Ulnar Nerve

What is the origin and root value of ulnar nerve?

Origin: It arises in the axilla from the medial cord of the brachial plexus.

Root value: Its root value is C₈ and T₁

It leaves the axilla and enters the anterior compartment of arm along the medial side of the brachial artery.
At the middle of the arm it pierces the medial intermuscular septum to enter the posterior compartment of the arm and runs downwards to the back of the medial epicondyle of humerus.
It enters the forearm by passing between the two heads of flexor carpi ulnaris .
In the upper 2/3rd of the forearmit runs deep to flexor carpi ulnaris and then it becomes superficial and lies lateral to flexor carpi ulnaris.
The nerve enters the palm by passing superficial to the flexor retinaculum and divides into its terminal superficial and deep branches.

Branches and Structures Supplied (distribution):

In the axilla: no branches.

In arm: branch to elbow joint.

In the forearm:

Motor branches:
- Nerve to flexor carpi ulnaris.
- Nerve to medial half of the flexor digitorum profundus.
Sensory branches:
- Palmar cutaneous branch innervates the skin over the hypothenar eminence.
- Dorsal cutaneous branch innervates the skin over the medial 1/3^rd of the dorsum of hand and medial 1 ½ digits.
Articular branch: to wrist joint.

In the palm:

Superficial branch:
- Motor : nerve to Palmaris brevis
- Sensory : innervates skin on the palmar surface of medial 1 ½ digits
Deep branch:
- Purely motor: supplies following muscles:
  - Hypothenar muscles
  - Medial two lumbricals
  - All palmar and dorsal interossei
  - Adductor pollicis

Ulnar nerve may get injured at the following sites:
- At elbow: due to fracture of medial condyle or entrapment between the two heads of flexor carpi ulnaris.
- Injury at this site results in:
  - Partial claw hand: affects little and ring fingers. Hyperextension at their metacarpophalangeal joints and flexion at interphalangeal joints due to paralysis of intrinsic muscles of hand (1st and 2nd lumbricals are supplied by median nerve , therefore they are spared) .
  - Flattening of hypothenar eminence
  - Loss of abduction and adduction of fingers , due to paralysis of palmar and dorsal interossei.
  - Loss of sensation over the palmar and dorsal surface of medial 1/3^rd of hand and medial 1 ½ digits.
- At wrist : its superficial postion makes it vulnerable to cuts and wounds at the wrist.
- Injury at this site results in:
  - Partial claw hand affecting little and ring fingers.
  - The deformity is more pronounced than the injury at elbow (ulnar paradox) because the medial half of flexor digitorum profundus is not paralysed , therefore flexion at distal interphalangeal joint is more marked.
  - Loss of abduction and adduction of fingers.
  - Loss of sensation over the palmar surface of medial 1 ½ digits (sensations on the dorsal surface of medial 1/3rd of hand and medial 1 1/2 digits is spared because the dorsal cutaneous branch is given in the forearm.

Complete claw hand:

hyperextension at metacarpophalangeal joint and flexion at interphalangeal joints occurs due to paralysis of all the lumbricals and interossei muscles. It occurs due to:
- Combined lesion of median and ulnar nerves.
- Lesion of lower trunk ( C₈ & T₁) of brachial plexus (Klumpke’s paralysis).