Effects of Subject-Specific Robot-Guided Off-Axis Stepping Training in Individuals With Medial Knee Osteoarthritis

Elevated peak knee adduction moment (pKAM) has been identified as a critical biomechanical factor driving medial knee osteoarthritis (KOA) initiation and progression, while impaired frontal plane neuromuscular control contributes to joint instability and accelerated disease advancement. Although gait modification strategies using real-time biofeedback have demonstrated pKAM reductions, most interventions apply the same modifications to all individuals and do not fully evaluate the combined effects of KAM reduction training and neuromuscular control training on joint loading, neuromuscular stability, and functional outcomes. A subject-specific robotic off-axis elliptical training system was developed to improve frontal plane neuromuscular control and reduce pKAM through foot progression angle (FPA) modification individually. Effects of the six-week subject-specific off-axis stepping training in reducing excessive knee loading and improving frontal-plane stability were demonstrated through 18 supervised training sessions in thirteen individuals with medial KOA. The training system perturbed the FPA slowly during continuous stepping without the subject noticing the perturbation to identify the optimal FPA for a targeted pKAM reduction. Furthermore, the optimized FPA was combined with real-time three-dimensional knee moment feedback and frontal plane footplate free-sliding challenges were used in the training. After the six-week training, participants demonstrated significant reductions in pKAM, sliding instability and maximum lateral sliding distance, while stepping speed increased significantly. Clinical outcomes showed improvements in KOOS Symptoms and Pain subscales. Functional performance enhanced in the 20-meter walk test, 30-second sit-to-stand test, overground gait velocity, and bilateral step length. Importantly, improvements in frontal plane stability metrics were maintained at six-week follow-up, suggesting lasting neuromuscular adaptations. The results indicate that robotic off-axis elliptical training with FPA optimization can potentially be used as a subject-specific therapeutic and research tool to train individuals with medial KOA for concurrent reductions in medial compartment overloading and improvements in frontal-plane neuromuscular control during functional weight-bearing stepping movements.