Background: Despite the use of modern instruments in total knee
arthroplasty, component malalignment remains a problem. Whether a
computer-assisted implantation technique can improve the accuracy of the
spatial positioning of an implant is a matter of debate. The objective of this
study was to determine whether computer-assisted total knee arthroplasty is
superior to the conventional surgical method with regard to the precision of
implant positioning.
Methods: The spatial positioning of the implant in sixty total knee
arthroplasties (thirty-two imageless computer-assisted and twenty-eight
conventional implantations) was determined three-dimensionally with use of
computed tomographic measurement, which allowed derotation and full extension
of the knee in order to avoid projection-related imaging errors.
Results: The overall mechanical axis showed a range of between
4.8° of valgus and 6.6° of varus alignment in the frontal plane for
conventionally implanted arthroplasty components compared with a significantly
smaller range of between 2.9° of valgus and 3.1° of varus alignment
for computer-assisted implantations (p = 0.004). In relation to the tibial
implant, the mean deviation (and standard deviation) from the mechanical axis
was 2.0° ± 1.7° for the conventional surgical method and
1.4° ± 0.9° for the navigated implantation. The rotational
deviation from the referenced axis of the femoral component was between
3.3° of internal rotation and 5.0° of external rotation for the
conventional implantation method, with a mean deviation of 0.1° ±
2.2°. Femoral components implanted with computer assistance showed a
deviation of between 4.7° of internal rotation and 2.2° of external
rotation, with a mean deviation of 0.3° ± 1.4°.
Conclusions: In this study, with our technique of filtering out
projection-related imaging errors, computer-assisted implantation of total
knee replacements improved the frontal and sagittal alignment of the femoral
component but not of the tibial component. We found that the rotational
alignment of the component was not improved through navigation by solely
referencing to the epicondylar axis for the femur and the tuberosity for the
tibia.
Level of Evidence: Therapeutic Level I. See Instructions
to Authors for a complete description of levels of evidence.