The arm has too many muscles. It also has too many nerves.
The problem is that someone comes in with weakness or numbness and you need to think, “Where in the brain/spine/nerve root/bits of brachial plexus/terminal branch is the actual problem?!”
One of the ways to help suss this out is by testing the deep tendon reflexes.
- Only biceps reflex absent – might be problem with musculocutaneous nerve or C5
- Both brachioradialis and triceps absent – problem with the radial nerve
- Only triceps absent – potential problem with C7
Of course you should correlate the reflex findings with the sensory findings and motor strength (remember the good old ASIA exam for testing specific nerve roots) to help determine if it is a terminal branch issue or something higher up.
And don’t forget to grade those reflexes!
|4+||Very brisk +/- Clonus|
Generally upper motor neuron (UMN) lesions result in hyperreflexia while lower motor neuron (LMN) lesions result in hyporeflexia.