Reproducibility of joint space width and the intermargin distance measurements in patients with medial osteoarthritis of the knee in various degrees of flexion

This study tested the variability and reproducibility of measurements of the joint space width (JSW) and intermargin distance (IMD) of the medial tibial plateau in specific positions of knee flexion in osteoarthritic knees in order to evaluate the most useful knee angle for radiographic measurements. Radiographs from 56 knees with osteoarthritis from 46 patients were taken with the knees in conventional full extension and 15, 30 and 45 of flexion with weight bearing. Three orthopedic surgeons independently measured the JSW and IMD at the narrowest point and the midpoint of medial tibial plateau using a computer-assisted method. The JSW and IMD were smallest at 15 flexion, both measured at the narrowest point and the midpoint of the medial compartment. Reproducibility of the IMD at the midpoint was better than at the narrowest point for all four flexion angles. Measurements of the medial JSW and IMD are smallest at 15 of knee flexion indicating that radiographs should be obtained at this angle in order to best demonstrate the extent of osteoarthritis.