Intraobserver and Interobserver Reliability of the Kneeling Technique of Stress Radiography for the Evaluation of Posterior Knee Laxity

Background: Stress radiography provides an objective tool to measure posterior knee instability. Intraobserver and interobserver reliability has been reported for the Telos device, but it has not been studied using the kneeling technique. Purpose: This study was conducted to evaluate the intraobserver and interobserver reliability of measurements made using kneeling stress radiography to quantify posterior knee instability. Study Design: Case series (diagnosis); Level of evidence, 4. Methods: One hundred thirty-two stress radiographs in 44 patients with suspected posterior knee instability were prospectively taken using the kneeling technique. The amount of posterior displacement on the radiographs was then measured independently by 3 blinded testers (an orthopaedic sports medicine faculty member, an orthopaedic chief resident, and a medical student) on 2 separate occasions. Changes in mean and intraclass correlation coefficients (ICCs) were examined to assess the intraobserver and interobserver reliability of the measurements. Results: Intraobserver changes in displacement means were small (−0.307 mm, −0.294 mm, and +0.035 mm) and only significant for observer 1. The combined intraobserver ICC was 0.973 for the 3 observers (0.976, 0.959, and 0.981). Interobserver comparisons revealed significant differences in trial 1 between observers 2 and 3 (0.675 mm), no differences in trial 2, and significant differences between observers 1 and 2 (0.333 mm) and observers 2 and 3 (0.510 mm) in the combined trial data. The combined interobserver ICC was 0.955 for the 3 observers (0.959 and 0.951 for the 2 trials). Conclusions: The kneeling technique for posterior cruciate ligament stress radiography provides a reproducible method to quantify posterior knee instability. Keywords: stress radiography posterior knee instability posterior cruciate ligament