Anatomic localization of motor points for the neuromuscular blockade of hand intrinsic muscles involved in thumb-in-palm

Objective: To determine the location of the motor points and intramuscular branches for the muscles Involved in thumb-In-palm and the abductor pollicis brevis muscle, the latter of which, because of its anatomic proximity, may be inadvertently blocked. Design: Hand intrinsic muscles from 20 fresh cadavers were dissected. The point of nerve entry to the muscle belly and the points where the intramuscular endings were located most proximally and distally were defined in relation to a reference line connecting the hook of hamate and the head of the first metacarpal bone. Results: We were able to define a region, located from 66.08% +/- 8.67% to 70.28% +/- 10.62% of the reference line, with the hook of hamate as starting point, where intramuscular endings for the thumb-in-palm muscles were dense and farther from the intramuscular endings for the abductor pollicis brevis. The region around 40% of the reference line was the point where the intramuscular endings were most dense for the abductor pollicis brevis. Conclusion: The results may provide guidelines that could help in localizing the appropriate points for the neuromuscular blockade of thumb-in-palm muscles and, at the same time, help in minimizing the inadvertent block of the abductor pollicis brevis.