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INTRODUCTION

OBJECTIVES

Following completion of this chapter, the student will be able to:

  • Identify sources of acute and persisting pain and appraise their positive and negative effects.

  • Choose a technique for assessing pain.

  • Describe the characteristics of sensory receptors.

  • Examine how the nervous system relays information about painful stimuli.

  • Distinguish between the different neurophysiologic mechanisms for pain control for the therapeutic modalities used by clinicians.

  • Discuss how pain perception can be modified by cognitive factors.

UNDERSTANDING PAIN

The understanding of pain, and thus approaches to pain management, continues to evolve. Once defined as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage,”1 it is clear that the sensation of pain is far more complex. Health conditions such as fibromyalgia and phantom limb pain defy the notion that all pain originates from an identifiable tissue source. Chimenti et al.2 classified pain as being nociceptive, nociplastic, neuropathic, psychosocial, or motor. While these classifications are not mutually exclusive, this paradigm is consistent with a contemporary view that pain is a brain-generated sensation and experience that may be, but is not necessarily, in response to nociceptive signals emanating from peripheral receptors in response to tissue injury or potential injury.

The assignment of patients to a classification is not merely an academic exercise but rather fundamental to plan of care decisions, including decisions regarding the use of therapeutic modalities. Nociception results from the response of the sensory system to tissue injury or potential tissue injury and aligns with earlier definitions of pain.

The sensory system however is not static. Changes throughout the system, from peripheral sensory organs and nerves to brain centers, alter signal transmission and thus sensation. Pain can be experienced in absence of tissue damage or the expression of pain can exceed what one might expect for a given extent of tissue injury.

Injury to, and inflammation of, peripheral nerves generates unique pain characteristics (burning and lancinating pain) which can be disabling and very difficult to manage. Treatments that reduce nociceptive pain, such as cold application, typically fail to relieve and often exacerbate neuropathic pain. Pain, especially persisting pain, is more than sensory. Pain impacts psychological well-being and the social/societal function of many patients. It is also apparent that health conditions, such as depression and life experiences resulting in posttraumatic stress disorder (PTSD), are associated with pain in absence of an existing tissue injury.

Motor mechanism-based pain may include muscle insufficiency (weakness) or facilitation (spasm and increased tone of muscles). We prefer to label this classification as “biomechanical” as the source of motor dysfunction may be arthrogenic (hypermobile or hypomobile synovial joints) inhibition or facilitation rather than the result of muscle/tendon injury. Regardless of the label, many patients with persisting musculoskeletal pain have identifiable biomechanical sources of their symptoms.

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