Evaluating The Change Of The Proximal Femoral Biomechanics Following Femoral Neck Shortening Based On Finite Element Analysis

Objectives:(1) To establish different types of proximal femoral neck shortening models by utilizing three-dimensional reconstruction software and to analyze the biomechanical changes of femoral neck shortening models by finite element method.Meanwhile, using the three-dimensions printing technique to validate the reliability of the finite element analysis results.(2) To demonstrate the bilateral proximal femur have no biomechanical differences with each other through finite element analysis of proximal femur of healthy adult males.(3) To evaluate the contralateral and ipsilateral proximal femoral biomechanical effects after femoral neck fracture treated with cannulated screws.Methods:(1) Collect the hip CT scanning data from a healthy adult male and import to the Mimics software to establish models with no shortening, femoral neck shorten4 mm, 8mm, 12 mm and 16 mm, of which group have five models and a total of twenty-five virtual proximal femurs. Meshing and material property assigning are carried out by using the pre-processing software Simpleware, then the manufactured models are importing to finite element analysis software Abaqus for mechanical load test, and the maximum stress, maximum coronal displacement, elements of the concentrated stress region account for the proportion of the whole model and the average elasticity modulus were obtained.(2) Collect the hip CT scanning data from7 healthy adult males, with the same experimental method above, to acquire the maximum and minimum stress, maximum and minimum strain, maximum coronal displacement and average elasticity modulus on the both sides of proximal femur.(3)Patients who suffered femoral neck fractures and fixed with cannulated screws from January 2012 to January 2014 were included in our study. To get the contralateral and ipsilateral finite element analysis results according to the experimental method above.By comparing gender, age, injured side and Garden classification to analyze the relation to the existence of femoral neck shortening or not after the internal fixation of femoral neck fractures.Results:(1) The maximum stress value of model with no shortening is(33.53 ±1.19)MPa, and significant difference were found in comparing with the shorten 4mm group, shorten 8mm group and shorten 12 group. The maximum coronal displacement of model with no shortening is(0.93 ± 0.07)mm, and the statistical significant difference were existed in comparing with the other groups. Elements numbers of the concentrated stress region account for the proportion of the whole model in no shortening group is(0.52 ± 0.02), which decreased significantly compared to the other groups. The average elasticity modulus in the concentrated stress region is(777.86 ±46.70)MPa, and gradually increased with the severity of shortening.(2) There is no statistical difference between the left side and right side in femoral neck length as well as the maximum and minimum stress, maximum and minimum strain, maximum coronal displacement and average elasticity modulus of seven healthy volunteers' proximal femurs.(3) A total of 90 femoral neck fracture patients are recruited in our research. There is no difference between the shortening >2mm group and shortening <2mm group in gender, injuried side and Garden classification. However, statistically difference were found in two groups regarding to the age. With the aggravation of the femoral neck shortening, the maximum stress and the maximum strain of the ipsilateral side increased compared with the contralateral side, and the maximum coronal displacement of the ipsilateral side decreased compared with the contralateral side. Despite the average elasticity modulus of the ipsilateral side is higher than the contralateral side, the difference is no statistically significant.Conclusions:(1) With the reduction of the femoral neck length, the biomechanical property of proximal femur change significantly. In addition, the mechanical test results of 3D printing models verify the reliability of the simulated finite element analysis results.(2) The age is considered to be a factor of femoral neck shortening following the internal fixation of the femoral neck fractures, and with the severity of shortening, the normal load-bearing structure of the proximal femur was changed evidently which may have an adverse effect to the hip function and is not conducive to the patient long-term functional recovery and life quality.