Peripheral nerve injuries/palsies Flashcards
What are the three basic types of peripheral nerve injury mechanisms?
- Stretch related - MOST COMMON; nerves are elastic but too strong traction –> complete tear e.g. Erb’s palsy
- Lacerations - due to blades
- Compressions e.g. Saturday Night palsy
What classification is used for PNI?
- Seddon classification = neuropraxia, axonotmesis, neurotmesis
- Sunderland classification = see below
What is neuropraxia? Recovery?
Local myelin damage usually secondary to compression
Recover quickly over minutes or longer, analogous to cerebral concussion
What is axonotmesis? Recovery?
Axon severed due to direct trauma or stretching
If endometrium intact then this is good for regeneration. Axons regenerate from the centre outwards if the cell body remains intact and recovery should be good if the nerves can grow down their origincal neurilemmal sheaths.
What is neurotmesis? Recovery?
Complete physiologic disruption of entrire nerve trunk
Each divided axon tends to die back to the next nodule of Ranvier or even further and there are retrograde changes in the motor cell body. Regeneration rarely occurs unless the nerve ends are opposed. Better in children but likely incomplete.
What is Saturday Night palsy?
Radial nerve compression
Which nerve may sometimes be sacrificed for grafting?
Sural nerve can be used for a graft elsewhere without too much functional loss
Compare upper and lower brachial plexus injuries.
Upper plexus injuries carry a better prognosis than lower plexus injuries.
What is the result of first thoracic root injury proximal to its ganglion?
Horner’s syndrome - myosis, anhydrosis, ptosis, enophthalmos
Where is the median nerve likely to be damaged?
Wrist, forearm or elbow
What is the result of median nerve injury?
Sensation loss over thumb, index, middle and occasionally ring finger
Hand of benediction = motor loss of:
- Thenar muscles except the adductor pollicis (ulnar nerve supply).
- Higher lesions can also paralyse the flexor digitorum profundus of the index and middle fingers
- Flexor digitorum superficialis so that index finger cannot be flexed at PIP/DIP joints.
Where is ulnar nerve injury most common?
Commonest at wrist or elbow - loss is mainly motor
What is the result of ulnar nerve injury?
Claw hand
- Ulnar nerve supplies intrinsic muscles in the hand which cause MCP flexion and IP extension so opposite position is assumed with its injury due to unopposed long flexors
- Less prominent with index finger as first two lumbricals are innervated by median nerve
Sensation loss over little finger and part of ring finger.
Where is the radial nerve most commonly damaged?
Middle humerus by fractures of pressure e.g. Saturday night palsy
What is the result of radial nerve injury?
Wrist drop - motor loss to the wrist, finger and thumb extensors
Little sensory loss
NB: motor branch to the tricepts is usually spared
How is the sciatic nerve damaged? What is the result of sciatic nerve injury?
Damaged in association with a dislocated hip
Causes complete loss of function and almost total anaesthesia below the knee (except saphenous nerve which arises from femoral nerve)
What is a common cause of femoral nerve injury? What is the result of this injury?
Penetrating injuries e.g. knife
Causes loss of quadriceps functioon –> standing and walking becomes difficult. Produces a characteristic gait where patient braces their knee
Why is the common peroneal nerve commonly injured?
Often injured after splintage because the nerve is vulnerable as it winds around the neck of the fibula
What is the result of CPN injury?
Foot drop - CPM innervates the anterior compartment of the leg; often fails to recover and a toe raising appliance may be needed to correct the catching of the toe when walking
Loss of sensation over the dorsum of the foot
Review the brachial plexus.
Review the lumbar plexus.
