Abstract
Introduction
Increasing attention to the functional outcome of total knee arthroplasty (TKA) has demonstrated that many patients experience limitations when attempting to perform demanding activities that are normal for age-matched peers, primarily because of knee symptoms. Episodes of instability following TKA are most commonly reported during activities in which significant transverse or torsional forces are supported by the joint with relatively low joint compression forces, including stair-descent and walking on sloped or uneven surfaces. This study was performed to examine the influence of conformity between the femoral and tibial components on the Antero-Posterior (AP) stability of knee during stair descent.
Methods
Six cadaveric knees were loaded in a six degree-of-freedom joint simulator, with the application of external forces simulating the action of the quadriceps and hamstring muscles and the external loads and moments occurring during stair descent, including the stages of terminal swing phase, weight-acceptance phase (prior to and after quadriceps contraction) and mid-stance. During these manoeuvres, the displacement and rotation of the femur and the tibia were measured with a multi-camera high resolution motion analysis system (Fig. 1). Each knee was tested in the intact and ACL deficient condition – and after implantation of total knee prosthesis with Cruciate-Retaining (CR), Cruciate-Sacrificing with an intact PCL (CS + PCL), Cruciate-Sacrificing with an absent PCL (CS-PCL) and Posterior-Stabilizing (PS) tibial inserts (Figs 2 and 3).
Results
Loading of the knee during stair descent caused the femur to displace anteriorly by 4.31 ± 1.47 mm prior to quadriceps contraction. After TKA, anterior displacement ranged from 1.11 ± 0.41 mm (PS) to 8.19 ± 3.17 mm (CS-PCL). Intermediate values were 1.46 + 0.42 mm (CS + PCL) and 3.03 ± 0.94 mm (CR). Quadriceps contraction was able to restore the femoral AP position (5.53 ± 1.08 mm posterior motion) in the intact knee, but larger quadriceps force were required for the other designs (8.22 ± 2.94 mm CS-PCL, 2.32 ± 0.83 mm CS + PCL, 2.02 ± 0.94 mm CR design, and 1.08 ± 0.38 mm with the PS.
Conclusion
Pain during high demand activities such as stair descent is a common complaint of patients after TKA, and this may be due to AP instability and extra-physiologic quadriceps demand. The only designs that restored anterior-posterior knee stability were a PS insert or a CS insert with an intact PCL. The CS design without a PCL demonstrated the worst AP stability, despite the fact that these inserts are designed to be used without a PCL.
