A Radiologic Study of the Reference Line for Measuring Posterior Slope Angle on Lateral View of the Knee

Abstract

Purpose: This study evaluated the radiological reference line of the posterior slope angle on the lateral view of a plain knee radiograph. Materials and Methods: The lateral view of the plain knee and whole tibia radiographs were analyzed from thirty seven patients (fifty-two cases) who had undergone total knee arthroplasty. The posterior slope angle was measured on the lateral view of the tibia. On the lateral view of the knee, the posterior slope angle was measured with reference to the proximal tibial anatomical axis, the proximal tibial anterior cortical line, the proximal tibial posterior cortical line and the proximal fibular anatomical axis. These values were compared with the posterior slope angle measured on the whole tibia lateral view. Results: The posterior slope angle, which was measured by the anterior cortical line as a reference line, was tilted slightly anteriorly to that measured by the whole tibial lateral anatomical axis (0.15 degree in average; anterior slope 3.95- posterior slope 5.57 degree). This difference was smallest among that of the measured angle by the other reference lines (p ＜ 0.001). Conclusion: The anterior cortical line of the proximal tibia appears to be the most reliable reference line for measuring the posterior slope angle on a knee lateral radiograph after TKA.