Contemporary Acupuncture and movement disorders: restoring motor and somatic sensory function

Introduction

Advances in the fields of neurophysiology and neurosciences in the last three decades have allowed to re-defining acupuncture as a straightforward peripheral nerve stimulation technique. This technique, now based in biomedical science, has been termed contemporary acupuncture to differentiate it from traditional acupuncture approaches.

Contemporary acupuncture can be defined as a therapeutic method in which fine solid needles are inserted on specific neuro-reactive sites of the body for the purpose of inducing autonomic, sensory and/or motor neuromodulatory responses. Neuromodulation is the property of the nervous system to regulate its own activity in response to exogenous or endogenous stimuli, e.g. exposure to a cold environment produces reflex vasoconstriction of the skin vessels, and the contraction of a muscle produces a reflex relaxation of its antagonist.

Control of movement is one of the most complex tasks of the somatic nervous system and involves several well known reflex neuromodulatory responses; contemporary acupuncture has proven to be effective in the modulation of some of these reflexes as it will be discussed later.

Neuro-reactive sites and somatic innervation

A contemporary acupuncture neuro-reactive site can be defined as any area of the body where there is somatic innervation. Somatic nerve fibers are those— within spinal and peripheral nerves—that innervate the muscles, joints and skin. Since the arterial network of the skin and musculoskeletal system is in turn innervated by the sympathetic nervous system, it is fair to assume that all neuro- reactive sites must also have some degree of sympathetic vascular innervation. Indeed, both spinal and peripheral nerves contain somatic sensory or motor axons together with sympathetic vascular nerve fibers.

Somatic motor axons are always myelinated and are classified functionally on the basis of their mean conduction velocity, into three categories—A-α, A-β, and A- γ—each one innervating different striated muscle fibers, i.e. extrafusal (A-α), intrafusal (A-γ), and both (A-β).

Somatic sensory axons are classified functionally into four types (I to IV) also on the basis of the speed of conduction. Within the muscle-tendon-joint region, sensory axons innervate a variety of specialized sensory receptors, i.e. muscle spindles (Ia, II), Golgi tendon organs (Ib), ligament receptors (Ib), Paciniform and Ruffini’s receptors in joint capsules (II), muscle deep pressure endings (III), and muscle free nerve endings (III, IV). Some of these categories of axons are also found in the skin and fascia. The fascia is particularly rich in sensory innervation with Pacinian corpuscles, Ruffini organs, small myelinated free nerve endings (A-δ fibers or mechano-nociceptors), and unmyelinated free nerve endings (C fibers also able to transmit pain and mechanical signals such as very gentle pressure and tension).

This rich variety of skin, fascial, and musculoskeletal somatic afferent fibers carrying exteroceptive information (pain, touch, temperature) and proprioceptive information (position sense, joint movement, muscle length, rate of change of muscle length, muscle stretch, tendon tension, ligament tension) explains the vast number of potential neuro-reactive sites or insertion sites available to contemporary acupuncture practitioners.

Contemporary acupuncture and the somatic nervous system

The anatomical and functional picture described above explains why, despite the abundance of potential insertion sites available for peripheral nerve stimulation, the most effective neuro-reactive sites used in contemporary acupuncture are invariably those associated with the areas of the musculoskeletal system where the somatic sensory and motor innervation is particularly rich, i.e. muscle belly, muscle-tendon junction, tenoperiosteal attachment, periosteum, joint capsule, ligaments, neurovascular bundles, neuromuscular junctions or motor points, and the omnipresent fascia.

For all the above reasons, it is easy to understand why contemporary acupuncture can be extremely effective in the treatment of movement disorders by virtue of stimulating relevant sensory and motor somatic receptors, therefore helping restore normal sensory-motor activity in the treated segment.

Unfortunately, most current acupuncture research efforts are focusing on the applications of acupuncture for the treatment of pain, while in the opinion of the author of this article the use of acupuncture as a segmental and regional

sensory-motor regulatory intervention could play in the near future a fundamental role in the area of treatment of movement disorders.

