MINIMALLY INVASIVE SURGERY COULD LIMIT THE ACCURACY OF NAVIGATION SYSTEMS FOR UNICOMPARTMENTAL KNEE PROSTHESES

Abstract

Purpose of the study: Navigation systems have proven efficacy for the implantation of unicompartmental knee prostheses. Minimally invasive methods, which limit access to non-operated compartments, might compromise system accuracy.

Material and methods: A standard navigation software was used for kinematic acquisition of the lower limb and to acquire anatomic landmarks for both femorotibial compartments. A modified version of the navigation software designed for minimally invasive surgery replaed palpation of the anatomic landmarks of the non-operated compartment by a computation method based on other data. Three groups of patients were analyzed. Group 1 included 64 patients who underwent minimally invasive surgery for implantation of a medial unicompartmental prosthesis. Group B included 60 patients selected randomly among 140 cases of medial unicompartmental prosthesis patients treated with the standard navigation technique. Group C included 30 patients selected randomly among 180 patients who underwent total knee arthroplasty with the standard navigation system. The quality of the implantation was assessed on the postoperative ap and lateral views by comparing five criteria describing the desired prosthetic alignment. The number of criteria describing correct alignment was noted for each patient, thus yielding a quality score from 0 to 5. ANOVA was used to compare the mean scores of the three groups using Boneffini-Dunn correction at the 5% risk level.

Results: The mean quality score was 3.5±1.2 for group A, 4.5±0.8 for group B and 4.2±1.0 for grup C (p< 0.001). Ther was no significant difference between groups B and C (p=0.24). The quality score was significantly lower in group A (A versus B: p=0.015; A versus C: p< 0.001).

Discussion: The minimally invasive approach is proposed to enable more rapid functional recovery after implantation of a unicompartmental knee prosthesis. The long-term outcome however depends on the quality of the implantation. The quality of the implantation with a minimally invasive method should thus be equivalent to that achieved with the standard method. Conventional minimally invasive methods are more difficult. Navigation could be expected to overcome this difficulty without sacrificing implantation quality. However, the version used here did no enable an implantation equal to the quality achieved with the standard navigation system.

Conclusion: The standard navigation system for the conventional access remains the gold standard for implantation quality. Changes resulting from a less invasive approach should be validated before routine use.