SAN ANTONIO, Texas ― The link between a high laxity knee and the development of knee OA is strong among white women, but less strong in white men and in African American men and women, according to findings presented at the annual meeting of the American College of Rheumatology.

"These findings will help us understand that the causes of knee osteoarthritis might be different in women than in men," said principal investigator Leena Sharma, MD, Associate Professor of Medicine at Northwestern University Feinberg School of Medicine in Chicago, Illinois. "Different factors may also be at work among various ethnic groups," she added.

Dr. Sharma and the other investigators conducted the study to further their understanding of why women develop knee OA more often than men. Hypothesizing that gender differences in local mechanical factors might contribute to this discrepancy, she and the study team chose to focus on varus-valgus laxity, a factor that reduces the fit of opposing joint surfaces and increases shear and compression forces. The investigating group had also observed that women with established knee OA tend to have more lax knees than men and they wondered whether the loss of bone and cartilage worsens varus-valgus laxity.

"If laxity also contributes to the gender difference in the risk of developing knee OA, then the discrepancy should exist ... before OA is present," Dr. Sharma said. To investigate this possibility, she and her team tested whether women are more likely than men to have a lax knee.

The investigators followed 1555 people with knee OA or at risk of developing it; 66% of participants were women and 34% were men. Among the subjects, 82% were white and 18% were African American. The participants were an average of 62 years old and had a mean body mass index (BMI) of 31. Among white participants, the mean BMI was 30.2; among African Americans it was 33.5.

The study sample was divided into 3 groups: those who did not have knee OA; those with possible knee OA; and those with established knee OA. The subjects' varus-valgus laxity, quadriceps strength, and level of physical activity – including recreational, occupational, and household activities – were assessed. Additionally, investigators tested whether any difference was independent of age, BMI, strength, and physical activity. Because of the prevalence of knee OA among African Americans, the study team also analyzed whether gender differences varied by race.

Knee X-rays that utilized a fixed-flexion protocol were obtained and knees were categorized as having no OA, possible OA, or definite OA. A high laxity knee was defined as greater than the cut-off for the highest quartile of knee laxity among both men and women without OA. The investigators then estimated an odds ratio (OR) representing the likelihood that a woman's knee, as opposed to a man's, would have high laxity.

In the overall sample, women were 2.14 times more likely than men to have a high laxity knee, even without knee OA, Dr. Sharma said. In those women with possible knee OA, the OR was 2.77; for confirmed knee OA, the OR was 2.94.

However, among African Americans, the difference was less marked. Among those without knee OA, women's OR was 1.37. Among those with possible knee OA, the OR, 0.74, was negligible. Among those with confirmed knee OA, women were 1.74 times more likely than men to have knee laxity.

The study results may help investigators understand susceptibility to knee OA, according to Dr. Sharma, who added that the findings "may help us understand why some women are more likely to develop OA."

References:

Sharma L, Lewis B, Torner J, et al. The impact of gender on varus-valgus laxity in knees with and without osteoarthritis. Presented at: Annual Meeting of the American College of Rheumatology; October 18, 2004; San Antonio, Tex. Abstract 598.