In the young and healthy shoulder, cranially directed forces during abduction are counteracted by co-contraction of the rotator cuff muscles. In this way, it is prevented that the humerus moves... Show moreIn the young and healthy shoulder, cranially directed forces during abduction are counteracted by co-contraction of the rotator cuff muscles. In this way, it is prevented that the humerus moves cranially towards the acromion, thus entrapping subacromial tissues. During ageing however, shoulder tissues are subject to marked degeneration, which particularly concerns the rotator cuff muscles. This may have two consequences. First, due to reduced contribution of the upper parts of the rotator cuff to the abduction movement, the deltoid has to compensate, which results in a more cranially, instead of mediocranially directed force. Second, reduced stabilising force by the rotator cuff may jeopardise counteraction of cranial deltoid forces. These changes could lead to cranialisation of the humerus with painful compression of subacromial tissues, as observed in patients with Subacromial Pain Syndrome (SAPS). Previous studies have shown that by co-contraction of arm adductors, humeral-head depression may be accomplished, for the purpose of unloading subacromial tissues. In this thesis, we investigated the role of adductor co-contraction in the ageing asymptomatic population and in patients with SAPS. This has resulted in eight scientific publications with which the fundaments for evidence-based therapy in SAPS have been built, with as cornerstone training of adductor co-contraction. Show less
Overbeek, C.; Kolk, A.; Witte, P.B. de; Nagels, J.; Nelissen, R.G.H.; Groot, J. de 2022
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... Show moreBackground: 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. Show less
