Walking speed tests identify a significant interaction between sex and radiographic knee osteoarthritis severity: data from the osteoarthritis initiative

Abstract

Purpose: Knee osteoarthritis (OA) is a debilitating disorder associated with increased physical disability. Objective physical function (e.g., performance-based measures of physical function and muscle strength) is considered clinically important as worse performance is associated with poor quality of life, a decline in physical activity levels, and mortality. Objective physical function decline is a complex multi-dimensional construct dependent on multiple factors. We aimed to 1) develop sex-specific reference values for objective physical function tests for adults with or at risk for knee OA across the spectrum of radiographic knee OA severity; and 2) determine if males and females exhibit similar functional limitations across greater radiographic knee OA severity. Methods: As part of a larger project to establish reference values and percentiles for objective physical function tests across sex, age, radiographic knee OA severity (Kellgren-Lawrence [KL] Grade), and body mass index (BMI), we included individuals in the Osteoarthritis Initiative with relevant complete data at their baseline visit (n=3,880). Objective physical function was quantified with all available objective physical function tests within the OAI: 20-meter walk speed, 400-meter walk speed, chair stand speed, and knee extension and flexion strength. Both strength assessments were normalized to body mass. For unilateral measures we determined the most affected knee based on three criteria: 1) the knee with the worst KL grade; 2) if KL grade was equal between knees then the knee with the worst Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) Pain score; 3) if WOMAC pain was equal between knees then the right knee was selected. We used KL grade to separate individuals into five grades of increasing radiographic knee OA severity: KL0-KL4. Sex-specific reference values were generated for each objective physical function test across each KL Grade. We used separate linear regressions to test for an interaction between sex and radiographic knee OA severity for each objective physical function test while controlling for self-reported physical activity (i.e., Physical Activity Scale for the Elderly), WOMAC knee pain, age, and BMI. Results: Participant characteristics of included and excluded individuals can be found in Table 1. Figure 1 presents the sex-specific medians for the objective physical function tests across the grades of radiographic knee OA severity. There was a significant interaction between sex and radiographic knee OA severity for 20-meter (p<0.0001) and 400-meter walk speed (p=0.002), but not for chair stand speed (p=0.32), knee extension strength (p=0.94), or knee flexion strength (p=0.63). For both walking speed assessments, females present with progressively worse walking speed with each increasing KL grade (Figure 1A, 1B). However, walking speed in males does not appear to decline with increasing radiographic knee OA severity (Figure 1A, 1B). In females, chair stand speed demonstrates progressive differences between grades from KL0 to KL4 (Figure 1C). In males, chair stand speed is different between KL0 and KL1, but appears to plateau from KL1 through KL4 (Figure 1C). For knee extension and knee flexion strength, males and females present with a similar progressive decline in knee strength with each increasing KL grade (Figure 1D, no Figure for flexion due to similar trend as extension). However, even after normalization to body mass females are much weaker compared to males, as males with KL4 present with greater strength than females with KL0 (Figure 1D). Conclusions: This investigation highlights the interaction between sex and radiographic knee OA severity on objective physical function measures of walking speed. In females, both walking speed tests indicate progressively worse physical function with greater KL grade. However, such difference were not observed in males. While there was not a significant interaction between sex and radiographic knee OA severity for chair stand speed and either strength tests, females consistently perform worse on these tests compared to males of similar KL grade. These sex-specific reference values provide evidence that a patient’s sex and KL grade should be taken into consideration when assessing an individual’s objective physical function.View Large Image Figure ViewerDownload Hi-res image Download (PPT)