A new technique for the selective recording of extensor carpi radialis longus and brevis EMG

Tennis Elbow or Lateral Epicondylalgia is manifested by pain over the regio n of the lateral epicondyle of the humerus, related to use of the wrist ext ensor muscles. Extensor carpi radialis longus (ECRL) and brevis (ECRB) have been implicated in the dysfunction associated with Lateral Epicondylalgia. For muscles in the human forearm, particularly those in close proximity, s elective recordings are nearly impossible without the use of fine wire, ind welling electrodes. These can be inserted in precise locations and have sma ll recording areas. Standard electromyography texts indicate, however, that the activity of ECRL and ECRB cannot be distinguished, even with intramusc ular electrodes. We present a new technique for determining the most approp riate sites at which to insert intramuscular electrodes for selective recor dings of ECRB and ECRL, The location of ECRB and ECRL was measured on 10 ca daver specimens, 5 right arms and 5 left arms. The distance from the muscle origin to (1) insertion, (2) largest portion of the muscle belly, (3) most proximal fibres and (4) most distal fibres were measured and expressed rel ative to forearm length. The mean distance and 95% confidence interval was calculated for each of the four measures. These data indicated a significan t separation of the belly of each muscle along the length of the forearm. T hese relative distances were used to mark electrode insertion points on thr ee volunteers. Fine wire electrodes were used to record the electromyogram in three participants. Each participant was required to perform isometric c ontractions to produce (1) wrist extension torque, (2) radial deviation tor que, (3) elbow flexion torque and (4) finger extension. The electromyograph ic recordings show clear differentiation of ECRB and ECRL with the relative activation patterns reflecting the underlying anatomical organisation of t he two muscles. This technique provides an important objective method that can be used in conjunction with manual muscle testing to provide a means of ensuring accurate intramuscular electromyographic recording from these two muscles. (C) 2000 Elsevier Science Ltd. All rights reserved.