Shoulder electromyography in multidirectional instability

doi:10.1016/j.jse.2003.09.005

Journal of Shoulder and Elbow Surgery

Volume 13, Issue 1, January–February 2004, Pages 24-29

https://doi.org/10.1016/j.jse.2003.09.005 Get rights and content

Abstract

We studied shoulder muscle activity in multidirectional instability (MDI) and multidirectional laxity (MDL) of the shoulder, our hypothesis being that altered muscle activity plays a role in their pathogenesis. Six muscles (supraspinatus, infraspinatus, subscapularis, anterior deltoid, middle deltoid, and posterior deltoid) were investigated by use of intramuscular dual fine-wire electrodes in 7 normal shoulders, 5 MDL shoulders, and 6 MDI shoulders. Each subject performed 5 types of exercise (rotation in neutral, 45° of abduction, 90° of abduction, flexion/extension, and abduction/adduction) on an isokinetic muscle dynamometer at two rates, 90°/s and 180°/s. After filtering, rectification, and smoothing, the electromyography signal was normalized by using the peak voltage of the movement cycle. In subjects with MDI, compared with normal subjects, activity patterns of the anterior deltoid were different during rotation in neutral and 90° of abduction, whereas those of the middle and posterior deltoid were different during rotation in 90° of abduction. In subjects with MDL, the posterior deltoid showed increased activity compared with normal subjects during adduction. Activity patterns of the supraspinatus, infraspinatus, and subscapularis appeared similar in both groups. Dual fine-wire electromyography offers insight into the complex role of shoulder girdle muscle function in normal movement and in instability. Altered patterns of shoulder girdle muscle activity and imbalances in muscle forces support the theory that impaired coordination of shoulder girdle muscle activity and inefficiency of the dynamic stabilizers of the glenohumeral joint are involved in the etiology of MDI. Interestingly, the abnormalities are in the deltoid rather than the muscles of the rotator cuff.

Section snippets

Methods

Studies were performed on 7 normal shoulders from 7 individuals with a mean age of 29 years (range, 25-34 years), body mass of 77 kg (range, 54-90 kg), and height of 177 cm (range, 165-186 cm); 5 MDL shoulders from 4 individuals with a mean age of 27 years (range, 20-35 years), body mass of 68 kg (range, 60-72 kg), and height of 175 cm (range, 160-184 cm); and 6 MDI shoulders from 6 individuals with a mean age of 27 years (range, 19-33 years), body mass of 60 kg (range, 48-84 kg), and height of

EMG data

The patterns of activity of the rotator cuff muscles (supraspinatus, infraspinatus, and subscapularis) were similar in all three groups for each exercise (results not shown). The differences lay in the three components of the deltoid. We take these separately.

Figure 1 shows that the activity pattern of the middle deltoid was different for subjects with MDI (squares) during exercise 5 (external/internal rotation in 90° of shoulder abduction at a velocity of 90°/s), showing an earlier decrease

Discussion

The stability of the glenohumeral joint is attributed both to the static effect of ligaments and tendons and to dynamic mechanisms associated with muscular contraction.6, 17 It is thought that impaired coordination of shoulder girdle muscle activity and a loss of the efficiency of the dynamic stabilizers of the glenohumeral joint may have an important role in the etiology of MDI.10, 11 Fine-wire EMG offers a unique way of measuring electrical activity of the muscle of the shoulder girdle. In

