INTRODUCTION

Polyethylene wear is one of the reasons for failure of total knee replacement (TKR). There are several reasons for wear, and the femoro-tibial contact area is an important factor. Mobile bearing, highly congruent prostheses might be more resistant to polyethylene wear than fixed bearing, incongruent prostheses. We evaluated the 5- to 8-year experience of three university departments by using an original system with following highlights: implantation with a navigation system, extended congruency up to 90° of flexion, floating polyethylene component with non-limited movements of rotation, antero-posterior translation and medio-lateral translation.

Polyethylene wear is one of the reasons for failure of total knee replacement (TKR). There are several reasons for wear, and the femoro-tibial contact area is an important factor. Mobile bearing, highly congruent prostheses might be more resistant to polyethylene wear than fixed bearing, incongruent prostheses. We evaluated the five- to eight-year experience of three university departments by using an original system with following highlights: implantation with a navigation system, extended congruency up to 90° of flexion, floating polyethylene component with non-limited movements of rotation, antero-posterior translation and medio-lateral translation.

347 patients have been operated on in the three participating departments with this new prosthesis system between 2001 and 2004, and have been prospectively followed with clinical and radiologic examination with a minimal follow-up time of five years. There were 246 women and 101 men, with a mean age of 67 years.

Clinical and functional results have been analyzed according to the Knee Society scoring system. Accuracy of implantation has been assessed on post-operative long leg antero-posterior and lateral X-rays. Survival rate up to eight years has been calculated according to Kaplan and Meier, with mechanical revision or any revision as end-points.

Complete patient history was obtained by 319 cases (92%). The mean clinical score was 93 points. The mean pain score was 47 points. The mean flexion angle was 118°. The mean functional score was 87 points. An optimal correction of the coronal femoro-tibial axis was obtained in 94% of the cases. Survival rate after eight years was 98.8% for mechanical revisions and 95.5% for all revisions.

We confirmed the influence of the navigation system on the accuracy of implantation. The clinical and functional results after five to eight years are in line with the better results of the current literature after conventional implantation of non-congruent prostheses. The survival rate is comparable to the current standards. The influence of the design on polyethylene wear will need a longer follow-up.

Introduction: Total knee arthroplasty in obese patients remains a challenge to most surgeons. Surgical complication rates as well as perioperative morbidity are higher than total knee arthroplasty in the nonobese. The purpose of this paper is to review our experience with total knee arthroplasty in superobese patients (BMI> 50).

Methods: From 1998–2005, 84 patients underwent 148 knee arthroplasties. Sixty-four patients underwent simultaneous bilateral total knee arthroplasties and 20 patients underwent unilateral knee arthroplasties. They were compared with similar group of nonobese patients who underwent knee arthroplasties during the same time period. All patients received combined regional and general anesthesia.

Results: Mean follow-up was 3.8 years (2–7). Knee society scores improved by 36 points in the superobese (pre-op 47 to 83 post-op) and by 45 points in the non-obese (pre-op 47 to 93 post-op) (p< .05). There was a greater incidence of complications in the superobese group, namely superficial wound infections and deep vein thrombosis. There was late loosening in three tibial components and instability in two patients that required revision in the superobese group. No reoperations in the nonobese group.

Conclusion: Although total knee arthroplasty may be safely performed in the superobese, it may be complicated by infection, loosening, instability, and lower knee scores.

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.

Aims: The latest software 3.0 and 4.0 of the OrthoPilot knee navigation system use a new mathematical algorithm to reconstruct mechanical axis. The purpose of the study is to evaluate the alignment of prosthetic components with this software and compare it with the results from older software as well as with manual technique. Method: Thirty navigated SEARCH knees with software 3.0 of an uninterrupted series were evaluated versus thirty navigated knees with older software and a similar series of conventionally instrumented knees of a different type. Results: The results, concerning the five parameters mechanical axis a.p., femoral axis a.p., femoral axis lateral, tibial axis a.p. and tibial axis lateral, are clearly superior to the old navigation group and the manual group. For example, the number of cases with a good mechanical axis, 0,1or 2° of deviation from optimum, was reached in 17 of the manual, 19 of the old navigation and 27 of the new navigation cases. The additional time for operation is 8.7 minutes. No specific complications occurred. Conclusions: The OrthoPilot-Software 3.0 and 4.0 are clearly superior to the old generations. More features, as for example resection-height of the distal femur and the orientation of the femoral component are solved in a convincing manor. The numbers of outliers is again diminished. Navigation in knee arthroplasty with the OrthoPilot has become more sure and intelligent.

Background: The aim of introduction of navigation in knee arthroplasty was to further contribute to precision of endoprosthetic alignment.

Methods and material: A multicentre comparative study was conducted including 821 patients. The SEARCH knee system was used throughout the series. 555 TKA’s were implanted with the use of a navigation system (OrthoPilot) and 266 cases were operated using manual instrumentation. Alignment was radiographically evaluated at the three months follow-up with respect to mechanical axis and femoral and tibial axes using one-leg stance x-rays and standardized lateral radiographs.

Results: The summarized results of the series are shown in the table below. The chi-square test was applied for the statistical analysis.

Conclusions: Endoprosthetic alignment using the navigation system was superior to manual implantation technique on the average with respect to all parameters. Results were more consistent on the tibial side. The navigation system proved to be reliable. The overall results justify the further use and development of navigation tools in knee arthroplasty.

Purpose: The purpose of this study was to conduct a multicentric comparison of total knee arthroplasty using the conventional technique versus digitalized navigation.

Material and methods: A prospective comparative study was conducted in five centres in 821 patients using the same implant (Search®, Aesculap, Chaumont): 555 procedures with the Orthopilot® navigation system (Aesculap, tutligen, group 1) and 266 conventional procedures, group 2). Radiographic results were analysed by an independent investigator who examined telemetric images obtained three months after surgery.

Results: The mechanical femorotibial axis was within desired limits (3° frontal deformation) in 88.6% of the knees in group 1 and in 72.2% of the knees in group 2 (p< 0.001). The rate of unacceptable implantations (> 5° deviation) was 2.5% in group 1 and 9.8% in group 2).

Frontal orientation of the femoral component was satisfactory in 89.4% of the knees in group 1 and in 77.1% in group 2. Sagittal orientation of the femoral component was satisfactory in 75.5% of the knees in group 1 and in 70.7% of the knees in group 2. Frontal orientation of the tibial component was satisfactory in 91.9% of the knees in group 1 and in 83.5% of the knees in group 2. The sagittal orientation of the tibial piece was satisfactory in 81.3% of the knees in group 1 and in 69.9% of the knees in group 2. Optimal implantation, considering all criteria studied, was achieved in 275 patients (49.5%) in group 1 and in 82 patients (30.8%) in group 2 (p< à.001). Ther was no difference in results between centres.

Discussion: Computer-assisted navigation facilitated prosthesis implantation with the desired orientation in comparison with manual instrumentation. The number of unacceptable implantations was significantly lower. After a short learning curve, the reliability of this system has proven very satisfactory, facilitating its use since this study.