BACKGROUNDAssessing the radiographic features of knee osteoarthritis (OA), especially joint space narrowing, is important for evaluating disease progression. The purpose of this study was to quantitatively analyze joint space narrowing by measuring 2 new variables: the average joint space width (aJSW) and the articulate angle (AA) on X-ray films, and to evaluate the relationship between the 2 variables, knee function and OA symptoms.

METHODSUsing the web-based radiology viewer (Cedara I-Reach™ 4.1.1), we measured the 2 variables in 50 knees of 41 patients with knee OA participating in the Shanghai OA Study. We also evaluated the Kellgren-Lawrence (K-L) grade, the Western Ontario and McMaster Universities OA Index (WOMAC), and additional questionnaire in OA knees. The study was approved by the ethics committee of Shanghai Ninth People's Hospital (No. 2009 - 28).

RESULTSThe aJSW correlated with the K-L grade (r = -0.57, P < 0.001), kneeling (r = -0.29, P = 0.04), sitting cross-legged on the floor (r = -0.31, P = 0.03), WOMAC pain (r = -0.31, P = 0.03), WOMAC disability (r = -0.35, P = 0.01), pain while squatting (r = -0.37, P = 0.01), and defecating in a squatting position (r = -0.39, P = 0.01). The AA correlated with defecating in a squatting position (r = 0.29, P = 0.05), WOMAC disability (r = 0.30, P = 0.04) and K-L grade (r = 0.44, P = 0.003). The K-L grade also correlated with pain while squatting (r = -0.40, P = 0.005) and defecating in a squatting position (r = -0.34, P = 0.02), WOMAC pain (r = 0.30, P = 0.04), and WOMAC disability (r = 0.30, P = 0.04).

CONCLUSIONSThe aJSW closely correlated with knee OA symptoms and function scores, and was more sensitive to knee OA related disabilities than K-L grade and the AA. The aJSW could be used as a new variable for knee OA evaluation.