What Is the Anatomy of the Shoulder?

The shoulder joint refers to the part where the upper limbs are connected to the trunk, including the upper part of the arm, the armpit, the anterior chest area, and the back area where the scapula is located. It consists of the scapula glenoid and humeral head. It is a ball and socket joint and is the largest and most flexible joint of the upper limbs. The articular capsule is looser and is attached to the periphery of the glenoid and anatomical neck. The synovial layer of the articular cavity bulges through the fibrous layer, forming a subscapular muscle synovial sac and an internodal synovial sheath enclosing the biceps long head tendon.

Chinese name: Shoulder joint
Foreign name: Shoulder joint
Constitute: Glenoid and humeral head

Subordinate: Ball and socket joint
Features: Bend, stretch, retract, stretch, rotate and loop
Related diseases: Frozen shoulder

Functional Anatomy of the Shoulder Joint:

The clavicle is the only bony structure that connects the free upper limbs to the trunk. The inside is the sternoclavicular joint, which is outwardly related to the acromion. The scapula is connected to the arm by the glenohumeral joint. One part of the muscles of the shoulder joint starts from the scapula and stops at the upper limb bone, and acts on the shoulder joint, called the internal muscle of the shoulder joint; and one part starts from the axial bones such as the thoracic spine, stops on the upper limb bone, and acts on the shoulder joint, called the external shoulder muscle.

Most of the nerves that innervate the shoulder joint muscles originate from the brachial plexus, and the nutritional blood vessels come from the subclavian artery or axillary artery.

Brachial plexus nerve:

The brachial plexus consists of the anterior branch of the C ₅ -T ₁ nerve root. It starts at the lower part of the neck and travels downwards and through the clavicle space between the clavicle and the first intercostal space. The lateral wall of the axillary can touch the brachial plexus on the inside of the humerus. Brachial plexus can be divided into four parts: root, stem, thigh, and bundle from the center to the periphery. According to the muscles it controls, the brachial plexus can be divided into two functional units: the medial and lateral bundles mainly dominate the pectoral muscle group and the muscles in front of the arms and forearms, that is, the flexor muscle groups; the posterior bundles mainly dominate the scapular area and the arms and forearms Muscle, the extensor group.

Bone and Joint:

The scapula is triangular in shape, and there is an oval, shallow glenoid called the glenoid at the lateral angle. There is a labrum around the glenoid to deepen and enlarge the glenoid. The upper edge of the scapula has a small, deep, semi-circular notch, called the scapular notch, on which there is a transverse scapular ligament. Hook-shaped coracoids protrude forward from the scapula neck. The front of the scapula is smooth and is called the subscapular fossa, which is the starting point of the subscapularis muscle. On the back, the scapula is divided into the upper and lower ganglia fossa, which respectively contain the superior and inferior ganglia muscles. The scapula extends outward to form the acromion, which forms the uppermost edge of the shoulder joint and forms the acromioclavicular joint with the clavicle-related segment. The acromion is connected with the coracoid process by the coracoid ligament. The scapula is connected with the clavicle and humerus. It is mainly connected with the trunk by muscle suspension.

The clavicle is a long bone with the medial and sternal related segments. The clavicle in the sternoclavicular joint protrudes upward and rearward. Lateral and acromion-associated knots. The clavicle keeps the upper limbs away from and indirectly attaches to the trunk, increasing the range of upper limb movement.

The humerus is long bone, and the humerus head is enlarged at the proximal end. There is a shallow groove between the humeral head articular surface and the humerus tuberosity, which is the anatomical neck of the humerus. The narrower area of the humerus below the size of a surgical neck finger nodule is named for its prone to fracture.

The glenohumeral joint is composed of the scapula and the proximal end of the humerus. The biceps tendon ends in the scapula nodules in the shoulder joint cavity. When the shoulder joint is repeatedly dislocated, the labrum will be torn from the edge of the labrum. The shoulder joint is mainly responsible for suspending the upper limbs. In addition to the joint capsule and ligaments, the suspension strength mainly comes from the muscles around the shoulder joint.

Bone structures such as shoulder nodules, acromion, and shoulder ligaments, short muscles, etc. limit the movement of this ball and socket joint and stabilize the shoulder joint.

