Anatomy of the shoulder joint[edit | edit code]
Bone anatomy of the shoulder joint[edit | edit code]
Bone anatomy of the shoulder joint
Shoulder joint
- a typical ball-and-socket joint formed by the head of the humerus and the glenoid cavity of the scapula. The glenoid cavity of the scapula is a flattened fossa in the shape of a pear or an inverted comma with a surface approximately 4 times smaller than the surface of the head of the humerus. The head of the humerus is rotated approximately 30° backward from the transverse axis of the elbow joint, and the scapula is rotated at the same angle forward from the frontal plane of the body; thus, the head of the humerus and the glenoid cavity of the scapula face exactly each other. During movements in the shoulder joint, the scapula rotates, turning its socket up, down, out or in, so that the center of the head of the humerus remains inside it. When this centered position of the head of the humerus in the glenoid cavity is disturbed, there is a danger of dislocation in the shoulder joint.
Biomechanics of the shoulder joint on x-ray
Clavicle joints[edit | edit code]
The medial end of the clavicle is involved in the formation of the sternoclavicular joint
, and the lateral end - in the formation of
the acromioclavicular joint
. The clavicle rotates around its axis and serves as a support for the shoulder joint, since it is the only one that connects the upper limb with the axial skeleton. At the same time, the clavicle acts as a spacer, holding the shoulder joint away from the chest for its greatest mobility.
Articular capsule, labrum and ligaments of the shoulder joint[edit | edit code]
Shoulder joint ligaments
Shoulder joint capsule
- the most spacious and freest compared to the capsules of all other large joints, but it also makes an important contribution to maintaining its stability. Together with the articular lip, it is attached to the scapula, and in front is strengthened by several ligaments: the coracobrachial and three articular-brachial ligaments: upper, middle and lower. There are anatomical variations in the shape and relative position of the articular lip and ligaments: for example, there is an opening between the anterior superior part of the articular lip and the edge of the articular cavity of the scapula, connecting the articular cavity with the subtendinous bursa of the subscapularis muscle. Some of these anatomical variations are particularly predisposing to shoulder injuries.
Articular labrum
not only serves as an attachment point for the articular capsule and its constituent ligaments, but also enlarges the articular cavity, deepening the articular fossa approximately 1.5 times. By raising the edges of the glenoid cavity, it acts as an additional support for the head of the humerus, preventing it from slipping out. After removal of the labrum, the shoulder joint largely loses its ability to withstand forces that move the articular surfaces relative to each other and becomes significantly less stable.
Anatomy of the muscles of the shoulder joint[edit | edit code]
Muscles of the shoulder joint
The muscles acting on the shoulder joint can be divided into three anatomical and functional groups: muscles of the shoulder girdle, muscles of the chest and back, and muscles of the shoulder.
- Muscles of the shoulder girdle
.
Four muscles from this group: supraspinatus, infraspinatus, teres minor and subscapularis - form the so-called muscle capsule of the shoulder joint, or rotator cuff. The supraspinatus muscle
starts from the walls of the supraspinatus fossa, goes outward, filling it, passes under the acromion and attaches to the greater tubercle of the humerus, simultaneously fusing the fibers of its tendon with the posterior surface of the capsule of the shoulder joint.
It is involved in abduction of the arm to its maximum angle, and its paralysis in suprascapular neuropathy reduces the force of abduction by almost half. The infraspinatus and teres minor muscles
originate from the posterior surface of the scapula below its spine and attach to the posterior surface of the greater tubercle of the humerus under the insertion of the supraspinatus muscle.
Their joint action is to extend and externally rotate the shoulder. Together, these two muscles provide approximately 80% of the total external rotation force of the adducted shoulder. The infraspinatus muscle is more active when the arm is lowered, and the teres minor muscle is more active when the arm is raised 90°. The subscapularis muscle
is the only anterior part of the rotator cuff; it starts from the anterior surface of the scapula, attaches to the lesser tubercle of the humerus and carries out its internal rotation, and if the arm is moved to the side, it brings the arm to the body, while simultaneously deflecting it forward. The subscapularis tendon is woven into the joint capsule and strengthens the shoulder joint at the front.
The deltoid muscle is the largest muscle in the shoulder girdle. Anatomy
: Starting in three bundles from the clavicle, acromion and spine of the scapula, it covers the shoulder joint and descends along the humerus, where halfway to the elbow joint it is attached to the deltoid tuberosity. The anterior part of the deltoid muscle flexes the arm at the shoulder joint and, together with the middle part, abducts the arm, and the posterior part of the muscle extends the arm. The deltoid muscle is capable of abducting the arm to the maximum angle even without the participation of the supraspinatus muscle, and its paralysis due to neuropathy of the axillary nerve halves the force of arm abduction.
The teres major muscle originates from the inferior angle of the scapula and inserts on the crest of the lesser tuberosity of the humerus behind the insertion of the latissimus dorsi muscle. Adjacent to it are the axillary nerve and the posterior circumflex artery of the humerus, which pass through a quadrilateral foramen bounded by the teres major muscle below, the teres minor muscle above, the long head of the triceps brachii muscle from the inside and the humerus from the outside. Together with the latissimus dorsi muscle, the teres major muscle extends the shoulder, rotates it inward and brings it to the body.
