Symptoms of lesions of the ulnar nerve and its branches

Ulnar nerve (n. ulnaris). The ulnar nerve is formed from the fibers of the CVIII - T: spinal nerves, which pass supraclavicularly as part of the primary lower trunk of the brachial plexus and subclavianly - as part of its secondary medial cord. Less often, the ulnar nerve additionally includes fibers from the CVII root.

The nerve is located initially medially from the axillary and upper part of the brachial artery. Then, at the level of the middle third of the arm, the ulnar nerve departs from the brachial artery. Below the middle of the arm, the nerve passes posteriorly through an opening in the medial intermuscular septum of the arm and, located between it and the medial head of the triceps brachii, shifts downward, reaching the space between the medial epicondyle of the humerus and the olecranon process of the ulna. The section of fascia thrown between these two formations is called the supracondylar ligament, and in the lower bone-fibrous canal - the supracondylar-ulnar groove. The thickness and consistency of the fascia section in this place vary from thin and web-like to dense and ligament-like. In this tunnel, the nerve usually lies against the periosteum of the medial epicondyle in the groove of the ulnar nerve and is accompanied by the recurrent ulnar artery. Here is the upper level of possible compression of the nerve in the ulnar region. The continuation of the supracondylo-ulnar groove is the cleft of the flexor carpi ulnaris. It exists at the level of the upper place of attachment of this muscle. This second possible place of compression of the ulnar nerve is called the cubital tunnel. The walls of this canal are limited externally by the olecranon process and the elbow joint, internally by the medial epicondyle and the ulnar collateral ligament, partially adjacent to the internal labrum of the trochlea of the humerus. The roof of the cubital tunnel is formed by a fascial band that extends from the olecranon process to the internal epicondyle, covering the ulnar and brachial bundles of the flexor carpi ulnaris and the space between them. This fibrous band, which has the shape of a triangle, is called the aponeurosis of the flexor carpi ulnaris, and its particularly thickened proximal base is called the arcuate ligament. The ulnar nerve emerges from the cubital canal and is then located on the forearm between the flexor carpi ulnaris and the flexor digitorum profundus. From the forearm to the hand, the nerve passes through the fibro-osseous canal of Guyon. Its length is 1-1.5 cm. This is the third tunnel in which the ulnar nerve can be compressed. The roof and bottom of Guyon's canal are connective tissue formations. The upper one is called the dorsal carpal ligament, which is a continuation of the superficial fascia of the forearm. This ligament is reinforced by tendinous fibers of the flexor carpi ulnaris and the palmaris brevis muscle. The bottom of Guyon's canal is formed mainly by the continuation of the flexor retinaculum, which in its radial part covers the carpal canal. In the distal part of Guyon's canal, its bottom includes, in addition to the flexor retinaculum, also the pisiform-uncate and pisiform-metacarpal ligaments.

The next level of possible compression of the deep branch of the ulnar nerve is the short tunnel through which this branch and the ulnar artery pass from Guyon's canal into the deep space of the palm. This tunnel is called the pisiform-uncinate tunnel. The roof of the entrance to this canal is formed by connective tissue located between the pisiform bone and the hook of the hamate bone. This dense convex tendinous arch is the origin of the muscle - the short flexor of the little finger. The bottom of the entrance to this tunnel is the pisiform-uncinate ligament. Passing between these two formations, the ulnar nerve then turns outward around the hook of the hamate bone and passes under the origin of the short flexor of the little finger and the muscle that opposes the little finger. At the level of the pisiform-uncinate canal and distal to it, fibers depart from the deep branch to all the proper muscles of the hand supplied by the ulnar nerve, except for the muscle that abducts the little finger. The branch to it usually departs from the common trunk of the ulnar nerve.

In the upper third of the forearm, branches extend from the ulnar nerve to the following muscles.

The flexor carpi ulnaris (innervated by the CIII-TX segment) flexes and adducts the wrist.

A test to determine its strength: the subject is asked to bend and adduct the wrist; the examiner resists this movement and palpates the contracted muscle.

Deep flexor of the fingers; its ulnar part (innervated by segment CVIII - TI) flexes the distal phalanx of the IV - V fingers.

Tests to determine the action of the ulnar portion of this muscle:

• the subject's hand is placed palm down and pressed firmly against a hard surface (table, book), after which he is asked to make scratching movements with his fingernail;
• The subject is asked to fold his fingers into a fist; if this muscle is paralyzed, the fingers are folded into a fist without the participation of the fourth and fifth fingers.

