OBJECTIVEReport on the intramuscular innervation and vascular supply of the flexor carpi ulnaris (FCU) and the flexor carpi radialis (FCR), the musculo tendon architecture, i.e., the physiological cross-sectional area and fiber length; and explore the possibility of splitting FCU and FCR into 2 parts with individual independent function.

METHODSAnatomic study, angiogram and Sibler's staining technique were carried on human and monkey cadavers. The electric stimulation study was used to reveal independent contraction of each part on monkey FCU and FCR.

RESULTSIt was found that the innervation and blood supply of FCU and FCR come primarily from the proximal neurovascular pedicles. The primary nerve and vascular branch supplying the muscles were divided into 2 subbranches and inserted the proximal quarter of the muscle belly. Then each of the nerve and blood subbranches mn parallel to the central tendon on each side supplying the radial and ulnar compartments of FCU and FCR toward the distal musculotendinous junction. Independence of function of each compartment was confirmed in electrical stimulation studies in primate FCU and FCR. The results of each compartment of the human FCU and FCR architectures were measured and compared with the extensor pollicis longus and the extensor digitorum communis to the index, middle, ring, and small.

CONCLUSIONSBoth FCU and FCR can be split from the distal to the proximal along its tendon into 2 independently functioning neuromuscular compartments. Both radial compartment and ulnar compartment have its own nerve and adequate blood supply. And the study provides useful information for enabling the local transfer of the two muscles as a whole or two separate compartments, both for resurfacing skin soft-tissue defects and for functional tendon transfer.