Integral Rehabilation of arms and legs using biomechatronics

Introduction:  The biomechanical response of cartilage and prostheses in cases of unicompartmental osteoarthritis by means of finite element method remains issues for attention. Linear elastic isotropic models are still used for cartilage analysis, in spite of its viscoelastic nature and changes in properties related to osteoarthritis, this could affect the biomechanical response of the knee joint and prosthesis.  

Methods:  Cartilage biomechanics response was studied using a non-linear finite element model and considering a viscohypoelastic material model for cartilage of knees under unicompartmental osteoarthritis. Femur, tibia and cartilage covering the condyle and tibial plateau were considering as deformable bodies in the knee model. Thus, the biomechanical response of the viscohypoelastic model for cartilage was studied applying a non-constant loads related to the knee gait cycle. Results were compared with linear elastic models of previous studies.  

Results:  Stress relaxation, creep and delay in recovery effects over time were observed in the biomechanical response of the viscohypoelastic cartilage model. In addition, comparing the behavior of this with linear elastic models currently used in other studies showed that the model used in this work behaves elastically to applied loads in a short period of time while it preserves the viscoelastic effects over time. Furthermore, this comparison showed that the stresses and strains obtained using the viscohypoelastic model are larger, up to 35.14% and 93.60%, respectively.  

Discussion:  Our findings suggest that the material model considered for cartilage in this study provides a more real behavior. Also, the viscoelastic nature and cartilage properties under unicompartimental osteoarthritis should be considered in finite element analysis of cartilage and unicompartmental knee prostheses, since the displacements and stresses related to the cartilage material model could affect the biomechanical response of tissues and the mechanical performance of prosthesis in the knee joint.