Title: CORR Insights®: Compensatory Movement Patterns Are Based on Abnormal Activity of the Biceps Brachii and Posterior Deltoid Muscles in Patients with Symptomatic Rotator Cuff Tears
Abstract: Where Are We Now? As clinicians, we have a poor understanding of why some patients with rotator cuff tears have pain and loss of function, while others have pain but seemingly good function, and still others have no pain and good function [7], despite having full-thickness rotator cuff tears [9]. Are some patients able to use compensatory muscles to overcome their rotator cuff deficits? Do some patients exhibit higher pain thresholds than others? Does the long head of the biceps brachii muscle have a say in all of this? We really don’t have good answers to any of these questions. However, we do know that a full-thickness rotator cuff tear alone does not fully explain patients’ symptoms of pain or weakness [12]. We also know that patients who undergo rotator cuff repairs and have incompletely healed or re-torn tendons consistently demonstrate improvements in pain and function [11]. There is a well-known association between pathologic findings of the long head of the biceps brachii and supraspinatus rotator cuff tears [14]. We also know that patients with rotator cuff tears who undergo tenotomy and tenodesis of the long head of the biceps have alleviated pain without an adverse effect on their strength or function [3]. Patients with rotator cuff tears respond differently to physical therapy and many compensate well. Additionally, many can avoid surgical repair altogether [1, 8]. Lastly, published data suggest that the biceps brachii, deltoid, and surrounding musculature have increased activity in patients with symptomatic rotator cuff tears [2, 4-6, 10]. In this issue of Clinical Orthopaedics and Related Research®, Veen et al. [13] compared patients who had symptomatic chronic rotator cuff tears with age-matched controls who had no shoulder pain or rotator cuff tears, as confirmed on imaging. Using EMG, they found that patients with symptomatic rotator cuff tears demonstrated hyperactivity of the posterior deltoid and biceps brachii muscles during shoulder elevation. There was decreased activity in these patients during the downward phase of shoulder motion. The posterior deltoid functioned less in conjunction with the remaining deltoid, and the intact portion of the rotator cuff demonstrated lower coactivation in these patients than in the control group. Based on this, surgeons might consider focusing physical therapy on addressing the biceps and posterior deltoid in patients with rotator cuff tears. Where Do We Need To Go? As exciting as this study is, many questions remain. What is it about the biceps and posterior deltoid that causes them to increase activity in patients with painful rotator cuff tears? Do they help to compensate for the loss of function of the torn supraspinatus tendon in some way? Are they responsible for pain and loss of function? Future studies should seek to determine whether the two muscles’ increased activation is helpful or a secondary effect of pain and weakness, because currently we don’t know whether this activation also occurs in patients with asymptomatic rotator cuff tears. Do patients who have good compensation for their rotator cuff tear with no pain and well-preserved function also have increased biceps brachii and posterior deltoid activity, without the activation of other surrounding muscles in compensation? There’s much we don’t know about the biceps brachii and its long head. What are the effects of a biceps tenotomy or tenodesis? If the tendon is important as a secondary humeral head depressor, then why do patients report improved pain and function after surgery? Are patients with rotator cuff tears more likely to experience proximal humeral migration after biceps tenotomy or tenodesis? Does removing the long head from the intraarticular space affect the likelihood of healing after rotator cuff repair? Should we stop removing the long head of the biceps from the intraarticular space? We also need to understand how physical therapy to strengthen or better coordinate the biceps and posterior deltoid may affect shoulder function in a patient with a rotator cuff tear or those undergoing repair. Can rehabilitation of those muscles prevent or minimize the chance of a rotator cuff tear from happening in the first place? Do the biceps and posterior deltoid actually help or are they overactivated and act as a source of pain? Do other muscles besides the biceps and posterior deltoid work differently in the setting of a full-thickness rotator cuff tear? There is some evidence that the latissimus dorsi and teres major also contribute, although the current study [13] did not find that they did. It seems unlikely that only the biceps and posterior deltoid function differently after rotator cuff tears. Further study of the shoulder muscles in patients with painful rotator cuff tears would be warranted. How Do We Get There? To better understand how the body compensates for a full-thickness rotator cuff tear, we need to evaluate the shoulder girdle’s musculature in asymptomatic patients with rotator cuff tears. These patients should be compared with patients with tears that are symptomatic and with individuals who have no shoulder pain and an intact cuff. This can be done with EMG, as in the current study [13], or perhaps with other visual and video methods such as with three-dimensional sensors and video markers. We also can study patients who have painful rotator cuff tears and compare them with patients who have undergone a regimented physical therapy program to see whether there are changes in muscle activation. Patients who respond to physical therapy can be compared using EMG with those who do not. There could be a specific focus on the biceps brachii and posterior deltoid during rehabilitation to see whether targeting those muscle groups improves patients’ pain and functional outcomes. Lastly, we might study patients with long-head biceps ruptures to see whether there is any effect on rotator cuff muscle function and subsequent proximal humeral migration. Additionally, patients who undergo long-head biceps tenotomy or tenodesis can be similarly studied to see whether this improves the rate of rotator cuff healing and patient-reported outcome scores as well as the position of the humeral head.