First of all, what evidence do you have that you have suffered injury to the nerves in your neck? Do you suffer from pain? It sounds like you are assuming since your arms lack development that it must be a nerve issue? You cannot make these assumptions. Any problems would have showed up in that MRI. If it came back with no problems, then I would believe the medical experts. If you had impingement, youll usually have significat pain.
It just sounds like you might need to tweak your training some and that you probably just dont have great genetics for arms. Most people have some weakness in their build. For a lot of guys it is calves. Some its arms. etc. Everyone is different. For me, chest never responded well and my legs never got a good sweep.
The truth of the matter is that there is only so much you can do to change the proportions of your bodyparts, and you are pretty much stuck with the overall shape that you were born with. As you have seen, the more your arms grow, the more the rest of your body grows and so they never catch up.
One thing that i changed that helped me was cutting back on the volume of sets for arms. I was overtraining them, and once I stopped that they caught up some. I got my arms up to a lean 19 inches or a bit more by doing that. Take a look at your training or maybe post it up in this thread and get some opinions.
this is what the MRi report shows:
C2-C3: no HNP, canal stenosis or nuero foraminal narrowing
C3-C4: mild annular bulge measuring approx 1mm
C4-C5: bilateral uncinate process hypertrophy causes mild to moderate right/mild left neural foraminal narrowing w/o canal stenosis
C5-C6: bilater ucinate process hypertrophy cuases mild right/moderate left neural forminal narrowing w/o canal stenosis
C6-C7: 2.5mm central disk bulge cuases mild left/moderate right neural foraminal narrowing w/o canal stenosis
C7-T1: no HNP, canal stenosis or neural foraminal narrowing
spinal alignment is satisfactory w/o evidence of compression fracture or subluxation. cranialcervical junction is normal. cervical cord is normal size. no signal of cord myelomalacia. no abnormal edema signal
MODERATE NEURAL FORAMINAL NARROWING ON THE LEFT AT C5-C6 AND ON THE RIGHT AT C6-C7.
thats directly from my report. for 2yrs ive had hand numbness when i sleep. it recently graduated to pain in my hands. my arms cold/flexed are 16" which is up from 15" 18 months ago. my chest is 56" i had found some goofy formula online that was charles poliquin thing that i put all my measuremnts in once. it showed that compared to all my other measurements my arms "should be" around 18" or something like that. i train on a periodization method 2on, 1off. first 2 weeks are heavy reps 4-6 with slow negatives. 3rd week reps 7-12 explosive reps. 4th week is more volumization reps 12-20 with drops, supers and monster sets. then i repeat. my diet is on, i sleep 7-9 hours depending on the day. but never less than that. my straight bar curls even when using dbol never go up past 135lbs for about 4-6 reps. i never try maxing really. seated d.b. curls are 35lbs for about 10-12 reps, can go up to 45's for about 6-7. d.b. preachers never go past 40lbs for 6-7 reps. flat bench its about 265lbs for 7-9(all reps are slow negs, explo pos). i dunno if all that helps. yeah my poundages arent up there, but i was a really skinny kid. im bigger than i probably should be for my strength. pls no sarcastic remarks. im really bummedout about this shit.