LEARNING CURVE OF A NAVIGATION SYSTEM FOR TOTAL KNEE REPLACEMENT. A MULTICENTRIC STUDY.

Abstract

Accuracy of implantation is an accepted prognostic factor for the long term survival of total knee replacement (TKR). The use of navigation demonstrated a significant higher accuracy of implant orientation in comparison to conventional methods. However, these systems are often thought to be technically demanding, to increase operating time and to involve a long learning curve. We performed a prospective, multicenter study to compare the accuracy of implantation of a TKR measured on post-operative X-rays in experienced and less experienced centers.

All centers used the same navigation system (Ortho-Pilot ®, Asculap, Tuttlingen, FRG): 4 had already a significant experience with it (group A – 182 cases), 9 centers were considered as beginners with less than 10 cases performed prior to the study (group B – 221 cases). Accuracy of implantation was measured on post-operative antero-posterior and lateral long leg X-rays with five items: mechanical femoro-tibial angle, coronal orientation of the femoral component, sagittal orientation of the femoral component, coronal orientation of the tibial component, sagittal orientation of the tibial component.

When the measured angle was in the expected range, one point was given. The accuracy note was defined as the sum of all points given for each patient, with a maximum of 5 points (all items fulfilled) and a minimum of 0 point (no item fulfilled). The mean accuracy note was compared in the two groups by a Student t-test at a 0.05 level of significance. Power of the study was 0.80.

There were no significant differences in pre-operative parameters between the two groups, except for the clinical KSS. The mean operative time was significantly longer in group B than in group A (110 minutes vs 90 minutes, p=0.01). However this difference occurred mainly during the first twenty cases in the beginner centres where we observed a clear tendency to achieve the same operative time as the experienced centres at the end of the study. The mean accuracy note was 4.3 ± 0.8 (range, 1 to 5) in the control group and 4.3 ± 0.9 (range, 1 to 5) in the study group (p > 0.05). The power of the study to detect a 0.25 point difference in the post-operative accuracy note was retrospectively calculated to be 0.80. There were no significant differences between the two groups for all individual radiographic items.

This study is, to our knowledge, the first one which investigates the learning curve of navigated TKR The used navigation system allowed a very accurate implantation of a TKR in both experienced and less experienced centers. There was no detectable learning curve with respect to accuracy of TKR implantation, clinical outcome and complication rate. The duration of the learning curve when considering the operating time was 30 cases.