Dear Mike,

there seems to be a few issues that needs to be clarified before we can try to be of any help.

Damien and Charlize already pointed out that if its a clinically true long thoracic nerve injury (LTN), then you should have a Wikipedia reference-linkwinged scapula when moving your affected arm forwards or out from your side. Get someone to observe your shoulder blades, it should be quite obvious. If not, try the same movement while holding a 5 kg/11 lbs weight. Or get on the floor and do a proper pushup while someone observes you. I've seen a few of these, when I worked as a physio in the military up here in the north , both cases triggered with heavy military rucksacks and both recovered completely without any intervention within 3 months. We say that normally these kind of nerve injuries, neuropraxia injuries, grows about 1-3 mm. a day with a generally good prognosis. Charlize points out that recovery might take up to 2 years, and I would add to this that poor recovery within 6 months will predict poor recovery also after 1 year.

Another thing that itch in my air, is that you say that "after a series of test, EMG's, etc" they determined LTN injury. What kind of series of tests? What does etc involve? Who were they? My understanding is that EMG's will seldom pick up neuropraxia (the mildest out of three on a nerve injury scale), even nerve conduction tests can be negative.

From the area you describe your pain (left shoulder/trap area) and the nature of your pain, I'd be REALLY interested in a thorough physical examination of your cervical (neck) spine, and with a focus on your left C5-6 and especially your left C6-7 Wikipedia reference-linkfacet joint. Carrying a ruck sack would transmit forces through muscles from your shoulder blade that attaches directly to this area, producing a compression within the joint. Needle injection studies have shown that a problem with these joints can refer pain into the area you describe and could be referred to as "secondary hyperalgesia", in other words, the source of your pain is different from where you feel your pain due to central pain modulation processes...

Very precise thumb pressures (posteroanterior mobilisations - PA's) to especially the left side of your neck at the C5-6 and C6-7 with different inclinations (also obviously compare with other side and the above and below vertebraes) aiming to reproduce the exact pain you are familiar with could provide evidence to this. Preferably it could be done WITH your ruck sack on to make it as close to your pain situation as possible. But wouldn't surprise me if the pains are reproducible with PA's even in sitting or when you lie on your front.

I stand shoulder to shoulder with Alophysio and Damien in suggesting that you should really get someone to look at your neck. Personally, based on the limited information given, I'd boldly say that long thoracic nerve injury sounds LESS likely. It's easy to disprove me on this; get someone to observe what happens to your shoulder blade while doing those movements as suggested. A minor difference between the shoulder blades could be caused by muscle imbalance/side preferential issues. We're not talking about a maybe or maybe not in case of a winging scapula caused by LTN injury, it should be hit-you-in-the-face obvious for the observer.

This buffy dude does a very good job in showing us how a damage to the LTN should look like:
YouTube - Long thoracic nerve damage.

Looking forward to hearing from you again.

Kind regards,
Sigurd Mikkelsen