Posted on Sun, 22 December 2013
As you might recall, I questioned the old "Mind the Gap" rule of safer rope placement ('The Gap' is the dip between the muscles on the outside of my arm above the red dot in the right hand image below) some while ago after blindly believing it myself for many years. I'm now convinced that, whilst it might lead to good placement, its reasoning is flawed. I'm not sure where the myth that the main radial nerve spiraled around in 'The Gap' originated but it seems to be one that I and some other notable authors swallowed, hook, line and sinker. I can only apologise for perpetuating what appears to be an internet myth. It is a relief to know that whilst the biological reasoning seems misguided, my advice to place the wraps a couple of fingers width apart either side of 'The Gap' was sound. It certainly appears from my 'Easy rule of thumb for wrap placement?' thread in my Fetlife Kinbaku group that field reports support it and avoiding the lower half of the upper
arm is a smart move generally. It is a medical fact that the radial usually spirals around much lower than 'The Gap' in the normal individuals. Therefore, in most people, the main branch is not in 'The Gap'. Thus, I speculate that the wraps are unlikely to damage it in a side or face down suspension using this sort of tie! Although, it is possible with some people that face up suspensions might carry a higher risk since some load might be on the back of the arm where the radial lies. The good thing about the rule is that if you place your wraps on the slope of the muscle each side of 'The Gap', so quite close to each other, you are likely to have optimal placement for most people most of the time.
True, there is a cutaneous branch running under the deltoid but I have yet to hear of an issue with this. If any of my readers have heard different, please let me know. Meanwhile, I'm assuming it is sufficiently protected not to be of concern.
Osada Steve told me he generally favoured high close wraps and had never caused a radial nerve problem. That is no guarantee it will work in every case. The 3-part image above shows a 3D representation in the first frame. We palpated and marked the path of my radial nerve, which seems a bit higher than many people's, in the next two photos. The red dot shows how an arbitrarily chosen spot moves as the arm is rotated into box-tie position. As you can see, the nerve twists more to the outside.
It is crucial to appreciate how the position is changed from standard medical position that is the norm in most representations that are to be found when searching the net. You can see the main branch does not run into 'The Gap', although the 3D diagram shows the sensory ancillary branch on the outside. I was very pleased to have this confirmed when a prominent hand and upper limb surgeon, and avid string-flinger, used these pictures to support a presentation at LFAJRB. He has also produced photos of the path marked on the bone which reflect my findings. He said typically the nerve is likely to spiral around between the mid-point and 10-12cm above the outermost point at the bottom of the humerus. Thus, this would appear to be the area to avoid.
How come we never figured out the path better? My suspicion is that we failed to check the so-called 'facts' that were circulating, misinterpreted medical diagrams or didn't take account of how different things are with the arms folded behind for the tie compared to standard medical position. We should always check our 'facts', especially those learned from the internet. Everyone can be a self-proclaimed expert with their own blog or site nowadays. Not only that, but we need to also be aware that even accepted scientific facts change. Don't forget that how many of those have changed even in a few decades, never mind from one century to another. Here are just a few scientific myths of the past and some more recent. Of course, on a more mundane level, those of us who have failed to defrost food sufficiently in a microwave oven will wonder why the myth that they heat food from the inside persists when they find the centre icy and crunchy :-) Even old illustrations like this one from Gray's Anatomy clearly show that the main nerve is on the inside, not the outside, of the upper arm at 'The Gap' level.
In other words, it is vulnerable roughly where the upper cinches might run. This is a highly vulnerable area for the radial and care should always be taken not to create bulk here that might compress the nerve. It usually curves to the outside somewhere below the mid-point of the arm and it is in this sector that the nerve is likely to be vulnerable on the outside to pressure from the lower wrap (see 3D image below, Path of radial nerve).
I suspect that many riggers, in a misguided effort to 'Mind the Gap', place their wraps too far apart. The consequence of this is that the lower wrap ends up below the mid-point, exactly where you don't want it, assuming you intend to go above the radial nerve. This is not to say that low bottom wraps are inevitably a problem. In an unloaded gote that is not tied ridiculously tight, running over the radial is unlikely to cause injury unless an undue susceptibility exists, in my opinion. It might also be possible to place the bottom wrap below the radial thus missing the vulnerable area if your partner's nerve spirals around higher than average. Of course, to do this, you need to trace their nerve path.
