2. Ulnar, Median + Radial

anterior division of the lower trunk continues as the medial cord, from which derives the ulnar nerve. Its fibres originate mainly from C8 and T1, although it may also receive a contribution from C7 It passes through the extensor compartment of the upper arm, lying medial to the axillary and brachial arteries. It then continues medially on the anterior aspect of the medial head of triceps to pass beneath the medial epicondyle of the humerus, where it lies in the ulnar groove. It enters the forearm between the two heads of flexor carpi ulnaris. In the upper part of the forearm, it lies deep to this muscle and separated from the ulnar artery. In the distal forearm, it lies lateral to flexor carpi ulnaris and near to the medial side of the artery. About 5 cm above the wrist, it gives off a dorsal branch before continuing into the hand lateral to the pisiform bone and above the flexor retinaculum.

The ulnar nerve provides the motor supply to flexor carpi ulnaris, to the medial part of flexor digitorum profundus and to the hypothenar muscles. It also supplies all the small muscles of the hand apart from the lateral two lumbricals and the three muscles of the thenar eminence (abductor pollicis brevis, opponens pollicis and part of flexor pollicis brevis). It innervates the deep head of flexor pollicis.

It supplies sensation to the elbow joint but gives off no branches in the upper arm. It supplies the skin over the hypothenar eminence and over the fifth finger as well as over the medial part of the fourth finger.

Ulnar nerve block provides analgesia for procedures on the medial (ulnar) side of the hand and forearm. The nerve supplies sensation to a relatively small area. Digital nerve blocks (‘ring’ blocks) are an easy and reliable method of providing anaesthesia for finger surgery, and so ulnar block is usually reserved for more proximal operations such as palmar fasciectomy. It would be used in isolation only for disease that was restricted to the fifth finger and so is commonly performed jointly with blocks of the other major nerves of the arm.

Damage: even when the arm is lying in the neutral position by the side of the anaesthetized patient, it is vulnerable to pressure, either from arm supports or from the table. It has become routine practice to protect the elbow with padding, and it has also become routine to blame anaesthesia for any ulnar nerve damage. This is despite the fact that ulnar nerve palsy has been reported even when every precaution has been taken. The nerve is also vulnerable to stretch, and so the upper arm should not be displaced posteriorly, nor abducted to greater than 90. Symptoms and signs of injury: apart from the sensory loss and paraesthesia of which the patient will complain, ulnar nerve injury is associated with the classic ‘main en griffe’, or ‘claw hand’. This is because the extensors of the fingers and the long flexors of the hand act unopposed. If the nerve is transected at the elbow the clawing is less marked. This so-called ulnar paradox occurs because the flexor digitorum profundus is also paralyzed.

radial nerve arises from the brachial plexus. The posterior divisions from each of the three trunks form the posterior cord from which derives the radial nerve. Its fibres therefore originate from C5, C6, C7, C8 and T1, and it is the largest branch of the brachial plexus. The radial nerve descends beneath the axillary artery and passes between the long and medial heads of the triceps muscle into the posterior compartment of the arm. It then passes obliquely behind the humerus where it lies in a shallow spiral groove

It is motor in the upper arm to triceps and in the lower arm to brachialis, brachioradialis and to the extensor muscles of the wrist and hand. The area of sensory innervation that is of particular anaesthetic relevance includes much of the dorsum of the hand and part of the radial side of the forearm. (The ulnar nerve supplies the skin over the distal phalanges, the fifth finger and medial side of the fourth finger, and over the fifth and fourth metacarpals.) The radial nerve also supplies cutaneous sensation to the posterior aspect of the forearm and to the skin over the dorsal base of the thumb. (The musculocutaneous nerve supplies much of the radial surface of the forearm.)

Its main use is in conjunction with other blocks to provide analgesia for procedures on the lateral, radial side of the hand and forearm. Digital nerve blocks provide reliable anaesthesia for finger surgery, but radial block can be used for procedures on the base of the thumb and, in combination with musculocutaneous block, to allow the creation of forearm arteriovenous fistulas for dialysis.

Radial Nerve Damage and Its Clinical Signs
Damage: the radial nerve is subject to various types of injury and may be damaged by compression against the upper humerus, as in the so-called Saturday night or crutch palsy. The pressure exerted by an arterial tourniquet can also damage the nerve by the same mechanism. Its close relation to the humerus makes it vulnerable to damage in mid-humeral fractures, and the posterior interosseous branch may be traumatized in injuries to the head of the radius.

Symptoms and signs of injury: overlap of innervation means that sensory loss and paraesthesia may be confined to a relatively small area on the dorsum of the hand. Otherwise radial nerve injury is typically associated with wrist drop due to paralysis of the extensor muscles. If the damage to the nerve has occurred below the elbow, then the functional preservation of extensor carpi radialis longus will minimize this effect.

The median nerve arises from the brachial plexus. The anterior divisions of the upper and middle trunks form the lateral cord, from which derives the lateral head of the median nerve. The anterior division of the lower trunk continues as the medial cord, from which derives the medial head of the median nerve. Its fibres originate therefore from C5, C6, C7, C8 and T1. The nerve passes into the arm lying lateral to the brachial artery, which it then crosses to descend on its medial side to the antecubital fossa, where it is protected by the bicipital aponeurosis.
It passes down into the forearm between the bellies of the deep and superficial flexors of the fingers (flexor digitorum profundus and superficialis) and

It is motor in the forearm to several of the superficial flexors (excluding flexor carpi ulnaris) and in the hand to muscles of the thenar eminence: abductor pollicis brevis, part of flexor pollicis brevis and the opponens pollicis. Its anterior interosseous branch also supplies flexor pollicis longus, pronator quadratus and part of flexor digitorum profundus.
The cutaneous innervation extends to the radial aspect of the palm, and the palmar surface of the radial 3½ digits, together with their dorsal tips as far as the first interphalangeal joint.

Damage: the median nerve is most vulnerable to trauma at the wrist, although it can be injured in supracondylar humeral fractures and following injury to the distal radius. The commonest lesion occurs as a result of compression of the nerve in the carpal tunnel.
Symptoms and signs of injury: trauma at the wrist will paralyze the thenar muscles and cause significant sensory loss. More proximal injury leads to weak wrist flexion, loss of pronation, and loss of flexion of the thumb, index and middle finger. Atrophic changes and wasting of the thenar eminence flatten the contours of the hand