Movement, proprioception, and subconscious stimulation

It is well known but often forgotten that most proprioceptive information is processed without conscious participation of the individual. One important practical implication of this point is that in order for acupuncture to stimulate proprioceptive receptors the intensity of the stimulus can be very low and its conscious perception is not necessary.

Unlike what is believed in traditional approaches, acupuncture points as such do not exist in contemporary acupuncture. Each insertion site is a combination of different nerve fibers and receptors, and effects depend mainly on the type of nerve fiber that responds to the stimulus provided by the needle insertion.

Consequently, the location of the insertion site, its deep neuroanatomy, and the quality of the execution of the full insertion are going to be the determining factors in producing the intended segmental and regional response.

It is also frequently forgotten that fully normal proprioception requires the participation of muscle spindles, joint receptors, and cutaneous mechanoreceptors. This redundancy probably reflects the importance of proprioception to the control of movement. People with total hip replacement retain good proprioception in midrange. This indicates that joint receptors are not essential for proprioception.

From a contemporary acupuncture practical standpoint, it is paramount to understand the importance of painless needle insertion, with a slow and painless advance of the needle through the different layers of tissue, since every layer of tissue (skin, fascia, muscle, and joint) is a potential contributor to the global proprioceptive message.

Obviously, there are a variety of neurophysiological strategies involved in movement control, but to better appreciate the potential role of contemporary acupuncture in the treatment of movement disorders, we can simply divide them from an anatomical standpoint into segmental, intersegmental, and supraspinal. Not uncommonly, the nervous system uses a combination of all of these when dealing with movement control. For instance, the activity of gamma motorneurons is regulated primarily by intersegmental and supraspinal pathways and little by segmental sensory inputs, while the autogenous inhibition reflex mediated by the Golgi tendon organs is mainly segmental in nature.

In general, a great deal of proprioceptive information related to the control of movement in a given area is processed segmentally and intersegmentally, such as the reciprocal inhibition and autogenous inhibition reflexes.

Summary of contemporary acupuncture effects relevant to the management of movement disorders

Physiological response to contemporary acupuncture interventions includes: segmental and systemic analgesia, neuromodulation of sensory, motor, autonomic and visceral functions, modulation of endocrine and immune functions, and modulation of central functions such as those associated with the activities of the limbic system.

Since the purpose of this article is to focus on the effects of contemporary acupuncture on the modulation of relevant sensory and motor functions of the musculoskeletal system, a summary of relevant effects follows.

The main set of segmental effects involves motor, sensory, and autonomic aspects at the spinal level, putting the three kinds of “gate controls” into action, with results such as:

• modulation of the transmission of signals in nociceptive and other sensory afferent fibers (gate control of the afferent system)
• normalization of segmental muscular tonus and functionality (gate control of the locomotor system)
• normalization of segmental sympathetic and parasympathetic activity (autonomic gate control).

Explanation of these spinal gates follows:

Spinal gate control of the sensory system

All kinds of somesthetic inputs to the spinal cord, both protopathic sensations, like nociception, and epicritic like proprioceptive afferents, are modulated at the metameral and upper levels of the nervous system.

In the case of pain, the activation of myelinic sensory fibers (nociceptive or not) modulates the activity of the nociceptive fibers, a process that results in clinical improvement of pain and local pain-related alterations, and sensory function normalization.

Spinal gate control of locomotor system

In contrast to the mechanisms that cause and sustain motor dysfunction, whether inhibition or hyperactivity, the motor gate control activation promotes restoration of muscular strength and release of the movements restrained by muscular hypertonicity, by means of changes induced on the activity of the motor neurons.

The modulation of muscle and tendon originated proprioception, activating physiologic spinal reflexes, results in a relaxation of segmental muscular tonus, and changes in reflex mechanisms, that increase the tonus of inhibited muscles.

