Shoulder Kinetics PDF

Kinetics of shoulder Mennat-Allah Aldesouky General revesion Trapezius The muscle’s attachments on both the clavicle and scapula indicate that it acts at both the sternoclavicular and scapulothoracic joints. Action: Elevation of sternoclavicular joint Scapular eleva...

Kinetics of shoulder Mennat-Allah Aldesouky General revesion Trapezius The muscle’s attachments on both the clavicle and scapula indicate that it acts at both the sternoclavicular and scapulothoracic joints. Action: Elevation of sternoclavicular joint Scapular elevation Scapular adduction Scapular upward rotation Middle trap Scapular adduction Scapular elevation a pure scapular adductor why??? …….. because of its horizontally aligned fibers…….. has the largest cross-sectional area of the three trapezius muscle segments so it’s.... provides considerable strength in scapular adduction and plays an important role in stabilizing the scapula Weakness of middle trap Isolated weakness of the middle trapezius is unusual, although some authors suggest that it can occur from prolonged stretch of the muscle as might occur in a posture characterized by scapular abduction Lower trap Scapular depression Scapular adduction Scapular upward rotation is ideal for depression of the scapula why? The line of pull of the lower trapezius  During prone you need activity of lower trap than during upright posture…..why? the weight of the upper extremity already pulls the scapula toward depression. Anatomical Force couple The combined action of the upper and lower trapezius muscles allows the scapula to rotate upwardly without being displaced superiorly or inferiorly on the thorax. An imbalance between these two muscles either from tightness or weakness of one of them can lead to difficulty in stabilizing the scapula during upward rotation of the scapulothoracic joint (i.e., during shoulder flexion or abduction).. up 90 ACTIONS OF THE ENTIRE TRAPEZIUS As a whole the trapezius adducts and upwardly rotates the scapula The trapezius as a whole is an important contributor to the scapular upward rotation that is a necessary ingredient of normal arm–trunk flexion or abduction. It appears to play a larger role in shoulder abduction than in shoulder flexion. Its greater role in shoulder abduction is consistent with the fact that the muscle lies primarily in the frontal plane Serratus Anterior Scapular abduction Scapular upward rotation Scapular elevation Textbooks often name the action of the serratus anterior protraction.  Transverse plane view of the scapula. A transverse Force couple formed by trapezius and view of the scapula on the thorax reveals how the pull serratus anterior. The adduction and of the serratus anterior on the medial border of the abduction pulls of the trapezius and serratus anterior counteract each other while the two scapula stabilizes the scapula against the pull of the muscles produce upward rotation of the trapezius on the lateral aspect of the scapula. scapula.  as in pushing a revolving door forward (Fig. 9.10). In this situation the door exerts a reaction force on the upper extremity (including the shoulder girdle) that tends to adduct the scapula. In the absence of sufficient serratus anterior strength, the scapula slides medially on the thorax. Levator Scapulae, Rhomboid Major, and Rhomboid Minor The rhomboid muscles cause contralateral rotation of the cervical spine, and the levator scapulae produces ipsilateral rotation of the cervical spine Scapular elevation Scapular adduction Scapular downward rotation  Downward rotation of the scapula may be used as an individual reaches into a back hip pocket or scratches the middle of the back ( Weakness s of the levator scapulae, rhomboid major, and rhomboid minor. Pulling actions such as pulling open doors and rowing can be impaired by weakness of the levator scapulae, rhomboid major, and rhomboid minor. Weakness of these muscles also is cited as a cause of a posture characterized by rounded shoulders. Pectoralis Minor The pectoralis minor muscle is an unusual axioscapular muscle because it lies entirely on the anterior surface of the thorax and attaches to the coracoid process, an anterior projection of the scapula Action of pectorals muscle Scapular anterior tilt when contracting alone Scapular elevation when contracting alone because the scapula lies on the posterior aspect of the thorax, for it to tip forward, it