A RADIOLOGICAL AND NAVIGATED STUDY OF THE ANATOMICAL AND MECHANICAL FEMUR AXES IN THE LATERAL PLANE.

Abstract

Introduction: Data about sagittal orientation of the femoral component of a total knee replacement (TKR) are scarce, mainly because the definition of the femur axes on the lateral plane is not fully validated.

Methods: We analyzed 60 patients scheduled for TKR. Following axes were drawn on pre-operative long leg lateral X-rays: distal anterior cortex axis, anatomic diaphyseal axis, and three different mechanical axes from the center of the femoral head: #1 to the lowest point of the Blumensaat line, #2 to the midportion of the femoral condyles, #3 to the junction between the anterior two-third and the posterior third of the femoral condyles. The cortical axis was considered as the reference, and the angles between this reference and the other axes were recorded (more fiexion was considered positive).

Results: The mean orientation of the diaphyseal axis and the reference was +0.6°±3° (range, −1° to +3°). The mean orientation of the mechanical axis 1 was −0.8°±2.1° (range, −5° to +4°). The mean orientation of the mechanical axis 2 was −0.6°±2.1° (range, −5° to +4°). The mean orientation of the mechanical axis 3 was +0.8°±2.1° (range, −3° to +5°).

Discussion: There were few differences between the orientation of the different axes of the femur on the lateral view. The cortical axis has the lowest variance and may be the more reliable to document the femoral orientation on the lateral view. However this axis does not take into account the anteversion of the femoral neck.