During the past twenty years, research on chronic pain has significantly increased, with advances in understanding its etiology, assessment, and treatment (Johannes et al. 2010). These discoveries have important healthcare implications as pain is the leading cause for why people seek out medical care, even more so for manual therapy. Whether or not pain relief is your immediate goal, the fact remains that the majority of people who walk into your office experience some degree of pain; as such, we must understand what pain is and most importantly what pain is not. It is no less important than knowing the anatomy of the body. This article is a review of the most recent understanding of pain, providing a summary of some of the latest pain science research that is both relevant and applicable to you and your clients. It proposes explanations for phenomena where, with your treatment, a clients’ pain may decrease, remain the same, or perhaps gets worse. Most importantly, understanding this phenomena is empowering for both you and your clients.
Client expectations and fears play important roles in the outcomes—positive and negative—of manual therapy. These expectations of treatment outcomes mainly include pain relief, improved function, and improved overall well-being—including mental well-being. That being said, having a good understanding of the neurobiology of pain will help practitioners meet their clients’ personal goals for seeking out care.
Within roughly the last twenty years, neuroscience and pain science have disproven the belief that pain exists solely in the physical tissues, a purely biomechanical explanation for pain (Gifford 1998, Lederman 2010). It is a major falsification of what we once believed. The International Association for the Study of Pain (IASP) defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” Simply put, pain is the brain’s perception of tissue damage (Butler & Moseley 2003). Perception is key, because pain is about how a person consciously and non-consciously creates meaning of his/her physical reality. When the perception of our tissue state is less accurate, as with chronic pain, the perception has become an illusion. This perception of tissue damage (i.e. pain) is modulated by a number of cognitive, emotional, and sensory inputs (Carlino et al. 2014; Gifford 1998).
When someone in pain walks into your office, they want answers to the following:
1. What’s wrong with me?
2. How long is this going to last?
3. Is there anything I (the client) can do about it?
4. Is there anything you (the practitioner) can do about it?
(Verbeek et al. 2004; Gifford 2013)
When considering these questions, they make sense in terms of survival. However, if these questions are left unanswered, we begin to worry about potential disability in the future. When experiencing physical pain we sensibly, but mistakenly, place all of our attention in the physical domain. This leads us to conclude that pain is entirely a reflection of the state of our tissues, assuming the biomechanical model for explaining pain: poor mechanics = pain. Today, we see that this conclusion is falsified.
One of the brain’s chief priorities is to keep us safe and protected. Pain warns us of danger and compels us to take action to relieve and/or avoid that danger. Thus, the experience of pain is based on a prediction of danger we are physically in, not how much we really are in. Our response to pain results in altering the way we sit, stand, and move. Even if there are no problems in the tissues, nerves, or immune system, you can still hurt if your brain thinks that you’re in danger (Butler & Moseley 2003).
One class of sensory receptors called nociceptors were once, incorrectly, referred to as pain receptors. Nociceptors are receptors that require higher thresholds of stimuli to trigger an action potential, which in turn sends larger, more amplified signals to the central nervous system (CNS). These larger signals serve to get a person’s attention by acting as warning signals. The brain, though, can ignore input from the body, large or small, if the brain is either distracted enough or does not value the incoming messages. Pain is context-dependent. A notable example of this is seen with soldiers in the heat of battle who are shot but don’t feel pain until much later, once they are out of the dangerous environment.
Nociception is quantitative, not qualitative. This means the body’s sensory system simply provides raw data to an individual’s CNS. It is the brain which must then interpret that data’s meaning. While nociception is not an essential part of one’s pain experience, it can be a very powerful contributor.
One of the most important factors in understanding pain is injury healing times and their relevancy. Wound healing is a complex and dynamic process consisting of four phases: hemostasis, inflammation, proliferation, and remodeling. Typically, most tissues heal within 1-6 months. Soft tissue, such as skin, takes around 10 days to 2 weeks. Deeper soft tissue can take 3-6 months, and depending on the type of deeper tissue, it may take up to a year to regain full tensile strength. Bone takes up to 3-6 months to heal and up to a year to fully remodel (Maxson et al. 2012). Pain is mostly experienced during the inflammatory phase of the healing cycle, where a flood of chemicals excite the nervous system and lead to pain; glutamate, aspartate, substance P, adrenaline, cortisol, and cholecystokinin. Pain serves an important role during healing to ensure the process is preserved, and to prevent further tissue damage in order to facilitate a full recovery (Lederman 2015; Figure 1). Regardless whether the discontinuity of tissues remain permanent, as sometimes in the case of section tissues, the phases of healing eventually end. Recovery is partly a resolution of inflammation and attenuation of nociceptive excitation. When tissues aren’t able to complete this phase it’s do to the absent of metabolic energy i.e., blood, whereas surgery may be needed.
