Pronator teres and quadratus are both supplied by median nerve (C5/C6/C7/C8/T1, so that's not super helpful.) Extension of the forearm is radial nerve (also C5-T1, also not helpful). This does tell us is it can't be isolated median or radial. Triceps tendon reflex is C7/C8, which narrows it down to these two.
Can anyone explain why it's C7 over C8?
Per UWorld (ID 15553)
The C7 root is the most frequently affected nerve root in patients with cervical radiculopathy, resulting in deficits across the median and radial nerve distributions.
"tingling sensation of fingers" → median nerve
"triceps muscle reflex is decreased" → radial nerve
My thought process on this question:
weakness of arm extension and pronation = sounds like musculocutaneous nerve (C5-C7)
Triceps stretch reflex (C7-C8);
Ruleouts: Biceps is C5-C6 so r/o C6. C8 doesn't fit musculocutaneous muscle actions action so r/o C6. Median and Radial nerves have different muscle actions so r/o those as well, leaving just C7 best fitting the vignette.
According to FA 2019 Tricep Reflex is mediated by C6, yes C6 NOT C8, and C7 [In BOLD, implying it is more important].
So I think that issue of wrist extension and/or finger drop would be more radial nerve. However, there was more proximal weakness, so it would be C7.
"7-8 lay them straight", the pt couldn't "lay them straight" so it would be C7 root
According to Uworld, QID: 11779 C7 myotome is involved in elbow extension. Looks like it settles!
Per Wikipedia: The triceps reflex, a deep tendon reflex, is a reflex as it elicits involuntary contraction of the triceps brachii muscle. It is initiated by the Cervical (of the neck region) spinal nerve 7 nerve root (the small segment of the nerve that emerges from the spinal cord). The reflex is tested as part of the neurological examination to assess the sensory and motor pathways within the C7 and C8 spinal nerves.
Also, from a different website: The triceps reflex is mediated by the C6 and C7 nerve roots, predominantly by C7. https://informatics.med.nyu.edu/modules/pub/neurosurgery/reflexes.html.
this is my way to think(please correct me if it's not correct: a. weakness of triceps muscle reflex --> C6 / C7 / C8 problem (FA P498 2019) b. weakness of extension of the forearm --> radial nerve is involved --> damage of C7 root leads to axillary or RADIAL nerve defect (FA P441 2019)
I’m confused about this one. Weakness of extension and pronation of the right forearm, with a decreased triceps muscle stretch reflex. The answer was C7 nerve root, but how are you able to localize to C7 and not C6 or C8? I figured that extension is radial, C5-T1, and pronation is median, also C5-T1. Triceps reflex is C7-C8 (FA2019 says C6-C7). How would you narrow down to just C7 damage?