Scapular muscle recruitment patterns and isokinetic strength ratios of the shoulder rotator muscles in individuals with and without impingement syndrome (original) (raw)

2008, Journal of Shoulder and Elbow Surgery

The aim of this study was to compare the recruitment patterns and latencies of the scapular muscles, as well as the isokinetic performance of the shoulder rotators in 10 subjects with unilateral impingement syndrome who comprised the impingement group (IG) with a control group (CG) of 10 asymptomatic subjects. The recruitment patterns and latencies were evaluated by electromyographic activity during arm elevation in the scapular plane. Isokinetic work ratios of the shoulder rotator muscles were used to analyze muscular performance. A 2 x 2 ANOVA detected that muscular performance and recruitment patterns were similar for both groups and sides. However, the ANOVA revealed a significant side and group interaction, indicating that the scapular muscle latencies of the affected shoulder was greater than that of the nonaffected side only for the IG (p < .001). These findings indicated that subjects with light to moderate impingement syndrome showed late recruitment of the scapular muscles during arm elevation. However, muscular performance of the shoulder rotator muscles was not affected. (J Shoulder Elbow Surg 2008;17:48S-53S.) Duetotheassociatedmovementsoftheentireshoulder joint complex, the shoulder girdle has the highest mobility of all joints of the human body. 10,24,9 In normal conditions, each joint acts in a consistent and coordinated way, following a specific movement pattern to allow the upper limb to perform several motor functions, without compromising the integrity of the complex. 13 This kinematic relationship is dependent on muscular coordina-tion, 7 which, at the same time, allows adequate performance of the desired movement and provides dynamic stability of all involved joints. Several studies 2,3,16,28 have demonstrated the importance of a coordinated, synchronized action of the scapular and glenohumeral muscles, as well as a proportional relationship of strength of the rotator cuff muscles during all ranges of motion of the shoulder. Minimal alteration in performance and coordination of these muscles have the potential to lead to dysfunctions and compensations that could compromise normal joint function and lead to disabilities, 13,16 resulting in inactivity 6 and lower quality of life. The impingement syndrome (IS) is the most common diagnosis of shoulder pain. Electromyographic studies of the scapular stabilizing muscles have found changes in patients with IS compared with asymptomatic individuals. In addition, imbalance of the rotator cuff muscles assessed by their isokinetic performance has been well documented. 15,29 Therefore, neuromuscular dynamic control and muscle imbalance have been the focus of investigations related to scapular positioning and function of the shoulder girdle. 16 However, studies evaluating electromyographic activity of the scapular stabilizers and rotator cuff in the same patientss with IS are lacking.