We often think of musculoskeletal pain as purely a physical experience – tissue is damaged, and our nervous system output is pain. But we know that pain is much more complex than this (see our December blog post on Pain Science). In fact, our mental health and status have a significant impact on pain as well as recovery from injury. Poor mental health has been linked to longer and more intense output of pain, and longer recovery times.
Let's briefly revisit our December blog post, "The Anatomy of Pain." Musculoskeletal pain and impairments affect muscles, bones, joints, ligaments, tendons, and even nerves. Pain, as defined, is an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage [1]. In essence, pain is generated by our brain in response to a potential or perceived threat to our body. The crucial element here is the "perceived" threat. A perceived threat may not necessarily result in damage, but our body, through various processes, determines that this threat could cause harm, leading to the creation of pain.
In a typical, healthy response to pain, our reflexes act to protect us from further harm (e.g., the reflex that creates the swift movement of our hand away from a hot stove). However, in cases of chronic pain, the response becomes maladaptive due to a complex cascade of events that impacts our nervous system.
Pain processing occurs within our nervous system and specific areas of the brain. Research indicates that the regions responsible for pain processing also play crucial roles in managing emotions, memories, and cognition. Additionally, studies have established a connection between chronic musculoskeletal pain and factors such as inadequate sleep quality, previous pain experiences, unhealthy beliefs about pain (which can impact our health behaviors), as well as conditions like depression, anxiety, and insufficient social support. Patients who understand how these factors work together can improve their health outcomes, making education a necessary component of modern musculoskeletal treatment.
Individuals experiencing musculoskeletal pain often contend with psychological comorbidities, a phenomenon extensively explored in those with chronic conditions such as low back pain, shoulder pain, and knee pain. Let's delve into three specific psychosocial factors that have been evaluated as contributing elements to the persistence of pain: depression, stress, and fear.
Depression and pain, especially chronic low back pain, has been extensively studied. People with chronic low back pain are about 3 to 4 times more likely to have depression compared to the general population. Persisting pain can result in depressive symptoms, but conversely depression is also a risk factor for pain becoming chronic. The exact reasons behind this are not fully understood, but recent research suggests significant connections between changes in the nervous system and brain caused by both pain and depression. These changes, known as neuroplasticity, seem to play a crucial role in the development of chronic pain and depression linked to persistent pain. [2]. Patients with pain and depression report more severe pain, greater disability, lower functioning, and poorer treatment outcomes for their pain [3].
A study in 2005 by Jarvik et al revealed just how impactful depression is in the development of pain. The authors collected lumbar spine MRI data on 123 veterans with no low back pain. At baseline, up to 84% of the participants had some form of abnormality on their MRI, including lumbar disc protrusion. The authors performed a 3-year follow-up to see if these MRI findings or baseline depression levels correlated with future low back pain, and found that self-identified depression at baseline was the strongest predictor of future low back pain, and disc protrusions the lowest predictor. This study reiterates the conviction that the psychosocial state of an individual might be a better predictor of true pain than the presence of abnormal imaging [4].
The link between stress and musculoskeletal pain has also been well established. Psychological stress can be defined as a perception of threat, with resulting discomfort, emotional tension, and difficulty in adjustment and can have a variety of triggers, including adverse life events, daily hassles, or work related stressors [5].
Chronic stress may be evoked by persisting fear of perceived threat to safety, status or well-being, and elicits the secretion of hormones, including cortisol, to promote survival and motivate success. Cortisol is a hormone and anti-inflammatory that functions to mobilize glucose (sugar) reserves for energy and modulate inflammation. It may also govern fear-based memories for future survival and avoidance of danger. Short term stress is important for our survival and may be adaptive, however maladaptive responses to stress can intensify cortisol secretion and condition a sensitized physiologic stress response. This exaggerated stress response can perpetuate cortisol dysfunction, inflammation and pain. The effects of maladaptive response to psychological stress parallels the response to pain [6]. Stress, in general, can cause pain signals from our body to the brain to be amplified and exaggerated.
Fear and accompanying behaviors are associated with musculoskeletal pain, and studies suggest it can influence treatment outcomes and injury prognosis. Fear can be defined as an emotional response to a recognizable and imminent danger, prompting specific behavioral and psychological reactions to confront the threat. Similar to stress, fear learning is an adaptive survival mechanism that helps to identify actual or potential threatening signals, allowing for us to initiate proper defensive mechanics (i.e. escaping) to prevent harm.
People learn to fear movements and activities that they experience as painful, and as a result can adopt different behaviors, such as avoidance, in order to control further injury to the body. This behavior can occasionally act as a protective mechanism when the injury is acute, but can be detrimental to recovery, especially when the injury becomes chronic [7].
Fear associated with movements may lead to general avoidance of activities that someone with an injury or pain may associate with creating tissue damage. This is referred to as fear-avoidance behavior. The anticipated threat of intense pain will often lead to constant vigilance and monitoring of pain sensations, which, in turn, can cause even low-intensity sensations of pain to become unbearable. Even just the anticipation of pain can further exacerbate avoidance behaviors [8].
Physical therapy has shifted from a purely biological treatment model, to what we refer to as the biopsychosocial model. The biopsychosocial model takes into play not only treating the physical impairments but also the psychological and social factors that contribute to pain or injury. To achieve optimal results in physical therapy, neither physical nor mental health should be treated in isolation. Here’s how physical therapists can help address mental health:
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