Ulnar Nerve Injuries Anatomy & Functions Explained

Ulnar nerve is the branch of the medial cord of the brachial plexus. Root value : C7,C8,T1

It is a mixed nerve.

Course of Ulnar nerve

Runs medially in arm  → Pierces medial intermuscular septum-> moves behind humerus medial epicondyle→ enter forearm under flexor carpi ulnaris → enters guyon canal→ divide into 2 terminal branches → then supply to superficial & deep branches.

Muscles Supplied by Ulnar Nerve

1. Abductor digiti minimi
2. Lumbricals
3. Palmar interossei
4. Dorsal interossei
5. Abductor pollicus

Motor Functions  for Ulnar Nerve

Ulnar nerve innervates muscles in anterior compartment of forearm and in the hand

• Flexor carpi ulnaris : flexes & adduct the hand at wrist
• Flexor digitorum profundus : Flexes the ring & little fingers at the distal interphalangeal joint

Also read : Flexor Retinaculum: Tarsal Tunnel Syndrome 

Sensory Functions 

• Palmar Cutaneous Branch : Innervated the medial half of palm
• Dorsal cutaneous branch : Innervated dorsal surface of the medial one & half fingers & associated dorsal hand area
• Superficial Branch : Innervates the palmar surface of medial one & half fingers

Ulnar Nerve Palsy

Damage at the Elbow

• Mechanism of injury: Trauma at the level of the medial epicondyle (e.g. isolated medial epicondyle fracture, supracondylar fracture). It can also be compressed in the cubital tunnel. 
• Motor functions:
  • All the muscles innervated by  ulnar nerve Flexion of the wrist can still occur but are accompanied by abduction (due to paralysis of flexor carpi ulnaris and medial half of flexor digitorum profundus).
  • Abduction and adduction of the fingers cannot occur (due to paralysis of the interossei).
  • Movement of the 4th and 5th digits is impaired (due to paralysis of the medial two lumbricals and hypothenar muscles).
  • Adduction of the thumb is impaired, and the patient will have a positive Froment’s sign (due to paralysis of adductor pollicis)
• Sensory functions: All sensory branches are affected, so there will be a loss of sensation over the areas that the ulnar nerve innervates.
• Characteristic signs: Patient cannot grip paper placed between fingers, positive Froment’s sign, wasting of hypothenar eminence.

Also read : Extravasation of Urine : Causes, Cases 

Damage to Wrist

• Mechanism of injury: Lacerations to the anterior wrist.
• Motor functions:
  • Only the intrinsic muscles of the hand are affected.
  • Abduction and adduction of the fingers cannot occur (due to paralysis of the interossei).
  • Movement of the 4th and 5th digits is impaired (due to paralysis of the medial two lumbricals and hypothenar muscles).
  • Adduction of the thumb is impaired, and the patient will have a positive Froment’s sign (due to paralysis of adductor pollicis).
• Sensory functions: The palmar branch and superficial branch are usually severed, but the dorsal branch is unaffected. This results in sensory loss over the palmar side of medial one and a half fingers only.
• Characteristic signs: Patient cannot grip paper placed between fingers, positive Froment’s sign, wasting of hypothenar eminence.

Also read : Cranio-Vertebral Joints

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