Changes in kinematic behavior and collateral ligament strain after medially stabilized TKA using a novel Intraoperative Navigation Platform: a cadaveric study

Objectives: This study aimed to analyze to what extent a novel intraoperative navigation platform (Next-AR, Medacta) for total knee arthroplasty (TKA) allows to restore the native knee joint kinematics and strains in the medial collateral ligament (MCL) and lateral collateral ligament (LCL) throughout a squatting motion. Material and methods: Computed tomography (CT) scans of 6 native cadaver legs were used to design patient-specific guides. Bony landmarks and virtual single-line collateral ligaments were identified to acquire real-time intraoperative feedback on bone resection, implant alignment, tibiofemoral kinematics, and collateral ligament elongations using the Next-AR system. The specimens were subjected to squatting (35°-100°) motion using a physiological ex vivo knee simulator while maintaining a constant vertical ankle load of 110N through active quadriceps and bilateral hamstring controls. Subsequently, each knee underwent a medially-stabilized TKA (Medacta) with mechanical alignment technique and was retested under the same conditions as in their native state. The tibiofemoral and patellofemoral kinematics, along with collateral ligament strains, were computed from 3D marker trajectories using a six-camera optical system (Vicon). MCL and LCL insertions—ant, mid, and post bundles—were identified in relation to bone-pin markers using a wand. Results: Both native and post-operative conditions exhibited similar tibial valgus orientation (Root Mean Square Error (RMSE = 1.7°), patellar flexion (RMSE = 1.2°), abduction (RMSE = 0.5°), and rotation (RMSE = 0.4°) during squatting (p > 0.13). However, a significant difference was observed in tibial internal rotation between 35° and 62° (p < 0.048, RMSE = 3.2°). MCL strains in anterior (RMSE = 1.5%), middle (RMSE = 0.7%), and posterior (RMSE = 0.8%) were closely matching in both conditions, showing no statistical differences (p > 0.05). Contrary, LCL strain in all bundles (RMSE < 4.6%) differed significantly from mid to deep flexion in both conditions (p < 0.048). Conclusion: The novel intraoperative Next-AR system not only targets planned knee alignment but also aids in restoring native knee kinematics and elongation of the collateral ligaments through real-time feedback.