Semi-automated longitudinal assessment of quantitative joint space width at the hip in a community-based cohort

Abstract

Purpose: Computer-assisted quantitative joint space (qJSW) measurements may provide a more accurate measurement of hip joint width and help identify other risk factors for hip OA. The aim of this study was to characterize qJSW over time in the Johnson County Osteoarthritis Project (JoCo OA), overall and by incident radiographic and symptomatic hip OA. Methods: The JoCo OA is a longitudinal study of civilian, non-institutionalized African American and white men and women greater than 45 years old at baseline who were residents of one of six designated townships in Johnson County for at least one year. For this analysis, we selected individuals with anteroposterior pelvis x-rays from baseline and 3 follow up time points, approximately 6 years apart. Per protocol, women under 50 years old did not have pelvis radiography. All hips were assigned a Kellgren-Lawrence grade (KLG) by an expert musculoskeletal radiologist (JBR). At all time points, participants were asked about the presence of hip symptoms (On most days, do you have pain, aching, or stiffness in your (right, left) hip?”). Incident radiographic hip radiographic OA (rHOA) was defined as KLG 2 or more at follow up (among those without rHOA at baseline), while incident symptomatic hip OA (sxHOA) required both rHOA and symptoms in the same hip. QJSW measurements were performed at 3 locations on each hip radiograph: 10, 30 and 50 degrees with respect to an anatomical landmark. Assessment was performed using a previously described method by an independent reader (JD) blinded to other radiographic or clinical information (Figure 1). With qJSW as the outcome over time from baseline, longitudinal mixed models (LMM) for each angle were stratified by sex, adjusted for continuous age, height, BMI, time, and categorical weight gain or loss (defined as a 5% change in BMI) to estimate model-based fixed effects (using restricted maximum likelihood); additional stratification by incident rHOA or sxHOA was also performed. LMM were assessed at the hip level with an unstructured covariance matrix, accounting for random effects at the participant level (intercept and time) and at the hip level (intercept). Results: There were 577 participants with 1154 hip x-rays meeting the above criteria; after exclusion of those missing hip films or with hip replacement, 397 participants and 784 hips were analyzed (59% women, 24% African American, average baseline age 57.5 for women and 55.2 for men). The overall incidence of rHOA and sxHOA was about 20% and 12%, respectively. In men, qJSW at the 10, 30, and 50 degree measurements did not vary significantly with time; in general, qJSW was wider with increasing height in males. In women, compared to 10 and 30 degrees, the qJSW measurements at 50 degrees were more sensitive to change over time and are discussed below and shown in Figure 2. As shown in Figure 2 A-B, taller women had greater qJSW although this declined with age. Taller women (e.g., at a representative value of 165cm) with higher BMI (here, at a representative value of 34 kg/m2) had more significant narrowing if they gained weight compared with those that maintained weight. Women with normal BMI (24 kg/m2) at the same height (165cm) had a similar decrease in qJSW regardless of gaining or maintaining weight. Shorter women (155cm) who were obese (34 kg/m2) had a decline in qJSW regardless of change in weight. However, shorter women (155cm) with average BMI (24 kg/m2) showed a significant decrease in qJSW if they maintained weight compared to those that gained weight. As shown in Figure 2 C-D, women who developed HOA according to KLG criteria had significantly narrower qJSW at baseline (this was also true for men, data not shown) and greater loss over time than those who did not develop HOA. Conclusions: In this community-based cohort, sex differences were observed in qJSW measurements of the hip, suggesting that qJSW changes over time may not be as sensitive in males, potentially due to anatomical differences in men and women. In women, the 50 degree measurements appear to be the most sensitive, and the impact of gaining or maintaining weight appeared to vary based on height. At 50 degrees in both men and women, rHOA and sxHOA were strongly associated with a narrower qJSW, suggesting that qJSW may prove to be a valid measurement tool.