An anatomical study of the superficial palmar communicating branch between the median and ulnar nerves

The palmar communicating branch between the median and ulnar nerves was investigated in 98 hands with the aim of outlining its most common branching patterns and describing its relationship to well-defined anatomical landmarks, including the bistyloid line, wrist crease and flexor retinaculum. Five branching patterns were identified and classified based on their proximal and distal attachments. The palmar communicating branch was found to lie between 26%–79% of the total distance between the metacarpophalangeal joint of the long finger and the wrist crease, and 35%–75% of the total distance between the metacarpophalangeal joint of the long finger and the middle of the bistyloid line. With the aid of the morphometric indices obtained from this study, a risk area where the palmar communicating branch is most likely to be found is outlined. Knowledge of the branching patterns and location of the palmar communicating branch can help clinicians to better assess variations in the patterns of sensation, preserve the nerve during surgical interventions to the palm and better assess post-operative complications involving the branch

A systematic method to quantify the presence of cross-talk in stimulus-evoked EMG responses: Implications for TMS studies

Surface electromyography (EMG) responses to noninvasive nerve and brain stimulation are routinely used to provide insight into neural function in humans. However, this could lead to erroneous conclusions if evoked EMG responses contain significant contributions from neighboring muscles (i.e., due to “cross-talk”). We addressed this issue with a simple nerve stimulation method to provide quantitative information regarding the size of EMG cross-talk between muscles of the forearm and hand. Peak to peak amplitude of EMG responses to electrical stimulation of the radial, median, and ulnar nerves (i.e., M-waves) were plotted against stimulation intensity for four wrist muscles and two hand muscles (n = 12). Since electrical stimulation can selectively activate specific groups of muscles, the method can differentiate between evoked EMG arising from target muscles and EMG cross-talk arising from nontarget muscles. Intramuscular EMG responses to nerve stimulation and root mean square EMG produced during maximal voluntary contractions (MVC) of the wrist were recorded for comparison. Cross-talk was present in evoked surface EMG responses recorded from all nontarget wrist (5.05–39.38% Mmax) and hand muscles (1.50–24.25% Mmax) and to a lesser degree in intramuscular EMG signals (∼3.7% Mmax). The degree of cross-talk was comparable for stimulus-evoked responses and voluntary activity recorded during MVC. Since cross-talk can make a considerable contribution to EMG responses in forearm and hand muscles, care is required to avoid misinterpretation of EMG data. The multiple nerve stimulation method described here can be used to quantify the potential contribution of EMG cross-talk in transcranial magnetic stimulation and reflex studies