Selection of knee radiographs for trials of structure-modifying drugs in patients with knee osteoarthritis: a prospective, longitudinal study of Lyon Schuss knee radiographs with the definition of adequate alignment of the medial tibial plateau.

OBJECTIVE: The quality of medial tibial plateau (MTP) alignment, which is assessed by measuring the distance between the anterior and posterior margins (intermargin distance [IMD]) of the tibial plateau, and the reproducibility of alignment in serial radiographs are suggested to be key elements in determining the accuracy and sensitivity to change in knee radiographs in patients with tibiofemoral osteoarthritis (OA). We evaluated the influence of both MTP alignment and radiograph superimposition on the sensitivity to change in radiographic joint space narrowing (JSN) in knee OA. METHODS: The study group comprised 106 patients with knee pain (73 with OA). Lyon schuss radiographic images of the knee were obtained twice (at baseline [month 0] and 12 months later), using a standardized radiographic procedure. Computerized measurement of the IMD for the assessment of MTP alignment was compared with the grading of MTP alignment by 2 observers using a 5-point scale (excellent, good, fair, poor, bad). To obtain the rate of JSN, computerized measurement of the joint space width was performed at month 0 and month 12. The sensitivity of the joint space width to change over 1 year was evaluated by the standardized response mean (SRM). RESULTS: The mean (+/-SD) IMD was 1.2 +/- 0.9 mm. The correlation between scoring and computer measurement of MTP alignment was highly significant. The cutoff value for satisfactory alignment (excellent or good) was an IMD of 1.2 mm at month 0 and/or month 12. CONCLUSION: The quality of MTP alignment at both baseline and the end point highly influences the sensitivity to change in radiographic JSN in knee OA. To obtain relevant data, only radiographs showing an IMD of

Measurement of radiographic joint space width in the tibiofemoral compartment of the osteoarthritic knee: comparison of standing anteroposterior and Lyon schuss views.

OBJECTIVE: To evaluate progression of joint space narrowing in radiographs of osteoarthritic (OA) knees imaged in both the standing anteroposterior (AP) and the Lyon schuss positions, using alternative methods to measure joint space width (JSW). METHODS: Standing AP (extended view) and Lyon schuss (posteroanterior [PA] view, with 20-30 degrees of flexion) radiographic images of 58 OA knees were obtained twice (at baseline and 2 years later). With both methods, fluoroscopy was used to align the anterior and posterior margins of the medial or lateral tibial plateau with the central x-ray beam. Minimum JSW, mean JSW, and joint space area (JSA) of the medial or lateral femorotibial joint space were measured using a new digital image analysis system. The effects of knee flexion versus extension and parallel versus nonparallel tibial plateau alignment were evaluated with respect to the reproducibility of JSW in repeated examinations (intraclass correlation coefficient [ICC]), the mean of within-knee standard deviations of repeated measurements (SD(m)), and the sensitivity to changes in JSW in serial radiographs (standardized response mean [SRM]). RESULTS: The performance of the new software, as assessed by the reproducibility of repeated measurements of minimum JSW on the same image, was excellent in both the standing AP (ICC = 0.98) and Lyon schuss radiographs (2 SD(m) = 0.5 mm, ICC = 0.98). The reproducibility in different radiographs of the same knee was not evaluated. However, over 2 years, the mean (+/- SD) decrease in the minimum JSW of OA knees was 0.17 +/- 0.75 mm in standing AP radiographs (P not significant) and 0.24 +/- 0.50 mm in Lyon schuss views (P = 0.007), with SRMs of 0.23 and 0.48, respectively. The quality of alignment of the tibial plateau was satisfactory (<1 mm between anterior and posterior margins of the medial tibial plateau) in 66% of the pairs of Lyon schuss radiographs and in 57% of the pairs of standing AP radiographs. In the Lyon schuss radiographs, SRM was highly dependent on tibial plateau alignment. Minimum JSW was more sensitive to change than was mean JSW or JSA, in paired Lyon schuss radiographs that exhibited satisfactory alignment. CONCLUSION: Compared with the standing AP radiograph, PA imaging of the knee in 20-30 degrees flexion (the schuss position) increases the reproducibility of radiographic JSW measurements in OA knees and the sensitivity to change in JSW in serial radiographs. Sensitivity to change in minimum JSW is notably increased by aligning the medial tibial plateau with the central x-ray beam in the Lyon schuss radiograph.