A Mechanism-Based Approach to Physical Therapist Management of Pain

Abstract

Pain reduction is a primary goal of physical therapy for patients who present with acute or persistent pain conditions. The purpose of this review is to describe a mechanism-based approach to physical therapy pain management. It is increasingly clear that patients need to be evaluated for changes in peripheral tissues and nociceptors, neuropathic pain signs and symptoms, reduced central inhibition and enhanced central excitability, psychosocial factors, and alterations of the movement system. In this Perspective, 5 categories of pain mechanisms (nociceptive, central, neuropathic, psychosocial, and movement system) are defined, and principles on how to evaluate signs and symptoms for each mechanism are provided. In addition, the underlying mechanisms targeted by common physical therapist treatments and how they affect each of the 5 categories are described. Several different mechanisms can simultaneously contribute to a patient's pain; alternatively, 1 or 2 primary mechanisms may cause a patient's pain. Further, within a single pain mechanism, there are likely many possible subgroups. For example, reduced central inhibition does not necessarily correlate with enhanced central excitability. To individualize care, common physical therapist interventions, such as education, exercise, manual therapy, and transcutaneous electrical nerve stimulation, can be used to target specific pain mechanisms. Although the evidence elucidating these pain mechanisms will continue to evolve, the approach outlined here provides a conceptual framework for applying new knowledge as advances are made.

Figure 1.

Schematic diagrams representing a mechanism-based approach to pain management. (A) Description and examples of 3 pain mechanisms (nociceptive, nociplastic, and neuropathic) that contribute to pain, as previously outlined by Phillips and Clauw. People with pain can have 1 or a combination of mechanisms contributing to their pain. (B) Schematic representation of 3 pain mechanisms occurring within the context of movement system and psychosocial factors.

Figure 2.

Diagram illustrating how peripheral and central sensitization can lead to pain. (A) Condition with no pain. Normal nociceptor activity and central neuron activity usually do not produce pain. (B) Condition with peripheral sensitization. Enhanced nociceptor activity activates nonsensitized central nociceptive neurons to result in pain. (C) Condition with central sensitization but without peripheral sensitization. Normal activation of nociceptors activates sensitized central neurons to result in pain. (D) Condition with both peripheral sensitization and central sensitization contributing to pain. Treatments aimed at peripheral nociceptive input would be effective in people with peripheral sensitization but would have minimal effects in people with central sensitization and partial effects in people with both peripheral sensitization and central sensitization.

Figure 3.

In pain conditions, peripheral sensitization and central sensitization vary across a continuum. Sensitization of the peripheral nervous system contributes to a large proportion of pain with an acute localized injury, whereas sensitization of the central nervous system contributes to a large proportion of pain with chronic widespread pain conditions, such as fibromyalgia (FM). For other diagnoses, depicted in the midrange as low back pain (LBP), osteoarthritis (OA), rheumatoid arthritis (RA), Achilles tendinopathy (AT), and temporomandibular joint disorder (TMD), people can have high levels of peripheral sensitization, high levels of central sensitization, or both.

Figure 4.

Four continua of movement system adaptations to pain and how they can affect an exercise program.

Figure 5.

(A) Scatterplot showing the variability in conditioned pain modulation (CPM) in people with fibromyalgia and healthy controls, represented as the percent change in pressure thresholds before and after the CPM test. In a comparison of people with fibromyalgia and healthy controls, although there was an overall decrease, on average there were clearly people with fibromyalgia who presented with normal CPM and healthy controls who presented with reduced CPM. (B) Analysis of data from an ongoing fibromyalgia activity study with transcutaneous electrical stimulation (n = 172) revealed the variability in psychological measures in people with fibromyalgia; 26% had high scores on the Pain Catastrophizing Scale (> 30/52), and 51% had high scores on the Tampa Scale of Kinesiophobia (> 37/68).

Figure 6.

(A) Diagram illustrating sites of action, based on currently available mechanistic data, of common physical therapist treatments on the 5 mechanistic categories for pain. Exercise works to modify all 5 mechanisms and can be considered a multimodal therapy. Currently known mechanisms of action of common physical therapist treatments on pain are outlined in detail in the text. TENS = transcutaneous electrical nerve stimulation. (B) Diagram illustrating sites of action, based on currently available mechanistic data, of common pharmacological treatments on the 5 mechanistic categories for pain. Many physical therapist treatments target multiple mechanisms, whereas most pharmaceutical agents target a single mechanism.