May 2012

Patient race contributes to burden of knee OA

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Evidence suggests that the prevalence and symptom severity of knee osteo­arthritis are greater in African-American pa­tients, underscoring the need for lower extremity practitioners to implement effec­tive strategies for disease prevention and management in this patient population.

By Kelli D. Allen, PhD

Osteoarthritis (OA) is one of the most common chronic health conditions in the US and a leading cause of pain and disability among adults.1-3 The knee is a frequently affected joint, and one study showed that the lifetime risk of symptomatic knee OA is 45%.4 Among older adults, the risk of disability attributable to knee OA is as great as that due to cardiovascular disease and greater than any other medical condition.5 Although OA has a substantial impact across all racial and ethnic groups in the US, there is accumulating evidence that some minorities, particularly African Americans, bear a greater burden than others.

Race and knee OA prevalence

Several large US studies have shown that knee OA is more common among African Americans than whites. For example, in the Third National Health and Nutrition Examination Survey (NHANES-III), African Americans were about 1.5 times as likely to have symptomatic knee OA as whites, even when adjusting for other factors that can lead to knee OA.6 The Johnston County Osteoarthritis Project (JoCo OA), based in rural North Carolina, focuses on racial differences in OA. In that study, African Americans had significantly greater prevalence than whites of radiographic knee OA (32.4% vs 26.8%), severe radiographic knee OA (13.9% vs 6.6%), symptomatic knee OA (19.0% vs 15.9%), and knee symptoms (47.1% vs 42.4%).7

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Data from JoCo OA also suggest that specific radiographic features of knee OA may differ between African Americans and whites.8 First, African Americans had more severe tibiofemoral OA than whites and were more likely to have tricompartmental OA. Second, the prevalence and severity of osteophytes were also greater among African Americans than whites, and African Americans were more likely than whites to have sclerosis. These findings suggest that bone plays an important role in the development of OA among African Americans, and this may relate to the higher levels of bone mineral density that are characteristic of African Americans.9,10 A third finding from the JoCo OA study, that prevalence and severity of joint space narrowing were generally greater among African Americans, is important because recent research indicates an important association of joint space narrowing with pain.11 Finally, racial differences in some individual radiographic features tended to be more pronounced in the lateral tibiofemoral compartment. Similarly, in the Multicenter Osteoarthritis Study (MOST), lateral joint space narrowing was more common among African Americans than whites (odds ratio = 2.4, 95% confidence interval = 1.7-3.3).12

Recent analyses from the Osteoarthritis Initiative, a large, longitudinal, prospective observational study of knee OA, showed that African Americans were more likely than whites to have valgus thrust during walking, which could contribute to the increased risk of lateral knee OA among African Americans.13 These findings highlight the importance of separately examining all three compartments of the knee in observational studies of racial differences in knee OA patterns and prevalence.

Pain and function

Knee OA research suggests that racial and ethnic differences in pain and function are even more pronounced than the differences in prevalence.14-20 For example, among participants in the JoCo OA study of radiographic knee OA, African Americans reported substantially worse mean scores than whites on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), a measure of lower extremity pain, stiffness, and function (32.8 vs 24.3, respectively; p < 0.001).15 These racial differences persisted when investigators controlled for radiographic severity and demographic factors (e.g., age, gender, and education). Importantly, this racial difference was no longer evident when the analyses also controlled for body mass index and depressive symptoms.

Recent data from the JoCo OA study also suggest that occupational tasks may contribute to racial differences in knee osteoarthritis pain.21 Specifically, exposure to more physically demanding occupational tasks (e.g., lifting, standing, squatting, climbing stairs, crawling, kneeling, and doing heavy work while standing) at participants’ longest-held jobs and at their current jobs were associated with greater WOMAC pain scores (p < 0.01).

The association of African American race with higher pain scores (compared with whites) remained statistically significant when investigators controlled for occupational tasks at the longest-held job, but this disparity was reduced by 26% and no longer statistically significant when they controlled for current occupational tasks.

Several studies have documented racial differences in pain and function among African American and white US veterans with lower extremity OA (including both knee and hip OA).16,17,20 For example, in a clinical trial of OA self-management among about 500 veterans with knee or hip OA or both, mean baseline scores were significantly worse on the Arthritis Impact Measurement Scales 2 pain and function subscales in African Americans than in whites (pain subscale, 6.3 vs 5.6, respectively, scale 0-10; function subscale, 2.8 vs 2.3, respectively, scale 0-10).16 These racial differences in pain and function were explained by differences in psychological variables including arthritis self-efficacy, pain coping, and affect (including mood and level of tension), as well as overall self-reported health.

In addition to differences in general physical function, some data have identified racial differences in gait mechanics.13,14 In one study of patients with radiographic knee OA, African Americans walked significantly slower than whites during fast walking and had more limited knee range of motion and slower loading rates at normal speeds.14 In general, African Americans had a pattern of gait mechanics that is generally associated with high levels of OA, even though they did not differ from whites in radiographic knee OA severity.  Also, as noted, African Americans have an incresed risk of valgus thrust compared with whites,13 which may raise their risk of lateral OA progression.

Clinical and public health implications

There is certainly a need for additional research to increase understanding of factors underlying racial differences in the prevalence and severity of knee OA. In particular, some important areas for future investigation include the potential roles of genetic factors, environmental factors (e.g., occupational or lifestyle-related physical tasks and nutritional factors), anatomical features (e.g., static alignment), and biomechanical factors (e.g., knee adduction moments). However, based on our current knowledge alone, there are a number of important opportunities for reducing racial disparities at both the clinical and public health levels.

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First, interventions aimed at reducing overweight and obesity among African Americans could be powerful tools for reducing racial disparities in the prevalence and severity of knee OA. Excess weight is a key risk factor for developing knee OA,22 and, in the US, rates of overweight and obesity are higher among African Americans than whites.23 Further, there is some direct evidence that overweight is a strong contributor to racial differences in symptom severity among adults with knee OA.

Physical activity interventions are another potential key tool for reducing racial disparities. Some evidence shows African Americans have less lower body strength than whites, which may contribute to OA risk or worse OA outcomes.24 Research also suggests that weight management and physical activity interventions can mitigate racial disparities in OA outcomes. In a combined sample of patients with knee OA who were participants from the Fitness Arthritis and Seniors Trial and the Arthritis, Diet, and Activity Promotion Trial,19 six-minute walk distances were lower (indicating poorer function and endurance) for African Americans than whites at the beginning of the study. However, following the exercise intervention periods, mean six-minute walk distances improved for both groups and there was no longer a significant racial difference, indicating that walking ability had equalized.

Public health efforts can play an important role on these fronts by concentrating efforts toward dissemination of effective weight management and physical activity programs in settings accessible to African Americans. In addition, clinicians can have a strong impact by regularly encouraging their African American patients with OA in their efforts to lose weight and increase physical activity. To this end, it is useful for clinicians to become familiar with community resources (e.g., senior centers and YMCAs) that provide free or low cost programs. The Arthritis Foundation (www.arthritis.org) is an excellent resource for identifying local programs for individuals with OA.

Given the evidence that pain coping and other psychological variables are key factors underlying racial differences in pain among patients with OA,15,25 interventions focused on enhancing such coping may be another way to reduce disparities. Studies have shown that programs that train individuals in coping skills improve pain, physical disability, psychological disability, and self-efficacy among patients with OA and other painful conditions.26-32 Such programs have not been widely studied or implemented in African Americans with OA, however, and more work is needed in this area.

Some medical centers and pain clinics offer pain management programs that incorporate coping skills. Practitioners should consider referring patients to these programs, when available, particularly if patients seem to have a difficult time dealing with their pain and its effect on their daily activities. In addition, given the strong link between pain and depression,33 as well as evidence that depression is a key factor underlying racial disparities in OA-related pain, practitioners should monitor patients with chronic pain for depressive symptoms and guide them toward appropriate treatments when needed.

There is also evidence of racial disparities in prescriptions of pain medications among patients with OA.34,35 Although the degree to which these differences in prescribing contribute to racial differences in outcomes is unclear, they signal a potential need for a more systematic approach to prescribing pain medications for patients with OA. Finding the best medication regimen is challenging and varies widely among patients, and organizations such as the American College of Rheumatology (www.rheuma­tology.org)36 and Osteoarthritis Research Society International (www.oarsi.org)37,38 have published recommendations for OA treatment that include guidelines for pharmacological management. Using these guidelines can help promote best practices in pain medication prescribing for patients with OA.

There are well-established racial differences with regard to the use of total knee replacement, with African Americans undergoing the surgery at a lower rate than whites.39-43 This discrepancy may also partially explain racial differences in OA symptom severity. Studies have indicated that racial disparities in the use of total joint replacement surgery are largely due to differences in patients’ expectations of and willingness to undergo the surgery rather than clinical appropriateness or provider referrals.20,44-50

There is ample evidence that African Americans expect substantially worse outcomes from this surgery than whites with respect to hospital stay, recovery time, and residual pain and functional limitations. Therefore, another key role for healthcare practitioners is to facilitate informed decision-making by helping African American patients with OA learn about the benefits and risks of total joint replacement surgery.

In summary, African Americans bear a greater burden of knee OA than whites in both prevalence and symptom severity. Eliminating these disparities is likely to require a long-term multifaceted approach involving efforts at both public health and clinician levels. There are no indications that OA should be treated differently across racial and ethnic groups. However, healthcare providers can help ensure the best possible outcomes for African Americans with OA by vigorously promoting all aspects of evidence-based recommendations for treating this condition. In particular, clinicians can have a strong impact by taking extra steps to help minority patients connect with resources that promote weight loss and physical activity and teach pain management skills.

Kelli D. Allen, PhD, is an associate professor in the Division of General Internal Medicine, Department of Medicine, at Duke University Medical Center in Durham, NC, and a research health scientist in Health Services Research & Development at the Durham VA Medical Center.

Acknowledgements: The views expressed in this manuscript are those of the author and do not necessarily represent the views of the Department of Veterans Affairs.

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