Rules of thumb are all very well but they are no substitute for knowing where the nerve runs on the person you are tying and acting on their feedback. This might be how some people are apparently tying very low get away with it but this is merely speculation in my part. How rope placement feels and exactly where it sits will change every time you tie, what works for them one day, might not on another. It's vital for the person being tied to be aware of the slightest warning signs, to give feedback and the rigger to respond fast. At the first twinge, get the load off. In suspensions, this means getting at least one leg down to provide support. Releasing wrists also allows the arms to drop and tension to be released. Path of radial nerve.
The signs pf a compromised nerve are unusual sensations running down the arm to the fingers. If you feel twinges or electric-like feelings, however slight, running down to the thumb and first two fingers, odds on its your radial expressing its displeasure at being tweaked. Take note and don't ignore it, act fast! It might be a whispered warning which will not be repeated.
If you feel sudden pain associated with rope movement, it could already be too late as it could indicate a torn nerve. In that case, the damage is done and it is a matter of time before your body joins it up again to resume function. If sudden pain is felt without loss of function or feeling, it is unlikely to be a nerve causing the problem. I've heard people checking nerves by getting their partner to make a fist or grip their hand. This is useless for checking for radial injury.
There are two types of damage depending on the function of the injured branch: Motor, effecting movement, and sensory providing sensation. If the former is injured you experience a degree of paralysis, whilst the latter will result in numbness. Often, both types will be affected. The squeeze or fist test will tell you nothing about compression of a sensory branch since this will only result in sensation loss/numbness of thumb and first two fingers. If the only symptom is numbness, it is likely the injury occurred in the forearm or wrist.
As I have said before here, the main culprit here is an overly tight wrist binding compressing the nerve on the thumb side. Restricting your partner's ability to shift arm position can also have the knock-on effect of not allowing them to move out of a dangerous position. This is something canny models often do. The pro's get hurt less often not only because their rigger knows their body, and what they can do with it, but because they do as well and listen to its warnings. That said, they are like anyone at the top of their profession: well-suited to the job. This usually means being almost bomb-proof in the nerve department. In some cases, trying to emulate them might be beyond us mere mortals :-)
If you have ever seen what Vlada can get away with doing with Falco, you'll understand what I mean! It's not for nothing that we nick-named him 'Superman'. From a personal investigation, his radial seems insensitive in the inside upper arm even with the sort of vigorous prodding that would have most of us jumping sky high.
The classic test for radial motor nerve damage is an inability raise the thumb (thumb extension). Wrist drop is odds on a symptom of damage to the motor branch in the upper arm. Likely sites of injury are the upper cinch area on the inside of the upper arm or the lower wraps on the outside below the mid-point. The 3D diagram below shows the radial nerve in standard medical position. The Top Marker A is the bony bit on the outside of your shoulder, D is the Bottom Marker which is the protuberance on the end of your upper arm bone (humerus). B is a point mid-point between A and D. C is around 10-12cm (about 4-4.75") above D. The radial is likely to be vulnerable between points C and D, i.e within the rectangular box, but more specifically it is likely to be between B and C. This is not an immutable law, you might be different. The only way to know for sure is to check.
My suggested wrap positioning
The image with musculature shows roughly where I tie most people, indicated in green to represent the wraps. The wraps are at the base of the deltoid and at the top of triceps. This has a further advantage in that your wraps will also lie beneath the should blades. Why does this make sense? Quite simply, it is a strong safe area which can take the load comfortably, safely and with minimal physical distortion under load. The muscles provide a natural anchor point to help stop the rope moving. Importantly, it is offers the smallest diameter in that area. Think what happens if you tie over a wider diameter. Yep, as you load the wrap, it will seek out the smallest diameter and thus you will lose tension. Lose your tension and the tie becomes unstable. If your wraps move unduly, they might end up in the wrong place or, worse, cause a nerve to shear. If you tie too high with somebody with rounder shoulders, there is a risk of the upper wrap slipping off entirely as you are tying 'on the slope'.
On the subject of 'slopes', breast size and height can make a difference. I find a larger breast can make me place my upper wrap too high due to the higher starting point. The other problem is that it might be difficult to keep the wraps sufficiently close, so I can see an argument for adding a 3rd rope. This is something Nina finds when tying the delightfully endowed MaYa.
In summary, my recommendation is to treat the portion of the upper arm below the mid-point with extreme care. The mid-region has the radial exposed on the outside and there's the ulnar lower down. It is my belief that tying closely spaced wraps with the upper on the lower slope of the deltoid is much safer than wide spacing or low bottom wraps. I stress this is a generalisation which will always have its exceptions to catch you out. I hope this has provided food for thought. I open it up to peer review and would be delighted to hear from anyone who has any views, amendments or additions. For revision, I thought it sensible to re-post my updated box-tie/gote tutorial as I have refined it slightly. No doubt it will be updated again soon: