Am I at Risk for Osteoarthritis?
Osteoarthritis (OA) is a significant health problem that causes disability and suffering. The incidence of OA is projected to increase due to our aging population and growing levels of obesity. Age, female gender, and obesity are all risk factors for the development of OA. There are few known modifiable risk factors.
Osteoarthritis Defined
The definition of OA varies in research reports and studies and can be separated into self-reported OA, radiographic OA, and symptomatic OA. Self-reported OA involves signs and symptoms obtained by questionnaire method. Radiographic OA involves physical changes reported on X-ray reports.
Symptomatic OA is defined with both self-reported symptoms and radiographic findings. Most experts prefer radiographic definition of incident OA. These findings are based on the Kellgren-Lawrence radiographic classification. This uses a grading of 1 to 4 to categorize the extent of the osteoarthritis. This grading scale relies on the presence and severity of certain specific features, such as joint space narrowing and osteophyte development.
The Etiology and Pathogenesis of Osteoarthritis
Researchers believe that the pathogenesis of OA is multifactorial, involving systemic risk factors such as obesity and old age as well as local risk factors, such as mechanical load. The systemic factors predispose an individual to OA, and the local abnormal joint biomechanics initiate changes in the joint structure that result in OA.
The prevalence of OA of the hand, foot, and knee is higher among women age 50 years and older than in men of the same age group. For people younger than 50 years, the prevalence of OA in most joints is higher in men than in women. Men have more hip OA than women, according to most studies. Researchers believe that the combination of inherited predisposition along with other systemic and local factors cause OA.
Risk Factors for Osteoarthritis: Systemic and Local
Experts identify both systemic and local risk factors for OA. The systemic factors include age, ethnicity, sex and hormones, nutritional, and genetics. The local factors include malalignment, obesity and excess weight, anatomical abnormalities, previous trauma or injury, sports participation and exercise, lifestyle and occupation, infection and inflammation, and other diseases.
Systemic Risk Factors
- Age – Advancing age has a negative effect on the joint’s ability to protect itself from biomechanical stress. This is thought to be associated with changes in the articular cartilage that results in thinning and increased joint laxity. One study found that there was a 10-fold increase incidence of OA in the hand, hip, and knee of participants aged 30 to 65 years.
- Ethnicity – Research reports on differences in knee OA between Caucasians vs. African-Americans found a higher prevalence in African-Americans. In addition, Chinese individuals have a higher risk of lateral compartment knee OA compared to Caucasians, who suffered more from medial knee OA.
- Sex and Hormones – There is some existing research evidence that aging women have higher rates of knee osteoarthritis than men. The Framingham Knee Osteoarthritis Study showed a 1.7 times higher incidence of osteoarthritis of the knee in women than in men. Some recent trials found there is a hormonal role regarding the development of OA, with a significant increase observed at the time of menopause. The hormone estrogen was found to be associated with a protective effect.
- Nutritional – Many holistic practitioners advise that antioxidant vitamins, such as vitamin C and D, have a protective effect against OA. Unfortunately, there is little scientific evidence to support these claims.
- Genetics – Twin studies found a correlation between genetics and the risk of radiographic knee and hand OA among women. Current reports using the Rotterdam cohort have recognized the 7z22 locus as a potential gene associated with generalized OA. The gene regions found to be susceptible in other studies include the GDF5, ASPN, and SMAD3 areas. The findings of a recent study showed an influence of genetic factors in radiographic knee and hand OA between 39% and 65%.
- When combining studies, heritability estimates suggest around half the variation in susceptibility to OA can be explained by genetic factors. Furthermore, there is evidence that a multifactorial genetic background is associated with the common forms of OA. Researchers advise that while OA may be inherited, other environmental factors affect these findings, such as smoking, sedentary patterns, obesity, body fat, and exercise.
- Congenital/Developmental Conditions – A few congenital and developmental abnormalities have been associated with occurrence of hip OA in later life. These include Legg-Calve-Perthes disease, congenital subluxation, and slipped capital femoral epiphysis. However, because these developmental deformities are rare, they probably cause few cases of hip OA in the general population.
Local Risk Factors
- Malalignment – Misalignment of the limbs combined with longstanding obesity is a predisposing risk factor for rapidly progressing knee OA. Researchers found that there was radiographic disease progression evident when limb alignment was assessed.
- Obesity – Several studies confirm that obesity and being overweight cause an increased incident of knee OA. The 598 participants of the Framingham study without knee OA were discovered to have an increased risk if they had a higher baseline BMI (body mass index). Heavier individuals have more knee OA than those with normal or below normal weight.
- Anatomical abnormalities – People with anatomical abnormalities have more OA. Individuals that are bowlegged (knees that bend outwards) or knock-kneed (knees bend towards each other) have joint imbalances that wear down cartilage at an uneven rate. Hip OA is more associated with these abnormalities. One report found acetabular dysplasia to be a significant risk factor in the incident radiographic hip disease in both men and women. An abnormal shaped femoral head on the thighbone is also related to higher levels of hip OA.
- Previous Trauma and Injury – Particularly for knee OA, injury has been found to be a risk factor for disease development. Injuries to the anterior cruciate ligament and/or meniscus cartilage were specifically related to later development of OA. These types of injuries are associated with early-age onset OA. To preserve both of these anatomical structures in young athletes, efforts to prevent acute injury should be optimized.
- Sports Participation and Exercise – There are conflicting data concerning the relationship between sports participation and exercise and the development of OA. Some studies found that high-level, intense sporting activities cause both knee and hip OA, and there is a higher incidence of osteophyte (bone spur) formation in the tibiofemoral joint at the knee in female ex-athletes. In contrast, a study of middle-aged runners proved there was no higher rate of OA development among the participants compared to non-runners.
- Lifestyle and Occupation – Because cartilage depends on joint use for growth and maintenance, being sedentary is a risk factor for OA. In addition, some jobs causing repetitive stress on a particular joint may predispose you to OA in that joint. In one study, men with occupations that required knee bending had higher rates of radiographic OA than those men who worked jobs that did not require bending.
- Infection and Inflammation – A previous joint infection is associated with OA development, and existence of other inflammatory forms of arthritis increases the risk of OA.
- Other Diseases – You are at increased risk for OA if you have specific metabolic and endocrine conditions that lead to a buildup of substances in the blood and body tissues. These include Wilson’s disease (excess copper), hemochromatosis (excess iron), and hyperparathyroidism (excess calcium).
Conclusion
OA is a complex, multifactorial disease that results from a combination of local and systemic factors. Identifying risk factors for OA is necessary for prevention. Although some risk factors for osteoarthritis cannot be adjusted, targeting known risk factors is a successful strategy for enhancing future disease outcomes.
References
- Chaganti, R.K. & Lane, N.E. (2011). Risk factors for incident osteoarthritis of the hip and knee. Current Review of Musculoskeletal Medicine, September, 4(3), 99- 105. Doi: 10.1007/s12178-011-9088-5
- Spector, T.D. & MacGregor, A.J. (2004). Risk factors for osteoarthritis: genetics. Osteoarthritis and Cartilage, 12, 39-44.
- MayoClinic.com (2012). Osteoarthritis. Retrieved on December 12, 2012 from: http://www.mayoclinic.com/health/osteoarthritis/DS00019/DSECTION=risk-factors
- Zhang, Y. & Jordan, J.M. (2010). Epidemiology of osteoarthritis. Clinics in Geriatric Medicine, 26(3): 355 0 369.
Last reviewed 26/Feb/2014
Dr Merlin Thomas
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