Unfortunately, many healthcare providers do not clearly communicate or adequately educate clients that all tissues eventually heal and that pain and severity is not positively correlated (Moseley 2003; Louw 2012). Many clients, and some clinicians, wrongly believe that once they are injured, they are always in a state of injury. In other words, their experience with episodic pain is an episodic injury, as seen with the term “re-injury.” Current research argues that this is not what is happening and thinking so actually impedes the recovery process, leading to more pain (Butler & Moseley 2003; Lederman 2015).A difficult aspect in understanding pain is that how it is not a sequential or linear process, but rather an emergent process of neuronal activity and processes. Pain is a substantial sensory and emotional experience that is modulated by psychological, social and contextual factors (Carlino et al. 2014).
PAIN IS A CONTEXT- DEPENDENT EXPERIENCE
Pain should never be seen as context-free but rather context-dependent (Turk & Monarch 2002; Gatchel 2004). Biopsychosocial research clearly shows that pain is a complex experience that never has a single stimulus. Pain may involve sensory, motor, autonomic, endocrine, immune, cognitive, affective, and behavioral components (Gatchel et al. 2007).
The biopsychosocial model (BPS) for chronic pain is a non-dualistic and integrated approach (Engel 1981). BPS is based on a systems approach as well as a way of understanding the client’s subjective experience as an essential contributor to diagnostic accuracy, health outcomes, and human care (Gifford 1998; Carrió 2004). The biological system (bio-) deals with anatomical, structural, and molecular substrates of disease—the client’s physiology. The psychological system (psycho-) deals with effects of psychodynamic factors like motivation, attitudes, and personality on the experience of and reaction to illness and pain. The social system (-social) examines the cultural, environmental, economic, familial, and social circumstances surrounding the expression and experience of illness and pain (Dogar 2007).
Biopsychosocial research clearly shows pain is a complex experience that never has a single stimulus (Figure 2). The production of pain may involve any combination of sensory, motor, autonomic, endocrine, immune, cognitive, affective, and behavioral components. Pain is filtered through an individual’s genetic composition, prior learning history, current psychological status, and sociocultural influences (Gatchel et al. 2007). Thus, tissue damage can occur in the absence of pain. It helps to see the CNS/brain as the central scrutinizing center, continuously sampling (conscious and non-conscious) from its environment, body, and past experiences (Gifford 1998; Figure 3).
STRESS AND ANXIETY
While stress and anxiety commonly overlap, individually they aren’t the same. Stress is a state of mental, emotional, and/or physical arousal due to demanding and adverse circumstances from the environment. This state of arousal results in an intense focus of attention, which may also serve as a distraction from pain. Stress activates the endogenous opioid system which raises the pain threshold, sometimes called “stress-induced analgesia.” Yet, prolonged states of chronic stress set up a feedback loop between pain and stress reactivity (Korte et al. 2005). Conversely, anxiety is defined by worry, apprehension, and anticipation of impending events or future pain, which lowers pain thresholds and results in hyperalgesia, sometimes called “anxiety-induced hyperalgesia” (Carlino et al. 2014).
Those suffering with chronic pain often have other forms of emotional and physical symptoms: anxiety, stress, depression, loss of appetite, fatigue, insomnia, tension, and fear avoidance (Lunderg 2011). Pain often exacerbates these symptoms resulting in complete debilitation. Just as pain can bring forth emotions, emotions can summon pain (Cervero 2012).
It’s normal to worry about the cause of our pain and to give way to anxiety about future disability or think that something is far worse than it actually is. However, anxiety has a great influence on sustaining and increasing the state of pain and sustaining chronic pain (Eccleston & Crombez 2007).
THE NEUROMATRIX THEORY OF PAIN
However, The current and widely accepted theory of pain is the neuromatrix theory of pain, developed by Ronald Melzack (2001; Figure 4). The neuromatrix is defined as an anatomical substrate for the widespread neuronal network processes that are sculpted by a multitude of sensory inputs, which describe the “body-self neuromatrix.” The neuromatrix reflects the emergent processes of neuronal activity in the brain. When there are repeated cyclical processes and syntheses of nerve impulses through the neuromatrix, the neuromatrix imparts a particular characteristic pattern, called a neurosignature. Put another way, a neurosignature is a particular neuronal pattern in the neuromatrix.
KNOWLEDGE IS POWER
When a client understands how pain works, they can bring conscious awareness to the triggers of their pain, and in doing so, decrease their pain. Fortunately, change in opinion gives clients more adaptive thoughts and behavior. Research conducted by Louw et al. (2014) showed that giving people a pain education significantly lessens their pain experience post-surgery and reduces medical expenses by 45%. Additionally, Louw et al. (2012) showed that for patients, knowing how a surgical procedure will affect their symptoms is for them the most important. Some practitioners think that their clients cannot understand pain physiology. However, Moseley (2003) showed health professionals inaccurately estimate client’s ability to understand the neurophysiology of pain and that despite clinicians’ beliefs that patients aren’t able to understand pain physiology, clients can and want to understand their pain.
