Elsevier

Manual Therapy

Volume 11, Issue 3, August 2006, Pages 231-237
Manual Therapy

Original article
Pathological muscle activation patterns in patients with massive rotator cuff tears, with and without subacromial anaesthetics

https://doi.org/10.1016/j.math.2006.07.004Get rights and content

Abstract

A mechanical deficit due to a massive rotator cuff tear is generally concurrent to a pain-induced decrease of maximum arm elevation and peak elevation torque. The purpose of this study was to measure shoulder muscle coordination in patients with massive cuff tears, including the effect of subacromial pain suppression.

Ten patients, with MRI-proven cuff tears, performed an isometric force task in which they were asked to exert a force in 24 equidistant intervals in a plane perpendicular to the humerus. By means of bi-polar surface electromyography (EMG) the direction of the maximal muscle activation or principal action of six muscles, as well as the external force, were identified prior to, and after subacromial pain suppression.

Subacromial lidocaine injection led to a significant reduction of pain and a significant increase in exerted arm force. Prior to the pain suppression, we observed an activation pattern of the arm adductors (pectoralis major pars clavicularis and/or latissimus dorsi and/or teres major) during abduction force delivery in eight patients. In these eight patients, adductor activation was different from the normal adductor activation pattern. Five out of these eight restored this aberrant activity (partly) in one or more adductor muscles after subacromial lidocaine injection.

Absence of glenoid directed forces of the supraspinate muscle and compensation for the lost supraspinate abduction torque by the deltoideus leads to destabilizating forces in the glenohumeral joint, with subsequent upward translation of the humeral head and pain. In order to reduce the superior translation force, arm adductors will be co-activated at the cost of arm force and abduction torque.

Pain seems to be the key factor in this (avoidance) mechanism, explaining the observed limitations in arm force and limitations in maximum arm elevation in patients suffering subacromial pathologies. Masking this pain may further deteriorate the subacromial tissues as a result of proximal migration of the humeral head and subsequent impingement of subacromial tissues.

Introduction

Muscle activation patterns (coordination) are bound to change after mechanical deficits like massive rotator cuff tears. Subacromial injection with lidocaine reduces pain and has been shown to coincide with an increase in active forward flexion and muscle strength in patients with specific subacromial disorders like impingement (Ben Yishay et al., 1994). In a comparable intervention it was found that patients with massive rotator cuff tears were well capable of arm abduction despite the absence of supraspinatus force, but were actively hampered to do so due to pain (van de Sande et al., 2006; de Groot et al., 2006). Their findings also showed that supraspinatus muscle force was not per se required to produce the necessary glenohumeral abduction torque.

Both series used active and isometric loading by a constant force in a direction rotating perpendicular around the longitudinal axis of the humerus. This so-called principal action method made it possible to define the direction of maximum muscle activation, in combination with the additional compensating muscle activity needed to produce force in exactly that direction (Flanders and Soechting, 1990; Arwert et al., 1997; de Groot et al., 2004; Meskers et al., 2004). The principal action method quantifies shoulder muscle contributions during an isometric force task and facilitates the analysis of the activation patterns of shoulder muscles.

This study was set up to analyse shoulder muscle coordination using the principal action method in patients with massive cuff tears. We analysed activation patterns prior to and after subacromial anaesthetics. In addition to de Groot et al. (2006) we addressed more muscles in order to explain the observed enhancement of external arm force, viz.; the deltoideus (three parts), the latissimus dorsi, the pectoralis major pars clavicularis and the teres major.

Section snippets

Subjects

Six male and four female patients (Table 1) with an average age of 61 years (SD=8) with MRI-proven massive rotator cuff tears were included in the study. All patients were informed and signed informed consent.

Procedure

The principal muscle activation patterns of six muscles were recorded as described by de Groot et al. (2004), and Meskers et al. (2004). Patients were seated with their injured arm in a splint with the humerus positioned in 30° of forward rotation relative to the frontal plane, about 45°

Results

Subacromial lidocaine injection led to an average significant reduction on the VAS scale (p=0.05), from 7.7 (SD 1.2) to 0.9 (SD 1.6), indicating a strong reduction in pain, although some patients still experienced pain after treatment (Fig. 2a). The exerted arm force during the task could significantly be increased by factor 1.6 (p=0.05) after pain reduction, from 10.4 N (SD 5.7) to 15.7 N (SD 7.4) (Fig. 2b). Patient no. 7 did not respond to the lidocaine injection on any of the three outcome

Discussion

As reported earlier (van de Sande et al., 2006; de Groot et al., 2006) and in agreement with impingement (Ben Yishay et al., 1994), external forces increased significantly after subacromial lidocaine injection in patients with massive rotator cuff tears, despite the (partially) absent supraspinatus forces.

The lidocaine intervention did lead to large changes in principal action, but not consistent for all subjects and therefore not significant for the whole patient group. No statistical

References (9)

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