Pressure change at ankle joint in supramalleolar osteotomy with or without fibular osteotomy according to different types of varus ankle

The need for additional fibular osteotomy (FO) when performing supramalleolar osteotomy (SMO) in the varus ankle arthritis (VAA) is controversial. Some cadaveric studies have been performed to prove this; however, it is difficult to implement deformities including talar tilting and translation in cadavers. In this study, we created a model of VAA with the tilting and translation using three-dimensional (3-D) finite element (FE) analysis and analyzed the results of SMO with or without FO depending on the types of VAA. The validated normal foot and ankle 3-D FE model was constructed including the ankle cartilages of the talar dome and tibia plafond. The VAA models were determined and reconstructed by following the classification of VAA, VAA with medial translation for stage 3a, VAA with varus tilting (7.5 degrees) for stage 3b. The postoperative SMO models (SMO with and without FO) were reconstructed by corresponding to each VAA models. The FE analysis conditions were commonly applied. The boundary condition of ankle joint was defined as "sliding condition" and applied 0.002 friction coefficient to realize lubricative property. Loading condition was assumed as a two-leg standing position and half of the subject body weight (325 N) was loaded on center of ground to vertical direction. Contact pressure changes were predicted at the medial ankle cartilage. As a result, in VAA with medial translation, isolated SMO may provide sufficient pressure reduction at the medial ankle joint. However, in VAA with varus tilting, SMO combined with FO could appropriately relieve concentrated pressure at the medial ankle joint.