ANATOMY OF RADIAL,MEDIAN &ULNAR NERVE PRESENTER: Dr ANKUR MITTAL
RADIAL NERVE•The radial nerve arises from the posteriorcord of the brachial plexus and receivescontribution from the fifth to eighthcervical roots and sometimes T1•It is primarily a motor nerveIt commences its decent into the arm bypassing anterior to the latissimusinsertion and dives into the triceps to lieon the posterior surface of the humerusapprox 97 to 142 mm distal to theacromion.
It lies on the surface of the medial head of the triceps, rather than the bonysurface –of the humerus and does not do so until it crosses to the lateralaspect of the humerus along the spiral groove.The lower portion of the radial nerve crosses the midline at an average of15 cm from the distal articular surface and pierces the lateralintermuscular septum at approximately 122 mm (range, 88–152 mm)from the lateral epicondyle. The radial nerve is relatively safe during a posterior approach to the humerus (splitting the triceps). In the posterior approach, the radial nerve islocated 13 to 15 cm proximal to the joint line. For lateral approaches to the humerus, the radial nerve is located approximately 7.5 to 10 cm proximal to the lateral epicondyle
Above the elbow, the radial nerve innervates thelong, lateral, and medial heads of the tricepsOne to 3 cm distal to the lateral epicondyle anddeep to the brachioradialis, the radialnerve splits into the superficial radial nerve andthe posterior interosseous nerve. The superficial radial nerve continues down theforearm along the lateral border of thebrachioradialis and becomes subcutaneous at itsmiddle 1⁄3, innervating the skin on the radialaspect of the forearm and the dorsal aspects ofthe radial three and one half digits3 . The posterior interosseous nerve continuesdown the forearm diving into the supinator andthen emerging to split into several branches thatsupply the extensors of the wrist and hand
The order of innervation of the musculature (proximal to distal) is importantin assessing entrapment syndromes of the radial nerveHowever, variability exists
CLINICAL APPLICATION OF RADIAL NERVECauses of injury of radial nerve:•In axilla Saturday night palsy , crutch palsy• fracture shaft of humerus (Most common)•Gunshot wounds (2nd most common)•Laceration of arm or forearm•Injection injuries•Prolonged local pressure•Entrapment syndromes
Entrapment syndrome..In arm : Fibrous arch of lateral head oftriceps. The posterior interosseousnerve is prone to entrapment at severallevels by various structures. Classically posterior interosseousnerve entrapment is known as radialtunnel syndromeThe radial tunnel begins shortly after thebifurcation of the radial nerve
Radial tunnelThe posterior interosseous nerve passes deepto fibrous bands that are confluent with thebrachialis, brachoradialis, extensor carpiradialis brevis and superficial head of thesupinator, which forms the most proximalroof of the radial tunnel. These fibrous bandsare the first structures that may compress theposterior interosseous nerve.Proximally, the floor : capsule of theradiocapitellar joint. As the posterior interosseous nervecontinues through the tunnel and reachesthe level of the radial neck, the roof ismade of recurrent vessels of the radialartery (Leash of Henry). The Leash ofHenry is the second structure that mayentrap the nerve.
The posterior interosseous nerve thenencounters the extensor carpi radialisbrevis and gives off a branch to it . Theextensor carpi radialis brevis maycompress the nerve at this location.The posterior interosseousnerve passes beneath the sharpproximal edge of the supinator (Arcade ofFrohse), which is the final location whereit may be compressed.Other causes of entrapment of PIN•Fracture dislocation or dislocation ofelbow•Volchemic ichaemic contracture•Neoplasm•Enlarged bursae•Anurysm•Rheumatoid synovitis of elbow
MEDIAN NERVEThe median nerve has contributions fromessentially the entire brachial plexus (C5-T1), and is formed by portions of thelateral and medial cord.The median nerve does not providemotor or sensory innervation until itreaches the elbow. The median nerve courses down the arm within the lateral intermuscular septum, deep to the short head of the biceps and lateral to the brachial artery.
