When accurately placed, fine-wire electrodes (FWEs) permit selective electromyographic recording during kinesiologic studies; however, their potential to limit contraction of the index finger muscles has not previously been evaluated. Given that these electrodes cannot be reinserted, reliable techniques are necessary to achieve proper placement while minimizing subject discomfort and electrode waste. The small size, close arrangement, and anatomic variability of hand and forearm muscles create challenges to achieving these goals. In this study, we simultaneously measured maximal fingertip forces and fine-wire electromyographic signals from all seven muscles of the index finger. Forces in five directions, with and without FWEs in place, were not statistically different (repeated-measures analysis of variance, P < 0.46) in five healthy adult subjects. To guide electrode placement, we identified skin penetration landmarks, direction of needle advancement, and depth of muscle fibers. Fibers of flexor digitorum superficialis and flexor digitorum profundus to the index finger were more distal than depicted in textbooks, requiring electrode placement at or distal to the midpoint of the forearm. For these muscles and the extensor digitorum, locating the desired fibers first with a monopolar needle electrode facilitated subsequent FWE placement. For the dorsal and palmar interossei, lumbrical, and extensor indicis proprius, insertion was aided by concurrent monitoring of the electromyographic signals. We achieved a 93% success rate during FWE placement in a total of 60 muscles. Techniques for recording from each of the seven index finger muscles are described.
1From the Veterans Affairs Palo Alto Health Care System, Rehabilitation Research and Development Center, Palo Alto, California, and the Divisions of Physical Medicine and Rehabilitation (C.G.B.) and Hand Surgery(V.R.H.), Department of Functional Restoration, and the Division of Biomechanical Engineering (F.J.V.-C.), Department of Mechanical Engineering, Stanford University, Stanford, California.
Supported by the Rehabilitation Research and Development Service, Department of Veterans Affairs.
2 All correspondence and requests for reprints should be addressed to: Rehabilitation Research and Development Center (153), VA Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, California 94304-1207.
1997 Series Number 17