Knee varus malalignment is one of the major drivers of osteoarthritis progression, increasing medial compartment overload and progressively impairing joint function. In this prospective study, we investigated how high tibial osteotomy (HTO) reshapes the internal loading environment of the knee during demanding daily activities such as walking, stair ascent, and stair descent.Using subject-specific musculoskeletal models combined with personalized radiographic measurements, our findings show that HTO does far more than simply correct limb alignment. The procedure significantly redistributes knee contact forces from the medial to the lateral compartment, reducing overload during the most mechanically challenging phases of movement. Notably, these biomechanical changes were especially evident during stair-related tasks, highlighting their potential value as sensitive indicators of surgical effectiveness.The study also reveals an important clinical insight: improvements in pain and patient-reported function after HTO are not explained solely by reductions in joint loading. While patients experienced substantial functional recovery and symptom relief, the relationship between biomechanical changes and subjective outcomes remained weak, suggesting that recovery is shaped by a broader interplay of neuromuscular, functional, and perceptual adaptations.

By combining advanced biomechanical modelling with clinical outcomes, this work provides new insight into how HTO influences knee mechanics in vivo and offers a deeper understanding of the complex relationship between surgical realignment, joint loading, and patient recovery.