Understanding pain gives clients confidence and self-efficacy in knowing that their bodies are sensitive, not vulnerable or fragile. Self-efficacy for people with chronic pain is when they have the internal resources to carry out certain activities or achieve a desired outcome in spite of experiencing pain (Lee et al. 2015). In other words, for a person seeking to engage in a particular behavior or activity, they’re more likely to do that if they feel like they have the internal resources to perform, regardless of their pain.
With 172 subjects, Costa et al. (2011) examined whether pain self-efficacy and/or fear of movement mediated the relationship between pain intensity and the disability of pain. What they found was that beliefs of pain self-efficacy and fear of movement partially mediated the effects of pain intensity and disability at the onset of pain. Moreover, 12 months after the onset of low back pain, subjects with high self-efficacy possessed less pain intensity and disability. Additional studies support the relationship between higher patient self-efficacy and lower levels of pain and disability (Reid et. al 2003; Denison et al. 2004; Dohnke et al. 2005). These conclusions were supported in a systematic review and meta-analysis examined by Lee et al. (2015). The study involved 2961 subjects where the research team tested what roles of fear, catastrophization, self-efficacy, and other variables such as psychological distress (depression and anxiety) have in determining disability with people with low back pain and neck pain. While all of these variables interrelate, they found that self-efficacy was the strongest mediator, followed by psychological distress, and then fear of pain. Catastrophizing was not statistically significant as a mediator.
Teaching a person with chronic pain the science of their pain is a cognitive behavioral management tool and treatment target. If done well, it has the potential to reduce clients’ fears, which decreases pain intensity and lowers overall disability. Pain education supports the intended goals in all forms of therapies and in motivating clients to play a more active role in their recovery (Nicholas et al. 1992; Altmaier et al. 1993). That said, pain education is no easy task. It must be appreciated how deep-seated clients’ beliefs are and the preconceived ideas they have of their body. Through a willingness to commit time and effort to properly educate clients, clinicians can have a profound effect on empowering clients to get back to living life more fully (Lederman 2015).
Practice makes perfect. Rehearsing any task results in higher proficiency of that task. This is a rule of neuroplasticity. The same applies if our attention is always focused on our pain: the nervous system, at all levels, will alter itself physically and chemically to be more sensitive. As pain persists, the nervous system becomes better at producing pain. How does this happen? The neurobiology is complicated but here is a short version: the peripheral nervous system (PNS) lays down more ion channels, which causes the nerve signals to be more amplified with smaller input. What previously was considered to be an innocuous stimulus may now be perceived as noxious, making it harder for ordinary CNS inhibitory mechanisms to operate effectively. Danger signals now are allowed to propagate more signals throughout the nervous system to flow to the brain uninhibited and amplified, leaving the brain to conclude that there is danger in the tissues (Kwon et al. 2014).
Our experience of pain is a top-down process—always. In fact, there is no such thing as myofascial pain, bone pain, organ pain, or even the existence of nerve pain. There’s just pain. This means damaged and pinched nerves do not have to hurt. Even in the presence of actual tissue damage—given pain is an output of the brain—it is our brain that concludes whether our tissues are in danger.
Pain is primarily a psychological experience (Craig and Hadjistavropoulos 2004). This is not to say that pain is all in your head, as in your imagination, but it is a construct of the brain. Modern pain science does NOT imply people imagine their pain. Pain is real. Pain is always real. Pain literally changes our PNS and CNS physically and chemically. This is the dark side of neuroplasticity.
Pain Science not only reveals our misunderstanding about how pain works but also examines how our common vernacular as practitioners actually cause more hurt in the end. First, we must be careful not to discount our client’s pain experience, even if we think we already have an understanding of their false beliefs. Commonly, clinicians feel rushed to get the educational portion of their treatment over with but this can only serve to further invalidate a client’s pain experience. By not allotting time to fully listen to our client’s complaints, stories, and values, we run the risk of invalidating their pain and truly misunderstand who they are as a victim of pain (Wernicke 2015). Secondly, we should be mindful of our speech. Are we using terms that incite fear and worry? Additionally, If we refer to pain as an experience (verb) rather than a thing (noun), we signal to our clients that their pain is a state that has the ability to change. This encourages a more active enrollment from our clients in their recovery. This also provides insight for them to see that their thoughts and behavior lead to positive or negative consequences. Sadly, referring to pain as a noun misplaces the multi-factorial experience pain is. Pain as a noun also can mislead both practitioners and clients to think pain is in tissues thus can be removed from their tissues (noun). This can only serve to cause more harm. If we’re speaking in wrong terms, we’re thinking in wrong terms.
Whether experiencing chronic or acute pain, incessant worry, fear avoidance, and self-diagnosing only further sensitizes one’s nervous system. When false beliefs are determined as the root of causing harm, providing client education is one of the most effective interventions. At the same time, we don’t want to cause too much cognitive dissonance at first when explaining pain. We must take special care when educating clients who seem to use their pain to self-identify.
Above all, explain pain on purpose!