Localization of motor entry points and terminal intramuscular nerve endings of the musculocutaneous nerve to biceps and brachialis muscles

To determine the 3D location of the intramuscular motor nerve endings of the biceps brachii and brachialis, we identified from 56 fresh cadaveric arms the regions where the intramuscular branches were most densely located in relation to a reference line connecting the medial epicondyle of humerus and the coracoid process. For the biceps, these points were most densely distributed at a length from 64.6 to 70.3% point of the reference line with the coracoid process as starting point, at a width of 21.6-32.6 mm lateral to the reference line. For the brachialis muscle, these points were located at a length of 75.4% point and width of 27.1-35.4 mm lateral to the reference line. At these points, the biceps was located at a depth of the upper two-third portion and the brachialis at the lower one-third portion of the upper arm, from skin to humeral bone.