- Muscles of the chest and back
. The pectoralis major muscle begins in two wide parts: the clavicular and sternocostal, separated by a groove, and narrows towards the shoulder, attaching to the crest of the greater tubercle of the humerus with lower bundles higher than the upper ones. Due to their strength, it and the latissimus dorsi muscle strengthen the shoulder joint, but they can also contribute to dislocation in it. It has been shown that with horizontal abduction of the arm, the lower bundles of the sternocostal part of the pectoralis major muscle are stretched to the limit, and since anterior subluxations of the shoulder arise, in particular, from a sharp horizontal abduction of the arm, it is possible that the direct cause of subluxation is the passive traction of the fibers of the pectoralis major muscle and the latissimus dorsi muscle.
- Shoulder muscles
. Both heads of the biceps brachii muscle originate from the scapula. The short head starts from the coracoid process of the scapula by a common tendon with the coracobrachialis muscle. The long head begins just above the edge of the glenoid cavity of the scapula - from the supraglenoid tubercle and the posterosuperior part of the articular labrum; its tendon passes through the cavity of the shoulder joint above the anterior surface of the head of the humerus and, having left the joint, descends along the intertubercular groove, surrounded by the intertubercular synovial sheath and covered by the transverse ligament of the humerus. Both heads unite into a long muscular belly, which is attached to the tuberosity of the radius. In this way, the biceps brachii muscle is able to act on both the shoulder and elbow joints. It is well known that it flexes the arm at the elbow and rotates the forearm outward. It was also assumed that, by contracting, it pulls the head of the humerus down, but recent electromyographic studies cast doubt on this, since the electrical activity of the biceps brachii muscle almost does not increase if there is no movement in the elbow joint. However, this does not mean that the biceps brachii muscle cannot strengthen the shoulder joint with its strong tendon, both at rest and during tension during flexion of the forearm.
Blood supply and innervation[edit | edit code]
The blood supply to the muscles of the shoulder girdle occurs almost entirely through the axillary artery and its branches. It crosses the axillary cavity, running from the outer edge of the first rib to the lower edge of the pectoralis major muscle, where it continues into the brachial artery. The axillary artery lies under the pectoralis major muscle, and in the middle it is crossed anteriorly by the pectoralis minor muscle before attaching to the coracoid process of the scapula. The artery is accompanied by a vein of the same name.
The muscles of the shoulder girdle are innervated by the brachial plexus nerves. It is formed by the union of the anterior rami of the four lower cervical spinal nerves and most of the anterior rami of the first thoracic nerve. The brachial plexus begins at the base of the neck, continues forward and downward and penetrates the axillary cavity, passing under the clavicle at the junction of its first and second distal thirds. Fractures of the clavicle at this location can damage the brachial plexus. It then passes under the coracoid process of the scapula and gives off nerves that continue further down the arm.
Superficial muscles
This muscle group consists of 2 parts: the subcutaneous muscle and the sternocleidomastoid muscle..
Sternocleidomastoid
The sternocleidomastoid muscle is responsible for flexing the head
It is a long splenius muscle with two heads . At birth, this muscle can be damaged and partially replaced by fibrous tissue. The latter shrinks and forms torticollis (a disease associated with curvature of the neck).
The muscle originates from the sternal head (the anterior surface of the manubrium of the sternum) and the clavicular head (the upper surface of the middle third of the clavicle). The place of its attachment is the mastoid process of the temple bone, or rather the outer surface of this process.
If both halves contract, the muscle pulls the head forward and bends the neck (for example, this happens when trying to lift the head from the pillow). When you inhale deeply, it lifts the ribs and sternum up. If one half contracts, the muscle tilts the head forward on the side of contraction. Responsible for rotating the head up and in the opposite direction.
Subcutaneous
This muscle is located just under the skin and is flat and thin . It begins in the chest area below the collarbone, passes medially and upward, occupying almost the entire anterolateral area of the neck. Only a small triangle-shaped area located above the jugular notch remains unclosed.
Bundles of the subcutaneous muscle rise into the facial area and are woven into the masticatory fascia. Some of them attach to the laughter muscle and the muscle that depresses the lower lip.
This muscle pulls back the skin and protects the veins from compression . It can also pull the corners of the mouth down, which is important for human facial expressions.
The saphenous muscle protects the veins from compression
What diseases of the neck muscles are there?
The most common diseases of the neck muscles include:
- Myofascial syndrome . The disease is widespread in clinical practice. May be accompanied by neck pain, numbness in the hands and other unpleasant symptoms. Usually seen in people who have to stay in the same position for a long time. Prolonged tension leads to muscle spasms. Spasmed areas transform into lumps and lumps (trigger points).
- Myositis . Occurs due to being in a draft for a long time. The peak incidence occurs in the summer and spring, when most homes and offices have open windows or air conditioners. Cold air irritates the nerve endings located in the skin. The latter send a nerve impulse to the brain, thereby triggering a chain reaction, causing painful muscle contracture.
- Fibromyalgia . It is a chronic disease. It is characterized by increased sensitivity and soreness of muscles, tendons, and joints.
Video: “Anatomy of the neck muscles”