Symptoms of involvement 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 separated from the medial and lateral secondary bundles of the brachial plexus. These two spinelets encompass the axillary artery from the front, join the common trunk, which is below located in the sulcus bicipitalis medialis along with the brachial artery. In the ulnar fold the nerve fits under the muscles - the round pronator and the superficial flexor of the fingers. On the forearm, the nerve passes between the superficial and deep flexors of the fingers, then in the same groove (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 wrist drop on the palmar surface of the brush and branches into the final branches. On the shoulder, the median nerve of the branches does not give, and on the forearm branches from all the muscles of the anterior flexor group of the hand and fingers depart, except for the elbow flexor of the hand and the deep flexor of the fingers.

This nerve supplies the following muscles of the forearm: round pronator, radial flexor of the wrist, long palmar muscle, superficial flexor of the fingers, long flexor of the thumb, deep flexor of the fingers, square muscle.

The round pronator penetrates the forearm and promotes its bending (innervated by segment CVI - CVII).

The radial flexor of the hand (innervated by the segment CVI - CVII) bends and retracts the brush.

Test to determine the strength of the radial flexor: suggest bending and withdrawing the brush; the examiner is resisting this movement and palpating the strained tendon in the area of the wrist joint.

The long palmar muscle (innervated by the segment CVII-CVIII) strains the palmar aponeurosis and flexes the wrist.

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

Test for determining the strength of the superficial flexor: the subject is offered to flex the middle phalanges of II-V fingers with fixed main; the examiner is resisting this movement.

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

Tests to determine the strength of the long flexor of the finger:

1. the subject is offered to flex the nail phalanx of the first finger; the examiner fixes the proximal phalanx of finger I and prevents this movement;
2. the subject is offered to squeeze the hand into a fist and press firmly the nail phalanx of the finger to the middle phalange of the third finger; The examiner tries to unbend the nail phalanx of the first finger.

The deep flexor of the fingers is innervated by segment СVII-ТI; the branches of the median nerve supply the flexor of the second and third fingers (supplying IV and V fingers - from n. Ulnaris).

Tests to determine its strength are different. Paresis of an easy degree can be revealed by the following test: the subject is offered to bend the nail phalanx of the second finger; the examiner fixes the proximal and middle phalanges in the unfolded state and provides resistance to this movement.

To determine the depth of the deep flexor of the fingers, another test is used involving the muscle that leads the thumb of the cyst: the subject is offered to press the nail phalanx of the index finger tightly against the nail phalanx of the thumb; the examiner tries to separate the fingers.

Carrying out tests to determine the action of the muscle that leads the thumb of the hand is possible without the active participation of the examiner: in the horizontal position of the hand with the support - the hand and forearm of the subject with the palm of the hand are laid down and pressed against the table, he is offered to make scraping movements II and III with his fingers and without support - offer to put your fingers in a fist. With paralysis of this muscle, folding is carried out without the participation of II - III fingers.

The square muscle (innervated by the CVI - CVIII segment) perforates the forearm. A test to determine the strength of this muscle and the round pronator: the subject is suggested to scan the pre-expanded forearm from the supination position; the examiner is resisting this movement.

Above the wrist joint, the median nerve gives a thin cutaneous branch (ramus palmaris), which supplies a small patch of skin in the area of the elevation of the thumb and palm. The median nerve on the palmar surface leaves through the canalis carpi ulnaris and is divided into three branches (nn. Digitales palmares communis) that run along the first, second and third interstitial spaces under the palmar aponeurosis towards the fingers.

From the first common palmar nerve branches to the next muscle. A short muscle that withdraws the thumb (innervated by the segment CVI-CVII), assigns a finger.

A test to determine its strength: offer to withdraw the first finger; the examiner is resisting this movement in the region of the base of the 1st finger.

The muscle that opposes the thumb is innervated by the CVI-CVII segment.

Tests to determine its strength:

1. offer to oppose I and V fingers; the examiner is resisting this movement;
2. offer to squeeze a strip of heavy paper between the I and V fingers; the examining person experiences pressing force.

The short flexor of the thumb (innervated by segment CII-TI, the surface head - n. Medianus, the deep head - n. Ulnaris) bends the proximal phalange of the 1st finger.

Test to determine its strength: suggest bending the proximal phalange of the 1st finger; the examiner is resisting this movement.

The functions of the vermiform 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 own palm nerves of the fingers, which go to both sides of the I-III fingers and to the radial side of the IV finger of the hand. These nerves supply the skin of the outer part of the palm, palmar surface of the fingers (I - III and half IV), as well as the skin of the diagonal phalanges of II - III fingers on the back.

