A Computational Framework for Modelling Subject Specific Changes in Knee Ligaments and Tibiofemoral Contact Associated With Varus Deformity.

Varus deformity is a pathological knee condition described by outward bowing of the joint and increased medial compartment loading, both of which contribute to the development and progression of knee osteoarthritis. This study presents a subject-specific musculoskeletal modelling framework to investigate ligamentous characteristics and tibiofemoral contact mechanics for subjects having a varus deformity. A cohort of osteoarthritic subjects with varus deformity and undergoing total knee replacement surgery was analyzed in a standing posture. For each subject, musculoskeletal models with subject-specific knee joint anatomy were developed. A Taguchi-based experimental design was implemented to quantify the influence of individual ligament group slack lengths on the varus alignment. Subsequently, subject-specific ligament slack lengths combinations were predicted using a search-based optimisation that minimises the muscle-volume-weighted sum of squared muscle activations. The MCL-G and LCL-G groups were identified as the dominant influencers of varus angles. Optimisation revealed that specific varus alignments were associated with distinct laxity of medial and lateral soft tissue. These ligamentous adjustments corresponded to a significant medial shift in the tibiofemoral contact centre relative to a neutral alignment. Furthermore, higher degrees of varus malalignment correlated with a substantial increase in the mean total knee joint reaction force and a concurrent increase in the knee adduction moment. The proposed framework provides a subject-specific in silico approach for quantifying ligament adaptations and contact forces associated with varus deformity.