Anatomic Localization Of Motor Points And Intramuscular Nerve Endings In Hamstring Muscles

Objective:This study elucidated the location of motor points and intramuscular nerve endings in hamstring muscles.Methods:Fifty lower extremities from fresh cadavers were dissected.The motor points (MPs) where the nerve branch enters the muscle belly and also the proximal and distal limits(PL and DL) where the intramuscular nerve endings were located most proximally-and distally were measured along one x-coordinate which was from superior medial aspect of ischial tuberosity to proximal aspect of medial femoral epicondyle in anatomic position.The motor points were also measured along one y-coordinate,being perpendicular to x-coordinate,which was from superior medial aspect of ischial tuberosity to lateral aspect of greater trochanter.Results:We found the MPs of the long head of biceps femoris were located at 41.5±9.4%(141±33mm) in X-coordinate and 36.3±10.8%(42±11mm) in Y-coordinate,the PL and DL were at 39.7±7.1%(135±29mm) and 72.9±7.0%(249±25mm)in X-coordinate.For short head of biceps femoris the data were 56.2±6.0% (191±23mm),59.7±10.8%(68±11mm),58.9±5.6%(200±35mm)and 80.2±6.9% (288±21mm).for the upper part of the semitendinous,the data were 20.3±5.7% (70±22mm),18.9±5.6%(22±6.0mm),18.6%±6.7%(63±23mm),36.8%±7.5% (126±28mm),and for the lower part were 59.9±6.6%(203±29mm),21.4±9.5% (24±11mm),56.6%±6.5%(193±27mm),79.1%±5.7%(269±25mm).For the semimembranous,the data were 62.2%±9.2%(211±33mm),18.8%±8.0% (21±9mm),55.9%±8.1%(190±29mm),89.1%±5.4%(303±22mm).Conclusion:1.The innervation of hamstring muscles was not randomly variable,but of a general pattern:both the long head of biceps femoris and the semimembranous had only one motor branch.Both the short head of biceps femoris and the semitendinous had two innervation patterns.82%of the long head of biceps femoris was supplied by one motor branch which was the dominant type while 18%received two motor branches.For the semitendinous,86%was innervated by two motor branches which was the dominant type while 14%was innervated by one motor branch.2.This study indicated the precise anatomic location of the motor points.When motor point block is performed,the best sites for injections are as follows:(1) For the long head of biceps femoris:2/5(41.5%) in X-coordinate,4cm in Y-coordinate(2) For the short head of biceps femoris:3/5(56.2%) in X-coordinate,7cm in Y-coordinate(3) For the upper part of the semitendinous:1/5(20.3%) in X-coordinate,2cm in Y-coordinateFor the lower part of the semitendinous:3/5(59.9%) in X-coordinate,2.5cm in Y-coordinate(4) For the semimembranous:3/5(62.2%) in X-coordinate,2cm in Y-coordinate3.This study identified the distribution of the intramuscular nerve endings in each hamstring muscles,the best injection areas for botulinum toxin are as follows:(1) For the long head of biceps femoris:from 2/5(39.7) to 3/4(72.9%) in X-coordinate(2) For the short head of biceps femoris:from 3/5(58.9%) to 4/5(72.9%) in X-coordinate(3) For the upper part of the semitendinous:from 1/5(18.6%) to 1/3(36.8%) in X-coordinateFor the lower part of the semitendinous:from 3/5(59.9%) to 4/5(79.1%) in X-coordinate (4) For the semimembranous:from 3/5(55.9%)to 9/10(89.1%)in X-coordinate...