VARIABILITY IN KNEE RADIOGRAPHING - IMPLICATION FOR DEFINITION OF RADIOLOGICAL PROGRESSION IN MEDIAL KNEE OSTEOARTHRITIS

Objectives - (1) To assess reproducibility of medial knee joint space width (JSW) measurement in healthy subjects and osteoarthritic (OA) pa tients. (2) To define minimal relevant radiological change in knee JSW based on the reproducibility of its measurement. Patients and methods - (1) Healthy volunteers: in the first part of the study, 20 knees of healthy adult volunteers were radio-graphed in the weightbearing, ant eroposterior extended view, twice, two weeks apart, using three differ ent radiographic procedures: (a) without guidelines, (b) with guidelin es and without fluoroscopy, (c) with guidelines and fluroroscopy. (2) Knee OA patients: in the second part of the study, 36 knees of OA pati ents were radiographed twice with guidelines and without fluoroscopy. JSW was measured blindly using a graduated magnifying glass. Based on the Bland and Altman graphic approach, cut off points defining minimal relevant radiological change are proposed. Results - Standard deviati on (SD) of differences in JSW measurement between two sets of knee rad iographs in healthy subjects were 0.66 mm for radiography performed wi thout guidelines, 0.37 mm for radiography performed with guidelines an d without fluoroscopy, and 0.31 mm for radiography with guidelines and fluoroscopy. SD of differences in JSW measurement in OA patients were 0.32 mm for radiography performed with guidelines and without fluoros copy. A minimal relevant change in JSW between two radiographs perform ed in healthy subjects can be defined by a change of at least 1.29 or 0.59 mm when radiographs are taken without guidelines, and with guidel ines and fluoroscopy, respectively. When radiographs are taken with gu idelines and without fluoroscopy, the change must be at least 0.73 mm. A similar figure, 0.64 mm was observed in knee OA patients. Conclusio n - Definition of radiological progression varies greatly according to the radiographic procedure chosen. Use of guidelines reduces the thre shold of progression required to consider that change between two meas ures is relevant.