Intramuscular wire electromyography of the subscapularis

Abstract

The action of the subscapularis muscle is an important component in maintaining shoulder stability. Because of its relative inaccessibility, there have been few electromyographic (EMG) studies of its normal patterns of activity. The subscapularis is innervated by two or more distinct nerves, and therefore the upper and lower parts of the muscle may have different functional roles depending on the position of the humerus. The purpose of this study was to develop safe, reproducible insertion paths to the upper and lower parts of the subscapularis. Six subjects with no previous history of shoulder injury were evaluated. The paths of insertion were designed based on previous anatomical studies as well as dissections. Two pairs of intramuscular wire electrodes were inserted: one directed toward the upper subscapularis and one toward the lower subscapularis. Electrode locations were confirmed using posteroanterior and lateral radiographs and through electrical stimulation. EMG data were recorded during isometric internal rotation exercises with the humerus in 0 or 90 degrees abduction. Significant differences were observed in the EMG activity recorded from the two pairs of electrodes. The EMG activity of the upper subscapularis either remained the same or decreased in going from 0 to 90 degrees abduction, while that of the lower subscapularis increased. The observed differential response confirmed that the electrodes were in different parts of the subscapularis. These preliminary results suggest that in future EMG studies, the subscapularis should be considered as at least two independent muscle units.

Hand grip increases shoulder muscle activity: An EMG analysis with static handcontractions in 9 subjects

“…In the supra-and infraspinatus muscles there was a positive correlation between the degree of the shoulder muscle activity and the intensity of the handgrip exertion in most of the tested arm-positions. Several studies have pointed out that some muscles-for instance, the deltoid muscle (Michiels and Bodem 1992), the trapezius muscle (Inman et al 1944, Jensen 1995, and the subscapularis muscle (Kadaba et al 1992)-should be regarded not as single muscles but rather as functional units which work on their own to a large extent. Recent studies have shown a complex interaction between the shoulder muscles in shoulder joint movements (Pearl et al 1992, Keating et al 1993.…”

Electromyographic assessment of muscle fatigue in massive rotator cuff tear

“…Disposable, self-adhesive pre-gelled Ag/AgCl bipolar electrodes with conducting area of 10mm diameter and inter-electrode distance of 20mm (Noraxon Inc., Arizon, USA) were used to record the EMG from anterior, middle, and posterior deltoid (AD, MD, PD), pectoralis major (PM), upper trapezius (UT), serratus anterior (SA), latissimus dorsi (LD), teres major (TM), brachioradialis (BR) and biceps brachii (BB) according to guidelines [Caldwell et al, 1993;Gartsman, 1997;Kadaba et al, 1992;SENIAM]. Skin preparation involved shaving and application of abrasive paste (Nuprep, Weaver and Company, Aurora, USA).…”

Effects of hand grip strength on shoulder muscle activity in breast cancer patients

“…A research reported that the rest rotator cuff related muscles as well as the supraspinatus contributed to the movement in abduction [21], and many pre-vious researches reported that not a single muscle but a functional unit performed movements in conducting a task [22][23][24].…”