A prospective, randomized study of computer-assisted and conventional total knee arthroplasty. Three-dimensional evaluation of implant alignment and rotation.

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 degrees of valgus and 6.6 degrees of varus alignment in the frontal plane for conventionally implanted arthroplasty components compared with a significantly smaller range of between 2.9 degrees of valgus and 3.1 degrees 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 degrees +/- 1.7 degrees for the conventional surgical method and 1.4 degrees +/- 0.9 degrees for the navigated implantation. The rotational deviation from the referenced axis of the femoral component was between 3.3 degrees of internal rotation and 5.0 degrees of external rotation for the conventional implantation method, with a mean deviation of 0.1 degrees +/- 2.2 degrees. Femoral components implanted with computer assistance showed a deviation of between 4.7 degrees of internal rotation and 2.2 degrees of external rotation, with a mean deviation of 0.3 degrees +/- 1.4 degrees.

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.