Description
Background: The goal of most total knee arthroplasty (TKA) implant designs is to mimic the medial pivot motion of a healthy knee. Unfortunately, conventional prostheses sometimes fail to reproduce such kinematics, leaving approximately 20% of TKA recipients dissatisfied. Recently, several innovative TKA designs have been developed that aim to replicate the medial pivot motion. However, it remains unclear whether these designs can consistently mimic the desired kinematics during daily activities. The aim of this study was to analyze the in vivo kinematics of patients with TKA during weight-bearing activities using the newer medial-pivot (MP) and posterior-stabilized (PS) designs. We postulated that the MP design would more closely mimic the natural medial pivot motion.
Patients and Methods: In this prospective, randomized, controlled study, 36 TKA recipients were enrolled with informed consent and followed for at least one year. One group of 18 knees was implanted with the MP TKA: EVOLUTIONTM (MicroPort Orthopedics Inc.) (MP group) and the other group of 18 knees was implanted with the PS TKA: Persona® (Zimmer Biomet Inc.) (PS group) under the same conditions of a constant medial tightness in intraoperative soft tissue balance. Outcome measures included the Knee Society Score(KSS) and the Knee Injury and Osteoarthritis Outcome Score(KOOS). Kinematic assessments were performed during lunge and step-up activities. A 2D-to-3D registration technique was used to determine antero-posterior translation of the medial and lateral femoral condyles and tibiofemoral axial rotation. The study was approved by our Institutional Review Board (approval number 2376).
Results: One year after surgery, all patients had pain relief and good knee function in daily activities. There was no statistically significant difference between the two groups in terms of postoperative implant positioning, femoro-tibial alignment and both clinical scores. Kinematic analysis during both activities showed that in the MP group the medial femoral condyle remained static while the lateral condyle shifted posteriorly with knee flexion. In contrast, the PS group showed an unexpected anterior shift of the medial femoral condyle, accompanied by a lateral pivot (Figure 1). Both groups showed an average internal tibial rotation of approximately 4°. During lunge and step-up activities, 83% and 72% of the MP group, respectively, showed a medial pivot pattern compared to 22% and 11% of the PS group, based on the analysis of the center of rotation.
Conclusion: The results of this study support our hypothesis. Our results showed that the in vivo kinematics of the EVOLUTIONTM were consistent with the intended design concept. However, the clinical significance of the medial pivoting motion remains unclear. Further studies with larger samples and longer follow-up are needed.
