Abstract
Total knee arthroplasty (TKA) is an effective technique to treat end-stage knee osteoarthritis, targeting the restore a physiological knee kinematics. However, studies have shown abnormal knee kinematics after TKA which may lead to suboptimal clinical outcomes. Posterior slope of the tibial component may significantly impact the knee kinematics. There is currently no consensus about the most appropriate slope. The goal of the present study was to analyse the impact of different prosthetic slopes on the kinematics of a PCL-preserving TKA, with the hypothesis that posterior slopes can alter the knee kinematics.
A PCL-retaining TKA (Optetrak CR, Exactech, Gainesville, FL) was performed by a board-certified orthopaedic surgeon on one fresh frozen cadaver that had a non arthritic knee with an intact PCL. Intact knee kinematic was assessed using a computer-assisted orthopaedic surgery (CAOS) system (ExactechGPS®, Blue-Ortho, Grenoble, FR) Then, TKA components were implanted using the guidance of the CAOS system. The implanted tibial baseplate was specially designed to allow modifying the posterior slope without repeatedly removing/assembling the tibial insert with varying posterior slopes, avoiding potential damages to the soft-tissue envelope. Knee kinematic was evaluated by performing a passive range of motion 3 separate times at each of the 4 posterior slopes: 10°, 7°, 4° and 1°, and recorded by the navigation system. Femorotibial rotation, antero-posterior (AP) translation and hip-knee-ankle (HKA) angle were plotted with regard to the knee flexion angle.
Tibial slopes of 1° and 4° significantly altered the normal rotational kinematics. Tibial slopes of 7° and 10° led to a kinematics close to the original native knee. All tibial slopes significantly altered the changes in HKA before 90° of knee flexion, without significant difference between the different slopes tested. The magnitude of change was small. There was no significant change in the AP kinematics between native knee and all tested tibial slopes.
Changing the tibial slope significantly impacted the TKA kinematics. However, in the implant studied, only the rotational kinematics were significantly impacted by the change in tibial slope. Tibial slopes of 7° and 10° led rotational kinematics that were closest to that of a normal knee. Alterations in knee kinematics related to changing tibial slope may be related to a change in the PCL strain. However, these results must be confirmed by other tests involving more specimens.