At the midbrachium, it crosses to the medial side of the brachial artery anddescends to the antecubital fossa.In the antecubital fossa, the median nervelies deep to the bicipital aponeurosis,medial to the antecubital vein, and medialto the brachial artery, Although the median nerve is anterior to the trochlea and superficial to the brachialis, it occasionally can be found medial to the trochlea, such that it lies anterior to the medial epicondyle. This is of clinical importance in elbow dislocations.
Distal to the elbow, the median nerve courses down the forearm deep to the flexor digitorum superficialis andsuperficial to the flexor digitorum profundus.In the distal 1⁄3 of the forearm, themedian nerve emerges from beneath theflexor digitorum superficialis to lie medialto the flexor carpi radialis and lateral tothe palmaris longus, before entering thecarpal tunnelAt the level of the junction of the twoheads of the pronator teres, the mediannerve gives off the anterior interosseousnerve
The anterior interosseous nerve quickly dives deep to the flexor and pronatormass and travels with the anterior interosseous artery (a branch of the ulnarartery) to travel on the volar surface of the interosseous membraneThe most consistent order of branches offthe median nerve isThe innervation to the pronator teresis proximal to the elbow, whereas theremaining muscles are innervateddistal to the elbow.
The median nerve gives a palmarcutaneous branch that provides sensationto thenar skin of the palm, and is mostcommonly branches 4 to 5 cm proximal tothe wrist, lying on the ulnar side of theflexor carpiradialisWithin the carpal tunnel, the mediannerve divides into three terminalbranches. The lateral branches : thumb and radial side of the index finger Terminal branches of the medial division: middle finger and radial aspect of the ring finger.
The lateral-most division gives off the terminal motor innervation of themedian nerve, the recurrent motor branch, that innervates the abductor pollicis brevis,flexor pollicis brevis, opponens pollicis, and the lateral two lumbricals before to dividinginto its terminal sensory branches. The recurrent motor branch is of particular interest because it has been observed to have a variable location of origin. Three variations, the most common of which had the nerve originating beyond the carpal tunnel (46%), within the tunnel but traversing to the thenar eminance distal to the tunnel (31%), a finally, one that originated within the tunnel and pierced the transverse carpal ligament (23%).
CLINICAL APPLICATION OF MEDIAN NERVECAUSES OF INJURY OF MEDIAN NERVE:•Near axilla : injury occur along with ulnar nerve , musculocutaneous nerve andbrachial artery.•Arm : Ligament of struthers : It is seen 5 cm proximal to the medial epicondyle and is a fibrous band that interconnects a bony spur on the distal humerus to the medial epicondyle•Elbow : supracondylar fracture Posterior dislocation of elbow•Forearm and wrist: lacerations
Compression of anterior interroseus nerve•Tentinous origin of flexor digitorum•Pronater teres•Tendons from flexor digitorum to flexor policis longus•Accessory head of flexor policis longus (gantzer muscle)•Aberrant radial artery•Thrombosis of ulnar colleteral artery•VIC
ULNAR NERVEIt composed of fibers from C8and T1 coming from medial cordof brachial plexus.Above the axilla: It courses withaxillary A. and vein and lie deepto pectoralis minorIn the axilla: It crosses medial tobrachial artery and lii deep topectoralis major
At the level of the distal attachment of thecoracobrachialis to the humerus (average10 cm proximal to the medial epicondyle),the ulnar nerve pierces the medialintermuscular septum to enter theposterior compartment of the brachium.Here it lies on the anterior border of themedial head of the tricepsThen it passes through the ligament ofStruthers and then behind the medialepicondyle through cubital tunnel
As the ulnar nerve exists the cubital tunnel, it courses between the twoheads of the flexor carpi ulnaris and enters the anterior compartment ofthe forearmShortly after exiting the cubital tunnel, the ulnar nerve gives off motorbranches to the flexor carpi ulnaris.It then lies on the anterior surface of the flexor digitorum profundus.At approximately 5 cm distal to the medial epicondyle, the ulnar nervegives off branches to the ulnar aspect of the flexor digitorum profundusproviding innervation to the long flexors of the ring and small fingers.In the middle of the forearm, at approximately 12 cm distal to the medial epicondyle,the ulnar nerve becomes superficial and meets with the ulnar artery as it travelstoward the wrist.
