Relevant anatomy of Tendonitis
Tendonitis is a common sports-related injury in areas where muscles anchor to a bone through a tendon. For example, tendonitis is prevalent in the knees, where the quadriceps is connected to the tibia through the patellar and quadriceps tendons. It is also common in the elbow, where the humerus attaches to the metacarpal bones through the extensor carpi radialis brevis tendon.
Mechanism and physiology of tendonitis
Tendonitis occurs through inflammation of a tendon, which occurs frequently in racket sports, swimming and running which involve repetitive, high intensity movements. Overuse and repetitive motions cause tears in the tendon and lead to inflammation. This is because the body’s natural repair mechanisms are not able to compete with the constant tearing. When cells are damaged, they release chemicals such as bradykinin and histamine that signal for pain and inflammation, preventing further use of the affected area. Bradykinin activates polymodal nociception receptors. These receptors activate unmyelinated C pain fibres associated with the continuous burning and throbbing sensations. In contrast, histamine binds H1 & H2 receptors in smooth muscle, causing vasodilation and inflammation.
Treatment, recovery and prevention
Tendonitis is almost always caused by repetitive strain and is therefore an intrinsic recovery mechanism. Physiotherapists often conclude that rest is the most effective treatment measure and can be mediated through use of a brace or other method that prevents movement. Rehabilitation post rest can be achieved through daily tendon focused stretching exercises including wrist flexion and extension for the elbow and hamstring and calf stretches for the knee. Stretching prevents further injury by slowly introducing the tendon to longer stretches, reducing tension and signalling for faster intrinsic recovery of the affected area. Stretching can be supplemented with weight and resistance training. This will strengthen the muscles connected to the tendon, decreasing the reliance on the tendon during repetitive activities.
Tendonitis and age
The frequency of tendonitis heavily correlates to age, as tendon physiology changes constantly with age. Age decreases cellular motility and healing in tendons, an essential component during the initial response to a repetitive strain injury and are often propagated through cellular components called focal adhesions (FA). Aging causes aggregation of proteins necessary for FA activity near the cell nucleus rather than their normal location near the cell surface. In this way, aging reduces the innate healing capacity for tendons. Additionally, aging decreases metabolism in the tendon, another important factor for healing. So, as one ages it becomes increasingly important to do strengthening and stretching exercises to prevent tendonitis and account for the bodies decreasing healing capabilities over time.
References:
Abrams, G. D., Renstrom, P. A., & Safran, M. R. (2012). Epidemiology of musculoskeletal injury in the tennis player. British Journal of Sports Medicine, 46(7), 492–498. https://doi.org/10.1136/bjsports-2012-091164
Kwan, K. Y. C., Ng, K. W. K., Rao, Y., Zhu, C., Qi, S., Tuan, R. S., Ker, D. F. E., & Wang, D. M. (2023). Effect of Aging on Tendon Biology, Biomechanics and Implications for Treatment Approaches. International Journal of Molecular Sciences, 24(20), 15183. https://doi.org/10.3390/ijms242015183
Obara, I., Telezhkin, V., Alrashdi, I., & Chazot, P. L. (2019). Histamine, histamine receptors, and neuropathic pain relief. British Journal of Pharmacology, 177(3). https://doi.org/10.1111/bph.14696
Tendon overuse injuries (tendinopathy): Overview. (2020). In www.ncbi.nlm.nih.gov. Institute for Quality and Efficiency in Health Care (IQWiG). https://www.ncbi.nlm.nih.gov/books/NBK555501/ Assessed and Endorsed by the MedReport Medical Review Board