Supraspinal muscle: It starts from supraspinatus fossa, passes through acromion and coracoacromial ligament, and ends at the upper part of greater tubercle of humerus. It is innervated by the suprascapular nerve (C5-6). Function: Shoulder abduction.
Infraspinatus: It starts from the infraspinatus fossa and ends in the middle of the greater tubercle of humerus. It is innervated by axillary nerve (C5-7). Function: make the joint rotate outward.
Teres minor: It starts from the back of the lateral margin of scapula and ends at the lower part of the greater tubercle of humerus. It is innervated by axillary nerve (C5-7). Function: make the joint rotate outward.
Teres major: It starts from the back of the lower angle of scapula and ends at the crest of humeral tubercle. It is innervated by the subscapular nerve (C5-6). Function: adduction, rotation and extension of shoulder joint.
Subscapular muscle: It starts from the subscapular fossa (in front of the scapula) and ends at the humeral tubercle. It is innervated by the subscapular nerve (C5-6). Function: make the shoulder joint rotate inward and inward.
Among them, supraspinatus, infraspinatus, teres minor and subscapular muscles form rotator cuff, and improper shoulder force can easily cause rotator cuff injury and affect shoulder joint activity.
Shoulder joint structure
(1) Bone: The shoulder joint consists of three bones (clavicle, scapula and humerus) and four joints (glenohumeral joint, acromioclavicular joint, acromioclavicular joint and sternoclavicular joint).
1. clavicle:
The front part is S-shaped, extending from the acromion to the sternum handle, as the fulcrum between the upper limb and the trunk, allowing the upper limb to move in the largest range and providing a stopping point for the muscles. Transmit strength from the upper limbs to the trunk.
2. Scapula:
It is a triangular flat bone located in the upper part of the posterolateral chest, between the second and seventh ribs. The anterior concave surface is beneficial to the formation of thoracic connection with ribs, and the posterior convex surface. The scapular crest protrudes backward, with a smaller supraspinatus fossa above and a larger infraspinatus fossa below. Acromion is the starting point of most deltoid muscles, one of the stopping points of trapezius muscles and the attachment point of acromioclavicular ligament. The coracoid process provides the starting point for the brachialis brevis tendon and coracoid muscle, and is also the attachment point of the pectoralis minor muscle and acromioclavicular ligament. The scapula has three angles, and the upper angle is flat with the second thoracic vertebra. The lower angle is level with the seventh thoracic vertebra. The pear-shaped shallow fossa above the scapula, called glenoid, is related to the humeral head. There is a rough protuberance above and below the glenoid, which is called supraglenoid nodule and subgglenoid nodule respectively.
3. Humerus:
The upper end is enlarged, and the humeral head is hemispherical, facing upward, backward and inward, with an average diameter of 43 mm There are raised large nodules and small nodules on the outside and in front of the humeral head, and a ridge extends downward, which is called large nodule crest and small nodule crest. There is a longitudinal groove between the two nodules, which is called the intertubercular groove.
1. The ball-and-socket joint of glenohumeral joint is the joint with the greatest mobility and poor stability.
The glenoid of triaxial motion is small and shallow, and the joint head is large, which can only accommodate the glenoid of joint head 1/4 ~ 1/3, making it slightly deep. The lower part of the glenoid lip is firmly fixed, and the upper part has large fluidity, poor blood supply and easy injury. The joint capsule is thin and loose.
2. Acromioclavicular joint: a plane sliding synovial joint formed by the lateral end of clavicle and the lateral edge of acromion inward 2-3cm. There is an incomplete articular disc in the upper part of the joint. Acromioclavicular ligament: The rotation of acromion and its forward and backward movement relative to clavicle are related to the movement of scapula and sternoclavicular joint.
3. The sternoclavicular joint is a synovial joint composed of the medial end of clavicle, the first costal cartilage and the outer upper edge of sternal stalk, which is saddle-shaped and can slide. The only connection between the axial bone in the body and the joint of the upper limb. Disc cartilage separates the joint cavity and can absorb the vibration transmitted from the upper limb to the axial bone. Anterior sternoclavicular ligament, posterior sternoclavicular ligament, clavicular ligament, costoclavicular ligament. With the movement of the shoulder joint, the sternoclavicular joint can rotate 30 degrees.
4. Shoulder-thoracic joint (scapulohumeral joint) is not a real joint, it allows the scapula to move relative to the chest.
(2) Ligament: It can protect joint stability.
1, coracoid process-brachial ligament: it starts under coracoid process and is fixed to humerus in the lateral front, which is equivalent to the attachment point of supraspinatus muscle and subscapular muscle. Its fibers are closely connected with the joint capsule. This ligament supports the humeral head and prevents excessive external rotation of the humerus. When the shoulder is frozen, this ligament will be widely inflamed. Therefore, the humeral head remains in the pronation position, which hinders the movement of the shoulder joint.
2. coracoacromial ligament: It is the barrier of the upper part of the shoulder joint, starting from the outer edge of the coracoid process and gradually narrowing at the base, ending at the acromion, separating the acromion descending capsule from the acromioclavicular joint.
3. glenohumeral ligament: it is the thickened part of the joint capsule and is divided into three ligaments: upper, middle and lower. It is located on the inner surface of the joint capsule and has the function of limiting joint external rotation.