I think there are a couple of things worth pointing out here -

First, as has been said before, there isn't just ONE cause for or kind of TOS, but many, and each person responds very individually, so one person's TOS is often VERY different from another. What predisposes you to develop TOS seems to be really key - whatever congenital susceptibility that makes you particularly vulnerable. If that's something easily imaged and usually successfully treated, like a cervical rib, the outlook is brighter (although getting correct dx and treatment still takes way too long and there are still too many Drs who will doubt you).

And some DO develop it through physical trauma that maybe weren't predisposed - but had fractured clavicles that healed badly, breast enhancement or other surgery that caused nerve trauma or entrapment, or injured themselves by putting extreme demands on the nerves, veins and arteries that feed the shoulder muscle through weightlifting, competitive swimming, playing music for a living or pitching for a pro baseball team.

Most of us don't have cervical ribs, or develop it through fractured clavicles or extreme sports. We have some other, congenital cause that predisposes us. If that isn't a c-rib, a long C-7 process, or a fractured clavicle, then it's a fibrous band - usually a scalene taking an abnormal route through the brachial plexus, impinging on the nerves, maybe screwing with the vein and artery as well. Dr David Roos describes at least 10 variations of these bands that he found at surgery and released. My TOS surgery findings, a scalene minimusthat wandered through the brachial plexus, and an anterior scalene with an abnormal route, are both mentioned.

In addition to the underlying predisposing reason, there's the inciting trigger - was the TOS brought about by acute trauma - what kind? RSI - what type of repeated movement - keyboarding, stocking shelves, working overhead, house painting - different movements = different nerves affected?

One thing that seems to play a big yet not understood role is the inflammation that accompanies TOS and, it seems, most chronic neuropathic pain. We know it exists. We know traditional anti-inflammatories don't help with this kind of inflammation. We know if we push our limits, it's probably the inflammation that's responsible for the rise in our pain later that day or the day after, and that fuels our "flares". If we're good, and do very little to irritate the nerves, we can somewhat control the inflammation, to a point.
But that comes at the price of having almost no life, and of course we can't control the weather. There are also medical and legal appts that have to be kept, as well as family responsibilities, as well as some unavoidable stress, and given the slightest opportunity inflammation strikes us down.

As well there are variables such as age, gender, fitness level (pre-TOS), pain severity, length of time person has had condition, level of disability, co-existing conditions, grief/loss/depression issues, access to treatment, treatment philosophies, legal matters, support systems, finances.

I guess my point here is we are so varied, different in so many ways, I find it risky for anyone to make a statement that "THIS" is the cause of TOS. I think there are more than one. But I think that when they learn more about the effects of nerve damage (and they are doing a lot of research in this area) then neurogenic TOS will be better understood as well.

2. I do think there are "subgroups" for lack of a better word, of people who have similar types of injury that caused their TOS to develop. The lower part of my scap wings, not very noticeably, but more so if I push against a wall. My shoulder fell an inch and a half after getting the tetanus booster that caused my reaction. I had slightly injured my long thoracic nerve (stretch injury) trying to pick up a bag of groceries while I had a bag of school books and things slung over my shoulder 4 months earlier. Just had a 30-second burn in the shoulder, dropped everything, didn't see a Dr, rested the arm. Didn't carry anything on the shoulder for a week. I was fine, full ROM, full strength, no sx of any kind.

The tetanus shot affected the spinal accessory nerve, but the long thoracic must not have been completely recovered, so the whole shoulder dropped. I'm positive this is why I needed the pec minor tenotomy. The EMG showed chronic denervation of the medial cord (and parts of the lateral cord). Well, it only follows that there would be major consequences in that area since the whole shoulder girdle collapsed down onto it!!

Anyway, if you are winging, I encourage you to consider what towelhorse has to say - either the long thoracic - or, if your shoulder is drooping, the spinal accessory, may be entrapped, palsied or somehow irritated. While not considered part of the brachial plexus, they do travel nearby and can be affected by many of the same problems. You can't maintain or achieve shoulder girdle stability if these nerves aren't functioning properly.

beth