MEDIAN NERVE

From Big Medical Encyclopedia

MEDIAN NERVE [n. medianus (PNA, JNA, BNA)] — the long branch of a brachial plexus innervating muscles of a forearm and a brush, skin of a palm and the palmar surface of the I—III fingers and the beam surface of the IV finger and also skin of their dorsum in distal phalanxes.

S.'s anatomy of N, a zone and objects of his innervation were in detail studied in 18 — 19 centuries by V. L. Gruber, F. Genle, Krause (To. F. T. Krause). In 20 century Borkhardt and Vyasmensky (M. of Borchardt, Wjasmenski), A. V. Triumfov, A. H. Maksimenkov submitted data on a puchkovy structure of a nerve, its bonds with the next nerves, quantity and a ratio of the N of nerve fibrils making S.

The anatomy

S. of N forms medial (radix med.) and lateral (radix lat.) roots respectively from medial and lateral bunches of a subclavial part brachial plexus (see). The specified roots cover a humeral artery and connect, forming S.'s trunk of N. Connection of roots of S. of N can come at various levels — from an axillary pole where bunches cover an axillary artery, to the lower third of a shoulder where bunches surround a humeral artery, and in 25% of observations the loop («fork») of S. of N can be and double (see tsvetn. the tab. to St. Elbow nerve , Beam nerve , fig. 1, 2, 4). In 80% of cases nerve fibrils C. of N belong to C5 — Th1, in 20% of cases — C6 — Th1. At the level of an upper third of a shoulder of S. of N contains from 1 to 24 bunches of nerve fibrils (on average 12) and to 38 at the level of an elbow pole where there is an intra barreled formation of muscular branches — to 38 bunches. The amount of nerve fibrils in S. of N fluctuates in considerable limits (see. Nerves ). So, on the middle of a shoulder there are 19 — 32 thousand myelin and 18 — 25 thousand amyelinic fibers. Amount of myelin fibers of various diameter in S. of N at people variously: fibers of a bottom of m to 3 microns — from 3 to 27%, to dia. 3,1 — 5 microns — from 8 to 24%, 5,1 — 10 microns — from 54 to 88%, St. 10 microns — from 0,5 to 10%.

In S.'s shoulder of N is located in a fascial vagina of a neurovascular bunch, being in an upper third of a shoulder in front and lateralno, and in the lower third — in front and medially from a humeral artery. In an elbow pole of S. of N lies at medial edge of a sinew of a biceps of a shoulder, further approaches under an aponeurosis of a biceps of a shoulder, between heads of the round pronator and on a forearm is located together with the median artery (a. mediana) accompanying it between superficial and deep sgibatel of fingers. In the lower third of a forearm of S. of N is in a median furrow (sulcus medianus) formed lateralno — a beam sgibatel of a wrist and medially — a superficial sgibatel of fingers; the furrow and a nerve are covered with a sinew of a long palmar muscle. On S.'s shoulder of N, as a rule, does not give branches, but quite often forms bonds with a musculocutaneous nerve (of communicans cum n. mus-culocutaneo). Anatomic options when the N completely replaces with S. a musculocutaneous nerve are noted; in such cases it gives branches in a shoulder to flexor muscles — two-headed, klyuvovidnoplechevy and humeral. In an elbow pole of S. of N forms the joint branch (of articularis) going to an elbow joint and muscular branches (rr. musculares) going to the round pronator, a long palmar, beam sgibatel of a wrist, a humero-ulnar muscle, a head of a superficial sgibatel of fingers. Muscular nerves can depart from S. of N the general trunk, to-ry in the subsequent gives muscular branches to separate muscles (a group way of an innervation), or is consecutive, branching off from S. N to muscles in the form of independent nerves (a single way of an innervation). In a forearm N depart from S.: front interosseous nerve (forearms) [n. interosseus (antebrachii) ant.]; muscular branch to a superficial sgibatel of fingers, in particular by the portion going to an index finger; palmar branch (of palmaris n. mediani — is changeable); the connecting branch going to an elbow nerve (of communicans cum n. ulnari) — to 30% of observations. The front interosseous nerve lies on an interosseous membrane of a forearm together with the vessels of the same name; it gives muscular branches (rr. musculares) to a long sgibatel of a thumb of a brush, a beam part of a deep sgibatel of fingers, the square pronator, a branch to bones of a forearm, an interosseous membrane of a forearm, a branch to a dorsum of a radiocarpal joint. The palmar branch of S. of N departing in the lower third of a forearm innervates a part of skin of a palm. On S.'s palm of N, having passed through the channel of a wrist, is divided into three general palmar manual nerves (nn. digitales palmares communes), to-rye close basis of proximal phalanxes I, II, III fingers are divided into 7 own palmar manual nerves (nn. digitales palmares proprii). These nerves innervate skin of beam and elbow surfaces I, II, III fingers and the beam surface of the IV finger, and also a dorsum of distal phalanxes of these fingers. Zones of an innervation of skin of a palmar surface of fingers are changeable, imposings of zones of a skin innervation of median and elbow nerves are observed. Muscular branches depart from the I general palmar manual nerve (rr. musculares) to muscles of the tenor or an eminence of the I finger of a palm — to the short muscle which is taking away a thumb, a superficial head of a short sgibatel of a thumb, the muscle opposing a thumb; to I, II cher-veobraznm to muscles. III general manual the nerve has a connecting branch with an elbow nerve (r. communicans cum n. ulnari) which arrangement can vary.