also must elevate Scapular depression when contracting with other shoulder depressors Scapular adduction Scapular abduction Scapular upward rotation  muscles contract to prevent the anterior tilting of the scapula caused by the pull on the coracoid process by the pectoralis minor, the pectoralis minor with these other muscles contributes to scapular depression. How pec minor do abduction ? the muscle’s position on the anterior aspect of the thorax means that its anterior pull on the coracoid process causes the scapula to slide anteriorly on the thorax, causing the scapula to abduct. Force couple between rhomboids and pectorals minor The ability of the pectoralis minor to abduct the scapula makes it a suitable partner with the levator scapulae, rhomboid major, and rhomboid minor muscles in an anatomical force couple for downward rotation of the scapula. The pectoralis minor’s action of abduction balances the adduction component of the levator scapulae, rhomboid major, and rhomboid minor, while together they contribute to the scapula’s downward rotation Subclavius The subclavius is a small muscle binding the clavicle to the first rib Sternoclavicular joint depression this muscle, like the pectoralis minor, is more likely a stabilizer of the clavicle against forces that tend to elevate the sternoclavicular joint, such as weight bearing on the upper extremity. EMG suggest that, this muscle contracts to stabilize the sternoclavicular joint, reinforcing the ligamentous supports Case study, During normal arm–trunk elevation occurs without significant scapular adduction. Thus the whole trapezius requires another muscle to balance its adduction component. What this muscle???? This balance is provided by the serratus anterior, SCAPULOHUMERAL MUSCLES The scapulohumeral muscles provide motion and dynamic stabilization to the glenohumeral joint (Fig. 9.23). The glenohumeral joint provides over 50% of the ROM of arm–trunk elevation. 50joints Therefore, these muscles are critical to the active mobility of the shoulder as a whole. The muscles of the scapulohumeral group are: the deltoid, teres major, coracobrachialis, and the four muscles of the rotator cuff, which are the supraspinatus, infraspinatus, teres minor, and subscapularis. ANTERIOR Deltoid POSTERIOR Shoulder extension Shoulder lateral rotation Shoulder abduction Shoulder flexion Shoulder adduction Shoulder horizontal abduction Shoulder medial rotation Shoulder abduction Shoulder horizontal adduction Middle deltoid: Shoulder abduction Shoulder flexion Shoulder extension  The supraspinatus helps stabilize the glenohumeral joint by exerting a horizontal pull to hold the humeral head against the glenoid process Pull of the supraspinatus. The medial pull of the supraspinatus helps prevent inferior displacement of the humeral head, since in an upwardly turned glenoid fossa, the humeral head must move laterally as it slides inferiorly on the fossa. infraspinatus Shoulder lateral rotation Shoulder horizontal abduction Shoulder abduction Shoulder stabilization The infraspinatus muscle is regarded by most authors as an important and powerful lateral rotator muscle DYNAMIC STABILIZATION BY THE ROTATOR CUFF contraction of the rotator cuff prevents visible instability of the glenohumeral joint during shoulder movement, even in the presence of large anterior disruptions of the joint capsule contraction of the rotator cuff muscles even prevents dislocation after complete anterior–posterior disruption of the capsule. decreased contraction force of the rotator cuff results in increased anterior and posterior gliding of the glenohumeral joint during abduction in the plane of the scapula. Weakness may also allow increased superior glide of the humeral head during shoulder elevation.  Thus abduction and flexion of the glenohumeral joint depend on three factors: the deltoid, the supraspinatus, and the depressors of the humeral head, including the infraspinatus, teres minor, and subscapularis muscles. The deltoid provides strength to the movement; the supraspinatus provides mechanical advantage early in the ROM and, with the rest of the rotator cuff, joint compression throughout the movement; and the infraspinatus, teres minor, and subscapularis muscles stabilize the humeral head inferiorly. Loss of any of these elements results in significant impairment in the ability to elevate the shoulder. Int.rotator  Thank u