Establishing the tolerance range of joint line orientation angle: a finite element study

With the emergence of new alignment techniques such as kinematic alignment (KA) and functional alignment (FA), personalized joint line restoration has gained attention, yet its theoretical underpinnings remain underdeveloped. This study aims to investigate the impact of different joint line orientation angles (JLOAs) on knee compartment loads during total knee arthroplasty (TKA), thereby establishing a biomechanical tolerance range for JLOA and providing theoretical guidance for new alignment techniques.

We collected computed tomography (CT) data from three patients with severe knee osteoarthritis (KOA) and established standard mechanical alignment (MA) finite element models for each case. Keeping hip-knee-ankle angle (HKA) neutral, we constructed a series of JLOA models from -9 ° to +9 ° (Positive numbers represent varus, negative numbers represent valgus). Subsequently, the maximum stress on the polyethylene liner surface was calculated with ANSYS in three positions: two-legged stance, one-legged stance, and squat. Finally, a mathematical model of maximum stress trend was established through statistical analyses.

In the three patients' models, during both the two-legged and one-legged standing positions, the maximum stress fluctuated smoothly from -3 ° to +4 °, while the maximum stress increased markedly when JLOA reached -4 ° and +5 °. In the squatting position, the stress increased markedly when it exceeded the -3 ° to +6 ° range. Quadratic regression analysis confirmed that all patient positions exhibited U-shaped curves (p < 0.05). T-tests comparing the three position tolerance ranges (-3° to +4 °) revealed that the two-legged standing position exhibited the highest stress increase ratio (46.01%, Cohen's d = 2.50) in the non-tolerance range. A three-way ANOVA confirmed that the tolerance range effect remained consistent across patients (p = 0.839), while stress levels varied significantly between patients (p < 0.001).

This in silico study demonstrated that the polyethylene liners maintain relative biomechanical homeostasis within the JLOA range of -3 ° to +4 °. It is recommended that the JLOA for personalized reconstruction can be controlled within this range, serving as biomechanical theoretical guidance for new alignment techniques.

IV; biomechanical computational study.