Anatomic localization of motor entry points and intramuscular nerve endings in the hamstring muscles

To elucidate the location of motor entry points (MEPs) and intramuscular nerve endings of the hamstring muscles.

We dissected 50 cadaveric lower extremities to identify the MEPs, where the nerve branch first pierced the muscle belly, and the proximal and distal limit points (PLPs and DLPs, respectively) of the terminal intramuscular nerve endings. These points were measured in relation to a reference line, expressed in x-coordinate, which connected the superior medial aspect of ischial tuberosity to the proximal aspect of the medial femoral epicondyle. We also expressed the MEP in y-coordinate, which is perpendicular to the x-coordinate connecting the superior medial aspect of ischial tuberosity to the lateral aspect of the greater trochanter. Finally, these distances were translated into percentage distances in relation to the total length of the reference lines and their mean values were calculated.

For the long head of biceps femoris muscles, the MEPs were located at 41.5 and 36.3% distance of the x and y coordinates, while the PLP and DLP were located at 39.7 and 72.9% distance of the x-coordinate. For the short head, the corresponding data were 56.2, 59.7, 58.9 and 80.2%. The semitendinosus showed two innervations zones; the data for the upper and lower zones were 20.3, 18.9, 18.6, 36.8% and 59.9, 21.4, 56.6, 79.1%, respectively. For the semimembranosus, the data were 62.2, 18.8, 55.9 and 89.1%.

The parameters provided from this study should help increase the efficacy and precision of motor point injections to the hamstring muscles.