Reliability of tunnel measurements and the quadrant method using fluoroscopic radiographs after anterior cruciate ligament reconstruction

Background: Anterior cruciate ligament (ACL) reconstruction tunnel placement is often evaluated by radiographs. This study examines the interobserver reliability of various radiographic measurements of ACL tunnels. Hypothesis: When ideal radiographic views are obtained the interobserver reliability of the measurements among experienced surgeons would be good to excellent. Study Design: Descriptive laboratory study. Methods: Tunnels for single-bundle ACL reconstruction were drilled and filled with metal interference screws or a tibial reamer on 73 cadaveric knees. Ideal fluoroscopic radiographs were obtained. Three independent reviewers performed 18 measurements including a modification of the grid method. For the grid method analysis reviewers fit a 16 × 12 grid to the lateral knee radiograph and the center of the femoral tunnel was marked. Interobserver reliability of the measurements was performed using intraclass correlation coefficients (ICCs). A precision grouping analysis was performed for the grid measurements to calculate the mean radius and standard deviation grouping distances. Results: The ICCs were excellent (>.75) for the tibial tunnel angles and tunnel measurements the clock face measurement and the Aglietti et al and Jonsson et al measurements. The ICCs were good (.4-.75) for an estimation of graft impingement Harner et al measurements and notch height. The mean radius for grid measurements was 0.6 ± 0.4 units (range 0-2.36 units) with each unit being 1 box in the 16 × 12 grid. When a circle was constructed with a 1.3-unit radius 95% of the 3 surgeons' measurements would be included in the area of that circle. Conclusion: Reliability of ACL tunnel measurements was good to excellent under ideal circumstances for the majority of measurements. The modified grid method demonstrated very acceptable reliability. Clinical Relevance: Measurements with good to excellent reliability can be used to evaluate ACL tunnel placement when ideal radiographic views are obtained.