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.
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).
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. In OA knees, the mean (+/-SD) annual rate of JSN and the SRM were statistically higher in knees with an IMD of </=1.2 mm at both month 0 and month 12 (0.34 +/- 0.50 mm and 0.68, respectively) than in knees with an IMD of >1.2 mm at month 0 and/or month 12.
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 </=1.2 mm at both baseline and the end point would have to be analyzed in studies of structure-modifying OA drugs.