When we talk about the shoulder we usually mean the deltoid. This reduction or simplification works well until somebody has an injury in the shoulder but not specifically in the deltoid. I take this opportunity to greet all Anonimous Injuried Rotator Cuffs! Be patient, stay focus, you´ll get over it. And focusing the topic:
The Deltoid muscle is the muscle forming the rounded contour of the shoulder. It is divided into three portions, anterior, lateral and posterior, with the fibers having different roles due to their orientation.
- The anterior fibers are involved in shoulder abduction when the shoulder is externally rotated. It also works with the subscapularis, pecs and lats to internally (medially) rotate the humerus.
- The posterior fibers are strongly involved in transverse extension particularly as the latissimus dorsi is very weak in strict transverse extension. The infraspinatus and teres minor, also work with the posterior deltoid as external rotators, antagonists to strong internal rotators like the pecs and lats. The posterior deltoid is also the primary shoulder hyperextensor, more so than the long head of the triceps which also assists in this function.
- The lateral fibers perform the shoulder abduction when it is internally rotated, and perform shoulder transverse abduction when the shoulder is externally rotated.
- Lateral, anterior 1/3 of the distal clavicle.
- Lateral boarder of the acromion.
- Scapular spine.
Deltoid tuberosity of the humerus.
The Teres major is a medial rotator and adductor of the humerus and assists the latissimus dorsi in drawing the previously raised humerus downward and backward (extension, but not hyperextension). It also helps stabilize the humeral head in the glenoid cavity. It is only functional when the Rhomboids fix the scapula. This muscle mainly helps latissimus dorsi.
Inferior, lateral margin of the scapula.
Crest of lesser tubercle (just medial to the insertion of latissimus dorsi)
The Supraspinatus muscle is one of the four muscles which make up the rotator cuff. Its main function is to stabilize the upper arm by holding the head of the humerus in position. It is important in throwing motions to control any forward motion of the head of the humerus. Contraction of the supraspinatus muscle leads to the abduction of the arm at the shoulder joint. It is the main agonist muscle for this movement during the first 10-15 degrees of its arc. Beyond 30 degrees, the deltoid muscle becomes increasingly more effective at abducting the arm and becomes the main propagator of this action.
- Supraspinous fossa.
- Muscle fascia.
Uppermost of three facets of the greater tubercle of the humerus.
The Infraspinatus muscle is another of the four rotator cuff muscles crossing the shoulder joint and is commonly injured. It is the main external rotator of the shoulder joint. When the arm is fixed, it abducts the inferior angle of the scapula. Its synergists are teres minor and the deltoid. The infraspinatus and teres minor rotate the head of the humerus outward (external, or lateral, rotation); they also assist in carrying the arm backward. Also reinforces the capsule of the shoulder joint.
- Infraspinous fossa.
- Muscle fascia.
The middle facet of greater tubercle of the humerus.
The subscapularis rotates the head of the humerus medially (internal rotation); when the arm is raised, it draws the humerus forward and downward. It is a powerful defense to the front of the shoulder-joint, preventing displacement of the head of the humerus.
Lesser tubercle of the humerus.
The Teres minor is a narrow, elongated muscle of the rotator cuff.
The Teres minor and the infraspinatus attach to the head of the humerus; they help hold the humeral head in the glenoid cavity of the scapula. They work in tandem with the posterior deltoid to externally (laterally) rotate the humerus, as well as perform transverse abduction, extension, and transverse extension.
The middle half of the scapula’s lateral margin.
Lowest of three facets of the greater tubercle of the humerus.
There are two types of rotator cuff injuries:
- Acute tears occur as a result of a sudden movement. This might include throwing a powerful pitch, holding a fast moving rope during water sports, falling over onto an outstretched hand at speed, or making a sudden thrust with the paddle in kayaking.
- A chronic tear develops over a period of time. They usually occur at or near the tendon, as a result of the tendon rubbing against the underlying bone.
Please, be careful 🙂