Pathology

S.'s Defeats N are a traumatic, kompression-but-ischemic, inflammatory and intoksikatsionny origin. Gunshot wounds and mechanical injury of S. of N are possible at any level from a brachial plexus to fingers of a hand. At home accidents of S. of N it is more often damaged on a forearm (especially in its distal third) in combination with a fracture of bones (almost in half of S.'s injuries of N) or with injury of sinews of a sgibately brush and fingers (e.g., at cut wounds of a forearm). Compression and ischemic damage of S. of N quite often arises at the level of the carpal channel (the channel of a wrist) or in the field of the round pronator of a forearm (see. Tunnel syndromes ), as a result of local fibrous and dystrophic process, at S.'s compression of N cicatricial tkanyo in cases of deep thermal burns, after injections of medicines, etc. S.'s ischemia of N is possible also at injury of an axillary or humeral artery. Functions C. of N are broken at his primary tumors (neurinoma, neurofibromas, lipofibromas) or as a result of a secondary prelum of a trunk of a nerve by tumors, coming from fabrics, adjacent to it (bones, muscles, connective tissue educations). The isolated inflammatory defeat of S. of N is observed seldom; usually the nerve is involved in process at deep phlegmons of a shoulder, forearm, osteomyelitis. Intoksikatsionny defeats of S. of N are noted in cases of poisoning with arsenous drugs, mercury, hlorofosy; at endogenous intoxication of a branch of S. of N are surprised together with distal branchings of other nerves of an upper extremity (see. Elbow nerve , Beam nerve , Peripheral nervous system , Polyneuritis ), napr, at a diabetes mellitus, hron. renal failure, etc.

Fig. 1. A hand of the patient with defeat of a median nerve: in attempt of compression in a fist I, II and III fingers are not bent, the I finger is not opposed.
Fig. 2. A hand of the patient with defeat of a median nerve («a monkey hand»): the palm is flattened owing to an atrophy of muscles of an eminence of a thumb, I and II worm-shaped muscles.
Fig. 3. The diagrammatic representation of zones of the broken skin sensitivity on back and palmar surfaces of a brush at defeat of a median nerve: zones of the broken skin sensitivity are shaded.

The wedge, picture of defeat of S. of N depends on level and extent of disturbance of its conductivity, and also on specific features of its structure and connection with the next nerves. Symptoms of defeat of S. of N on the site from a brachial plexus to an otkhozhdeniye of a muscular branch to the round pronator are identical: disturbance of pronation of a forearm, weakening of bending of a brush, I, II and III fingers (at test of compression in a fist), difficulty of extension of distal and average phalanxes II and III fingers, bendings and oppositions of a thumb, reduction and assignment II and III fingers (fig. 1); the clearest atrophy of muscles in the field of an eminence of the I finger, and also I and II worm-shaped muscles (mm. lumbricales) owing to what the palm is flattened, the I finger is closely given (in one plane) to the II finger that gives to a brush a peculiar look — a so-called monkey hand (fig. 2). Zones of disturbance of skin sensitivity (anesthesia) are found at S.'s defeat N on the palmar and back surfaces of distal and partially average phalanxes of II, III and beam surfaces of the IV fingers (fig. 3), the hypesthesia of skin of a palmar surface of the I finger and a beam surface of a brush (in this zone the hyperpathia is possible) is observed; deep sensitivity is broken in interphalangeal joints of II and less often than the III finger, vibration — in distal and average phalanxes II and III fingers.

