OBJECTIVES

The use of a mobile bearing has been suggested to decrease the rate of patellar complications after total knee arthroplasty (TKA). However, to resurface or retain the native patella remains debated. Few long-term results have been documented. The present retrospective study was designed to evaluate the long-term (more than 10 years) results of mobile bearing TKAs on a national scale, and to compare pain results and survivorship according to the status of the patella.

The primary hypothesis of this study was that the 10 year survival rate of mobile bearing TKAs with patella resurfacing will be different from that of mobile bearing TKAs with native patella retaining.

Introduction: The accurate positioning of the cup implant is a relevant prognostic factor for both short- and long-term results after total hip replacement. Conventional, manual control has proved to be less than optimal. Navigation systems might improve the accuracy. We designed this study to validate the accuracy of a non image based navigation system for cup orientation during total hip replacement, with post-operative 3D CT-scan analysis.

Material and methods: 60 cases of navigated total hip replacement have been analysed. Navigation was performed with the OrthoPilot® system (Aesculap, Tuttlingen, FRG), a non image based system. A localizer was implanted on a screw on the anterior iliac crest. Three relevant landmarks (both antero-superior iliac spines and pubis) were palpated with a navigated stylus, defining the anterior pelvic plane (Lewinnek plane). Acetabular preparation and cup implantation were performed under navigation control. Safe zone for acetabular implantation was defined pre-operatively: 40 to 50° of abduction, 10 to 20° of flexion in comparision to the anterior pelvic plane. The final orientation of the cup was registered intra-operatively by the navigation system, and compared to the 3D CT-scan measurement of the cup positioning with the same reference frame.

Results: There was no significant difference between the intra-operative and post-operative measurements of the cup abduction. There was a significant difference between the intra-operative and post-operative measurements of the cup flexion, mainly ±5°. 50 implants were positioned within the safe zone (83%).

Discussion: The navigation system used allowed an accurate positioning of the cup in abduction. The flexion positioning was less accurate, but the differences observed (mainly less than 5°) are probably clinically irrelevant. Furthermore, the accuracy was higher than that observed with conventional, manual implantation.

Conclusion: The navigation system used allows improving the accuracy of cup placement in comparison to conventional, manual techniques.

Introduction: Unicompartmental knee replacement (UKR) is accepted as a valuable treatment for isolated medial knee osteoarthritis. Minimal invasive implantation might be associated with an earlier hospital discharge and a faster rehabilitation. However these techniques might decrease the accuracy of implantation, and it seems logical to combine minimal invasive techniques with navigation systems to address this issue.

Materials and methods: The authors are using a non image based navigation system (OrthoPilot TM, Aesculap, FRG) on a routine basis for UKR. The used version of the software helps the surgeon orienting the bone resections through a minimal invasive medial approach without splitting the quadriceps tendon or the vastus medialis muscle. The proximal tibial resection is performed with a conventional motorized saw blade guided by a free hand navigated orienting device. For the femoral resection, a bow is fixed by three percutaneous screws to the distal femur. The bow is navigated to be oriented along the knee flexion axis. A guide is fixed on the bow and oriented under navigation control to perform the distal femoral resection with a burr. Neither guides are fixed directly into the joint.

42 patients have been operated on in the 4 participating centers for an isolated medial osteoarthritis. There were 29 women and 13 men, with a mean age of 65 years. The post-operative coronal and sagittal orientation of both prosthetic components were measured, and the time to get 90° of knee flexion was recorded.

Results: The mean coronal angle between the femoral component and the femoral mechanical axis was 89° for an expected goal of 90°. The mean coronal obliquity of the femoral component was 91°, for an expected goal of 90°. The mean coronal angle between the tibial component and the tibial mechanical axis was 86° for an expected goal of 88°. The mean coronal obliquity of the tibial component was 88°, for an expected goal between 85 and 90°. The mean sagittal obliquity of the femoral component was 6°, for an expected goal of 10. The mean sagittal obliquity of the tibial component was 88°, with an expected goal of 87. The patients achieved 90° of knee flexion after a mean period of time of 9 days.

Discussion: The used navigation system is based on an anatomic and kinematic analysis of the knee joint during the implantation. The modification of the existing software for its use with a minimal invasive approach has been successful. It enhances the quality of implantation of the prosthetic components and avoids the inconvenients of a smaller incision with potentiel less optimal visuliazation of the intra-articular reference points. However, all centers observed a significant learning curve of the procedure, with a significant additional operative time during the first implantations. The postoperative rehabilitation was actually easier and faster, despite the additional percutaneous fixation of the navigation device.

Conclusion: This system has the potentiel to allow the combination of the high accuracy of a navigation system and the low invasiveness of a small skin incision and joint opening.

Introduction: Navigation systems might enhance the accuracy of ACL replacement.

Methods: The authors used a non image based navigation system with both kinematic and anatomic registration. Navigated aimers were positioned to simulate the intra-articular hole of both femoral and tibial tunnels. The system displayed the position of the guide wire, the expected isometricity of the graft and the potential impingement within the intercondylar notch.

40 patients were operated on for an arthroscopic assisted bone – patellar tendon – bone ACL replacement with an outside-in femoral tunnel. The guide wires were placed according to the standard technique, and their position recorded by the system. The recorded position was compared:

to the conventional radiographic measurement of the position of the tunnels on plain antero-posterior and lateral X-rays,

Results: There was a significant difference in the paired absolute values of the mediolateral position of the tibial tunnel between radiographic and navigated measurements (p = 0.008). However there was a significant correlation between these two measurements (p = 0.05).

There was no significant difference in the paired absolute values of the mediolateral position of the tibial tunnel or of the antero-posterior position of the femoral tunnel between radiographic and navigated measurements.

There was no significant difference in the paired absolute values of the antero-posterior and medio-lateral position of the tibial tunnel or of the antero-posterior position of the femoral tunnel between CT and navigated measurements.

Discussion: CT-scan measurement of the positioning of the ACL replacement tunnels is currently the gold standard technique. According to this reference, the antero-posterior position of both the femoral and the tibial tunnels can be accurately assessed by the navigation system used. The X–ray measurement is less accurate and should not be considered as a confident control of the accuracy of the tunnel placement.

Summary: The antero-posterior position of both the femoral and the tibial tunnels can be accurately assessed by the system.