[Computer-assisted surgery in total knee replacement. Preliminary results: report of 60 cases]

Conventional techniques proposed for total knee arthroplasty (TKA), necessarily require an acceptable alignment of the lower limb. Computer-assisted surgery is becoming increasingly popular in order to improve the precision of the component alignment, an essential element for good long-term results. The purpose of this prospective study was to present our preliminary results with computer-assisted implantation of TKA.

This was a prospective study of 55 patients (60 knees) included at random for computer-assisted TKA between April 2004 and September 2005. Mean age was 70.5 years. The preoperative assessment noted genu varum in 56 knees and genu valgum in four knees. Three knees with unilateral degenerative disease presented a post traumatic tibia malunion. The same surgeon performed all of the operations using the same prosthesis and navigation system (P.F.C. Sigma). Lower limb alignment and orientation of the prosthetic implants were assessed with standard pre- and postoperative gonometry. Sagittal alignment was measured on the standard X-rays (lateral and anteroposterior view).

Knee alignment improved from 8.1+/-4.5 degrees varus (10 degrees valgus to 18 degrees varus) preoperatively, to 0.4+/-0.6 degrees varus (1 degrees valgus to 2 degrees varus) postoperatively. In the frontal plane, the mean angle of the femoral component on the anteroposterior (ap) view was 89.7+/-0.7 degrees (88-91 degrees). The mean angle of the tibial component on the ap view was 89.9+/-0.7 degrees (88.5-91 degrees). The femorotibial mechanical axis was within +/-2 degrees for all prostheses. In the sagittal plane, the mean angle of the femoral component on the lateral view was 4.8 degrees (3-6.5 degrees). The mean tibial slope was 2.7 degrees (1-4 degrees) for the prostheses with a fixed tibial plateau and 0.2 degrees (-1 degrees to +1 degrees) for those with a rotating plateau. The mean operative time was 135 min (110-180 min) and was inversely proportional to experience. There was one conversion to conventional surgery due to software dysfunction. There were no complications related to the operative technique.

The best outcome, particularly in terms of aseptic loosening, is reported for knees with a valgus or varus angle within 3 degrees . The improved accuracy of computer-assisted implantation has enabled better orientation of the components in the frontal, sagittal and horizontal planes with implantations well within this range.