Osteoarthritis: Five facts you didn’t know!
Fact 1: Osteoarthritis is the main cause of pain, disability and decreased daily functioning in elderly affecting over 80% of the population above 55 years. The exact cause of it is still unknown but it is suggested that long lasting mechanical overload can be a trigger.
Fact 2: Osteoarthritis does not only affect the bone cartilage. Contrary to what most people think, osteoarthritis affects the entire bone and ligaments but also the brain. Inflammation at the knee will cause catabolic reactions of the bone cartilage resulting in degradation. Degradation starts on the surface, but when the severity of osteoarthritis increases, certain parts of the bone are no longer covered with cartilage. Free nerve endings in the bone or in the synovium can be triggered by inflammation and will send a nociceptive stimulus to the brain. In the brain, this stimulus will be processed. The brain has the capacity to ignore the received pain stimulus (which we call endogenous pain inhibition) and one will feel less or no pain. On the other hand, the brain can also decide to make the received pain stimulus more worse than it actually is (which we call pain facilitation), with (more) pain as result. In some osteoarthritic patients, there will be more pain facilitation than inhibition leading to an increased pain feeling. This phenomenon we call ‘central sensitization’.
Fact 3: Ageing, gender and obesity are the most important risk factors for osteoarthritis. The increase of osteoarthritis with age is related to the capacity of the tissue to react properly on a biomechanical insult. Tissues will become less elastic, muscles develop less power and ligaments become stiffer. All these changes can make elderly react less well to a biomechanical insult. Furthermore, women have a higher risk than men because there is a link between the development of osteoarthritis and the hormonal changes during the menopause. Besides age and gender, two risk factors you cannot control yourself, obesity is also a risk factor which you can control yourself. The risk of developing osteoarthritis increases by a factor 3 in overweight people. However, when one loses 5kg over 10 years, the risk of osteoarthritis decreases by 50%.
Fact 4: Pain because of osteoarthritis is not (always) related to the damage of the bone and cartilage. Patients can have radiographic osteoarthritis without symptomatic osteoarthritis and vice versa. X-rays may tell something about the knee joint structure and damage. When radiographic signs of osteoarthritis are present, we speak of radiographic osteoarthritis. However, this is not always associated with pain, morning stiffness, crepitus, etc. which are symptoms one can feel because of osteoarthritis. When such symptoms are present, we speak of symptomatic osteoarthritis. Nevertheless, it can be that one suffers from osteoarthritic pain without seeing radiographic signs of osteoarthritis.
Fact 5: Performing exercises and being active is good for osteoarthritic patients. Currently, there is no cure for osteoarthritis. However, reduction of symptoms and disease progression can be established. Exercise therapy is recommended as the first choice non-pharmacological treatment since it has beneficial effects on pain and physical function, which is been scientifically proven. Muscle strengthening training is suggested to be associated with anti-inflammatory effects while behavioural graded activity is suggested to counteract central sensitization, leading both to a reduction of pain. However, the exact working mechanism of exercise therapy on pain reduction is still a black box and will be investigated in my PhD project (more information on: https://rere.research.vub.be/koa-project). This research is important to optimize the exercise content for larger symptom relief in the future.
Sofie Puts
Junior PhD student with a background in Biomedical Sciences. Her research focusing on knee osteoarthritis pain is interdisciplinary as it covers the domains of exercise therapy, pain and inflammation. She is a member of the Rehabilitation Research, Frailty in Ageing and Pain in Motion research groups at Vrije Universiteit Brussel.
References and further reading:
https://www.ncbi.nlm.nih.gov/pubmed/23026409
https://www.ncbi.nlm.nih.gov/pubmed/22786458