Abstract
Introduction
The knowledge of the right amount of tension of the collateral ligaments in native knees is one of the hot topics to restore the normal kinematics in TKA. To guarantee stability in TKA there should be enough tension necessary but no overtensioning. In this study we could confirm that the tension of the ligaments is not more than 20–25N on each side (in total 40–50N) to achieve stability in the knee joint.
Methods and materials
During an experimental activity we examined 5 cadaveric knee specimenwith intact ligaments. With the knee in full extension, a constant force was applied on the femoral bone and the displacement was measured up a plateau was reached. This test was conducted for a knee joints with intact cruciates, then we sacrificed the anterior cruciate and in a third step the posterior cruciate even to find out if there is any change in extending the joint comparing distance and tension.
Results
In all cases the tension was with intact ACL and after sacrificing it not more than 20 N (18–22N) in average, after sacrificing the PCL the tension for maximum laxity was in average 24 N (22–26N).
Summary
Most devices for ligament tension work with more than 80 N to balance the knee. Especially in cases with weak ligaments or asymmetric stability can occur the problem of over- or under-tensioning to balance the knee.
In our study we could show, that less tension of the ligaments are enough to stabilize the knee.
Conclusion
The most important point in restoring the normal kinematics in TA is preserving the soft tissue envelope. Of course there is still the need to proceed the correct cuts to secure survivorship of TKA, but there are still 20% dissatisfied patients. We think that there is a strict correlation to the soft tissue situation, even in the tension of ligaments, capsule and muscles. Proper adaption to the normal tension situation to avoid overtensioning will improve results and show the need of measurement devices to reach this aim.
