African-Americans are more likely than Caucasians to have osteoarthritis, or OA, in the knee and in multiple large joints, but less likely than Caucasians to have it in their hands. And because of these differences, doctors might not notice when African-American patients have OA, according to a study analyzing how the joint disease presents in the two races.

“We think of multiple OA often being hand and knee or hands and hips and knee, which is more the pattern of Caucasian women. So we could miss [cases] in African-Americans who actually have large, weight-bearing joints that are involved,” explains study author Amanda E. Nelson, MD, an assistant professor of medicine in the Division of Rheumatology, Allergy, and Immunology at the University of North Carolina Thurston Arthritis Research Center in Chapel Hill.

This study in Arthritis & Rheumatism is part of the ongoing Johnston County Osteoarthritis Project, which studies OA and its risk factors in a rural, biracial population.

For this study, researchers analyzed thousands of X-rays of hands, knees, hips and spines of black and white participants older than age 45. They looked at 16 types of hand OA in more than 2,000 patients and 32 combinations of OA in multiple joints of 1,400 participants.

They found that African-Americans were two-and-a-half times as likely as Caucasians to have knee OA, and 77 percent more likely to have both knee and spine OA than Caucasians. Although it wasn’t determined to be statistically significant, African-Americans also had a 30 to 40 percent increased chance of having OA in a hip alone or in a hip, knee and back combined.

“All the large, weight-bearing joints were more likely to be involved together in African-Americans,” Dr. Nelson explains. “This is really the first study to look at this. We don’t really understand it yet.”

“I think it’s a very interesting article and it highlights the fact that, although osteoarthritis is so common, there is still a lot we have to learn about the clinical presentation of the disease, especially in different populations,” says Carla Scanzello, MD, PhD, of the department of rheumatology at Rush University Medical Center in Chicago. “Hand OA creates a different type of disability than OA affecting large joints like knees and hips. So understanding how those patterns differ in different individuals will allow us to apply treatment modalities and support in appropriate patient populations."