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Building an Evidence Base in Chiropractic Medicine: A Conversation With Petra Schweinhardt

30 July 2020

PRF Interviews


Editor’s note: Petra Schweinhardt, MD PhD, is the head of research of the Department of Chiropractic Medicine at the Balgrist University Hospital and the University of Zurich, Switzerland. Her clinical research is focused on outcomes in patients with musculoskeletal pain treated by chiropractors and potential predictors of treatment outcome. In her experimental work, she investigates how sensitization in the central nervous system contributes to musculoskeletal pain. Methods she uses include psychophysics, kinematic modeling, and brain imaging. Before moving to Switzerland, Dr. Schweinhardt held an associate professorship and a Canada Research Chair Tier II at McGill University in Montreal, Canada, where her research centered on cerebral pain processing and modulation as well as brain alterations in chronic pain patients. She earned her medical degree at Ruprecht-Karls-Universität Heidelberg, Germany, and a PhD in the neurosciences at the University of Oxford, UK. 


Dr. Schweinhardt was kind enough to sit down recently for an interview with Catherine Paré, a PhD student at McGill University, to discuss what attracted her to musculoskeletal pain research, how to build an evidence base in chiropractic medicine, and much more. Below is an edited transcript of the conversation.


What drew you to musculoskeletal pain research?


I had been doing pain research for a while, focusing on pain processing in the brain and how the brain is different in patients with chronic pain. I had just gotten tenure at McGill when I first took notice of the Lancet papers on the Global Burden of Disease, which showed that the pain conditions among the top 10 causes for years lived with disability were musculoskeletal conditions. There was a huge mismatch between what we were doing in research and what mattered, globally, regarding pain issues. I was going to try to make a bigger impact in that direction and dive into musculoskeletal pain, especially back pain.


How did you become involved with the Integrative Spinal Research Group (ISR) at Balgrist University Hospital?


I had decided to move toward musculoskeletal pain and understanding individual phenotypes. I was at McGill at the time, but I was commuting between Canada and Switzerland, where my family and I had recently moved. I was looking to work with spine patients with unclear pathologies ‒ nonspecific low back pain, thoracic pain, and neck pain ‒ and found that, in Switzerland, chiropractors are primary care specialists for musculoskeletal disorders, and especially spine disorders. About 80% to 90% of the patients whom chiropractors treat are patients I am interested in research-wise. The Integrative Spinal Research Group is part of the Department of Chiropractic Medicine, which is part of the University of Zurich and Balgrist University Hospital, and specializes in musculoskeletal conditions. For me, that just seemed like a perfect fit.


How does chiropractic medicine differ between Europe and North America?


It’s obvious that, in some places, chiropractic is a quite contentious area, but chiropractic is regulated very differently in every country. So we cannot speak of a European chiropractic degree versus a North American chiropractic degree ‒ Canada is different from the US; Germany is very different from Switzerland. There are also extremes, like countries where the “vitalist” movement is quite strong. These are people with ideas that do not really fit into our biopsychosocial understanding of the body or of pain. Vitalists think that spinal adjustments, which are biomechanical events being applied to the spinal column, can promote self-healing properties of the body. These people treat any condition, whether it’s Alzheimer’s or autism or COVID-19, with spinal adjustments. They also take other extreme positions on healthcare, like telling their patients not to get vaccinated.


On the other end of the spectrum are professional organizations, like the Swiss Association of Chiropractors, that aim to be evidence based. It’s also their mandate to only work with musculoskeletal conditions. A lot of their treatments are manual therapy treatments, like joint manipulation, where it makes pathophysiological and pathoanatomical sense to treat the musculoskeletal system in this way. They would never touch a patient with another condition, and they’re very clear on that.


Switzerland and Denmark are the only two countries in the world where chiropractic is a program in the Faculty of Medicine taught at the university level. It’s not integrated into Faculties of Medicine in other countries, where it is often taught at colleges. It’s a profession that has been endorsed in Switzerland since the 1960s. At the University of Zurich, we’ve had a chair of chiropractic medicine since 2008. The fact that it’s called chiropractic medicine also signifies how well it is integrated with the rest of medicine; it’s very much aligned with medical school. Chiropractors are also really well trained in differential diagnosis and in recognizing if it is appropriate for them to treat a particular patient. Patients that chiropractors see here in Switzerland have pretty good outcomes, which is fascinating because these are patients that many medical specialties, like spinal surgery and rheumatology, have a hard time dealing with.


