Individualized multimodal integration of optimized dual fluoroscopic imaging registration and finite element modeling for knee joint stress during stair ascent.

Stair ascent imposes high mechanical demands on the knee, but the effect of stair height on internal joint stress remains unclear. This study developed a subject-specific workflow to quantify meniscal and cruciate ligament stresses during stair ascent in a female. One female ascended stair with five stair heights (120-200 mm). Dual fluoroscopic imaging system (DFIS), CT, motion capture, force plate, and EMG were integrated to obtain in vivo knee kinematics and muscle forces via OpenSim. These data drove a quasi-dynamic finite element model of the tibiofemoral joint to compute region-specific meniscal and anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) stresses at key stance phases. Meniscal stress increased with stair height and concentrated in the medial meniscus body between 25 and 50% of the support phase. PCL stress peaked early in stance and rose markedly with stair height, whereas ACL stress peaked at mid-stance and showed a more moderate height-dependent increase. This individualized multimodal framework enables realistic assessment of knee loading during stair ascent and identifies stair height as a key factor influencing meniscal and cruciate ligament stress in adults.