Advanced Nerve Safety [Level 2]

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Article:

The Myth of Safe Numbness

We tend to think of tingling and numbness in rope bondage as having two distinct causes -- loss of circulation ("not dangerous") and nerve compression ("dangerous"). Many experienced bottoms believe they can tell the difference between these sensations. However, this is really just a convenient shorthand for thinking about a much more complicated set of phenomena and in actual fact there is no distinct line between these two categories.

Let's start by examining what is commonly meant by each of these terms in the bondage community:

Nerve compression means mechanical pressure that is put on a nerve at the site of (potential) injury, which may be a crushing force applied by the rope, something else digging into the body, or a positioning of the body that either constricts an area the nerve passes through or stretches the nerve itself. This is generally assumed to be the source of nerve injuries in bondage.

Loss of circulation implies an effect on nerves due to reduced oxygenation of the surrounding tissue rather than direct pressure on the nerve. This is generally assumed to not be a significant danger on the basis that sufficient restriction of circulation to cause tissue damage would be difficult to achieve and an obvious problem.

Problems With This Model

Loss of Circulation is Not Actually Common

Transient paresthesia is the medical term for a condition of tingling/numbness due to loss of regular nerve function that rapidly resolves when the proximate cause is eliminated. It includes the common experience of an arm or foot going to sleep in daily life due to being in an awkward position. However, this experience is not due to loss of circulation according to any reputable source I have found; rather, the common cause of transient paresthesia is direct pressure on the nerve (NIH, WedMD).

Lack of oxygen supply to the nerve (ischemia) is a common factor in chronic paresthesia caused by conditions such as diabetes or Raynaud's that chronically impair peripheral circulation. However, absent such chronic conditions there is no reason to believe transient paresthesias in rope are due to circulation rather than mechanical stress.

It's Hard to Restrict Circulation Without Mechanical Pressure

You might argue that while transient paresthesia in daily life is not generally caused by restricted circulation, rope bondage could restrict circulation in ways not otherwise likely to occur. There are two obvious mechanisms whereby rope bondage could restrict circulation: putting the body in stress positions, or by directly tourniquetting an extremity. Since stress positions are essentially similar to the daily causes of limbs going to sleep, tourniquetting effects seem the more plausible culprit for novel ischemic effects. Luckily, this is something that's been studied extensively in the medical literature. One of the clearest summaries I've found appears in this paper:

The 2 main mechanisms of pneumatic tourniquet-induced nerve injury are ischemia and direct mechanical effects (Hodgson 1994). Ochoa et al. (1972) found that compressive neurapraxia rather than ischemic neuropathy or muscle damage was the underlying cause of tourniquet paralysis.

There is some interesting additional reading here and here. In general, references agree that there is a complicated relationship between mechanical pressure and ischemia in tourniquetting. Regardless, the key point is that any significant reduction in circulation is likely accompanied by mechanical nerve compression, and that the latter is likely to be a larger factor in interfering with nerve function.

Conclusions

The thing to take away from all this is that if you get tingling and numbness in rope, probably a nerve is being compressed. That isn't necessarily going to cause injury -- we sustain and recover from minor nerve compression all the time in daily life -- but the difference between a compression that is harmless and one that causes serious injury is only a matter of degree. Something that you've always recovered from immediately in the past could cause lasting injury next time if you do it slightly longer or harder, or if your body is just in a different state.

So What About Generalized vs Focused Sensations?

The anecdotal experience from many bottoms is that tingling and numbness that has a slow onset and is dispersed over a large area seems less likely to result in injury than that which occurs immediately and is highly localized. While both of these scenarios likely result from nerve compression, that doesn't mean there is no actual difference. For instance, it may be that more generalized sensations mean that pressure on nerves is distributed over a larger area vs. a single point. Slow onset might be associated with lower levels of pressure.

The unfortunate fact is we just don't know how meaningful these signals are in terms of avoiding injury. Some injuries are not associated with any sensation at the time they occur, so there's no silver bullet.

Stages of Damage to Nerves

There are two distinct types of injury to nerves likely to occur in rope bondage, and understanding the difference can help shed light on differing experiences with recovery from injuries.

Neurapraxia is a condition where a nerve's ability to properly conduct electrical impulses is impaired by damage to the myelin nerve sheath. This may be caused by either mechanical stress or ischemia (in other words, any sustained paresthesia may become neurapraxia). Because the nerve fiber (axon) itself is not significantly damaged, it may retain partial function, and will gradually regain normal function as the myelin is repaired; complete recovery within 6-8 weeks is typical, often with significant improvement in the first 2-3 weeks, or even sooner for less severe cases. This is the most common form of nerve injury in rope.