It should be noted a significant variability in the formation and structure of the median nerve. In some individuals, this nerve is formed high-in the armpit, others are low - at the level of the lower third of the shoulder. The zones of its branching, especially the muscular branches, are also not permanent. Sometimes they branch off from the main trunk in the proximal or middle part of the carpal tunnel and perforate the flexor flexor retainer. At the site of perforation of the ligament, the muscle branch of the median nerve lies in the hole - the so-called tenar tunnel. The muscular branch can branch off from the main trunk of the median nerve in the carpal canal from the ulnar side of it, then rounds the nerve trunk in front under the flexor retainer and perforates it, it goes to the muscles of the tenar. In the carpal canal, the median nerve is under the flexor holder between the synovial vagina of the tendon of the first finger flexor and the vagina of the superficial and deep flexor of the fingers.

External topographical orientations of the median nerve in the region of the hand can be the skin folds of the palm, the bump of bone-trapezium and the tendon of the long palmar muscle. At the entrance to the carpal drip at the level of the distal dermal fold of the palm from the inner edge of the pea to the elbow of the median nerve - on average 15 mm, and between the inner edge of the trapezium and the radial margin of the nerve - 5 mm. In the brush region, the projection of the median nerve corresponds to the proximal end of the skin fold line that limits the elevation of the thumb. The ulnar margin of the median nerve always corresponds to the point of maximum curvature of this line.

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

Consider the areas of possible compression of the median nerve. On the shoulder, the median nerve can be squeezed in the "supra-nodular ring" or "humeral canal". This channel exists only in cases when the humerus has an additional process, the so-called supramontal apophysis, which is located 6 cm above the medial epicondyle at the middle distance between it and the anterior margin of the shoulder. From the medial epicondyle of the shoulder of the pre-supra-capillary apophyses, a fibrous cord extends. As a result, a bone-ligament canal is formed through which the median nerve and the brachial or ulnar artery pass. The existence of an over-apical apophysis changes the way of the median nerve. The nerve moves to the outside, reaching the inner biceps groove, and stretches.

The median nerve can also be compressed in the region of the forearm, where it passes two fibro-muscular tunnels (muscle buttonhole of the round pronator and arcade of the superficial flexor of the fingers). The two upper bundles of the round pronator (the supracondylar - from the inside and the coronary - from the outside) form a ring, passing through which the median nerve is separated from the lateral artery from it. Somewhat below 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 beam, on the inner slope of the coronal process. The anatomical basis for nerve irritation is the hypertrophy of the round pronator or, sometimes, the unusually thick aponeurotic edge of the superficial flexor of the fingers.

The next level of possible compression of the median nerve is the wrist. There is a carpal tunnel, the bottom and side walls of which form the bones of the wrist, and the roof - a transverse wrist ligament. Through the canal pass tendons of the flexor of the fingers, and between them and the transverse wrist ligament - the median nerve. Thickening of the flexor tendons of the fingers or the transverse wrist ligament can lead to compression of the median nerve and vessels feeding it.

Lesions of the median nerve develop: in some diseases with proliferation of connective tissue (endocrine diseases and disorders - toxicosis in pregnancy, insufficiency of ovarian function, diabetes mellitus, acromegaly, myxedema, etc.); diffuse connective tissue diseases (rheumatoid polyarthritis, systemic scleroderma, polymyositis); diseases associated with metabolic disorders - gout; with local lesions of the walls and the contents of the carpal tunnel (short-term extreme loads or less intense long-term loads in gymnasts, milkmaids, laundresses, knitters, typists, etc.). In addition, the median nerve can be affected by trauma, wounds, wrist arthrosis and finger joints, inflammatory processes of carpal tunnel contents (tendovaginitis, insect bites). It is possible that the median nerve is affected by pseudotumorous hyperplasia and carpal tunnel tumors (lipo- matic hyperplasia of the median nerve in the canal region, neurofibromatosis, extraneural angiomas, myeloma) and abnormalities in the structure of the skeleton, muscles and vessels in the carpal tunnel.

Here are the syndromes of the median nerve at different levels. The syndrome of the supratembral ulnar trough is a tunnel syndrome characterized by pain, paresthesia and hypesisesia in the innervation zone of the median nerve, the weakness of the flexor of the hand and the fingers of the muscles opposing and withdrawing the thumb. Painful sensations provoke extension of the forearm and pronation in combination with forced flexion of the fingers. The supra-adrenal apophysis occurs in the population in about 3% of individuals. Syndrome nadnomyshlkovogo apophysis rarely occurs.

Syndrome of the round pronator - compression of the median nerve as it passes, both through the ring of the round pronator, and through the arcade of the superficial flexor of the fingers. The clinical picture includes paresthesia and pain in the fingers and hands. Pains are often irradiated on the forearm, less often on the forearm and shoulder. Hypescension is detected not only in the finger zone of innervation of the median nerve, but also in the inner half of the palmar surface of the hand. Often a paresis of the flexor of the fingers is detected, and also the muscle of the opposite arm and the short deflecting muscle of the first finger. The diagnosis is helped to identify local soreness with pressure in the area of the round pronator and the occurrence of paresthesia in the fingers, as well as the elevation and turnstile tests.

[1], [2], [3], [4]