The Three-dimensional Finite Element Analysis On The Diaphyseal-modular Prosthesis In Proximal Femur Reconstruction

The diaphyseal modular prosthesis was one of common methods for reconstruction of bone defect in proximal femur.The application time of prosthesis was short and the doctor didn't know the stability of the prosthesis in reconstruction of bone defects,furthermore,the influence of Proximal stem's length and additional side plate on the stability of prosthesis also required further study.In order to provide theoretical basis on selecting diaphyseal modular prosthesis and optimizing the design of the prosthesis,this paper analyzed the mechanical properties of diaphyseal modular prosthesis in proximal femur reconstruction and verified the biomechanical stability of diaphyseal modular prosthesis,furthermore,this paper further explored the impact of changing in the length of Proximal stem and additional side plate on prosthesis stability.First,the CT scanning data and 3D reconstruction software was used to reconstruct the cortical bone and cancellous bone of intact femur and different size parameters diaphyseal modular prosthesis model.Then,these models were imported into the finite element analysis software ANSYS to simulate segmental resection and prosthesis implantation.Finally,we established the finite element model of femur-prosthesis with assembled relationship.This experiment simulated the loading condition of one foot standing stance during walking.The contact condition simulated no sliding interface of the prosthesis and the bone cement,namely the interface of bone and cement and the interface of prosthesis and cement were set as bonding contact.To benefit the comparison analysis,according to the variation of prosthesis parameter,we set non-plate group prosthesis system,single nail group prosthesis system and three nails group prosthesis system.Through the observation of medial and lateral stress distribution of proximal femur and the prosthesis and bone cement of different length stem prosthesis in non-plate group,we discussed the impact of changing in the length of Proximal stem on prosthesis stability.Under the same condition of proximal stem length,we observed medial and lateral stress distribution of proximal femur and the prosthesis in non-plate group and single nail group and three nails group,we discussed the impact of additional side plate on prosthesis stability.The numerical results showed that the stress distribution of the proximal femur was significantly affected by changing in the length of proximal stem.Compared with normal femur,the peak stress of medial proximal femur decreased significantly after bone reconstruction and different degrees of stress shielding were produced around the osteotomy interface.The peak stress of medial proximal femur decreased 15.9%,25.2%,32.2%,36.5% after 4cm,5cm,6cm,7cm long stem prosthesis reconstruct the defection of proximal femur.We analyzed the stress distribution of proximal femur in non-plate group and single nail group and three nails group,and we found that the stress of proximal femur in three nail group and single nail group were significantly lower than the stress of proximal femur in non-plate group,however,there was a bit difference in three nail group and single nail group.The stress distribution of prosthesis stem showed that the stress gradually increased from proximal to distal and reached the maximum value in distal of the stem.For stability,the prosthesis with plate aided is better than the prosthesis without p late.But the serious stress shield will be presented in proximal femur which will go against with the stability of the prosthesis in long-term.Due to the shorter prosthesis acquired more physiological condition,the stability of shorter shaft prosthesis may worse than the longer shaft prosthesis in long –term,but better in short –term.