High tibial osteotomy (HTO) is a surgical procedure to treat unicompartmental osteoarthritis through correcting the lower limb alignment. Biomechanical models have been used for making simulation based decisions on the optimal alignment correction to achieve during HTO. However, in many models generated with this aim, the role of soft tissues has been neglected. Our objective was to investigate the impact that the connective tissues can have on simulation-based decisions.