Frequency of varus and valgus thrust and factors associated with thrust presence in persons with or at higher risk of developing knee osteoarthritis

Abstract

Objective: Varus thrust observed during gait has been shown to be associated with a 4-fold increase in the risk of medial knee osteoarthritis (OA) progression. Valgus thrust is believed to be less common than varus thrust; the prevalence of each is uncertain. Racial differences in risk factors may help explain variations in the natural history of knee OA. We undertook this study to determine the frequency of varus and valgus thrust in African Americans and Caucasians and to identify factors associated with thrust presence.

Methods: The Osteoarthritis Initiative cohort includes men and women who have knee OA or are at increased risk of developing it. Trained examiners assessed thrust presence by gait observation. Logistic regression with generalized estimating equations was used to identify factors associated with thrust presence, and odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated.

Results: Compared with Caucasians, African Americans had lower odds of varus thrust, controlling for age, sex, body mass index (BMI), injury, surgery, disease severity, strength, pain, and alignment in persons without knee OA (adjusted OR 0.50 [95% CI 0.36, 0.72]) and in those with knee OA (adjusted OR 0.46 [95% CI 0.34, 0.61]). Also independently associated with varus thrust were age, sex, BMI, disease severity, strength, and alignment. The odds of valgus thrust were greater for African Americans than for Caucasians in persons without knee OA (adjusted OR 1.69 [95% CI 1.02, 2.80]) and in those with knee OA (adjusted OR 1.98 [95% CI 1.35, 2.91]). Also independently associated with valgus thrust were disease severity and malalignment.

Conclusion: Compared with Caucasians, African Americans had lower odds of varus thrust and greater odds of valgus thrust. These findings may help explain the difference between these groups in the pattern of OA involvement at the knee.

Figures

Figure 1

The figure shows the frequency, among persons without radiographic knee OA, of varus and valgus thrust in African-Americans (AA) and Caucasians (C). In all persons without radiographic knee OA, 32.1% (502 of 1566) had varus thrust and 7.2% (113 of 1566) had valgus thrust. When stratified by race, varus thrust was significantly more frequent in C than in AA (difference = 10.3, 95% CI = 4.3, 16.3) and, although not statistically significant, the frequency of valgus thrust in AA exceeded that in C (difference = −3.5, 95% CI = −7.6, 0.6).

Figure 2

The figure shows the frequency, among persons with radiographic knee OA, of varus and valgus thrust in African-Americans (AA) and Caucasians (C). In all persons with radiographic knee OA, 36.7% (743 of 2026) had varus thrust and 9.1% (185 of 2026) had valgus thrust. When stratified by race, varus thrust was significantly more frequent in C than in AA (difference = 15.7, 95% CI = 10.7, 20.7) and valgus thrust was significantly more frequent in AA than in C (difference = −4.5, 95% CI = −8.2, −0.8).