EPIDEMIOLOGY OF KNEE OA
Epidemiology is the branch of clinical research that focuses on how diseases occur or are spread. These studies often include hundreds or thousands of individuals. Much of the understanding pertaining to the incidence, prevalence, and risk factors of OA are derived from several large epidemiological studies that have taken place over the past 40 years. Some of Incidence and prevalence Arthritis is a catch-all term that describes many different conditions, including osteoarthritis, rheumatoid arthritis, gout, lupus, and many other diseases that affect the joints. Osteoarthritis is by far the most common type of arthritis, and it is associated with a substantial economic burden. The number of individuals with knee OA has been steadily increasing over the past several decades. Recent estimates suggest that 14 million individuals in the United States are afflicted with symptomatic knee OA (Deshpande et al., 2016). Although OA is often thought of as a disease that affects older people, individuals younger than age 45 years were found to comprise 2 million of the 14 million affected individuals, and more than half of those with symptomatic knee OA were younger than age 65. The trend towards younger patients is particularly concerning as these individuals may have a substantial increase in pain and decline in function due to OA over the remaining decades of their life. Risk factors Knowing which patient characteristics predict the future development or progression of OA is essential to reducing the burden of the disease. Treatment targets are needed before interventions can be developed and tested. Several large epidemiological studies have identified consistent and significant risk factors. The Framingham Heart Study, a prospective, health- based epidemiological study that was initiated several decades ago, has provided some of the first epidemiological information regarding who is at risk for knee OA. More recent and targeted epidemiological studies include the Johnston County Osteoarthritis Project, the Osteoarthritis Initiative (OAI), and the Multicenter Osteoarthritis Study (MOST). These studies have enrolled and tested thousands of people with or at risk for OA and have followed them for multiple years. Scientists evaluate the data to identify factors such as radiographic, symptomatic, biomechanical, and functional changes that are associated with OA development or progression. Results from these studies have provided the majority of information regarding characteristics that increase the risk of developing joint disease. Risk factors can be classified in many different ways, but most can be classified as either systemic or local. Systemic risk factors are things that occur in the body, outside of the joint, that may make the knee joint more susceptible to OA. For example, recent advances in genetic testing have revealed that there may be a genetic predilection to OA (Ramos et al., 2014), which would be considered a systemic risk factor. A local risk factor would be something that occurs within the joint itself, placing the cartilage at greater risk for deterioration. An example of this would be a previous joint injury. Several studies have shown that individuals who have had damage to the joint, be it a meniscal injury or ligament rupture, are more likely to develop OA in the future (Silverwood et al., 2015). Risk factors also can be classified as modifiable or nonmodifiable. Modifiable risk factors are characteristics that can be changed or altered through the course of an intervention. These risk factors can be targeted by physical therapy interventions in order to reduce the risk of future disability from OA. One common modifiable risk factor is body weight. There is a strong link between body mass and OA risk; heavier individuals are much more likely to develop OA in the future. A recent meta-analysis found that individuals age 50 years or older who were overweight or obese were more likely to have or develop knee OA (Silverwood et al., 2015). Body mass is something that can be changed through dietary and exercise interventions and
these studies only included individuals with OA, while other studies have included the general population. Because OA is a common condition, even the studies that have included the general population often have a large number of individuals with knee OA.
Younger individuals who have been diagnosed recently with OA have a considerable amount of psychological distress, work- related disability, and lower quality of life (Ackerman et al., 2015). Increased disability may lead to a greater societal impact of this condition, and physical therapists should be aware of this trend. Costs associated with OA include not only the healthcare-related expenses, but also the expenses due to loss of labor productivity due to work absences and costs of informal care provided by family and friends. Recent estimates put the national cost of this condition at 0.25% to 0.50% of the country’s gross domestic product (Puig-Junoy & Ruiz Zamora, 2015). In the United States, this could mean that the total economic cost of OA could reach close to 85 billion dollars. While this value includes osteoarthritis from all joints, the knee is the most common joint to be affected. should be considered a primary or secondary outcome when treating patients with knee pain or knee OA. Nonmodifiable risk factors are things that cannot be changed, such as biological sex. Women are more likely to develop knee OA compared to their male counterparts (Silverwood et al., 2015). While this is not something that can be changed through rehabilitation interventions, considering this risk when developing treatment plans can be important. For example, an older woman with several other risk factors for OA (such as higher BMI and previous joint injury) should be educated on her greater risk for OA and provided information or treatment to reduce this elevated risk. Body mass has been one of the most consistent risk factors that has emerged from various epidemiological studies and meta- analyses. A recent study used statistical techniques to determine how many new cases of OA could be attributed to different risk factors and the greatest indicator by far was body weight. Of all the new diagnoses of knee OA, it is estimated that nearly one-quarter of those cases (24.6%) could be attributed to having a BMI of greater than 25 (Silverwood et al., 2015). Previous knee joint injury was the next highest attributable condition, accounting for 5.1% of new cases of OA. Vocational and recreational participation may be another contributor to knee OA risk. As previously mentioned, participation in sports in which there is a knee injury increases the risk of OA. This is concerning not only because people with previous knee injury are 2.83 times more likely to develop OA (Silverwood et al., 2015), but also because the onset of OA can happen quickly and at a young age after knee injury. In a recent study, almost 50% of patients who sustained a noncontact rupture of the ACL had signs of knee OA on X-rays within 5 years (Wellsandt et al., 2016). Individuals who developed OA also walked with less force through the injured limb, suggesting that underloading of the knee may be a predictor of OA progression after injury. Rehabilitation strategies that normalize movement patterns and restore normal and symmetrical joint biomechanics may offer some protective effect against OA. Vocational activities that include squatting, kneeling, bending, and lifting also have been explored as potential risks for knee OA. There is fairly strong evidence that supports a causal link between squatting and lifting and future knee OA (Silverwood et al., 2015). Other vocations, such as farming and construction, also have potential links to OA development. Physical therapists should include vocational history when evaluating patients with
EliteLearning.com/Physical-Therapy
Book Code: PTNC1023
Page 4
Powered by FlippingBook