Symptoms of lesions of the median nerve and its branches

The median nerve (n. medianus) is formed by the fibers of the spinal nerves CV - CVIII and TI, with two roots departing from the medial and lateral secondary bundles of the brachial plexus. These two roots embrace the axillary artery in front, join into a common trunk, which is located below in the sulcus bicipitalis medialis together with the brachial artery. In the elbow bend, the nerve goes under the muscles - the round pronator and the superficial flexor of the fingers. On the forearm, the nerve goes between the superficial and deep flexors of the fingers, then in the groove of the same name (sulcus medianus). Proximal to the wrist joint, the median nerve lies superficially between the tendons of m. flexor carpi radialis and m. palmaris longus, then passes through the carpal tunnel onto the palmar surface of the hand and branches into terminal branches. On the shoulder, the median nerve does not give off branches, but on the forearm, branches extend from it to all the muscles of the anterior flexor group of the hand and fingers, with the exception of the ulnar flexor of the hand and the deep flexor of the fingers.

This nerve supplies the following muscles of the forearm: pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, flexor pollicis longus, flexor digitorum profundus, and quadratus.

The pronator teres pronates the forearm and facilitates its flexion (innervated by segment CVI - CVII).

The flexor carpi radialis (innervated by segment CVI - CVII) flexes and abducts the wrist.

Test to determine the strength of the radial flexor: the wrist is asked to flex and abduct; the examiner resists this movement and palpates the tense tendon in the wrist area.

The palmaris longus muscle (innervated by segment CVII-CVIII) tenses the palmar aponeurosis and flexes the wrist.

The superficial flexor of the fingers (innervated by the CVIII - TI segment) flexes the middle phalanx of the II - V fingers.

Test to determine the strength of the superficial flexor: the subject is asked to bend the middle phalanges of the II - V fingers with the main ones fixed; the examiner resists this movement.

In the upper third of the forearm, a branch departs from the median nerve - n. interosseus antebrachii volaris (interosseous nerve of the forearm of the palmar side), which supplies three muscles. The long flexor of the thumb (innervated by segment CVI - CVIII) - flexes the distal phalanx of the first finger.

Tests to determine the strength of the flexor digitorum longus:

1. the subject is asked to bend the nail phalanx of the first finger; the examiner fixes the proximal phalanx of the first finger and prevents this movement;
2. The subject is asked to clench his hand into a fist and firmly press the nail phalanx of the first finger to the middle phalanx of the third finger; the examiner tries to straighten the nail phalanx of the first finger.

The deep flexor of the fingers is innervated by the CVII-TI segment; branches of the median nerve supply the flexor of the II and III fingers (supply of the IV and V fingers is from the n. ulnaris).

Tests to determine its strength vary. Mild paresis can be detected by the following test: the subject is asked to bend the nail phalanx of the second finger; the examiner fixes the proximal and middle phalanges in an extended state and resists this movement.

To determine paresis of the deep flexor of the fingers, another test is used involving the muscle that adducts the thumb: the subject is asked to tightly press the nail phalanx of the index finger to the nail phalanx of the thumb; the examiner tries to separate the fingers.

Conducting tests to determine the action of the muscle that adducts the thumb of the hand is possible without the active participation of the examiner: in a horizontal position of the hand with support - the hand and forearm of the subject are placed palm down and pressed to the table, he is asked to make scratching movements with the II and III fingers and without support - he is asked to fold the fingers into a fist. In case of paralysis of this muscle, folding is carried out without the participation of the II - III fingers.

The quadratus teres muscle (innervated by segment CVI - CVIII) pronates the forearm. Test to determine the strength of this muscle and the pronator teres: the subject is asked to pronate the previously extended forearm from a supinated position; the examiner resists this movement.

Above the wrist joint, the median nerve gives off a thin cutaneous branch (ramus palmaris), which supplies a small area of skin in the area of the eminence of the thumb and palm. The median nerve exits onto the palmar surface through the canalis carpi ulnaris and divides into three branches (nn. digitales palmares communis), which run along the first, second and third intercarpal spaces under the palmar aponeurosis towards the fingers.

The first common palmar nerve sends branches to the following muscles. The short muscle that abducts the thumb (innervated by the CVI-CVII segment) abducts the first finger.

A test to determine its strength: they ask you to move your first finger away; the examiner resists this movement in the area of the base of the first finger.

The opposing digitorum muscle is innervated by segment CVI - CVII.

Tests to determine its strength:

1. they suggest opposing the first and fifth fingers; the examiner resists this movement;
2. They ask you to squeeze a strip of thick paper between your first and fifth fingers; the examiner tests the force of the squeeze.

The flexor pollicis brevis (innervated by the CII-TI segment, superficial head - n. medianus, deep head - n. ulnaris) flexes the proximal phalanx of the first finger.

A test to determine its strength: they ask you to bend the proximal phalanx of the first finger; the examiner resists this movement.

The functions of the lumbrical muscles (third and fourth) are examined together with other muscles innervated by the branches of the ulnar nerve.

The common palmar nerves (3), in turn, are divided into seven proper palmar nerves of the fingers, which go to both sides of the first to third fingers and to the radial side of the fourth finger of the hand. These nerves supply the skin of the outer part of the palm, the palmar surface of the fingers (I-III and half of IV), as well as the skin of the phalanges of the second to third fingers on the back side.

