Reference values of the femur and tibia mechanical axes and angles in the sagittal plane, determined on the basis of three-dimensional modeling

Abstract

Background: The reference values of the anatomical, mechanical lines and angles of the femur and tibia in the frontal plane have been sufficiently studied. At the same time, the data concerning the mechanical axis and angles in the sagittal plane are rather contradictory. Aims and objectives. The aim of this study was to determine the 3D reference values of the mechanical axes and angles of the femur and tibia in the sagittal plane. Materials and Methods: The study included data of 23 adult volunteers for whom computer tomography (CT) was done. The inclusion criteria were: absence of the deformity confirmed by long-leg films (using known reference lines and angles (RLA) assessment), absence of torsional deformity confirmed by CT and extended position of the limb. Results: It was found that the mechanical axis of the lower limb in the sagittal plane divides the distal joint line of the femur into two segments: anteriorly - 43.8+7.9%, posteriorly - 56.2+7.9%. The proximal joint line of the tibia, correspondingly, is divided into 23.3+8.8% anteriorly and 76.7+8.8% posteriorly. The found values of mechanical angles were the following: mechanical Posterior Proximal Femoral Angle (mPPFA) - 84.7 + 8.8 °, mechanical Posterior Distal Femoral Angle (mPDFA) - 81.1 + 3.95 °, mechanical Posterior Proximal Tibial Angle (mPPTA) - 81.6 + 2.8 °, mechanical Anterior Distal Tibial Angle (mADTA) - 79.9 + 2.98°. Conclusion: The obtained data on the mechanical axis of the lower limb for the sagittal plane can be used both for deformity assessing, planning and estimating the accuracy of deformity correction.