Before the flexor carpi ulnaris becomestendinous, the ulnar nerve divides. Themore superficial of the two branchescourses dorsally toward the distal ulnaand dorsum of the hand and becomes thedorsal sensory branch of the ulnar nerve. Near the wrist the ulnar nerve rises superficial to the flexor retinaculum and lies under the tendon of the flexor carpi ulnaris before its attachment to the pisiform . The ulnar nerve then turns radial to the pisiform to lie in a fibrous tunnel known as Guyon’s Canal
Within the canal, the ulnar nerve dividesinto motor and sensory branches.Branches of nerve here shows manyvariations so surgeon should be verycautious will disecting here. Within Guyon’s canal there are three locations where the nerve may be entrapped: Zone I : proximal in the canal, before the division of the deep and superficial nerve. A patient with a Zone I entrapment will have motor weakness of all intrinsics, and numbness in the ulnar ring and entire small finger.
Zone II : at the distal radial aspect after the superficial and deep branchesof the ulnar nerve have divided. In Zone II entrapment, the superficialbranch is spared and there is no loss of sensation in the ring and smallfingers, but the intrinsics are weak, with the exception of some of thehypothenar muscles, particularly the palmaris brevis.. Zone III also is distal, but the compression occurs more medially in the canal, compressing the superficial branch and presents as numbness in the ring and small fingers Finally, there are two well described connections between the median and ulna nerves that should be mentioned: Riche-Cannieu anastomosis.: It occurs distally as a communication between the palmar cutaneous branches of the median and ulnar nerves.
The Martin-Gruber or proximal anastomosis : It is an anastomoticconnection between the median and ulnar nerve in the forearm. It is of 4 types: Type I, anterior interosseous nerve to the ulnar; Type II, median to the ulnar; Type III, branches to flexor digitorum profundus and to the ulnar; and Type IV, a combination of Types I, II, and III. The significance of these findings is the crossover contributions from the median nerve that may lead to an underestimation of an injury to the ulnar nerve clinically and electrodiagnostically
CLINICAL APPLICATION OF ULNAR NERVECauses of injury of ulnar nerve according to level:Upper arm : it get injured along with other structures like median N andbrachial A.Middle arm : Relatively protectedDistal arm or elbow : Dislocation of elbow Supracondylar or condylar fractureDistal forearm and wrist : ( Most commonly injured) Gunshot wounds Laceration Fractures Dislocation
Tardy ulnar palsy : Malunited fracture of lateral humeral epicondylein children Displaced fracture of meial humeral epicondyle Dislocation of elbow Contusion Shallow ulnar groove Hypoplasis of humeral trochlea Recurrent subluxation or dislocation of ulnar nerveEntrapment syndrome:Arcade of struthers: A thick fascial band thatconnects the medial head of the triceps to the intermuscular septum crosses the ulnar nerve at approximately 8 cm proximal to the medialepicondyleCubital tunnel: A fibrous sheath (Osborne’sligament) laterally, and the head of the flexorcarpi ulnaris posteromedially
Guyon’s canal: floor: the transverse carpal ligament, and also the flexordigitorum profundus, pisohamate and pisometacarpal ligaments, and theopponents digiti minimi.The roof : the palmar carpal ligament and the palmaris brevis, and distallypasses ulnar to the hook of the hamate •Tight fascia or ligament •Neoplasms •Rheumatoid synovitis •Aneurysm •Vascular thromboses •Anomolous muscles •Prologed direct pressure during surgery