Ulnar Nerve

Question 1

Nerve roots and trunk origins?

Answer 1

C8-T1

medial cord of brachial plexus

formed from anterior division of inferior trunk

Question 2

Nerve course?

Answer 2

the ulnar nerve runs down the arm on the medial side of the brachial artery

it passes behind the medial epicondyle of the humerus and enters the forearm between the two heads of flexor carpi ulnaris

it travels through the anterior compartment of the forearm beneath flexor carpi ulnaris with the ulnar artery
it then enters the palm of the hand through Guyon’s canal

Question 3

Sensory supply

Answer 3

the ulnar nerve does not supply any sensory innervation to the axilla or upper arm

skin over hypothenar eminence

medial ⅓ palm of hand

palmar aspect of lateral 1½ fingers

medial ⅓ dorsum of hand

dorsal aspect of medial 1½ fingers (little finger and half of ring finger)

Question 4

Motor supply?

Answer 4

two muscles of anterior compartment of forearm
flexor carpi ulnaris – flexes and adducts wrist

medial two parts of flexor digitorum profundus – flex ring and little fingers at DIPJs

most of the intrinsic muscles of the hand – HILA muscles
hypothenar eminence: opponens digiti minimi,
flexor digiti minimi brevis and abductor digiti minimi – oppose, flex and abduct little finger
interossei – palmar interossei adduct, dorsal interossei abduct

medial two lumbricals – flex MCPJs and extend IPJs of ring and little finger

adductor pollicis – adducts thumb

NB// adductor pollicis is not part of the thenar eminence and actually lies deep beneath it as a separate structure

Question 5

Nerve palsy

Answer 5

SENSORY LOSS
numbness over hypothenar eminence and ulnar distribution of hand

MOTOR DEFICIT
paralysis of flexor carpi ulnaris – weak wrist flexion and adduction
paralysis of medial two parts of flexor digitorum profundus – weak flexion of ring and little finger DIPJs
paralysis of most of the intrinsic muscles of the hand – weak MCPJ flexion and IPJ extension of ring and little fingers, loss of finger abduction and adduction, loss of opposition of little finger

DEFORMITY
wasting of hypothenar eminence and intrinsic muscles of hand
“CLAW HAND” deformity at rest and on attempted finger extension – the patient cannot extend the IPJs of their ring or little fingers, resulting in fixed flexion of the IPJs and hyperextension of the MCPJs of these two fingers. The clawed appearance is most pronounced when the nerve is injured at the wrist, for example by compression in Guyon’s canal, as the function of flexor digitorum profundus will be preserved. A claw hand affecting all four fingers is much less common and is usually due to a lesion of the lower part of brachial plexus, such as Klumpke’s palsy