Anatomical partitioning of three human forearm muscles

Anatomical partitioning has been found in the human biceps brachii, extensor carpi radialis longus and flexor carpi radialis muscles. The purpose of this study was to determine if the human extensor carpi ulnaris, flexor carpi ulnaris and flexor digitorum profundus are anatomically partitioned. Evidence for or against anatomical partitioning was obtained by observation of the architectural and innervation characteristics of each of the investigated muscles. Twelve samples (11 were used for extensor carpi ulnaris) of each specific muscle type were harvested from perfused human cadavers. The architectural characteristics of tendinous boundaries, muscle fiber direction, and muscle fiber angle magnitude were observed, measured and documented. Microdissection technique was used to investigate the primary nerve branching pattern throughout each muscle. A primary nerve branch to a specific muscle region indicated possible partitioning by innervation. The extensor carpi ulnaris was found to have a variable number of primary nerve branches. The extensor carpi ulnaris may have four partitions by innervation alone or three congruent partitions by innervation and muscle fiber architecture. The nerve to the flexor carpi ulnaris clearly innervates two architectural partitions within the muscle. The innervation pattern to the flexor carpi ulnaris is congruent with muscle fiber architecture characteristics indicating consistent anatomical partitioning within the flexor carpi ulnaris. Two muscle nerves innervate the flexor digitorum profundus with branches innervating the medial and lateral regions of the muscle. Up to eight architectural partitions were found in a medial-to-lateral direction.