389 STUDY OF LOCATION SPECIFIC LATERAL COMPARTMENT RADIOGRAPHIC JOINT SPACE WIDTH FOR KNEE OSTEOARTHRITIS PROGRESSION: ANALYSIS OF LONGITUDINAL DATA FROM THE OSTEOARTHRITIS INITIATIVE (OAI)

Abstract

Purpose: To study the performance of location-specific radiographic joint space width (JSW) in the lateral compartment. Lateral compartment JSW is a potentially important measurement for subjects with lateral compartment OA, and as a measure of pseudowidening for medial compartment disease. Methods: Baseline and Year 1 knee radiographs of 50 subjects from the Progression Cohort of the Osteoarthritis Initiative (OAI) were analyzed using a software technique that measured the radiographic joint space width (JSW). The data were a subset of OAI Image Releases 0.1.1, 0.B.1, and 1.B.1. Radiographic JSW and the baseline varus-valgus anatomical alignment angle was measured on a single indexed knee for each subject. Measurements of lateral and medial compartment JSW at fixed locations were facilitated by the use of automated software that delineated the femoral and tibial margins of the joint. Measures of JSW were defined as the distance from the tibial margin to the femur margin at fixed locations on the coordinate system shown in Figure 1. JSW was measured at nine fixed locations (x = 0.7, x = 0.725, x = 0.75, x = 0.775 x = 0.8, x = 0.825, x = 0.85, x = 0.875, and x = 0.9) A subset of 22 subjects were defined as having lateral compartment OA based on an anatomical angle of greater than 3 degrees valgus. Lateral compartment minimum JSW (mJSW) was measured for this subset. A human reader operated custom software to verify and correct the software-drawn margins where necessary. Paired images were displayed with the reader blinded to the time point. The average and standard deviation of the JSW loss, and the standardized response means (SRMs) are reported. Results: Table 1 provides measurements of JSW gain for the 28 subjects defined as having medial compartment OA. Increased JSW is observed for locations in the outer portion of the joint (higher x value). Table 2 gives the results for the 22 subjects defined as having lateral compartment OA. Here, decreased JSW is evident for locations in the more central portion of the joint (lower x value). To investigate the lateral compartment widening for medial compartment OA, we examined the correlation between JSW (x = 0.2) and JSW (x = 0.8), for the 28 subjects with an anatomical angle 3 degrees. A modest negative correlation was observed (R=−0.20, p = 0.15, Figure 2).