In-Vivo kinematic evaluation of a new design total knee arthroplasty using dynamic RSA

Background: TKA posterior stabilized (PS) is the best surgical choice when the posterior cruciate ligament is unfunctional. The central cam stabilizes the anterior‐posterior translation. Moreover, the multi‐radius feature of the investigated implant makes a smooth transition throughout the range of motion and minimizes the anterior movement. Purpose/Aim of Study: The aim of this study is to describe the in vivo kinematics of the knee after PS Rotating Platform TKA implantation Attune (TM) Knee System, DePuy Synthes, J&J, Warsaw, IN, USA) using dynamic RSA. Materials and Methods: A cohort of 8 patients (mean age 67.6 yr) was evaluated at 9 months of follow up after the TKA. The patients were asked to perform a lunge: from the neutral position, the patient makes a step, then flexes, and return to the stand position. Kinematical data were evaluated relating to the flexion angle versus Internal‐External rotations, Varus‐ Valgus rotations and Antero‐Posterior translations and and low‐point contact areas of the femur with respect to the tibia, using the Grood and Suntay decomposition. Findings/Results: During the lunge phase, from 20° to 40° of knee flexion, an internal rotation of about 3° was evaluated. Then, from 40° to 80° an external rotation was observed. During the flexion, from 20° to 80° the kinematics indicates a posterior translation of the femur respect to the tibia. Then it turns to an anterior translation during the extension. Low Point kinematics showed a slight medial pivot from 50° to 55° of knee flexion. Conclusions: The kinematical results obtained with dynamic RSA showed that this prosthesis model is not affected by the paradoxical anterior translations during lounge motion task reported by other designs. Further studies are needed to evaluate the impact of different TKA designs on clinical results.