Biomechanical Analysis of Femoral Stem Features in Hinged Revision TKA with Valgus or Varus Deformity: A Comparative Finite Elements Study

Abstract

Featured Application: The present study intends to help and support clinicians and specialists in the decision process concerning the length and type of stems to use in case varus–valgus deformity is present in a patient. Hinged total knee arthroplasty (TKA) is a valid option to treat patients during revision of an implant; however, in case of varus/valgus deformity, the force transmission from the femur to the tibia could be altered and therefore the performance of the implant could be detrimental. To be able to evaluate this, the goal of this study was to investigate, using a validated finite element analysis, the effect of varus/valgus load configurations in the bones when a hinged TKA is used. In detail, short and long stem lengths (50 mm, and 120 mm), were analyzed both under cemented or press-fit fixation under the following varus and valgus deformity: 5°, 10°, 20°, and 30°. The main outputs of the study were average bone stress in different regions of interest, together with tibio-femoral contact pressure and force. Results demonstrated that changes in the varus or valgus deformity degrees induce a change in the medio-lateral stress and force distribution, together with a change in the contact area. The effect of stem length and cement do not alter the tibio-femoral contact biomechanics but its effect is mainly localized in the distal femoral region, and it is negligible in the proximal regions.