Effect of Joint Line Elevation after Posterior-stabilized and Cruciate-retaining Total Knee Arthroplasty on Clinical Function and Kinematics

BACKGROUND: Joint line (JL) is a very important factor for total knee arthroplasty (TKA) to restore. The objective of this study was to evaluate the early clinical and kinematic results of TKAs with posterior-stabilized (PS) or cruciate retaining (CR) implants in which the JL was elevated postoperatively. METHODS: Data were collected from patients who underwent TKA in our department between April 2011 and April 2014. The patients were divided into two groups based on the prosthesis they received (PS or CR). At 1-year postoperatively, clinical outcomes were evaluated by the American Knee Society (AKS) knee score, AKS function score, and patella score. In vivo kinematic analysis after TKA was performed on all patients and a previously validated three-dimensional to two-dimensional image registration technique was used to obtain the kinematic data. Anteroposterior (AP) translation of the medial and lateral femoral condyles, and axial rotation relative to the tibial plateau, were analyzed. The data were assessed using the Mann–Whitney test. RESULTS: At time of follow-up, there were differences in the AKS knee scores (P = 0.005), AKS function scores (P = 0.025), patella scores (P = 0.015), and postoperative range of motions (P = 0.004) between the PS group and the CR group. In the PS group, the magnitude of AP translation for the medial and lateral condyle was 4.9 ± 3.0 mm and 12.8 ± 3.3 mm, respectively. Axial rotation of the tibial component relative to the femoral component was 12.9 ± 4.5°. In the CR group, the magnitude of AP translation for the medial and lateral condyle was 4.3 ± 3.5 mm and 7.9 ± 4.2 mm, respectively. The axial rotation was 6.7 ± 5.9°. There were statistically different between PS group and CR group in kinematics postoperatively. CONCLUSION: Our results demonstrate that postoperative JL elevation had more adverse effects on the clinical and kinematic outcomes of CR TKAs than PS TKAs.