How Pain Can Affect Your Work

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage (Lee and Tracey, 2010). Typically, pain is transient, lasting until only the noxious stimulus is removed or the underlying pathology has healed.  In some cases, however, the pain persists despite removal of the stimulus and healing of the body. The pain experience is quite complex, taking into account many different factors, including both biological and psychological mechanisms. In the work disability framework, the interaction between these biological and psychological mechanisms of pain is a crucial factor in impeding return to work.

When considering return to work, there is a danger that only the most simplistic view of pain would be addressed, such as injury and inflammation involved in acute pain. In this experience, a stimulus activates nociceptors sending impulses to an interneuron in the spinal cord, which in turn then relays the information to the lateral spinothalamic tract (Loisel, 2012a). This tract carries the pain message to higher centers in the brain. Key in this process, the initial stimulus causes a transient decrease in the threshold of the interneuron (Loisel, 2012a). When the initial stimulus is removed and the tissue has healed, the brain, recognizing this, exerts descending control to the interneuron, restoring its normal threshold (Loisel, 2012a).

Understanding the changes in the above mentioned thresholds helps us understand the experience of persistent pain--the predominant pain experienced by those in which pain is impeding their return to work. The ‘Gate Control Theory’ of pain stipulates that physical pain is not only a direct activation of pain receptor neurons, but is also modulated by the interaction between different neurons in the spinal cord which can either block signals or allow them to continue to the brain (Loisel, 2012b). Control of the gates is performed by higher centers in the brain (Loisel, 2012b). Based on both perception and experiences, these areas of the brain exert descending control on the gate in the spinal cord (Loisel, 2012b). Positive experiences can actually close the gate and allow the person to not feel pain. Negative experiences such as fear avoidance, kinesiophobia, depression, anxiety, stress, and catastrophism increase descending control on the gates in the spinal cord interneuron, lowering the threshold and increasing perception of pain (Loisel, 2012b). 

The main difference between acute and persistent pain is the effect of the negative experiences and cognitions on decreasing the threshold of the interneuron in persistent pain. It is through these descending inhibitory mechanisms that pain can impede continuing work. In a paper by Coutu et al (2010), subjects in the study were all on a prolonged leave from work due to a musculoskeletal disorder and had some similar and different perceptions of pain. Coutu et al. (2010) showed that their perception of the pain directly affected their ability to return back to work. There were 3 main pain representations that were in effect. Normal pain, which they believed was under their control, was expected, and inevitable (Coutu et al., 2010). Abnormal pain occurred when the subjects experienced pain for longer periods of time, with an increased intensity, and the cause appeared to be external to their body (Coutu et al., 2010). Subjects who learned to perceive their abnormal pain as being under their control and something they could live with were able to return to work (Coutu et al., 2010). Subjects who continued to experience their pain as abnormal were less likely to return to work (Coutu et al., 2010),

The results of the above study can be explained using the Gate Control Theory. In subjects who learned to perceive their pain as being normal and under their control, higher brain centres exhibited positive descending control on the interneurons in the spinal cord, thus restoring or increasing their threshold of pain. In subjects whose perception of pain continued to be abnormal and not under their control, their higher brain centres continued to exhibit negative descending control on the interneurons in the spinal cord, thus lowering their threshold for pain, leading to the persistent pain.

The consequences of having a lowered threshold and increase in perception of pain also has implications on return to work, due to the physical work tasks themselves. Decreased thresholds mean that less of a stimulus will produce a pain response similar to the original stimulus that initiated the tissue injury or pain. Work tasks that involve repetitive tasks, heavy lifting, or vibrations--that will not normally initiate a pain response--can initiate a response in those workers with persistent pain (Loisel, unknown year).  As a result, a worker with persistent pain would be impeded in returning to these particular tasks.  To combat this predicament, task modification including lifting lighter loads, less repetitive movements, frequent breaks, as well as decreasing exposure to vibration, might be a good place to start in the return to work process.

Pain may impede continuing work if persons perceive their pain as something that is not under their control. If the perception of pain can be changed then the client will have a much greater chance of returning to work. It has been shown that biological mechanisms, psychological mechanisms, and their interactions with one another influence the perception of pain, and have implications on the return to work process. Biological mechanisms, including decreased pain thresholds impede the physical tasks that one is able to do. Psychological mechanisms of pain perception influence the biological pathways.

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References:

Coutu, Marie-France, et al. (2010). Transforming the meaning of pain: An important step for return to work. Work (35): 209-219

Lee, M., and Tracey, I. (2010). Unravelling the Mystery of Pain, Suffering, and Relief with Brain Imaging.  Curr Pain Headache Rep (14): 124-131

Loisel, P. 2012a. Pathophysiology of Musculoskeletal Pain: Physical Mechanisms. Lecture Notes, pages, 1-14

Loisel, P. 2012b. Pathophysiology of Musculoskeletal Pain:  Psychosocial Mechanisms. Lecture Notes, pages 1-14

Loisel, P. (unknown year).  Pain in the Workplace, Compensation and Disability Management. Pages 1703-1705