What Is the Posterior Deltoid?

The deltoid muscle, commonly known as the "tiger's head muscle", is a triangular muscle with a bottom-up, point-down, and subcutaneous area of the shoulder, covering the shoulder joint from the front, back, and outside. The bulging shape of the shoulder is formed by this muscle. The muscle bundle is divided into front, middle and back.

The deltoid muscle, commonly known as the "tiger's head muscle", is a triangular muscle with a bottom-up, point-down, and subcutaneous area of the shoulder, covering the shoulder joint from the front, back, and outside. The bulging shape of the shoulder is formed by this muscle. The muscle bundle is divided into front, middle and back.

Chinese name

Deltoid muscle

Foreign name

Deltoid muscle

Commonly known

Tiger head muscle

Shape

Protruding upper arm, exactly like a tiger's head

Location

On the shoulder

Function

Abduction of the shoulder joint

Deltoid muscle anatomy

The leading edge is separated from the pectoralis major clavicle by the triangular pectoral groove. The trailing edge is free from front to back, covering the lateral part of the lateral head of the brachio brachii, biceps brachii, triceps brachii, the upper small round muscle of the long head and the subganglia muscle. From the anterior edge of the lateral clavicle, the lateral edge of the acromion, the lower lip of the scapula and the inferior ganglia of the trapezius muscle. The muscle fibers gradually concentrate outward and downward, ending at the deltoid trochanter on the outer side of the humerus. The physiological cross section of the muscle is 19.60 cm 2.

Starting point: the anterior muscle bundle starts from the lateral half of the clavicle, the middle muscle bundle starts from the acromion, and the posterior muscle bundle starts from the shoulder shoulder.

Stop: humerus deltoid trochanter.

Innervating nerve: axillary nerve originating from the spinal nerve brachial plexus.

Deltoid function

Near-fixed anterior fiber contraction flexes and rotates the upper arm at the shoulder joint. The central fiber contraction causes the upper arm to abduct. The posterior fiber contraction causes the upper arm to extend and rotate outward at the shoulder joint. The overall contraction allows the upper arm to abduct. In addition, this muscle has a certain effect on strengthening and stabilizing the shoulder joint. When the arm is at an angle of less than 60 °, the abduction efficiency of this muscle is quite low, and it exhibits the largest contraction effect at an angle between 90 ° and 180 °.

Related tissues around the deltoid muscle

On the deep side of the muscle, between the deep layer of the deltoid fascia and the great tubercle of the humerus, there is a constant large mucus sac, called the deltoid sac. As a result, the bursa bulges with many protrusions, especially the most obvious protruding below the acromion, which is called the acromion bursa. The capsule is prone to degeneration, injury, and adhesion, which causes the humeral head to be displaced and fixed upward, and it is difficult to raise the humerus. Observed from the deep side of the deltoid muscle, it can be found that the muscle fiber bundle is multi-feathered. Therefore, the muscle is relatively thick and strong. However, its range of motion is limited, and the humerus can be abducted by 70 ° when contracted. The structure of the anterior and posterior muscle bundles is different from that in the middle. The muscle fibers are parallel to each other. The anterior muscle bundles cause the humerus to bend forward and rotate inwardly. The lowermost muscle bundle adducts the humerus. The main role of this muscle is to abduct the shoulder joint. The deltoid muscle is innervated by the axillary nerve.

Deltoid muscle related diseases and treatment

1. Deltoid muscle contracture is usually caused by repeated intramuscular injections, trauma, or unknown causes. The clinical manifestations are shoulder adduction dysfunction, shoulder abduction contracture, obvious fibrous cords in the deltoid muscle, winged scapula, The skin is sunken at the fiber rope. The fibrous cable structure in the deltoid muscle is an important sign for the diagnosis of deltoid muscle contracture.

2. The deltoid muscle can be divided into 3 parts, namely the anterior part (clavicle part), the middle part (acromion part), and the posterior part (spinous part). The anterior part and the posterior part are composed of long striated muscle fibers, and the middle part is feathers. The muscles of this type are short but numerous, scattered in parallel to the tendon edges, and inserted into three similarly distributed tendons, which start and end in the deltoid muscle tuberosity. The fibrosis of these short twill muscles can cause scattered tendons to merge, however they are not normally connected together. Therefore, fibrosis of only a few muscle fibers can cause deltoid contracture. This particular structure of the middle section and the appropriate location for frequent intramuscular injection may be the cause of frequent deltoid contractures. Contracture tissue mainly occurs in the middle bundle and deep fascia of the deltoid muscle. A few are posterior bundles, which adhere to the subcutaneous tissue. The contracture cord is fibrotic and bright. The contracture cord is obviously tense when the joint is adducted. Pathology showed that the contracture of the fibrous cords was dense fibrous connective tissue, hyaline degeneration, with atrophy or disappearance of striated muscle, and the linear grooves on the surface of deltoid muscle and muscle tissue were filled with adipose tissue. Although most patients with deltoid contracture are usually easily diagnosed based on their typical clinical manifestations, some patients are overlooked. The existence of fibrous cord is the most significant clinical manifestation and the main basis for making a correct diagnosis. In the traditional sense, the discovery of fibrous cords is often palpation, but palpation finds that fibrous cords are only limited to patients with obvious tension. Compared with palpation, MR can clearly show the location of the lesion and the extent of the lesion. It has an important effect on the treatment method, especially the surgical guidance.

3. Treatment: All were treated with surgery. Take a longitudinal incision from the acromion to the upper side of the humerus, with fibrous changes in the subcutaneous fat tissue, especially the subcutaneous tissue in the skin depression with the deltoid muscle.After cutting the deep fascia, you can find a fibrous cord in the middle of the deltoid muscle. The fiber cords extend from the acromion to the deltoid muscle stop, with clear boundaries; 4 cases of the fiber cords in this group are hard, deep to the periosteum, and scarlike, and 3 cases of partial fibrosis in the back of the deltoid muscles; gradually cut off the white fiber cords During the process, the range of motion of the shoulder joint gradually returned to normal, the scapula was fixed, and the shoulder joint was fully adducted.

4. In short, deltoid contracture is a disease of unknown etiology. There is no self-limiting and effective conservative treatment for the disease. The condition worsens with age. The effect of surgical treatment is certain. The smaller the age of surgery, the effect The better. Therefore, early diagnosis and early surgical treatment should be performed.