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Rathi S.1,2, Taylor N.1, Green R.3
1La Trobe University, Melbourne, Australia, 2St John of God Healthcare, Bendigo, Australia, 3La Trobe University, Bendigo, Australia
Background: The function of rotator cuff muscles in limiting glenohumeral translation in young healthy shoulders has been established in a previous study using real time ultrasound (RTUS) and electromyography (EMG). This method of measurement needs to be tested in patients with rotator cuff pathology to determine whether pathology of these muscles affects the shoulder movements, specifically glenohumeral joint translations.
Purpose: The aims were to determine whether
(1) patients with rotator cuff pathology have more glenohumeral laxity than controls with and without rotator cuff isometric contraction and
(2) the pattern of rotator cuff muscle activity is different in patients in comparison to controls.
(1) patients with rotator cuff pathology have more glenohumeral laxity than controls with and without rotator cuff isometric contraction and
(2) the pattern of rotator cuff muscle activity is different in patients in comparison to controls.
Methods: Forty participants were included in the study; 20 with a diagnosed rotator cuff tear (pathology group:
12 supraspinatus tears, 7 mixed supraspinatus and subscapularis tears, 1 full rotator cuff tear) and 20 age- and gender-matched control participants. Intramuscular electrodes were inserted in the rotator cuff muscles. Anterior and posterior glenohumeral translations were measured using RTUS in two positions (shoulder neutral, abduction), two views (anterior, posterior) and six testing conditions (rest, isometric internal rotation (IR), isometric external rotation (ER), passive accessory motion testing (PAMT), PAMT with IR and PAMT with ER). A standardised PAMT force (60N) was applied by an assistant to the glenohumeral joint in anteroposterior and posteroanterior directions.
To assess whether there were significant differences in glenohumeral laxity with and without rotator cuff isometric contraction a series of analysis of variance (ANOVAs) were conducted. As all injured participants had a supraspinatus tear, a planned comparison of supraspinatus EMG activity between groups was performed using ANOVAs.
Results: The pathology group demonstrated increased translation with internal rotation contraction as compared to external rotation, with anteroposterior PAMT force in neutral position (interaction effect, p 0.05). There was also increased translation in the pathology group compared to the control group in the abducted posterior position with PAMT force (no rotator cuff contraction) (p 0.05) that also approached significance in neutral posterior position (p=0.06). Across both groups there was reduced glenohumeral translation with rotator cuff muscle contraction in all positions (main effect, p 0.05). There was reduced supraspinatus muscle EMG activity in the pathology group compared to the control group in abducted posterior position (p 0.04).
Conclusion(s): Our results suggest that patients with rotator cuff pathology have increased glenohumeral translation both when a PAMT force was applied alone, and when it was applied with internal rotation isometric contraction in the neutral posterior position when compared to age-matched controls. Along with the finding of reduced muscle activity in the pathological muscle (supraspinatus), specifically in neutral posterior and abducted posterior positions, these results suggest that patients with rotator cuff pathology may be demonstrating signs of glenohumeral laxity and impaired motor control.
Implications: Although patients with rotator cuff injury are still able to reduce glenohumeral translation with rotator cuff muscle contraction they may have impaired motor control as demonstrated by increased glenohumeral translation in response to PAMT forces. These results provide insights that may inform rehabilitation strategies aiming to enhance glenohumeral stability.
Funding acknowledgements: None
Topic: Musculoskeletal: peripheral
Ethics approval: This project was approved by La Trobe University Human Ethics Committee (ref. no: 14-079).
All authors, affiliations and abstracts have been published as submitted.
