Shehxad HussainTechnologist

Introduction

In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest unprotected nerve in the human body (meaning unprotected by muscle or bone), so injury is common.

The ulnar nerve originates from the C8-T1 nerve roots (and occasionally carries C7 fibres) which form part of the medial cord of the brachial plexus, and descends on the postero-medial aspect of the humerus. The ulnar nerve is derived from the brachial plexus. It is a continuation of the medial cord, containing fibres from spinal roots C8 and T1.

After arising from the brachial plexus, the ulnar nerve descends down the medial side of the upper arm ( postero-medial aspect of the humerus).

From axilla to arm:From the axilla it enters in the arm and stays

between the brachial artery and vein , through the cubital tunnel at elbow.

Because of the mild pain and tingling throughout the forearm associated with an inadvertent impact of the nerve at this point, this is usually called the “FUNNY BONE”.

At the elbow the ulnar nerve lies in a groove(Retrocondylar groove) which is formed bymedial epicondyle humerus and olecranonprocess of ulna, referred as "funny bone".

The ulnar nerve is trapped between the bone and the overlying skin at this point. It enters the forearm through the aponeuroticarcade (Cubital Tunnel)

It enters the anterior (flexor) compartment of the forearm between the humeral and ulnar heads, lying under the aponeurosis of flexor carpi ulnaris alongside the ulna. There it supplies one and a half muscles (flexor carpi ulnaris and the medial half of flexor digitorum profundus) and courses with the ulnar artery, travelling inferiorly with it deep to the flexor carpi ulnaris muscle.

The ulnar nerve enters the anterior (flexor)compartment of the forearm through the twoheads of flexor Carpi ulnaris and runs alongsidethe ulna bone.

There it innervates purely the Flexor Carpi Ulnaris(FCU) muscle & medial half of Flexor DigitorumProfundus III & IV (FDP) muscle.

No further muscle is supplied by the ulnar nervein the medial forearm until it enters the wristthrough guyon’s canal.

In the forearm the ulnar nerve gives 2 superficialsensory branches before entering the Guyon’scanal. These two sensory branches are as;

1. Dorsal Cutaneous Nerve2. Palmar cutaneous Nerve

In the forearm the ulnar nerve runs distally on the ulnar artery, and about five to eight centimeters proximal to the wrist , the dorsal ulnar cutaneous sensory branch exits, which supplies sensation to the dorsal medial hand and the dorsal little finger as far distally as the nail & the 4 finger (3) digit.

The palmar branch of the ulnar nerve arises about five cm proximal to the wrist (At the level of the ulnar styloid ) from where the ulnar nerve splits into palmar and dorsal branches.

The palmar branch represents the continuation of the ulnar nerve as it crosses the flexor retinaculum of the hand on the lateral side of the pisiform bone.

The last branch arises in the hand itself: Superficial branch – Innervates the palmar surface of

the medial one and a half fingers. It also supplies Palmaris Brevis, a thin muscle beneath the skin which cannot be studied in EMG.

It passes between the abductor and flexor digitiminimi.

The deep branch gives off motor innervation tothe hand muscles.

Then it disappears under the origin of opponensdigiti minimi, grooves the hook of hamate andarches radially leaving the canal. Within this

course, it supplies the three hypothenar musclesand later all the interrosseus muscles, adductorpollicis and usually the two ulnar lumbricals.

Forearm: Flexor Carpi Ulnaris (C7, C8, T1) Flexor Digitorum Profundus III & IV (C7, C8) Thenar: Hypothenar Muscles (C8, T1) Adductor Pollicis (C8, T1) Flexor Pollicis Brevis (C8, T1) Fingers: Palmer Interosseous (C8, T1) Dorsal Interosseous (C8, T1) III & IV Lumbricles (C8, T1) Digiti Minimi: Abductor Digiti Minimi (Quinti) (C8, T1) Opponens Dgiti Minimi (C8-T1) Flexor Digiti Minimi. : ( C8-T1)

Sensory recording: Ring electrodes with Gl placed over themetacarpal-phalangeal joint ,G2 placed 3-4 cm

distally over the distal interphalangeal jointStimulationWrist: medial wrtist, adjacent to theSite: flexor carpi ulnaris tendon.Distance= 11cm/12cm•Key point: Antidromic study Forstimulation and recording sites are reversed.

In a motor NCS, the active electrode G1 placed over the belly of a muscle supplied by the nerve. The reference electrode G2 placed 3-4 cm distal to G1 electrode, preferably on a bony predominance. Ground is placed in b/w active recording and stimulation electrode.