Ligamentkontrollierte Positionierung der Knieprothesenkomponenten

Arthroplasty of the Knee: Current Techniques for Implant Alignment

When a total knee arthroplasty (TKA) is implanted using the traditional mechanical alignment technique, this typically results in a straight leg, independently of pre-operative or even pre-arthrotic varus or valgus alignment. With mechanical alignment, we distinguish between 2 different alignment techniques: ligament balancing and bony referencing according to bony skeletal landmarks. In ligament balanced technique beside the straight mechanical axis, the prosthesis is implanted at 90° to the latter. The rotational alignment of the femur is set according to the ligament tension. In the skeletal referenced technique, the rotation of the femur is also set according to bony skeletal landmarks. As a variation of this technique, the prosthesis can be implanted with anatomical alignment. In this technique, the medial slope of the joint line of 3° in the frontal plane is respected during the implantation of TKA. Both techniques result in comparable long-term results with survival rates of almost 80% after 25 years. On the other hand, 15 – 20% of TKA patients report dissatisfaction with their clinical result. For more than 10 years now, the kinematic TKA alignment concept has been developed with the goal to achieve implantation that is adapted to the individual anatomy of the patient. The advocates of this technique expect better function of TKA. This strategy aims to reconstruct the pre-arthrotic anatomy of a given patient while preserving the existing joint line and the mechanical axis without performing ligamentary release. Studies have shown that the function of the prothesis is at least that good as in the conventional techniques. Long-term results are still sparse, but initial studies show that TKA implanted using the kinematic alignment technique exhibit comparable 10-year-survival rates to those implanted using the traditional mechanical alignment technique. Future studies need to show the limitations of this new technique and to identify patients who will or will not significantly benefit from this technique.

Evaluation of benefits and accuracy of a mobile application in planning total knee arthroplasties

Objective

To evaluate the usefulness of an application when planning total knee arthroplasties (TKA), besides the accuracy when measuring the anatomical-mechanical femoral angle (AMFA), comparing, also, the time spent during planning a TKA manually and by using the application.

Methods

An interdisciplinary team involving health and computer science areas established activities in order to develop the application. After development, 24 physicians underwent an application usability test. Each one planned a primary total knee arthroplasty (TKA) initially, in a conventional manner and then by using the application. Data concerning AMFA measurement and time spent during planning were collected, in both manners. The Mann–Whitney and Wilcoxon tests were used to evaluate statistical significance related to angle and time.

Results

Users considered it important checking AMFA and drawing the bone cut lines orthogonal to the mechanical axis, when planning TKAs. They also assessed that the application could be useful for training surgeons and for specialists. There was no statistically significant difference between the AMFA, as measured by the application and by the conventional manner. The planning time was shorter when the application was used (39% of the time spent manually).

Conclusions

The application has proved to be useful in planning TKAs and has revealed accuracy when measuring the AMFA when it was compared to the manual form of preoperative planning. The application was able to reduce planning time by more than half and it demonstrated reliability in measuring the AMFA.