At S.'s defeats N at the level of a forearm motive frustration are limited only to a radiocarpal joint and fingers of a hand; bending and opposition of a thumb, reduction and assignment II and III fingers, extension of distal and average phalanxes of these fingers are impossible, bending of a brush is weakened; disorders of sensitivity are expressed more clearly, than at S.'s damage by N on a shoulder. The halfbent brush, the halfbent and given fingers, ekstenziya of a brush and fingers, a hypesthesia which sometimes are sharply expressed with a hyperpathia, painful rigidity in radiocarpal, metacarpophalangeal and interphalangeal joints are characteristic of partial disturbance of conductivity of S. of N.

Constants and the expressed signs of defeat of S. of N are vascular and vegetative and trophic frustration: cyanosis, disturbance of sweating (at full disturbance of conductivity of a nerve — an anhidrosis, at partial — hypo - or a hyperhidrosis), thinning of skin of fingers, dryness and fragility of nails. Occasionally trophic distal phalanx ulcers II and III fingers develop. Almost constant symptom of defeat of S. of N are intensive and persistent pains in a brush and fingers (in a zone of a hypesthesia). More than in 1/4 observations of pain gain character kauzalgiya (see). The most severe forms of a kauzalgiya observe at partial injury of a nerve and at combined (injury of a bone and blood vessels).

Apply the following tests to detection of paresis of the muscles innervated by S. in N: compression of a brush in a fist — II and III fingers are bent insufficiently and do not rest against a palm; pressing of a brush to a table a palm down — impossibility to make the scratching movement II a finger; bending of distal phalanxes of I and II fingers — impossibility to concern a tip of a thumb of a distal phalanx of index. Apply effleurage on the course of a nerve to diagnosis of level of defeat of S. of N — sometimes at percussion at the level of defeat there are pain and paresthesias in the I—IV fingers and in a palm. The damage rate of a nerve is defined by electrophysiologic methods of a research (see. Hronaksimetriya , Electromyography ).

Fig. 4. Diagrammatic representation of quick accesses (fat solid lines) to a median nerve: the projection of a median nerve is shown by a dotted line.

Treatment of defeat of S. of N is defined by character caused it patol. influences. Conservative treatment is similar to treatment at damages of other peripheral nerves of a hand and is directed to stimulation of regeneration of a nerve and elimination of a pain syndrome. An operative measure produce at S.'s rupture N, his tumors, a compression of a nerve a bone callosity, tumors, coming from surrounding fabrics, at ischemia and a compression of a trunk of a nerve in patholologically the changed osteofibrous canals, and also at the expressed and persistent pain syndrome. Operations are performed in special hospitals with use of microneurosurgical tools and optics (see. Microsurgery ). The principles of treatment and technology of carrying out operations at defeats of peripheral nerves of a hand — see. Elbow nerve, Beam nerve. Quick accesses to S. of N at various levels are shown in fig. 4. A contraindication to operation are the remote term after an injury, the expressed atrophy of muscles, irreversible changes in the sukhozhilnosvyazochny device from an unremovable tugopodvizhnostyo or an ankilozama in joints of a brush and fingers. Prevention of pain syndromes at S.'s damage by N consists in prevention of commissural process at primary and delayed operations of recovery of an integrity of a nerve (an enveloping of a nerve a film, fatty tissue, a muscle on a leg, etc.). Operational treatment of already arisen pain syndromes, especially kauzalgy, consists in a ganglioektomiya (removal star-shaped, Th2 — Th3 of nodes of a sympathetic trunk), ramicotomies (see. Gangliectomy , Ramicotomy ).

At a compression of a nerve in the channel of a wrist operation consists in a section of a cross ligament of wrist and S.'s decompression of N. Postoperative fixing of an extremity ensures safety of epinev-ralny and fascicular seams.

Efficiency of operations of recovery of a nerve depends on terms of operation after an injury, an atravmatichnost of manipulations on a nerve, the accuracy of comparison without tension of the ends of a nerve and sewing together of neurofibrilla (see. Nervous seam ). Use sovr. microsurgical methods of an interfastsikulyarny seam promotes full recovery of functions of a hand at most of patients with S.'s damage by N.



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D. K. Bogorodinsky, A. A. Skoromets; S. S. Mikhaylov (An.), V. S. Mikhaylovsky (neyrokhir.).

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