PNS 4 - Ulnar Nerve Flashcards
(27 cards)
What muscles are innervated by the ulnar nerve?
Flexor carpi ulnaris (FCU), flexor digitorum profundus (medial half), adductor pollicis, and small digital muscles including palmaris brevis, abductor digiti minimi, opponens digiti minimi, flexor digiti minimi, interossei (PADs and DABs), lumbricals to digits 4 & 5, and deep head of flexor pollicis brevis.
What are the motor functions of the ulnar nerve?
• Finger adduction and abduction (except thumb)
• Thumb adduction
• Flexion of digits 4 & 5
• Wrist flexion and adduction (shared with median and radial nerves)
What sensory innervation is provided by the ulnar nerve?
Skin over the medial surface of the hand via the superficial branch.
What shoulder-level injuries can cause ulnar nerve lesions?
• Shoulder wrenching injuries
• Compression (e.g., crutch use)
(Note: Ulnar nerve exits brachial plexus in the lowest position and often avoids dislocation damage)
What arm-level issues can affect the ulnar nerve?
Entrapment at the Arcade of Struthers (thick fascia from medial triceps to intermuscular septum between triceps and biceps)
Why is the elbow a common site of ulnar nerve injury?
Due to superficial position and lack of soft tissue protection; common injuries include:
• Blows, falls, dislocations, medial epicondylar fractures
• Compression as nerve passes posterior to the medial epicondyle
• Cubital Tunnel Syndrome
What causes Cubital Tunnel Syndrome?
• Prolonged elbow flexion during sleep (“sleep palsy”)
• Iatrogenic compression
• Entrapment between two heads of FCU and ulnar part of FDP
What forearm-level injuries affect the ulnar nerve?
• Ulnar fractures
• Lacerations or protective stance-related blocking injuries
What wrist and hand conditions can damage the ulnar nerve?
• Fractures, dislocations, abduction sprains
Hand:
• Lacerations
• Compression at the Tunnel of Guyon (caused by entrapment, RSI, carpal fractures, neural tumors, or surgical complications)
• Hook of hamate fractures (e.g., softball catchers)
• “Handlebar palsy” in cyclists
What is the motor order of innervation for the ulnar nerve?
- FCU
- FDP (medial half)
- (Palmaris Brevis)
- Abductor Digiti Minimi
- Opponens Digiti Minimi
- Flexor Digiti Minimi
- Interossei (PADs and DABs)
- Lumbricals to fingers 4 & 5
- Adductor Pollicis
- Flexor Pollicis Brevis (deep half)
What motor impairments occur with ulnar nerve damage?
• Wrist Flexion: Paresis (shared with median nerve)
• Wrist Adduction: Paresis (mainly radial via ECU; FCU not contributing due to ulnar lesion)
• Thumb Flexion: Paresis (shared with median nerve)
• Digit Minimi Movements (Abduction, Opposition): Paralysis (flexor, abductor, and opponens digiti minimi)
• Thumb Adduction: Paralysis (only muscle: adductor pollicis)
• Finger 2–5 Adduction/Abduction: Paralysis (interossei solely innervated by ulnar)
• Flexion of digits 4 & 5: Affected
What is the ulnar nerve’s isolated sensory supply?
Digiti minimi and ulnar border of the hand (anaesthesia in lesion).
What is the ulnar nerve’s primary sensory zone?
• Medial ½ of ring finger (anterior and posterior)
• Strips of palmar and dorsal hand surfaces extending from medial ½ ring finger to wrist
• Hypoesthesia in lesion
What proprioception is affected by ulnar nerve damage?
• Medial aspect of wrist joint
• Majority of the 5th digit
• Anterior joint surface of 4th digit (ring finger)
Does ulnar nerve damage cause vasomotor/ANS dysfunction?
No; no vasomotor deficits are typically seen.
What functional disabilities result from full ulnar nerve loss?
• Reduced grip strength
• Claw hand deformity
• Atrophy of hypothenar muscles
• Atrophy of adductor pollicis (thumb in abduction)
• Atrophy of interossei (tunneling between metacarpals and MCP hyperextension)
What is Froment’s sign and what does it indicate?
• A test for adductor pollicis function
• Patient grips object between thumb and index finger
• Loss of adductor pollicis leads to compensatory use of flexor pollicis longus (median nerve)
• Positive sign: flexion at terminal phalanx of thumb
How is ulnar nerve tested clinically?
• Rule out cervical spine and thoracic outlet syndrome
• Neural tension testing
• Muscle strength testing:
- Grip strength
- 5th digit abduction
- Thumb adduction
- FCU
- Interossei
• Special tests:
- Tinel’s sign at the elbow
- Froment’s sign
What happens with unopposed antagonists in ulnar nerve lesions?
• Thumb abductors take over
• Extensors of digits 4 and 5 lead to MCP hyperextension, contributing to claw hand
What type of nerve injury is indicated by complete loss of ulnar nerve function?
A neurotmesis injury, which has occurred proximal to any motor or sensory innervation points, likely in the proximal elbow region or humerus.
What happens to wrist flexion when the ulnar nerve is completely lost?
Flaccid paresis occurs; however, wrist flexion is shared with the median nerve, which is assumed to be intact.
What happens to wrist adduction with a complete ulnar nerve lesion?
Flaccid paresis occurs; wrist adduction is shared with the radial nerve.
What is the result of a complete ulnar nerve lesion on thumb flexion?
Flaccid paresis occurs, but thumb flexion is shared with the median nerve, which is assumed to be intact.
What happens to abduction and opposition of the digiti minimi with complete ulnar nerve loss?
Flaccid paralysis – there is complete motor loss.