Axonotmesis is when the axon is damaged to the extent that it must regenerate from the point of injury outward. This regeneration is very slow (generally quoted as 1mm/day under good conditions), and so this type of injury takes many months to recover from, and you don't see the same early improvements as with neurapraxia (because until the new axon reaches its destination, it's not doing any good). Recovery is generally good, but not always complete. In rope bondage, this type of injury appears to be less common than neurapraxia, but with similar causes/circumstances.

There are some cool pictures here.

Wrist Drop and the Myth of the Correct Box Tie

The vast majority of debilitating rope bondage injuries are caused by a single tie, the box tie or takate-kote (TK), so it merits a bit of specific discussion. Some authorities whose entire style/career rely upon this tie have tried to promulgate the notion that injuries from TKs are entirely the result of incompetent practitioners, and that if you tie a TK "correctly" it is perfectly (or at least reasonably) safe. However, there are several major flaws with this idea.

Nobody Can Agree What Is Correct

If there were in fact a correct way to tie a TK, you would expect acknowledged experts on Japanese bondage to generally use similar approaches; but in fact there is tremendous diversity in all aspects of TK construction and wrap placement. Depending on whose style you observe, wraps may be high or low on the arm, with a large or small gap between wraps, totally parallel or with a sharp angle. Upper or lower kannuki may be present or absent in any combination. Suspensions may be loaded from the stem or the top wrap or both wraps.

Of course you may argue that each of these options has a time and place with a certain body and a certain suspension. However, there are no generally agreed-upon guidelines for selecting such combinations. Perhaps you are intended to come to intuit those choices after years of experience -- leading to a conundrum around what injuries you're going to cause on the way to gaining said experience.

The Data Indicates No Correct Choice

I performed a survey of TK-related injuries, analysis of which indicates that there's no single approach to placing the wraps of a TK that can be known in advance to be safe for any given individual.

Something That Must Always Be Perfect Is Not Safe

Even if you ignore all the evidence to the contrary and take as given that a sufficiently skilled practitioner can somehow choose the exact right TK for the situation at hand, then you have to ask -- is that person also infallible? If you assume that all the celebrated practitioners who nevertheless have caused injuries were insufficiently trained, and the lack of agreement between experts is due to the great subtlety of the art, then the "correct" TK must truly be a work of extreme skill and precision. Under such conditions, presumably even a small error could make the difference between a "safe" and unsafe TK. And who doesn't ever make a small error?

In any safety-critical field, you'll find numerous mechanisms in place to guard against the inevitable mistakes that human experts make. Pilots have checklists. Climbers inspect each others' knots. To call a system safe, you need to have a margin for error. In the theory of the "correct" TK, it's not clear where that margin would be.

Conclusions

The TK is not a safe tie. Is it less safe than other ties that put pressure on the upper arms? That's hard to say; it certainly causes the most injuries, but it is also by far the most popular.

Does that mean you shouldn't use this type of tie? That depends on your risk tolerances. However, in considering any potentially dangerous play informed consent relies on being informed. If you are misleading your partner (or yourself) into believing this is not a dangerous type of play, then your consent process is broken.

Comments

  1. userpic
    Rahere | Apr 8th, 2019 3:59pm PDT #

    One common mistake is to tie to bind tightly, rather than to hold inescapably: the difference between the two need not be great.

    Fortunately for those needing to restrain others more seriously, the human skeleton has bumps, so it's possible to tie loosely enough to stop the rope passing over the bumps. This is why we've departed in the Western tradition from the more orthodox single-rope practices, for example in the hog-ties, where we start with harnesses and anchors (mostly wrist and ankle cuffs) and then do things with them with a second layer of rope. If tied correctly, they spread the load away from areas best protected. However, ties like the ebi are definitely flirting with troubles.

    A secondary point to watch is that although an initial tie may be in and of itself objective, later work on the same limb may disturb that. If, for example, a folded arm is then pulled in a different direction from the original stasis (the balance the subject has found), the initial ropework can then cause concerns, particularly where nerves are necessarily close to joints.

    Reply to this comment

    1. userpic
      AlliChemist | Feb 8th, 2021 9:58am PST #

      The link to "cool pictures" under Axonotmesis seems to be broken? I couldn't find it on Internet Archive either, unfortunately.