What work have you been doing to increase the evidence base in chiropractic medicine?


I’m trying to understand pain mechanisms in patients with spine pain, on an individual basis, so that we can better characterize these patients. About 90% of patients with low back pain are classified as having nonspecific low back pain. This is such an unfortunate category; it sounds as if all patients with low back pain belong to a homogeneous group, which they certainly do not. So I’m working with extensive phenotyping protocols to try to subdivide that category into something meaningful. With this, we hope we can better predict pain trajectories and assess certain treatments for patients with different types of low back pain.


Another component of this question that is very interesting is the attempts to be evidence-based in musculoskeletal pain treatment. There are actually very good guidelines for nonspecific back pain ‒ for acute and chronic pain ‒ and what should be done and what shouldn’t be done, like early imaging of the spine for uncomplicated cases, for example. However, in many instances, we do not really know where the benefits of the recommended treatments come from. Mobilization, or passively moving the patient’s joint, is good for them, but is it the actual mobilization, or is it the touch component of the treatment encounter, or something else? In addition, the little evidence that there is, especially with respect to what should not be done with patients, is often not followed. There is a certain evidence base, and obviously we are working on increasing that, but we also need to apply the evidence that is already there.


Can you say a little bit more about the phenotyping work?


It’s a three-year clinical research priority program from the University of Zurich, with a possible extension of another three years. It’s a collaboration across many different departments and disciplines at the University and the ETH [Swiss Federal Institute of Technology in Zurich] to work on “Pain ‒ from phenotypes to mechanisms,” as the grant is called, or pain phenotypes revealing pain mechanisms.


We are investigating patients with many different types of pain, from nonspecific low back pain to more specific spinal disorders like cervical myelopathy or pain after spinal cord injuries. Across all these patients, we do the same standardized testing battery: classical quantitative sensory testing, assessments of descending modulation, and evoked potentials. With the low back pain patients, I also have the opportunity to do a very detailed clinical examination. We’re also doing magnetic resonance spectroscopy to look at the brainstem, i.e., the PAG [periaqueductal gray] and the insula.


Overall, we’re trying to get at that interplay between increased excitation and decreased inhibition, and understand sensitization patterns in individual patients. For the nonspecific back pain patients, we’re using this information to identify clinical test clusters that allow us, with a certain likelihood, to identify the source of pain so that we can get rid of this unfortunate category of nonspecific low back pain.


Last year you wrote a paper asserting that the “bio” component has been somewhat neglected from the biopsychosocial view of postoperative pain. What did you mean by that?


That paper arose from the Taormina pain conference in 2018, where I gave a talk on that subject. My fundamental question was whether the importance of psychological factors in the development of chronic postoperative pain has taken on a life of its own. In the instance of joint replacement for knee osteoarthritis, people typically have very severe pain before they’re operated on. Most of the time, it is as simple as taking the affected joint out, replacing it, and the pain is gone ‒ 80% of people are completely pain-free three to six months after surgery.


Now, a common assumption is that psychosocial factors are to blame in the 20% who are not pain-free several months after surgery. However, there are other “biological” hypotheses to consider. For example, total hip replacements are successful for 90% of people. Although people getting knee replacements might be psychosocially different from people getting hip replacements, the biomechanics of the knee joint are known to be more complex than the hip joint so it’s more difficult to do a knee replacement. Then, there are patients who had infections after surgery, whose prosthesis didn’t work perfectly, or in whom the joint alignment wasn’t perfect, all of which could explain long-term problems with pain.


I estimate that if we accounted for these issues, there would be a single-digit percentage of people left with a persistent pain problem and maybe, for those 4% to 5% of people, psychosocial factors play a role in the insufficient resolution of the pain problem. Of course, psychosocial factors can be important for the individual patient, but we sometimes seem to forget that there might also be an ongoing nociceptive component, and a need for a biomechanical understanding, at least in the instance of joint replacements.


Your musculoskeletal pain research has taken you all the way to space, so to speak, which is pretty “far out”! What brought about a project like this?