Spinal gate control of the autonomic system

The modulation of segmental autonomic system activity generates consequences that include the treatment of regional autonomic components of pain. It plays an important role in the restoration of the regional functional normality, especially of the circulatory segment, and in the reduction of one of the main factors that perpetuate regional chronic pain – the sympathetic hyperactivity.

It is easy to see how the interaction of these three spinal gate control mechanisms will help normalize sensory-motor integration at the affected segment and in the adjacent ones, with normalization of vasomotor tone and improved perfusion of the affected tissues locally. To accomplish these effects needles can be inserted both at the peripheral segmental level on the affected muscles and joints or their relevant nerves or on the paravertebral musculature also at the relevant segmental somatic (dermatome, myotome, sclerotome) and segmental autonomic levels (reflex vascular areas).

Mid-range and high frequencies (15-20 Hz and up) reinforce the segmental effects of these inputs, while low frequencies (2-4 Hz) engage supraspinal mechanisms in the neuromodulation of the segmental and intersegmental activities.

Contemporary acupuncture in the treatment of movement disorders: the chronic functional ankle instability model

Some of the strategies of contemporary acupuncture in the treatment of movement disorders can be exemplified by the treatment of chronic functional ankle instability.

It is well known that individuals with this conditions exhibit important motor deficits in the absence of significant structural problems, with a clinical picture of repeated episodes of giving way, decreased the strength of periarticular muscles, and decreased proprioception and balance.

Recently, a pilot study showed that in these individuals, a single session of electro-stimulation of two needles—one inserted into the sinus tarsi and the other on the proximal aspect of the peroneus longus muscle at the level of the fibular neck (right by the trunk of the common peroneal nerve)—produced significant changes in strength, proprioception, balance, perceived discomfort, and the number of reported episodes of giving way, with all the improvements still remaining one month post-treatment.

The only explanation for this spectacular clinical improvement is the segmental normalization of sensory-motor activity with the elimination of the prior regional motor inhibition. This is consistent with contemporary concepts on the pathophysiology of this condition. Namely, that the presence of abnormal signals from the interosseous talocalcaneal ligament produces a segmental motor inhibition of the movers of the subtalar joint. This motor inhibition is reversible with an injection of local anesthetic into the sinus tarsi. Strength remains as long as the effect of the local anesthetic does. Objective changes on EMG activity of the peroneal muscles have been reported after these anesthetic injections into the sinus tarsi. Unfortunately, these changes revert once the anesthetic effect is over.

So, it seems that acupuncture can somehow override abnormal sensory signals and produce the normalization of segmental activity which will result in normalization of motor activity and normalization of sensory-motor integration in the region.

These experimental results validate some of the acupuncture approaches used empirically on the treatment of movement disorders.

Contemporary acupuncture selection of inputs in movement disorders: final thoughts

As a summary of the contemporary acupuncture strategies discussed in this article, when dealing with movement disorders:

• identify the affected joint or joints using clinical history and range of motion;
• identify weak muscles—agonists, antagonists, or stabilizers—using motor testing; identify tight muscles;
• determine abnormal recruitment patterns;
• identify the associated spinal segmental levels of dysfunction using the affected peripheral dermatome, myotome, and sclerotome as the guiding functional units;
• identify central factors;

Now you are ready to select the most appropriate contemporary acupuncture inputs:

• treat agonists and antagonists involved
• treat joint involved
• treat motor and sensory nerves involved
• treat spinal segments involved

The discussion of the technical aspects involved in each of these strategies is beyond the scope of this article, but the anatomical and functional basis of the model have been explained early on this article. The ultimate key is to select the most relevant neurological receptors and pathways involved in the dysfunction.

Contemporary acupuncture seems to have a pre-eminent role to play in the management of movement disorders, mainly as a normalizer of segmental and regional sensory and motor function, including neuromodulation of vasomotor tone with a restoration of perfusion in the affected tissues.

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