      On a somewhat unrelated note, I found a nice graphic hosted on rvarope.com, although I couldn't find where it was originally meant to be displayed. https://rvarope.com/wp-content/uploads/2017/12/nerves-os.jpg

      Reply to this comment

      1. userpic
        AlliChemist | Feb 8th, 2021 10:01am PST #

        "Better Bondage for Every Body" also has some really wonderful graphics

        Reply to this comment

      2. userpic
        dashengfu | Aug 22nd, 2022 7:39am PDT #

        不真实的“安全麻木” 通常我们可以认为,捆绑中发生的神经刺痛和麻木是出于两个不同的原因——血液循环障碍(“不危险”)和神经受压迫(“很危险”)。许多有经验的m相信ta们能分辨出两种感觉之间的区别。然而,这样的归因方法,实际上仅是一种用于判断更复杂的现象的速记方式,实际上这两个类别之间并没有明显的界限。 首先,让我们来审视以往绳圈中这些术语的公认定义: 神经压迫是指在(潜在)受伤部位的神经上施加了物理压力,这压力可能来源于绳索施加的挤压力,或是一些深入身体的外来物,抑或身体的姿势会压迫到有神经穿过的区域,或是会拉伸到神经本身。通常认为这是捆绑中造成神经损伤的根源。 血液循环障碍造成的神经刺痛,是由于神经周围组织细胞的氧气供应减少,而不是对神经的直接压迫。这通常不被认为是重大危险,因为阻碍血液循环而导致组织细胞损伤并非那么轻易,而且该症状较为明显,易于被察觉。

        这些说法的问题 ——血液循环障碍实际上并不常见 短暂性知觉异常(Transient paresthesia),指由于失去正常神经功能而导致的刺痛/麻木状况,如果消除病因,该症状会迅速消退。比如生活中常见的尴尬状况——睡觉时手臂或脚由于姿势不好,被压迫而导致的麻木。然而,根据我所搜寻到的任何具有权威的信息,这种经历并非来源于血液循环受阻;相反,短暂性知觉异常的常见原因是对神经的直接压迫(理论来自NIH美国国立卫生研究院,WedMD美国互联网医疗健康信息服务平台)。 神经缺氧(缺血)是慢性知觉异常的常见因素,这一症状往往是由会慢性损害末梢学血管循环的慢性病,如糖尿病或雷诺氏病等引起的。然而,如果身体没有这类慢性疾病,就没有理由认为捆绑中的短暂知觉异常是由于血液循环受阻,而非物理压力直接压迫神经造成的。

        没有物理压迫很难限制血液循环 您可能会争辩说,虽然日常生活中的短暂神经知觉异常,通常并非来源于血液循环受限,但绳索捆绑可能会以正常生活中不可能发生的方式限制血液循环。在捆绑中,绳索舒服可能会通过两种明显的机制限制血液循环:将身体置于较大面积受压环境下,或直接对肢体进行捆扎。由于身体大面积受压类似于日常入睡时导致的四肢麻木,将直接捆扎身体部位视为神经组织缺血的罪魁祸首,看起来更合理。幸运的是,这一领域在医学文献中得到了广泛研究。我所查找到最清晰的结论之一出现在这篇论文中: 气动止血带(类比捆绑中的绳索)引起神经损伤的两个主要机制,是局部缺血和直接物理压迫(Hodgson 1994)。而Ochoa (1972)等人发现,造成止血带麻痹的根本原因是压迫性神经异常,而非神经缺血病变或者肌肉损伤。 这里有一些有趣的额外阅读内容。总而言之,医学研究认为,在止血带引起的麻痹中,物理压迫神经和神经缺血之间存在复杂的关系。无论如何,我们关注的重点是:血液循环的任何显着减少,大概率都伴随着对神经的物理压迫,并且物理性神经压迫很可能是干扰神经功能的更重要因素。

        结论 从这一系列讨论中得到的有效结果是:如果你被捆绑时感到肢体刺痛和麻木,可能是因为神经被压到了,而这不一定会对身体造成伤害——我们在日常生活中一直在不断承受轻微的神经压迫,并从轻微的神经压迫中恢复——但是无害的压迫和造成严重伤害的压迫之间的区别只是程度轻重的问题。一些过去你总是立即恢复的情况,如果你持续的时间稍微长一点或更用力一点,或者你的身体只是处于不同的状态,可能就会造成长期的伤害。

        那么大面积与局部的麻痹呢? 在很多m的认知中,与突然出现且高度局部化的刺痛和麻木相比,那种出现缓慢且分散在大面积区域的刺痛麻痹,似乎并不容易造成伤害。虽然这两种情况都可能是由神经受压引起的,但它们之间并非没有区别。例如,更大面积的麻痹感可能意味着神经受压的区域较大而非单点受压迫;而麻木感出现缓慢可能是因为受到的压力比较小。 不幸的是,我们还不知道这些身体发出的信号在避免受伤方面有多大意义。有些伤害在发生时并不会产生任何感觉,因此此处没有捷径。

