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True abduction: supraspinatus (first 15 degrees), deltoid; Upward rotation: trapezius, serratus anterior Arm adduction [14] Arm adduction is the opposite motion of arm abduction. It can be broken down into two parts: downward rotation of the scapula and true adduction of the arm.
The scapula (pl.: scapulae or scapulas [1]), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side of the body being roughly a mirror image of the other.
Abduction is a motion that pulls a structure or part away from the midline of the body, carried out by one or more abductor muscles. In the case of fingers and toes, it is spreading the digits apart, away from the centerline of the hand or foot. [ 15 ]
Lateral rotation (in abduction: 95°; in adduction: 70°) Infraspinatus: Infraspinous fossa of scapula Greater tubercle of humerus Teres minor Upper two thirds of lateral border of scapula Greater tubercle of humerus Posterior fibers of deltoid Spine of scapula Middle of lateral surface of shaft of humerus Medial rotation (in abduction: 40 ...
Medial rotation is carried out by the anterior fibres of the deltoid, teres major, subscapularis, pectoralis major and the latissimus dorsi. Lateral rotation is carried out by the posterior fibres of the deltoid, infraspinatus and the teres minor. Circumduction of the shoulder (a combination of flexion/extension and abduction/adduction).
In addition to scapular translation, the trapezius induces scapular rotation. The upper and lower fibers tend to rotate the scapula around the sternoclavicular articulation so that the acromion and inferior angles move up and the medial border moves down (upward rotation).
Combining abduction with 30° flexion in the plane of the scapula causes a delay in the tightening of the ligament resulting in a maximum abduction of 110°. [3] During rotation of the arm lateral rotation stretches all three ligaments while medial rotation relaxes them. [3]
The rotator cuff compresses the glenohumeral joint during abduction of the arm, an action known as concavity compression, in order to allow the large deltoid muscle to further elevate the arm. In other words, without the rotator cuff, the humeral head would ride up partially out of the glenoid fossa, lessening the efficiency of the deltoid muscle.