situ. The purpose of Study 1 was to determine whether the PL provides synergistic contributions to thenar contractions by recording PL muscle activity using indwelling EMG during thumb movements; and to quantify changes in PL muscle architecture using ultrasonography. This study supports morphological observations indicating the PL acts as an extrinsic hand muscle in enhancing thenar muscle actions. The purpose of Study 2 was to compare the proportion of type I and type II muscle fibers in the abductor pollicis brevis (APB) based on its morphological relationship with the PL tendon for indirect insight into the functional synergy, contractile capacity and digastric arrangement amongst contiguous APB and PL musculature. The results indicate that APB fascicles arranged in a digastric relationship with the PL have greater type II fiber type proportions, which support observations of greater thenar abduction strength attributed to PL musculature. The purpose of Study 3 was to investigate PB EMG activity during dynamic grasping tasks, and to quantify its changes in muscle morphology using ultrasound imaging. The results indicate that the PB is voluntarily activated during prehensile movements of the hand with significant changes in muscle architecture, which supports its proposed protective role as a muscular barrier to neurovasculature within the ulnar canal. The purpose of Study 4 was to histologically examine the PB by determining the proportion of type I and type II muscle fibers using immunohistochemistry. The results indicate that the PB is composed primarily of type I muscle fibers (\u3e70%), which may allow the PB to contract for prolonged durations during repetitive intermittent grasping tasks based on its fiber type profile