The lateral view radiograph for assessment of the tibiofemoral joint space in knee osteoarthritis: Its reliability, sensitivity to change, and longitudinal validity

Abstract

Objective To evaluate the reliability, validity, and sensitivity to change of tibiofemoral (TF) narrowing on lateral radiographic views. Methods In a natural history study of symptomatic knee osteoarthritis (OA), both lateral view and fluoroscopically positioned posteroanterior (PA) semiflexed view radiographs of the knee in 30° of flexion and with weight bearing were obtained at baseline and at 30 months. Test–retest reliability was evaluated using repeat radiographs, with joint space width measured using electronic calipers. All radiographs were scored on a 0–3 scale, and progression of joint space loss was defined as narrowing of the joint space by 1 grade. We evaluated sensitivity to change compared with the PA view. We evaluated validity by examining whether knees with progression showed expected malalignment on full‐limb films. Results Test–retest reliability of the TF joint space using the lateral view had a root mean square error of 0.303 mm, with 92.5% of repeats within 1 mm. More knees showed progression on the lateral view alone (n = 41) than on the PA view alone (n = 27). Compared with knees without joint space loss, knees with medial compartment loss on the lateral view only were more varus malaligned (P < 0.001), while those with lateral compartment loss were more valgus malaligned (P = 0.008). Conclusion In the assessment of TF joint space loss, lateral view radiographs are reliable, valid, and more sensitive to change than fluoroscopically positioned PA radiographs.