A test to determine the strength of this muscle: the distal phalanx of the IV-V fingers is asked to be bent; the examiner fixes the proximal and middle phalanges in an extended state and resists bending the distal phalanges.

At the level of the middle third of the forearm, a sensitive palmar branch departs from the ulnar nerve, which innervates the skin of the area of the eminence of the little finger and slightly higher. Below (along the border with the lower third of the forearm, 3-10 cm above the wrist) another sensitive dorsal branch of the hand departs. This branch is not affected by pathology in the Guyon canal. It passes between the tendon of the ulnar flexor of the hand and the ulna to the back of the hand and divides into five dorsal nerves of the fingers, which end in the skin of the back of the V, IV and ulnar side of the III finger. In this case, the nerve of the V finger is the longest and reaches the nail phalanx, the rest reach only the middle phalanges.

The continuation of the main trunk of the ulnar nerve is called its palmar branch. It enters Guyon's canal and in it, 4-20 mm below the styloid process of the radius, it divides into two branches: superficial (mainly sensory) and deep (mainly motor).

The superficial branch passes under the transverse carpal ligament and innervates the palmaris brevis muscle. This muscle pulls the skin to the palmar aponeurosis (innervated by the CVIII - TI segment).

Below the ramus superficialis it divides into two branches: the actual digital palmar nerve (supplies the palmar surface of the ulnar side of the fifth finger) and the common digital palmar nerve. The latter goes in the direction of the fourth interdigital space and divides into two more proper digital nerves, which continue along the palmar surface of the radial and ulnar sides of the fourth finger. In addition, these digital nerves send branches to the back of the nail phalanx of the fifth finger and the ulnar half of the middle and nail phalanx of the fourth finger.

The deep branch penetrates into the palm through the space between the flexor of the fifth finger and the muscle that abducts the little finger. This branch arcs toward the radial side of the hand and supplies the following muscles.

The muscle that adducts the thumb (innervated by segment CVIII).

Tests to determine its strength:

• the subject is asked to move the first finger; the examiner resists this movement;
• The subject is asked to press an object (a strip of thick paper, tape) with the proximal phalanx of the first finger to the metacarpal bone of the index finger; the examiner pulls out this object.

When this muscle is paresis, the patient reflexively presses the object with the nail phalanx of the first finger, i.e. uses the long flexor of the first finger, innervated by the median nerve.

The abductor muscle of the little finger (innervated by segment CVIII - TI).

A test to determine its strength: the subject is asked to move the fifth finger; the examiner resists this movement.

The flexor digiti minimi brevis (innervated by segment CVIII) flexes the phalanx of the fifth finger.

A test to determine its strength: the subject is asked to bend the proximal phalanx of the fifth finger and straighten the other fingers; the subject resists this movement.

The opposing muscle of the little finger (innervated by segment CVII - CVIII) pulls the fifth finger to the midline of the hand and opposes it.

A test to determine the action of this muscle: they suggest bringing the extended V finger to the I finger. When the muscle is paresis, there is no movement of the fifth metacarpal bone.

Flexor pollicis brevis; its deep head (innervated by segment CVII - TI) is supplied jointly with the median nerve.

The lumbrical muscles (innervated by the CVIII - TI segment) flex the proximal and extend the middle and distal phalanges of the II - V fingers (I and II mm. lumbricales are supplied by the median nerve).

The interosseous muscles (dorsal and palmar) flex the main phalanges and simultaneously extend the middle nail phalanges of the II - V fingers. In addition, the dorsal interosseous muscles abduct the II and IV fingers from the III; the palmar muscles adduct the II, IV and V fingers to the III finger.

A test to determine the action of the lumbrical and interosseous muscles: they ask you to bend the main phalanx of the II - V fingers and simultaneously extend the middle and nail.

When these muscles are paralyzed, the fingers become claw-like.

Tests to determine the strength of these mice:

• the subject is asked to bend the main phalanx of the II - III fingers, when the middle and nail are extended; the examiner resists this movement;
• the same is suggested to be done for the IV - V fingers;
• then they ask to straighten the middle phalanx of the II-III fingers when the main ones are bent; the examiner resists this movement; d) the subject does the same for the IV-V fingers.

Test to determine the action of the dorsal interosseous muscles: the subject is asked to spread his fingers with the hand in a horizontal position.

Tests to determine their strength: they ask to move the 2nd finger away from the 3rd; the examiner resists this movement and palpates the contracted muscle; the same is done for the 4th finger.

A test to determine the action of the palmar interosseous muscles: the subject is asked to bring the fingers together with the hand in a horizontal position.