This project is run by a senior colleague of mine, Dr. Jaap Swanenburg. Last year, the innovation center at the University of Zurich Space Hub opened, which we are a part of. Dr. Swanenburg investigates spinal stabilization mechanisms in extreme conditions, like hyper- and hypogravity. We haven’t actually been to space, but we’ve done three parabolic flights to test these mechanisms in hypogravity. He also replicated hypergravity conditions on Earth with additional axial load for people.


So he is exploiting these different gravity conditions in order to understand spine stabilization mechanisms ‒ the biomechanics, the passive structures like the ligaments, and the muscles. He’s combining measurements of the rigidity of the spine with electromyography [EMG], lumbar curvature, and other factors, and discovering that spinal stabilization mechanisms are different from what had always been assumed. It’s also very interesting because the results he obtained during those flights are shockingly consistent. This is the type of research where you don’t have many subjects because of the need for parabolic flights ‒ he’s now measured nine ‒ but so far, all the subjects are behaving the same way.


He’s also started to work with astronauts, who have a very high prevalence of back pain, even higher than what would be expected because they’re healthy and fit. He’s working with them to try to understand what sort of exercise they need to do in space in order to prevent this pain.


What other research projects on musculoskeletal pain are you working on?


Another line of research at the ISR group is directed by another colleague of mine, Dr. Michael Meier, who is looking into spinal kinematics and movement patterns. We are developing a paradigm where we look at the neurological control of the spine kinematics. We have a system consisting of 10 cameras and markers on the skin to get a 3D model of what the spine is doing. That’s a really interesting line of research because it’s very likely that maladaptive movement strategies contribute at least to the chronification of back pain, but maybe even to back pain in the first place. We know that people with back pain and people who are vulnerable to back pain move in a less diverse pattern, which means similar tissues are getting the additional load. Dr. Meier is also developing a modeling procedure for the kinematic data to calculate the loads that different spinal tissues are experiencing. So far, we’ve found that, in healthy controls, the kinematics of the lower back when people bend their back to pick up a flowerpot from the floor is related to their levels of fear of pain.


Something else I started doing in Montreal and that I’m following up on here is brain imaging to understand widespread pain. We had really interesting results with regard to the balance of excitatory and inhibitory neurotransmitters in the brains of patients with fibromyalgia. We are now investigating whether certain pain characteristics in patients with back pain depend on the balance of excitatory and inhibitory neurotransmitters.


One other research project that I’m supervising is looking at the extent to which sensitization induced by threat manipulation via the brain ‒ top-down, in other words ‒ is similar to sensitization induced by intensive nociceptive input such as afferent barrage, a bottom-up process. This is another example of comparing top-down and bottom-up sensation processes. One of the motivations for this project is that, the more we can show that there is a biological basis for what have previously been thought of as psychological phenomena, the easier it is for that to gain acceptance.


We are also working on assessment methods for deep tissues. Musculoskeletal conditions often arise from deep structures and deep tissues, yet people typically do sensory assessments on cutaneous afferents even though the deep afferents would be more important for these conditions. Of course, it’s simpler to assess the skin, but that is not a good-enough justification.


We are also starting to look more at the active ingredients of chiropractic treatments. It is interesting that chiropractic clinics and different practitioners often seem to have very good therapeutic relationships with their patients. Therapeutic relationships have been identified in the last few years as an important prerequisite for treatment success. I think there’s a lot in the practice of chiropractic for us, as pain researchers, to explore and to research.


Are there any myths that you want to dispel about musculoskeletal pain among the general public? Or maybe even among pain researchers?


The one thing that everybody should be aware of is that the old advice that you should not move when you have back pain is wrong. You should keep walking and be active in general.


For pain researchers, I think many of the ways we subcategorize patients don’t make much sense. We have to pay much more attention to the causes of pain, to which activities and movements evoke pain, and to the time courses of pain ‒ for example, if the pain is relapsing-remitting, episodic, and so forth ‒ rather than just saying, “Oh, they have had pain for more than three months, so their pain is chronic.” We are also missing a lot of information in our research by neglecting this completely.


Catherine Paré is a PhD student at McGill University, Montreal, Canada.

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