The rotator cuff is a group of muscles-supraspinatus, infraspinatus, subscapularis, teres minor-responsible for movement and stabilization of the shoulder joint.
One of the most common reasons for the inability to abduct the arm or pain with the abduction of the arm is a tear of the rotator cuff. Specifically, they facilitate abduction of the arm from 90 degrees and further upwards.
MOVE UP AND DOWN IN ESSENTIAL ANATOMY 3 FULL
The trapezius and serratus anterior muscles work in tandem to coordinate rotation and movement of the scapula to accommodate the full range of motion of the arm. Its primary function is to laterally rotate and protract the scapula. The serratus anterior is a saw-shaped muscle originating from the upper eight ribs and inserting upon the inner medial border of the scapula. It can also function to extend and laterally flex the neck if the scapula is kept in a fixed position. The trapezius functions to laterally rotate, elevate, and retract the scapula. The inferior fibers originate from the spinous processes of T4-T12 and converge near the scapula in the form of an aponeurosis. The middle fibers also originate from the spinous process of C7, as well as the spinous processes of T1-T3, and insert upon acromion and the spine of the scapula. The superior fibers of the trapezius originate from the medial third of the superior nuchal line, spinous process of C7, external occipital protuberance, and nuchal ligament they converge and insert on the posterior portion of the lateral third of the clavicle. The trapezius is a large, superficial muscle of the back that divides into three functional parts: descending (superior), middle, and ascending (inferior). It also serves as a stabilizer of the humeral head, especially in instances of load carrying. The deltoid is the primary muscle responsible for the abduction of the arm from 15 to 90 degrees. All heads of the deltoid come together to insert on the deltoid tuberosity of the humerus. The posterior head originates from the posterior border of the spine of the scapula. The lateral head originates from the superior surface of the acromion process. The anterior head originates from the anterior surface of the lateral third of the clavicle. The deltoid, aptly named after the Greek letter delta, is a triangular-shaped muscle found over the glenohumeral joint and is composed of three different heads: anterior, lateral, and posterior. Additionally, the supraspinatus contributes to shoulder joint stability by providing resistance to gravitational forces acting on the joint and maintaining contact between the head of the humerus and the glenoid fossa. Past 15 degrees, it assists the deltoid with the abduction of the arm up to 90 degrees.
It is responsible for the initiation of arm abduction and is in control of the motion up to the first 15 degrees of abduction. The supraspinatus muscle originates from the supraspinous fossa of the scapula, passes under the acromion, and inserts on the superior facet of the greater tubercle of the humerus.
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