Sorry about the wording of the question -- hope someone understands what I mean.
My son suffered a C5 burst fracture 19 months ago. His doctors now classify him as C6 Asia C.
What I don't understand is: The physiatrist says he hasn't "much" triceps, and that triceps are "mostly C7". I believe that which levels of the cord innervate which muscles is not so cut and dried, that there is some overlap -- that C6 could partially innervate the triceps.
My son also has working muscles much further down: little finger and ring finger on one hand, hip flexors, quadriceps and lots of back muscles.
How is it that his hands (C8 to T1) don't seem to be innervated (apart from the two fingers mentioned) but his quadriceps are?

Can anyone explain this to me? Thanks.