[Computer-assisted knee arthroplasty: comparison with a conventional procedure. Results of 50 cases in a prospective randomized study].

PURPOSE OF THE STUDY

The aim of this work was to compare the radiographic findings after two techniques for total knee arthroplasty, one using a computer-assisted approach and the other a conventional approach.

MATERIAL AND METHODS

Between January 1998 and April 1999, we conducted a prospective study randomizing 25 patients for conventional surgery (group A) and 25 for computer-assisted surgery (group B). All patients volunteered to participate in this study and gave their written informed consent. There were 35 women and 15 men, mean age 69.5 years (range 47-85). The two groups were comparable for age, gender, height, weight, orthopedic history, etiology and preoperative mobility. The preoperative hip-knee angle (HKA) was also comparable between the two groups. Mean HKA was 175 degrees, i.e. 5 degrees varus (range 162 degrees (18 degrees varus) to 210 degrees (30 degrees valgus)). Genu varum was found in 80 p. 100 of the patients in group A and in 76 p. 100 in group B, genu valgum in 16 p. 100 in group A and 24 p. 100 in group B. The same operator performed all the procedures) with the same type ok prosthesis for all patients. The goal of the operation was to position the prosthesis to produce an HKA of 180 +/- 3 degrees, a femoral angle of 90 degrees (from the mechanical axis), a tibial angle of 90 degrees and a posterior tibial slope of 0 degrees (tibial plateau at 90 degrees to the lateral tibial axis). Statview 5 PC was used for the statistical analysis. Comparisons between groups were made with the Student's t test to compare means when the validity conditions were met.

RESULTS

The patients were reviewed by two surgeons, independently of the operator and the designers of the computer-assistance program. Mean duration of the procedure was longer in group B (102 mn versus 70 mn, p<0.001). There was no statistically significant difference in mean postoperative bleeding (group A=380 cc, group B=480 cc). The postoperative HKA was 181.2 +/- 2.72 degrees in group A and 179.04 +/- 2.53 degrees in group B (p > 0.05). The HKA was between 177 degrees and 183 degrees in 75 p. 100 of the patients in group A and in 84 p. 100 of those in group B. Implantation of the femoral component showed a mean angle of 91.12 +/- 2.07 degrees in group A and 89.56 +/- 1.61 degrees in group B (p=0.048). The mean tibial angle was 90.167 +/- 1.61 degrees in group A and 89.5 +/- 1.34 degrees in group B (p=0.11). On the lateral view, the femoral component was at 90 degrees to the mechanical axis in 16/21 patients in group B. These data were missing in group A. The posterior tibial slope was 90.76 +/- 2.19 degrees in group A and 89.44 +/- 2.14 in group B (p=0.18).

CONCLUSION

Computer-assisted surgery for total knee arthroplasty was found to provide remarkably reliable results. Once the "growing pains" of this new material have been mastered, all surgeons should be able to expect an improvement in the positioning of prosthetic implantations.