Changing from analog to digital images: Does it affect the accuracy of alignment measurements of the lower extremity?

BACKGROUND AND PURPOSE: Medical imaging has changed from analog films to digital media. We examined and compared the accuracy of orthopedic measurements using different media. METHODS: Before knee arthroplasty, full-length standing radiographs of 52 legs were obtained. The mechanical axis (MA), tibio-femoral angle (TFA), and femur angle (FA) were measured and analyzed twice, by 2 radiologists, using (1) true-size films, (2) short films, (3) a digital high-resolution workstation, and (4) a web-based personal computer. The agreement between the 4 media was evaluated using the Bland-Altman method (limits of agreement) using the true-size films as a reference standard. RESULTS: The mean differences in measurements between the traditional true-size films and the 3 other methods were small: for MA –0.20 to 0.07 degrees, and for TFA –0.02 to 0.18 degrees. Also, the limits of agreement between the traditional true-size films and the three other methods were small. INTERPRETATION: The agreement of the alignment measurements across the 4 different media was good. Orthopedic angles can be measured as accurately from analog films as from digital screens, regardless of film or monitor size.