Knee osteoarthritis (KOA) is a commonly diagnosed disorder among older adults. Despite its high prevalence, treatment options are limited. Physical exercise is often prescribed as treatment as it has the potential to relieve pain. Although the underlying mechanisms are not completely understood, studies have shown that incorporating mindfulness into an exercise program may also have promising effects on pain reduction for those suffering with KOA.
Recently, the central nervous system (CNS; the part of the nervous system contained within the brain and spinal cord) has been shown to play a role in the pain associated with KOA. Using a technique called positron emission spectroscopy, patients who expressed greater levels of arthritic pain were also shown to have greater availability of opioid receptors in brain regions called the periaqueductal grey (PAG) and the striatum. In other words, think of these two brain regions as having parking lots with many free parking spaces (receptors) for chemicals called opiates or those that resemble opiates.
The PAG is a key player in the descending opioidergic pathway and receives information from various brain regions which then communicate with the spinal cord. This pathway contains neurons (cells of the nervous system) that use chemicals called endorphins as neurotransmitters (chemicals that transmit information within the brain). These endorphins resemble the chemicals called opiates and can thus park in the free parking spaces (receptors) in the pathway and mimic the action of opiates like morphine, for example, to relieve pain. The striatum is a key player in the dopaminergic “reward” pathway which begins in the ventral tegmental area of the brain and communicates with brain regions such as the nucleus accumbens which is in the ventral region of the striatum. The reward pathway increases motivation to repeat a certain behavior which is then accompanied by a rewarding feeling that further motivates you to continue repeating the behavior.
Thus, it is thought that both of these pathways are altered in people with KOA such that there is an increased amount of free parking spaces (receptors). An increase in empty opioid receptors in the PAG and the striatum would suggest that both the opioidergic and reward pathways are not as active as they normally would be in healthy individuals. This is not optimal as both of these pathways interact with each other to modulate pain. In addition to the pathways mentioned above, the immune system is also thought to contribute to osteoarthritis pain through substances called immune factors. These immune factors play a role in the inflammatory response, and thus inflammation.
Liu et al. (2019) examined the effects of various 12-week exercise programs on KOA pain by comparing connectivity in key regions of the opioidergic and reward pathways, immune factors in the blood, and subjective pain levels before and after the 12-week program. Over 100 Individuals diagnosed with KOA by a rheumatologist were randomly assigned to 12 weeks of Tai Chi, Baduanjin, stationary cycling, or a health education group consisting of lessons on how to cope with KOA and other health-related information. The individuals participated in their assigned programs 5 times a week for 12 weeks with each session being one-hour long. The “Knee injury and Osteoarthritis Outcome Score” (KOOS) was used to determine each individual’s baseline pain level before beginning the 12-week program and again afterwards. Blood samples were taken and a functional MRI scan (a brain imaging technique) was also completed for each individual before and after the 12-week program.
Once the 12-week program was completed, Liu et al. (2019) found that the individuals who participated in Tai Chi, Baduanjin, and stationary cycling had significantly improved KOOS scores compared to those who were assigned to the health education group. They also found that various immune factors had decreased in concentration in the blood, thus reducing inflammation which may have given some pain relief. Lastly, they found that connections within the opioidergic and reward pathways had been modified. While the differences between the general exercise group (stationary cycling) and the groups incorporating mindfulness (Tai Chi and Baduanjin) were not significant, they did find slightly more improvement in pain in individuals incorporating mindfulness.
Liu et al. (2019) have shown that exercise, especially when incorporating mindfulness, can work to decrease inflammation and alter the opioidergic and reward pathways to significantly reduce pain in individuals with KOA after only 12 weeks. Therefore, before opting for more invasive treatment options for KOA pain, incorporating exercise and mindfulness into daily life might be worth a shot.
Reference
Liu, J., Chen, L., Chen, X., Hu, K., Tu, Y., Lin, M., … & Zhu, J. (2019). Modulatory effects of different exercise modalities on the functional connectivity of the periaqueductal grey and ventral tegmental area in patients with knee osteoarthritis: a randomised multimodal magnetic resonance imaging study. British Journal of Anaesthesia, 123(4), 506-518.
