RELATIONSHIP BETWEEN ANATOMICAL REFERENCES AND SAGITTAL MECHANICAL AXES OF COMPUTER ASSISTED NAVIGATION FOR TOTAL KNEE ARTHROPLASTY

Abstract

Despite the well-documented improvement in coronal alignment achieved by computer assisted navigation, varying results have been reported for sagittal alignment. Current navigation systems rely on a sagittal femoral mechanical axis identified by the navigation system, but little information is available on the relationship between the sagittal mechanical axis and anatomical axes for intra-operative or postoperative radiographic assessments. We asked whether deviations exist between sagittal femoral mechanical axis and anatomical axes and attempted to identify predictors of the deviations found.

In 100 consecutive patients (200 knees) undergoing TKA, angles between two anatomical axes (the anterior cortical line and mid-medullary line) and two sagittal mechanical axes identified by current navigation systems were measured as proxies of the deviations between them on true lateral radiographs of the whole femur. Correlation analyses and multivariate regression were carried out to identify predictors of deviations.

Significant deviations existed with wide ranges between the anatomical axes and the sagittal mechanical axes. Degree of femoral bowing and femoral length were found to be predictors of deviations between sagittal femoral mechanical axes and anatomical axes.

This study suggests that surgeons applying navigation technology to TKA need to consider deviations between the sagittal femoral mechanical axes and anatomical axes when they intend to place a femoral component at a target sagittal orientation with respect to an anatomical reference.