Cutaneous nerve, superficial vein and fascia:

Skin sensation: The skin sensation above the anterior thoracic region is dominated by the supraclavicular nerve, which is a branch of the cervical plexus C ₃ _, ₄ ; the thoracic region is dominated by the intercostal nerve, T ₂ dominates the level of the sternal stalk, and T ₄ dominates the level of the mastoid; back skin It is innervated by intercostal nerves; the upper part of the lateral arms is innervated by the axillary nerves; the base of the axillary and the inner sides of the arms are innervated by the intercostal arm nerves from T ₂ or T ₂ _, ₃ ;

The superficial shoulder vein is mainly seen at the upper end of the cephalic vein. This vein is located between the deltoid muscle and the pectoralis major muscle and penetrates the thoracic fascia into the axillary vein.

The deep fascia of the shoulder area surrounds the muscles and other structures encountered in layers, and then combines with the bone tissue. The deep fascia between the pectoralis minor and the clavicle forms the clavicle fascia, with the thoracic acromion artery, the cranial vein, and the lateral thorax nerve passing. The fascia at the base of the axilla is called the axillary fascia, which is thinner in the center and penetrated by many blood vessels, lymphatic vessels, and nerves.

ligament:

1. Colic-humeral ligament:

From the coracoid to the nodule of the humerus, some fibers are fused with the joint capsule at the posterior and upper part, strengthening the upper part of the joint capsule and preventing the humeral head from dislocating upward.

2. glenohumeral ligament:

It is located in the anterior wall of the articular capsule and can be divided into upper, middle and lower parts, from the anterior part of the glenoid to the small humerus nodules. Strengthen the anterior wall of the joint capsule.

3. Transverse ligament of humerus:

It is the inherent ligament of the humerus. It crosses the nodular groove and fixes the long head of the biceps brachii to the nodular groove.

Shoulder motion:

The generalized shoulder joint movement includes the movement of the scapula and the glenohumeral joint.

(1) The movements of the scapula include lifting up, pulling down, internal rotation, external rotation, anterior extension and posterior extension:

1. Lifting: Four muscles can lift the scapula, the upper fibers of the trapezius can lift the external angle of the scapula; the scapular muscle and the rhomboid muscles can lift the scapula spinal margin.

2. Pull-down: The pectoralis minor, subclavian muscle, latissimus dorsi, lower trapezius muscle, anterior serratus, and pectoralis major all participate in this action. Only the anterior serratus had external rotation of the lower scapula, and the rest had internal rotation of the scapula.

3. External rotation: The external rotation of the lower angle of the scapula is performed by the cooperation of trapezius and anterior serratus.

4. Internal rotation: The internal rotation of the lower angle of the scapula is mainly accomplished by the rhomboid muscles and scapular levator muscles to raise the medial edge of the scapula. The gravitational effects of the pectoralis major, pectoralis minor, latissimus dorsi and upper limbs reduce the external angle of the scapula. The internal rotation of the scapula is often accompanied by a scapular descending motion to assist the upper limbs in downward movement.

5. Anterior extension: refers to the forward and lateral movement of the scapula along the chest wall.

6, posterior extension: refers to the scapula moving along the chest wall to the posterior medial, close to the spine. The middle or all fibers of the trapezius muscle can contract at the same time, which can make the scapula extend backward. The rhomboid muscle and latissimus dorsi also have the effect of extending the scapula.

(2) The movements of the glenohumeral joint include forward flexion, extension, adduction, abduction, internal rotation and external rotation:

1. Anterior flexion: The anterior flexion of the shoulder joint is mainly completed by the anterior deltoid fibers, the pectoralis major clavicle, the rostral brachii, and the biceps brachii. The anterior deltoid fibers are the most obvious.

2. Posterior extension: The muscles of the posterior extension of the shoulder joint are mainly the posterior deltoid fibers, latissimus dorsi, pectoralis major, pectoralis major, and long head of triceps. Among them, the posterior deltoid fibers play the most important role.

3. Adduction: There are mainly pectoralis major, great round muscles, latissimus dorsi, coccybrachidum, and biceps long heads. In addition, the deltoid and anterior fibers also adduct.

4. Abduction: The abduction of the shoulder joint is performed by the deltoid muscle (mainly the middle bundle) and the supraspinalis muscle. When the shoulder is in the internal rotation or external rotation position, the outermost part of the deltoid muscle is the main abductor muscle. When the shoulder is rotated outward, the abductor muscle is stronger.

5. Internal rotation: The internal rotation muscle is mainly the subscapularis muscle. When the shoulder joint is in a specific position, the anterior fibers of the pectoralis major deltoid muscle, the great round muscle and the latissimus dorsi also have a certain internal rotation.

6. External rotation: The external rotation muscles of the shoulder joint include subganglion, small round muscle and posterior deltoid fibers.

What Is the Anatomy of the Shoulder?

Functional Anatomy of the Shoulder Joint:

Shoulder motion:

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