Reliability of stress radiography for evaluation of posterior knee laxity

Background: Although stress radiography has been recommended for quantifying posterior tibial displacement in knees with posterior cruciate ligament insufficiency, the intratester reliability and intertester reliability of this measurement method have not been evaluated. Hypothesis: Stress radiography is a reproducible measurement method in the assessment of posterior knee laxity in patients with posterior cruciate ligament lesions. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: Stress radiographs of 787 patients with suspected posterior cruciate ligament lesions taken using the Telos device were evaluated independently by 3 testers: 2 of the testers were clinically experienced in the evaluation of stress radiographs, and 1 tester was a novice tester. Change in mean, standard error of measurement with calculated confidence intervals, and intraclass correlation coefficients were determined to assess intratester and intertester reliability. Results: There was no significant intratester change in mean. Intratester standard error of measurement was 1.03 mm; 95% confidence intervals were +/- 2.02 mm for a single measurement and +/- 2.86 mm for a change in measurement. The intratester intraclass correlation coefficient was 0.95. Intertester reliability revealed a significant change in mean between the experienced testers and the novice tester (P <.001). There was no substantial difference for the standard error of measurement of each tester. The mean intertester standard error of measurement was 1.41 mm; 95% confidence intervals were +/- 2.77 mm for a single measurement and +/- 3.91 mm for a change in measurement. The intertester intraclass correlation coefficient was 0.91. Conclusion: Stress radiography was found to be a measurement method with a useful reliability for evaluation of posterior laxity in patients with posterior cruciate ligament lesions. The reproducibility of stress radiography may be influenced by multiple variables, and standardized methods are needed to minimize measurement error.