Interface Mechanics And Medium And Long Term Stability Analysis Of Uncemented Hip Prosthesis

The biological femoral stem can effectively avoid prosthesis failure caused by bone cement fatigue and bone cement particles.It is widely used in young patients and people with high activity intensity.In biological femoral stem,bone ingrowth is the premise of long-term stability of the prosthesis.However,the bone ingrowth process is affected by many factors,among which the initial stability and bone remodeling will significantly affect the process,and even cause the risk of prosthesis failure.To reduce the risk of failure of the biological femoral stem,this thesis takes the hip joint as the research object,establishes the finite element model of the femur-prosthesis for the initial stability of the biological femoral stem,and studies the influence of the percussion process on the initial stability of the femoral stem.The effect of the initial stability on the interface tissue percentage and the interface mechanical properties were studied based on the finite element method and the bone ingrowth algorithm,and the trend of the stability of the prosthesis at different stages of bone ingrowth was further explored.Combining the theory of adaptive bone remodeling and the femoral-prosthesis finite element model,the influence of postoperative gait changes on bone remodeling was analyzed.The research work of the thesis aims to provide guidance for the formulation of the preoperative implantation plan of the biological femoral stem,the design and optimization of the prosthesis,and the rehabilitation of postoperative patients.The research work of the thesis mainly includes the following three aspects:To clarify the stability of biological prosthesis,a finite element model of femur-prosthesis was developed.The effect of hammering force and times on the stability of the prosthesis were studied.The relationship between the initial stability of the femoral stem and the hammering force and times were revealed.The results show that: the hammering force of 4-8 k N will not damage the femur and femoral stem.The initial stability of the femoral stem increased with the increase of hammering force.In un-interference conditions,the micro-motion of 25-48 μm is produced on the contact surface by the hammering force of 4-8 k N under gait motion.The micro-motion of 42-85 μm under stair climbing motion.The existence of interface interference could significantly reduce micromotion.In 50 μm interference condition,the micro-motion of the contact surface is below 30 μm,and only a large micro-motion occurs at the end and near the contact surface.The increase of impact times will not affect the interface micromotion.For the long-term fixation of the biological prosthesis,a micro-contact interface finite element model of porous coating prosthesis was established based on the theory of mechanical regulation of tissue differentiation and the theory of bone remodeling.Bone ingrowth simulation is based on MATLAB,PYTHON,and ABAQUS.The trends of bone ingrowth at different micro-motion were studied,and the relationship between interface micro-motion and the percent of tissue and interface mechanical properties were analyzed.Based on these,spring element was applied to simulate the mechanical properties after bone ingrowth,and the relationship between interface mechanical properties and spring stiffness were established.The stability of the prosthesis after wove bone ingrowth and remodeling were analyzed.The result shows that interface micro-motion has a dual effect on bone ingrowth.At the initial stage of bone ingrowth,the increase of micro-motion leads to the increase of fibrous tissue and the decrease of bone tissue in the coating,and the decrease of the interface mechanical properties.At the remodeling stage,micro-motion promotes the transformation of woven bone to lamellar bone.After bone ingrowth,the stability of the prosthesis was improved and the interface micromotion was reduced.The effect of bone ingrowth at the point of greater micro-motion is greater than that at the point of lower micromotion.For the bone remodeling around the prosthesis after hip replacement,two finite element models were established to represent the pre-replacement and post-replacement based on adaptive bone remodeling theory,and gait level after the replacement was considered.The variation trend of bone density around the implant was studied.It reveals the influence of gait level in postoperative initial and long-term stages on bone density.The result shows that the improvement in postoperative gait movement has a positive effect on bone remodeling.In the postoperative initial stage,obvious variation exists in constant gait and change gait groups.The maximum difference occurs in the low gait group,resulting in the reduction of bone density of41% in the greater trochanter region.The improvement of gait level promotes the enhancement of bone density in the proximal and middle end of the prosthesis,resulting in the increase of bone density(47%).Long-term gait recovery promoted an increase of 2%-9% in bone density at the middle and end of the prosthesis and inhibited the decrease of bone density in the proximal area of the prosthesis,and the inhibitory effect increased with the increase of gait movement.