Abstract
INTRODUCTION
Applying the proper amount of tension to knees collateral ligaments during surgery is a prerequisite to achieve optimal performance after TKA. It must be taken into account that lower values of ligament tension could lead to an instable joint while higher values could induce over-tensioning thus leading to problems at later follow-up: a “functional stability” must then be defined and achieved to guarantee the best results.
In this study, an experimental cadaveric activity was performed to measure the minimum tension required to achieve functional stability in the knee joint.
METHODS
Ten cadaveric knee specimens were investigated; each femur and tibia was fixed with polyurethane foam in specific designed 3D-printed fixtures and clamped to a loading frame.
A constant displacement rate of 0.05 mm/s was applied to the femoral clamp in order to achieve joint stability and the relative force was measured by the machine: the lowest force guaranteeing joint stability was then determined to be the one corresponding to the slope change in the force/displacement curve, representing the activation of the elastic region of both collateral ligaments.
The force span between the slack region and the found point was considered to be the tension required to reach the functional stability of the joint.
This methodology was applied on intact knee, after ACL-resection and after further PCL-resection in order to simulate the knee behavior in CR and PS implants.
The test was performed at 0, 30, 60 and 90° of flexion using a specifically designed device. Each configuration was analyzed three times for the sake of repeatability.
RESULTS
Results demonstrated that an overall tension of 40–50N is sufficient to reach stability in native knee with intact cruciate ligaments. Similar values appear to be sufficient in an ACL-resected knee, while higher tension is required (up to 60N) for stability after ACL and PCL resection.
Moreover, the tension required for stabilization was slightly higher at 60° of flexion compared to the one required at the other angles, reflecting thus the mid-flection instability behavior.
DISCUSSION AND CONCLUSIONS
The results are in agreement to other experimental studies1,2 and show that the tensions necessary to stabilize a knee joint in different ligament conditions are way lower than the ones usually applied via tensioners nowadays.
To reach functional stability, surgeons should consider such results intraoperatively to avoid laxity, mid-flexion instability or ligament over-tension.
