Nerve Injuries Flashcards
What is the MRC classification used for? Describe it
For assessing the power of a particular muscle group: 5 - normal power 4 - weakness 3 - movement against gravity 2 - movement with gravity eliminated 1 - flicker of muscle 0 - no detectable movement
What is Erb’s palsy?
Lesion of the upper brachial plexus (C5/C6) at birth
- Abductors and external rotators are paralysed
- ‘Waiter’s tip’ position: arm held close to body, internally rotated
- Loss of sensation to C5/C6 dermatomes
What is Klumpke paralysis?
Lesion of the lower brachial plexus (C8/T1) - rare
- Loss of intrinsic muscles of hand
- Claw hand
- Loss of sensation in C8/T1 dermatomes
Describe the functions of the radial nerve
Origin: posterior cord of brachial plexus (C5-C8)
Motor to: extensors of elbow, wrist, and fingers
Sensory to: dorsal aspect of lateral 3 1/2 digits; specifically area between 1st and 2nd MCPJs
Describe the causes and pattern of injury to the radial nerve at the axilla
- Saturday night palsy
- Crutch palsy
Motor deficit:
- Loss of extension of forearm (triceps)
- Weakness of supination
- Loss of extension of hands and fingers - ‘wrist drop’
Sensory deficit:
- Lateral arm
- Posterior forearm
- Dorsal aspect of lateral 3 1/2 digits
Describe the causes and pattern of injury to the radial nerve at the mid-arm
- Mid-shaft humeral fracture (where nerve travels in radial groove)
- Prolonged tourniquet time
Motor deficit:
- Triceps function spared
- Weakness of supination
- Loss of extension of hands and fingers - ‘wrist drop’
Sensory deficit:
- Posterior forearm
- Dorsal aspect of lateral 3 1/2 digits
Describe the causes and pattern of injury to the radial nerve just below the elbow
- Fractures around elbow or forearm
- Tight cast
- Rheumatoid nodules
- Injections due to tennis elbow
- Posterior interosseous nerve syndrome
Motor deficit:
- Weakness of extension of hands and fingers
- Finger drop, partial wrist drop, and radial wrist deviation on extension (since the extensor carpi radialis longus and brachioradialis muscles are working)
Sensory deficit:
- None, as sensation is supplied by the superficial radial nerve
Describe the causes and pattern of injury to the radial nerve in the distal forearm
- Wartenburg’s syndrome
- Tight jewellery
Motor deficit: none
Sensory deficit:
- Numbness and tingling in radial half of dorsum of hand and dorsal aspect of lateral 3 1/2 digits
What is Wartenburg’s syndrome? What condition does it closely resemble? Which test may be positive
Radial nerve palsy due to nerve entrapment beneath the tendinous insertion of brachioradialis.
There is significant radial wrist pain, and close resemblance to symptoms in de Quervain’s tenosynovitis. Finkelstein’s test may be positive.
What is posterior interosseous nerve entrapment?
Compression of the deep motor branch of the radial nerve due to entrapment at the Arcade of Frohse (part of the Supinator).
Posterior interosseous neuropathy is purely a motor syndrome resulting in finger drop, and radial wrist deviation on extension.
What is Saturday night palsy?
From falling asleep with one’s arm hanging over the arm rest of a chair, compressing the radial nerve at the spiral groove.
Motor deficit:
- Loss of extension of forearm (triceps paralysis)
- Weakness of supination
- Loss of extension of hands and fingers - ‘wrist drop’
Sensory deficit:
- Lateral arm
- Posterior forearm
- Dorsal aspect of lateral 3 1/2 digits
What is the cause of a ‘claw-like hand’?
Damage to the ulnar nerve usually occurs at the elbow or the wrist.
What does the ulnar nerve supply?
The ulnar nerve supplies all of the interossei, half of the flexor digitorum profundus (FDP) and the lumbricals to the ring and little fingers.
Describe the ulnar paradox
A lesion at the wrist causes unopposed action of the extensors and the FDP, especially of the little and ring fingers, causing them to claw (the FDP is supplied just below the elbow and so a cut at the level of the wrist will not paralyse this).
Lesions at the elbow often have less clawing, since the ulnar half of FDP is now paralysed and the fingers are therefore straighter.
List the causes of a true claw hand
- Volkman’s contracture
2. Proximal lesions of the brachial plexus
