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A B M P m e m b e r s ea r n F R E E C E h o u r s by rea d i n g t h i s i s s u e ! 25 subacromial impingement, labral injuries, nerve injury, and clavicular fracture. The second category is neck related. Most neck pain from SD is considered mechanical because it usually results from excess compression or tension on structures in the neck or shoulder region. An example would be altered neck and shoulder movement that adversely affects facet joints. Ligament injury or referred pain from myofascial trigger points are other examples of mechanical neck pain that may result from altered shoulder movement. Posture-related issues, the third category, include conditions such as upper thoracic kyphosis or excessive cervical lordosis, which impair shoulder mechanics. For example, in an upper thoracic kyphosis, the scapula is more protracted (sliding around the rib cage anteriorly) as the upper thoracic region slumps forward. This altered position increases the likelihood of dysfunctional mechanics in shoulder movements. Force couple with upper trapezius and serratus anterior. Image courtesy of Complete Anatomy. 2 alter proper scapular mechanics, such as glenoid labrum injuries, adhesive capsulitis, ligament sprains, subacromial impingement, and biceps tendon disorder. The primary shoulder joint is the glenohumeral, which has the greatest range of motion of any joint in our body. However, four joints make up the entire shoulder complex: the glenohumeral (between the scapula and humerus), acromioclavicular (between the scapula and clavicle), sternoclavicular (between the sternum and clavicle), and scapulothoracic (between the scapula and the rib cage). The scapulothoracic articulation is not a true joint because it doesn't have a joint capsule or other features of synovial joints, but it plays a crucial role in SD. The most significant motion problems in SD are f lexion and abduction of the shoulder. A look at shoulder abduction illustrates the critical importance of scapular mechanics and the primary issues arising from SD. When you lift your arm into full abduction, most of that motion occurs at the glenohumeral joint. However, the scapula also moves upward and tilts that glenoid fossa up so the humerus can fully abduct. A biomechanical principle called force couple helps create this upward rotation of the scapula. It is a coordinated movement A B M P m e m b e r s ea r n F R E E C E h o u r s by rea d i n g t h i s i s s u e ! 25 pattern between the upper trapezius and the serratus anterior muscles (Image 2). The upper trapezius pulls the distal and upper margin of the scapula superiorly, while the serratus anterior hooks the scapula from the lower and medial side to pull it into upward rotation. During shoulder abduction, another coordinated motion pattern, the scapulohumeral rhythm, also involves the scapulothoracic articulation and glenohumeral joint. There is roughly a 2:1 ratio of glenohumeral to scapulothoracic movement—for every three degrees of shoulder abduction, two happen at the glenohumeral joint and one at the scapulothoracic articulation (Image 3). An altered scapulohumeral rhythm is often the root of many SD issues. But first, let's more clearly define the categories of scapular dyskinesis and look at some of the main contributing factors. VARIATIONS OF SCAPULAR DYSKINESIA Scapular dyskinesis is divided into three categories. The fi rst is shoulder-related and includes altered scapular movements that result from shoulder pathology. Common examples include acromioclavicular joint injury, rotator cuff injury, and Upper trapezius Serratus anterior Two degrees at glenohumeral joint One degree at scapulothoracic articulation The scapulothoracic rhythm. Image courtesy of Complete Anatomy. 3