An accurate method for measuring knee joint space width despite variations in beam projection angles

Background: Assessing knee osteoarthritis (OA) severity through joint space width (JSW) measurements can be difficult due to anatomical variations, beam projection angle (BPA) errors, and patient posture during X-rays. Although various methods address these issues, a consensus on the reference point for accurate measurement is lacking. Therefore, establishing a precise evaluation method for JSW is imperative.Methods: Simulation on 30 knees with advanced OA to measure the JSW using digital reconstruction radiographs from computed tomography (CT) images was conducted. The distance between the medial femoral condyle and the anterior and posterior borders of the medial tibial plateau (represented by D-AB and D-PB, respectively) and their average (AVD) were used to evaluate JSW. Discrepancies were analyzed for various BPAs. Additionally, the reliability of measuring JSW using D-AB, D-PB, and AVD was evaluated in a proof-of-concept study on 100 knees using anteroposterior X-rays at three BPAs (neutral, 5 degrees caudal, and 5 degrees cephalic tilt).Results: In the simulation study, the AVD method had discrepancies below 1 mm from BPA 0 degrees of 5 degrees, 10 degrees caudal tilt, and 5 degrees cephalic tilt (P = 0.066, P = 0.120, and P < 0.001, respectively). However, the values of D-AB and D-PB showed significant discrepancies from BPA 0 degrees (all over 1 mm and all P < 0.001) for various BPAs. The AVD measurement demonstrated the least discrepancy in JSW measurements based on BPA variations compared with D-AB and D-PB methods in the proof-of-concept study.Conclusions: A simple method for accurately measuring joint space width, even when Xrays are taken at unintended angles can be applied in clinical practice.(c) 2023 Elsevier B.V. All rights reserved.