        神经损伤的不同类型 捆绑中可能发生两种不同类型的神经损伤,了解其中的差异有助于弄清怎样从损伤中恢复。 神经机能性麻痹/神经失用症(Neurapraxia)是一种神经传导电脉冲的能力因髓鞘神经鞘受损而损伤的病症,具体症状为发病部位瘫痪或感知能力减弱。它可能是由物理压迫或缺血引起的(换句话说,任何持续的神经感知能力异常都可能是神经机能性麻痹)。由于神经纤维(轴突)本身并未明显损伤,神经可能会保留着部分功能,并随髓鞘的修复而逐渐恢复正常功能;通常可以在 6-8 周内完全康复,在最初的 2-3 周内有显着改善,对于不太严重的病例甚至更快。这是捆绑中最常见的神经损伤形式。 轴突断裂是指轴突受损严重,以至于必须从损伤点向外再生的程度。这种再生速度非常缓慢(在良好条件下通常为 1 毫米/天),因此这种类型的神经受损往往需要数月才能恢复,并且这种情况下不会出现与神经失用症相同的早期改善(因为直到新的轴突生长到它的目的地,它才能开始发挥作用)。这种症状一般可以恢复得很好,但并不总是能完全自愈。在捆绑中,这种类型的神经损伤似乎并不如神经失用常见,但造成它的原因/情景是相似的。 这里有一些很酷的图片。

        手腕受伤和对“正确”后手缚的迷信 绝大多数使人神经受损的捆绑受伤是由后手缚(box tie)或日式后高手缚(takate-kote ,下文简称TK) 引起的,因此这个问题很值得进行具体讨论。一些捆绑风格和习惯高度依赖这种绑法的所谓权威人士试图宣传这样一种观念,即各种日式后手缚造成的伤害完全是因为绳师不称职而造成的;如果你“正确”地捆绑了日式后手缚,它是完全(或至少按理来说)安全的。然而,这个观点有几个主要缺陷。

        没有人能确保什么是正确的 如果世界上真有一种完全正确的方法来绑日式后手,你应该会看到公认的日本绳艺专家会使用这种统一的方法;但事实上,日式后手缚的结构和缠绕方式在各个方面都有着巨大的差异。根据您观察的类型不同,手臂上缠绕的绳子可能或高或低,绳索之间的距离或大或小,绳圈可能完全平行或呈锐角。更高上或更低后手乳缚可以任意组合存在或不存在。用来吊缚的悬架可以连接背后的绳柄、顶部的绳圈,或者二者兼具。 当然,您可能会质疑说,上面这些变量中的每一个都有特定的时间、地点,有特定的身体状况和特定的吊缚条件。但是,对于如何选择这些组合,并没有一个得到普遍认可的指导方针。也许你打算在拥有多年的捆绑经验之后,任凭自己的直觉来做出选择——但你在获得上述经验的过程中又会对别人造成什么伤害呢?

        数据表明没有正确的选择 我对与日式后手缚相关的伤害进行了一项调查,其分析表明,并没有一种确定的、可以保证对所有人都安全的日式后手绑法。

        “永远”完美的事物从不安全 即使您无视所有相反的证据,并认为一个足够熟练的绳师有能力为面临的新情况选择出正确日式后手绑法,那么您也必须问——这个人也是万无一失的吗?如果你假设:所有造成伤害的著名绳师都是因为没有得到足够的训练,这些权威之间缺乏一致意见是由于绳艺的精妙性,那么“正确”的日式后手缚必须真正是一项极其精确和高度重复的工作.在这种情况下,可能即使只是一个很小的错误也会导致“安全”和不安全的日式后手缚之间的差异。人非圣贤孰能无过? 在任何安全至关重要的领域,您都会发现有许多系统性的机制和规定,它们可以避免我们人类犯一些惯常错误。就像飞行员有起飞前清单。登山者会检查彼此的结。要形成系统性的安全,您需要为自己留有犯错的余地。而在日式后手缚的现有理论中,尚不清楚允许我们犯错的余地的边界在哪里。

        结论 日式后手缚并不是安全的绑法。那它是否比其他对上臂施加压力的绑法更安全?这很难说;它确实造成了最多的伤害事件,但它也是迄今为止最受欢迎的绑法。 而这是否意味着你不应该使用这种类型的绑法?这取决于你的风险承受能力。然而,在考虑进行任何有潜在危险的捆绑前,m的同意效力应当依赖于知情。 如果您误导您的partner(或您自己)相信这不是一种危险的捆绑类型,那么您的同意程序就会被破坏,自然也不具有效力。

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