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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.
When the serratus anterior contracts, upward rotation, abduction, and weak elevation of the scapula occurs, allowing the arm to be raised above the head. [4] The long thoracic nerve innervates the serratus anterior; therefore, damage to or impingement of this nerve can result in weakening or paralysis of the muscle. [5]
In primates, the thoracic cage is wide and the scapula is rotated onto its posterior side to have the glenoid cavity face laterally. Additionally, the clavicle takes care of medial forces. In cursorial mammals (for example the horse and other quadrupeds), the scapula is hanging vertically on the side of the thorax and the clavicle is absent ...
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).
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]
Range of motion tests external and internal rotation, abduction and adduction, passive and active weakness, and true weakness versus weakness due to pain. The Apley scratch test is the most useful: touch opposite scapular by reaching behind the head for adduction and external rotation and behind the back for abduction and internal rotation.
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 ...