Precise localization of the motor nerve branches to the hamstring muscles: An aid to the conduct of neurolytic procedures

Objective: To identify the precise locations of the motor branches and motor points to the hamstring musculature and define these locations in relation to bony landmarks. Design: Descriptive study of adult cadaver limb dissection. The number, location, and course of the motor branches and motor points to each hamstring muscle from the sciatic nerve were defined relative to bony landmarks. Setting: Department of anatomy at a university school of medicine. Participants: Anatomic dissection of 30 adult cadaver limbs (17 individuals) was completed. Adult cadavers were selected randomly without regard to gender, age, and race. Exclusion criteria included femoral fracture, surgery, inability to obtain neutral position, and posterior thigh trauma. Main Outcome Measure: A descriptive anatomic study based on linear measures in centimeters from bony landmarks. Results: Two zones located along a line from the ischial tuberosity to the lateral femoral condyle were observed to exist. Zone one, containing the first motor branch to the biceps long head and semitendimosus, is found at approximately 20% (6.9cm ± 1.8 and 7.1cm ± 2.2 from the ischial tuberosity, respectively) of femur length along the stated line. Zone two, containing the primary branch to the semimembranosus and the secondary branches to the biceps and semitendinosus, is found at approximately 33% (13.1cm ± 3.6, 12.6cm ± 3.9, and 14.3cm ± 3.9 from the ischial tuberosity, respectively) of femur length. Conclusions: The drawing of one surface line, when combined with our anthropometric observations, should increase the ease and accuracy with which motor branch blocks to the hamstrings are performed.