Pain does not explain reduced teres major co-contraction during abduction in patients with Subacromial Pain Syndrome. (January 2022)

• Record Type: Journal Article
• Authors: Overbeek, Celeste L.; Kolk, Arjen; de Witte, Pieter Bas; Nagels, Jochem; Nelissen, Rob G.H.H.; de Groot, Jurriaan H.
• Is Part Of: Clinical biomechanics. Volume 91(2022)
• Publication Date: 2022-01
• Subjects: Subacromial impingement -- Shoulder -- Subacromial Pain Syndrome -- Electromyography -- Co-contraction -- Teres major; Biomechanics -- Periodicals; Osteopathic medicine -- Periodicals; Biomechanics -- Periodicals; Osteopathic Medicine -- Periodicals; 612.76
• DOI: 10.1016/j.clinbiomech.2021.105548
• Languages: English
• ISSNs: 0268-0033

Abstract

Abstract: Background: Patients with Subacromial Pain Syndrome show reduced co-contraction of the teres major during abduction. Consequent insufficient humeral depressor function may contribute to painful irritation of subacromial tissues and offers a potential target for therapy. A crucial gap in knowledge is whether the degree of teres major co-contraction in these patients is influenced by pain itself. To gain insight into this matter, we assessed whether relief of subacromial pain with local analgesics leads to increased adductor co-contraction in 34 patients with subacromial pain. Methods: In a single-arm interventional study with 34 patients, electromyographic activity of the latissimus dorsi, pectoralis major, teres major and deltoid was assessed during isometric force tasks in 24 directions before and after subacromial Lidocaine injection. Co-contraction was quantified using the activation ratio; range [−1 (sole antagonistic activation, i.e. co-contraction) to 1 (sole agonistic activation)]. Findings: There were no changes in activation ratio of the teres major after the intervention ( Z -score: −0.6, p = 0.569). The activation ratio of the latissimus dorsi increased to 0.38 (quartiles: 0.13–0.76), indicating decreased co-contraction ( Z -score: −2.0, p = 0.045). Interpretation: Subacromial analgesics led to a decrease in co-contraction of the latissimus dorsi, whereas no change in the degree of teres major co-contraction was observed. This study shows that decreased teres major co-contraction in patients with subacromial pain, likely is not the consequence of pain itself, opening a window for physical therapy with training of teres major co-contraction to reduce subacromial irritation and pain. Level of evidence: Level II treatment study. Highlights: Patients with subacromial pain have less teres major co-contraction than controls. Teres major co-contraction may reduce subacromial pain by humeral head depression. Subacromial pain has no influence on the degree of teres major co-contraction. This may open a window for evidence-based physiotherapy with teres major training.