Longitudinal performance evaluation and validation of fixed-flexion radiography of the knee for detection of joint space loss

Objective. The ability of nonfluoroscopically guided radiography of the knee to assess joint space loss is an important issue in studies of progression and treatment of knee osteoarthritis (OA), given the practical limitations of protocols involving fluoroscopically guided radiography of the knee. We evaluated the ability of the nonfluoroscopically guided fixed-flexion radiography protocol to detect knee joint space loss over 3 years. Methods. We assessed the same-day test-retest precision for measuring minimum joint space width (JSW), the sensitivity for detection of joint space loss using serial films obtained a median of 37 months (range 23-47 months) apart, and the relationship of joint space loss to radiographic and magnetic resonance imaging (MRI) measures of knee OA. Participants were men and women (ages 70-79 years) with knee pain who were participating in the Health, Aging, and Body Composition Study. We assessed baseline radiographic OA and measured JSW using a computerized algorithm. Serial knee MRIs obtained over the same interval were evaluated for cartilage lesions. Results. A total of 153 knees were studied, 35% of which had radiographic OA at baseline. The mean +/- SD joint space loss for all knees over 3 years was 0.24 +/- 0.59 mm (P < 0.001 for change). In knees with OA at baseline, the mean +/- SD joint space loss over 3 years was 0.43 +/- 0.66 nun (P < 0.001), and in knees with joint space narrowing at baseline, joint space loss was 0.50 +/- 0.67 mm (P < 0.001). Joint space loss and its standardized response mean increased with the severity of baseline joint space narrowing and with the presence of cartilage lesions at baseline and worsening during followup. Conclusion. Radiography of the knee in the fixed-flexion view provides a sensitive and valid measure of joint space loss in multiyear longitudinal studies of knee OA, without the use of fluoroscopy to aid knee positioning.