Mechanisms behind chronic pain: Better understanding for better outcomes in prevention of post-surgical chronification of pain

This article is part of an ongoing series to raise awareness of a broad set of topics impacting orthopaedic practice to broaden the collaborative discussion around improving patient surgical outcomes, especially postoperative pain management and with developing solutions that improve practices across Europe. The opinions expressed in this interview are meant as an informal conversation to facilitate dialogue.

Prof. Enric Càceres

Prof. Enric Càceres is the chair of orthopaedics at Universitat Autònoma de Barcelona, the head of the spine unit at Institut Universitari Dexeus and part of the spine research unit at Hospital Universitari Vall d’Hebron, both in Barcelona. As main investigator in the spine unit, Càceres has ongoing practical experience with spine disease. Treatments, both conservative and surgical, cover pathologies where ongoing research informs Càceres and the teams with whom he works, including special projects in deformity, tumor conditions, cellular therapy and pain control.

During our discussions on postoperative pain management (POPM), there are a number of consistent themes that continue to arise, which we have addressed throughout the series of articles. This month, we revisited our discussion with Càceres, who in his previous contribution to the series provided a detailed analysis of treatment approaches for chronic pain patients with visible brain changes.

Chronification of pain following surgery is a significant concern and impacts the approaches to be taken throughout engagement with the patient, not only following surgery, but in the preparation of the patient in the lead-up to any procedure. Our discussion with Càceres provides further details on the mechanisms behind the chronification of pain and how better understanding of those mechanisms can provide practitioners with a more effective approach not only to pain management, but also to pain prevention.

Pathophysiological changes

When speaking about acute pain, Càceres noted that acute pain after orthopaedic surgery is the result of tissue injury from the procedure. The mechanisms that cause this pain can also contribute to the chronification of the pain post-surgery.

“The link between a surgical incision and the pain experienced by the patient is mediated by distinct neural pathways. The surgical intervention activates receptors (nociceptors), which send a signal from the site of surgery via slow conducting A delta and C fibbers within peripheral nerves, which are geographically integrated in the dorsal column of the spinal cord, and transmitted to the brain. The signal is transmitted up the lateral spinothalamic tracts in the spinal cord into the lateral thalamus and is projected geographically onto the sensory cortex. Further modulation is possible at any of the upward transmission sites,” Càceres said.

This process leads to the fact that the most frontal brain areas are directly activated on account of this acute pain, maintaining memory in future evolution which then transforms into chronic pain.

By understanding this mechanism and remembering it in the context of perioperative procedures and pain treatment planning, practitioners can then ensure to take the risk of chronification into account, understanding that at times a simple approach leveraged heavily on chronic treatment with major opioids could contribute to chronic pain evolution after orthopaedic surgery. For further discussion on the overview of opioid usage, see the May 2019 POPM article.

Keeping in mind this chemical process and its contribution to chronic pain evolution, the first 48 hours post-surgery are imperative toward cancelling the evolution of chronic pain.

Càceres said, “Tissue injury also causes nociceptors to release a number of chemical mediators, such as bradykinin, serotonin, substance P and histamine. The gradually increasing transmission from peripheral nociceptors and the accompanying perception of increased pain from decreasing levels of stimulation could develop chronic pain.”

Early intervention in this process, therefore, is imperative to counterbalance the perception of increased pain and its association with decreasing stimuli postoperatively.

Management and prevention

Initial acute pain begins with the surgical incision also implies that with the complexity of the variety of surgical options available for different interventions there are varying degrees of risk to the intensity of pain that can be perceived following the procedure.

“In orthopaedic surgery, there is the high probability that many surgical procedures will cross several dermatomes. Each dermatome will have nociceptors that signal the dorsal column of the spinal cord at that spinal level. The active, repetitive nociception at several adjacent dermatomes magnifies the stimulus to expand the pain receptor fields in the spinal colun and increase the potential for central hypersensitivity,” Càceres said.

Due to this, regional analgesia is recommended as a perioperative practice to reduce this potential. The hypersensitivity produced may have significant effects on the likelihood of the evolution from acute pain perception to pain chronification. Among these practices, there is the popular use of ketamine and COX-2 inhibitors to help reduce the development of chronic pain in the postoperative period. Càceres also refers to peripheral nerve block, field block and wound infiltration as choices routinely available for orthopaedic procures.

He said, “Plexus brachial or lumbosacral blockade with catheter could be useful to decrease the risk or chronification of pain after orthopaedic surgery.”
He also noted some studies have suggested that injection of local anesthetic into joint spaces decreases postoperative pain with intra-articular surgery.
“The analgesia achieved greatly outlasts the duration of action of the local anesthetic agent injected, especially if combined with morphine,” he said.

Càceres cited good results in his own practice with spine surgery where they have used multifidus and paravertebral infusion of local anesthetics prior to a procedure with good initial results. The emphasis on preoperative and perioperative practices to arrive at a prevention of the evolution from acute to chronic pain post-surgery is a positive step forward to provide options for surgeons and the teams they work with to put in place practices that focus on pain management, as well as pain prevention, with the hope of having the best outcomes to prevent issues of chronic pain.

In addition, Càceres said he has seen a variety in the approaches with which these strategies are managed in different countries in Europe, as well as overseas. He hypothesised this is due to the different approaches related to which profile is tasked with managing the postoperative pain situation. For many physicians, he noted the significance of having strategies that treat acute pain in a manner that provides postoperative controlled is still undervalued.

“There is a clear relation between the intensity of the postoperative acute pain situation and the time of exposure to the development of a chronic pain situation,” Càceres said. The longer the patient is exposed to acute pain, the worse outcomes there are in the prevention of chronic pain following surgery. Therefore, Càceres suggested using an aggressive initial treatment within the first 48 hours following surgery and recommended that a clear and correct treatment and approach throughout the planned intervention is outlined to avoid the development of chronic pain following the procedure.

Rules of thumb

Càceres cited continuous evaluation of the pain situation in postoperative orthopaedics as a mandatory practice to better control and void the evolution of acute pain into chronic pain following a procedure. He also noted that within his practice, there is a clear rule to focus on the multimodal treatment options available to the patient. It is also important to consistently use a multidisciplinary approach in which physicians are part of a team with surgeons, anesthesiologists, nurses and pain specialists who are all focused on pain management and prevention, a theme that has been a constant in this series of discussions of postoperative pain regardless of the topic being addressed.


For more information:

Coming up in June 2019 in Lisbon, the 20th EFORT Congress will provide the opportunity to discuss these topics further face-to-face with key opinion leaders like our supporting contributors. Until then, and still following those discussions, we will continue to bring you the topics that most interest you.

To further discuss the opinions expressed in this article, engage on Twitter, Facebook and LinkedIn at #painmanagement, #changepain and #POPM. The article was initially published in Orthopaedics Today Europe, June 2019

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