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Muscle activity and scapular kinematics in individuals with multidirectional shoulder instability: A systematic review
2021, Annals of Physical and Rehabilitation Medicine
Citation Excerpt :
Because these rotator cuff muscles create compressive forces that prevent excessive glenohumeral translations [23,44,45], their increased or prolonged activity presumably reflects an attempt to control the humeral head better and longer [46]. By contrast, 3 other studies could not confirm the increased/prolonged involvement of the supraspinatus or infraspinatus [35,39,40]. In these studies, the sample sizes may have been too small (respectively 7, 10, and 6 participants) [35,39,40], and in Sciascia et al. [39] and Morris et al. [40], the number of included groups too large to detect differences between the MDI and control group for these muscles (4 and 3 groups, respectively).
Several studies reported the importance of glenohumeral and scapular muscle activity and scapular kinematics in multidirectional shoulder instability (MDI), yet a systematic overview is currently lacking.
This systematic review evaluates and summarizes the evidence regarding muscle activity and shoulder kinematics in individuals with MDI compared to healthy controls.
The electronic databases PubMed and Web of Science were searched in September 2020 with key words regarding MDI (population), muscle activity, and glenohumeral and scapular movement patterns (outcomes). All studies that compared muscle activity or scapular kinematics between shoulders with MDI and healthy shoulders were eligible for this review, except for case reports and case series. All articles were screened on the title and abstract, and remaining eligible articles were screened on full text. The risk of bias of included articles was assessed by a checklist for case–control data, as advised by the Cochrane collaboration.
After full text screening, 12 articles remained for inclusion and one study was obtained by hand search. According to the guidelines of the Dutch Institute for Healthcare Improvement, most studies were of moderate methodological quality. We found moderate evidence that MDI individuals show increased or prolonged activity of several rotator cuff muscles that control and centre the humeral head. Furthermore, we found evidence of decreased and/or shortened activity of muscles that move or accelerate the arm and shoulder girdle as well as increased and/or lengthened activity of muscles that decelerate the arm and shoulder girdle. The most consistent kinematic finding was that MDI individuals show significantly less upward rotation and more internal rotation of the scapula during elevation of the arm in the scapular plane as compared with controls. Finally, several studies also suggest that the humeral head demonstrates increased translations relative to the glenoid surface.
There is moderate evidence for altered muscle activity and altered humeral and scapular kinematics in MDI individuals as compared with controls.
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Pathologic activation pattern of muscles can cause shoulder instability. We propose to call this pathology functional shoulder instability (FSI). The purpose of this prospective study was to provide an in-detail description of the characteristics of FSI.
In the year 2017, a total of 36 consecutive cases of FSI presenting to our outpatient clinic were prospectively collected. Diagnostic investigation included a pathology-specific questionnaire, standardized clinical scores, clinical examination, psychological evaluation, video and dynamic fluoroscopy documentation of the instability mechanism, as well as magnetic resonance imaging (MRI). In a final reviewing process, the material from all collected cases was evaluated and, according to the observed pattern, different subtypes of FSI were determined and compared.
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FSI can be classified into 4 subtypes based on pathomechanism and volitional control. Depending on the subtype, patients show different degrees of functional impairment. The majority of patients suffer from unidirectional posterior FSI.
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Citation Excerpt :
Congenital factors may contribute to bilateral shoulder involvement in MDI patients.46 Patients with MDI have altered neuromuscular control of the glenohumeral joint and scapula when compared with normal controls18,57-60 and typically have scapulae that sit in downward rotation and display reduced scapular upward rotation through range.4,34,57,61 This phenomenon causes a relative absence of effective depth of the humeral head on the glenoid at rest, and as the arm is elevated, resulting in an increase in the inferior joint instability.4,42,60
Multidirectional instability of the shoulder is a type of glenohumeral joint shoulder instability. There are discrepancies in the definition and classification of this condition, which can make diagnosis and treatment selection challenging. Knowledge of contributing factors, the typical clinical presentation, and current best evidence for treatment options can assist in the diagnosis and appropriate treatment selection for this pathology. The purpose of this article is to present an overview of the current literature regarding the etiology, classification, assessment, and management of multidirectional instability of the glenohumeral joint.

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^☆: This work was supported by a Laming Evans Research Fellowship awarded to A.D.M. by the Royal College of Surgeons of England, as well as a grant from the Wishbone Trust.

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Original articleShoulder electromyography in multidirectional instability☆

Abstract

Section snippets

Methods

EMG data

Discussion

J Biomech

J Shoulder Elbow Surg

J Shoulder Elbow Surg

J Shoulder Elbow Surg

J Electromyogr Kinesiol

J Shoulder Elbow Surg

Muscles alive. Their functions revealed by electromyography

Treatment of instability of the shoulder with an exercise program

J Bone Joint Surg Am

Original article
Shoulder electromyography in multidirectional instability☆