It should be noted that the formation and structure of the median nerve varies considerably. In some individuals, this nerve forms high - in the armpit, in others, it forms low - at the level of the lower third of the shoulder. The zones of its branching, especially of the muscular branches, are also inconstant. Sometimes they branch off from the main trunk in the proximal or middle part of the carpal tunnel and pierce the flexor retinaculum of the fingers. At the site of the ligament perforation, the muscular branch of the median nerve lies in an opening - the so-called thenar tunnel. The muscular branch can branch off from the main trunk of the median nerve in the carpal tunnel on its ulnar side, then bends around the trunk of the nerve from the front under the flexor retinaculum and, piercing it, goes to the thenar muscles. In the carpal tunnel, the median nerve is located under the flexor retinaculum between the synovial sheaths of the tendon of the flexor digitorum major and the sheaths of the superficial and deep flexors of the fingers.

External topographic landmarks of the median nerve in the area of the hand may be the skin folds of the palm, the tubercle of the trapezium bone and the tendon of the long palmaris muscle. At the entrance to the carpal tunnel at the level of the distal skin fold of the palm from the inner edge of the pisiform bone to the ulnar edge of the median nerve - on average 15 mm, and between the inner edge of the trapezium and the radial edge of the nerve - 5 mm. In the area of the hand, the projection of the median nerve corresponds to the proximal end of the skin fold line limiting the eminence of the thumb. The ulnar edge of the median nerve always corresponds to the point of maximum curvature of this line.

These anatomical details must be taken into account both in the diagnosis and treatment of patients with carpal tunnel syndrome.

Let's look at the areas where the median nerve can be compressed. In the shoulder, the median nerve can be compressed in the "supracondylar ring" or "brachial canal." This canal exists only when the humerus has an additional process, the so-called supracondylar apophysis, which is located 6 cm above the medial epicondyle, midway between it and the anterior edge of the humerus. A fibrous cord extends from the medial epicondyle of the humerus to the supracondylar apophysis. As a result, an osteoligamentous canal is formed through which the median nerve and the brachial or ulnar artery pass. The existence of the supracondylar apophysis changes the path of the median nerve. The nerve is displaced outward, reaching the internal groove of the biceps, and is stretched.

The median nerve can also be compressed in the forearm, where it passes through two fibromuscular tunnels (the muscular boutonniere of the round pronator and the arcade of the superficial flexor of the fingers). The two upper bundles of the round pronator (the supracondylar - from the inside and the coronoid - from the outside) form a ring, passing through which the median nerve separates from the brachial artery located laterally from it. Somewhat lower, the nerve, accompanied by the ulnar artery and veins, passes through the arcade of the superficial flexor of the fingers. The arcade is located in the most convex part of the oblique line of the radium, on the inner slope of the coronoid process. The anatomical basis for irritation of the nerve is hypertrophy of the round pronator or, sometimes, an unusually thick aponeurotic edge of the superficial flexor of the fingers.

The next level of possible compression of the median nerve is the wrist. The carpal tunnel is located here, the bottom and side walls of which are formed by the carpal bones, and the roof is formed by the transverse carpal ligament. The flexor tendons of the fingers pass through the tunnel, and the median nerve passes between them and the transverse carpal ligament. Thickening of the flexor tendons of the fingers or the transverse carpal ligament can lead to compression of the median nerve and the vessels that feed it.

Damage to the median nerve develops: in some diseases with proliferation of connective tissue (endocrine diseases and disorders - toxicosis during pregnancy, ovarian failure, diabetes mellitus, acromegaly, myxedema, etc.); diffuse diseases of connective tissue (rheumatoid polyarthritis, systemic scleroderma, polymyositis); diseases associated with metabolic disorders - gout; with local lesions of the walls and contents of the carpal canal (short-term extreme loads or less intense long-term loads in gymnasts, milkmaids, laundresses, knitters, typists, etc.). In addition, the median nerve can be damaged by trauma, wounds, arthrosis of the wrist and finger joints, inflammatory processes of the contents of the carpal canal (tendonitis, insect bites). Possible damage to the median nerve in pseudotumor hyperplasia and tumors of the carpal tunnel (lipomatous hyperplasia of the median nerve in the canal area, neurofibromatosis, extraneural angiomas, myeloma disease) and in case of anomalies in the structure of the skeleton, muscles and blood vessels in the carpal tunnel area.

Let us present syndromes of damage to the median nerve at different levels. The supracondylar ulnar groove syndrome is a tunnel syndrome characterized by pain, paresthesia and hypoesthesia in the innervation zone of the median nerve, weakness of the flexors of the wrist and fingers, opposing and abducting the thumb. Painful sensations provoke extension of the forearm and pronation in combination with forced flexion of the fingers. The supracondylar apophysis is found in the population in approximately 3% of people. The supracondylar apophysis syndrome is rare.

Pronator teres syndrome is a compression of the median nerve as it passes through both the pronator teres ring and the arcade of the superficial flexor of the fingers. The clinical picture includes paresthesia and pain in the fingers and hand. Pain often radiates to the forearm, less often to the forearm and shoulder. Hypoesthesia is detected not only in the digital zone of innervation of the median nerve, but also in the inner half of the palmar surface of the hand. Paresis of the flexors of the fingers, as well as the opposing muscle and the short abductor muscle of the first finger are often detected. The diagnosis is aided by the detection of local pain upon pressure in the area of the pronator teres and the occurrence of paresthesia in the fingers, as well as the elevation and tourniquet tests.

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