Tests to determine the strength of the palmar interosseous muscles:

• the subject is asked to hold a flat object (ribbon, piece of paper) between the second and third fingers; the examiner tries to pull it out;
• They suggest bringing the second finger to the third; the examiner resists this movement and palpates the contracted muscle.

Symptoms of ulnar nerve damage consist of motor, sensory, vasomotor and trophic disorders. Due to paresis of m. flexoris carpi ulnaris and the predominance of the action of antagonist muscles, the hand deviates to the radial side. Due to paresis of mm. adductoris pollicis and the antagonistic action of m. abductoris pollicis longus et brevis, the first finger is abducted outward; holding objects between the first and second fingers is difficult. The fifth finger is also slightly abducted from the fourth finger. The predominance of the extensor function leads to hyperextension of the main and flexed position of the distal phalanges of the fingers - a "claw-shaped hand" typical of ulnar nerve damage develops. The claw-shaped nature is more pronounced in the fourth and fifth fingers. Adduction and abduction of the fingers are impaired, the patient cannot grasp and hold objects between the fingers. Atrophy of the muscles of the first dorsal space, hypothenar and interosseous muscles develops.

Sensory disturbances extend to the ulnar part of the hand on the palmar side, the area of the V and ulnar side of the IV fingers, and on the back side - to the area of the V, IV and half of the III fingers. Deep sensitivity is impaired in the joints of the V finger.

Cyanosis, coldness of the inner edge of the hand and especially the little finger, thinning and dryness of the skin are often observed.

When the ulnar nerve is damaged at different levels, the following syndromes occur.

Cubital syndrome of the ulnar nerve develops in rheumatoid arthritis, in osteophytes of the distal end of the humerus, in fractures of the epicondyle of the humerus and bones forming the elbow joint. In this case, the angle of movement of the ulnar nerve increases and its path on the shoulder and forearm is lengthened, which is noticeable when bending the forearm. Microtraumatization of the ulnar nerve occurs, and it is affected by a compression-ischemic mechanism (tunnel syndrome).

Occasionally, a habitual displacement of the ulnar nerve (dislocation) occurs, which is facilitated by congenital factors (posterior position of the medial epicondyle, narrow and shallow supracondylo-ulnar groove, weakness of the deep fascia and ligamentous formations above this groove) and acquired (weakness after injury). When the forearm is flexed, the ulnar nerve is displaced to the anterior surface of the medial epicondyle and returns back to the posterior surface of the epicondyle during extension. External compression of the nerve occurs in people who remain in one position for a long time (at a desk, writing table).

Subjective sensory symptoms usually appear before motor symptoms. Paresthesia and numbness are localized in the ulnar nerve supply zone. After several months or years, weakness and hypotrophy of the corresponding hand muscles join in. In acute cubital syndrome caused by nerve compression during surgery, numbness occurs immediately after recovery from anesthesia. Paresis of the long muscles (e.g., the ulnar flexor of the wrist) is detected less frequently than paresis of the hand muscles. Hypesthesia is localized on the palmar and dorsal surfaces of the hand, the fifth finger, and the ulnar side of the fourth finger.

Ulnar nerve damage in the hand occurs in the following variants:

1. with sensitive prolapses and weakness of the hand's own muscles;
2. without sensory loss, but with paresis of all the muscles of the hand supplied by the ulnar nerve;
3. without loss of sensitivity, but with weakness of the muscles innervated by the ulnar nerve, excluding the hypothenar muscles;
4. only with sensitive loss, in the absence of motor loss.

There are three types of syndromes, combining isolated lesions of the deep motor branch into one group. The first type of syndrome includes paresis of all muscles of the hand supplied by the ulnar nerve, as well as loss of sensitivity along the palmar surface of the hypothenar, fourth and fifth fingers. These symptoms can be caused by compression of the nerve slightly above Guyon's canal or in the canal itself. In the second type of syndrome, weakness of the muscles innervated by the deep branch of the ulnar nerve appears. Superficial sensitivity in the hand is not impaired. The nerve can be compressed in the area of the hook of the hamate bone between the attachment of the abductor muscle and the flexor of the little finger, when the ulnar nerve passes through the opposing muscle of the little finger and, less often, in cases where the nerve crosses the palm behind the flexor tendons of the fingers and in front of the metacarpal bones. The number of affected muscles depends on the site of compression along the deep branch of the ulnar nerve. With fractures of the forearm bones, tunnel syndromes and compression of the median and ulnar nerves in the wrist area may occur simultaneously - the third type of syndrome.

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