Introduction Applying proper tension to ligaments during Total-Knee-Arthroplasty surgery is fundamental for optimal implant performance: low tensions lead to joint instability, over-tensioning to pain and stiffness. “Functional stability” must then be defined and achieved. An experimental cadaveric activity was performed to measure the minimum tension required to achieve this stability.
Methods Ten knee specimens were investigated; femur and tibia were clamped to a loading-frame; constant displacement rate was applied and resulting tension force was measured. Joint stability was determined as the slope change in the force/displacement curve, representing the ligaments’ elastic-region activation; the tension required to reach functional stability is the span between ligaments toe-region and this point. Intact, ACL(Anterior-Cruciate-Ligament)-resected and ACL&PCL(Posterior-Cruciate-Ligament)-resected knees were tested. Different flexion angles were tested.
Results Results demonstrated an overall tension of 40-50N to be enough to reach stability in intact knees. Similar values are sufficient in ACL-resected knees; higher tension is required (up to 60N) after ACL&PCL resection; slightly higher values were found for 60° flexion. Results agree with other experimental studies, showing that the tensions required to stabilize the joint are lower than the ones currently applied via surgical tensioners.
Conclusion To reach functional stability, surgeons should consider such results intraoperatively to avoid ligament laxity or over-tensioning.