A Study Of Femoral Geometry For The Chinese AVN Population With A Novel Design Of AVN-Specialized Stem

Background:With the development of biomechanics and continuous improvement of prosthetic design in THA,the common failures of prosthesis in the past,such as prosthesis fracture and dislocation,rarely occurred.As long as the implant procedure is correctly done,high success rates can be achieved either in short term or long term follow-ups.Aseptic loosening of prosthesis has become the main reason for failure. From the prospect of prosthesis design,increasing the prosthesis and bone adaptation to reduce the initial micromotion and increase long term bone ingrowth is the only way to achieve long term fixation.This kind of adaptation is determined by both the shapes of medullary cavity and prosthesis.Therefore it must incorporate the shape of femoral medullary cavity into prosthesis design considerations.Research for the factors which affect variety of medullary cavity has become a valuable and scientific trend.In addition, many studies of patients with AVN showed plenty of special characteristics,such as age distribution and bone quality.Objective:To study the geometric features of proximal femur for the Chinese AVN population,in order to prove the existence of special characteristic of proximal femur for the disease and then develop an AVN-specialized stem evaluated by a validated finite element analysis(FEA).Methods:1.The author investigated the standard X-ray data of 127 cases(179 hips) with definite diagnosis of AVN to provide anatomical references for this disease.At the same time,we conducted a meta-analysis of anatomical studies of normal proximal femur data,including the section of LT+20,LT,LT-20 and CFI to identify the potential difference between AVN and normal population.Furthermore,the author also performed a comparison of proximal femur canal curve between AVN and traumatic FNF(as a substituent of normal population).2.With the help of modern CAD technology,the stem was designed by the medial,lateral,anterior,posterior canal curves and consummated by the CT scanning data.3.In this FEA study:â‘ A validated FEM was set up by CAD software SolidWorks and FE software Ansys,â‘¡the features of stem was evaluated in respects of fill,fit and section stress distribution,â‘¢the comparison study among AVN stem and another two common-used prostheses, including fill status,stress distribution of medial proximal femur,max micromotion and percentage at critical micromotion point.Results:1.The author gained a large series data of AVN proximal femur and indentified the changes of AVN population at the plane of LT+20,LT,LT-20. Furthermore,the difference of canal cures was found in comparison of traumatic FNF and AVN.As a result,a developed stem special for AVN patient does not only posses scientific meaning but also meet the demand of market.2.A novel AVN stem was designed with the characteristics of canal curve.3.A validated FEM of stem replacement was set up in realistic form,integritive structure to simulate the load for artificial hip stems,so that it can be well used to assess and verify the biomechanical characteristics of the new prosthesis design.AVN stem showed a better match feature(fit & fill) than the Versys prosthesis,but the fill status of AVN stem did not overweigh Fitmore prosthesis at some plane.In the stress analysis of medial cortex,Fitmore showed higher stress than AVN stem in the proximal 2 cm area,but the stress did not drop back quickly after it achieved the highest value.In the following fretting test,the largest micromotion of Fitmore was more than 150 microns,and the area with micromotion over 150 microns occupied 4.5%in the medio-proximal and medio-distal part of stem.Over 61.2%of bone ingrowth area is not reliable,while AVN stem is more likely to gain the initial stability and more beneficial to long term bone ingrowth with no micromotion over 150 microns.Conclusions:1.This study enriches the data for proximal femur anatomic parameters of AVN population.2.Newly designed AVN-specialized stem does not only posses scientific meaning but also meets the demand of market.3.A validated FEM of stem replacement was established,it is beneficial to assess and verify the biomechanical characteristics of the new stem design.4.The AVN stem confirmed by FEA was especially adaptive for AVN patient with features of good match and stress distribution in the proximal femur,which predicted better initial stability and long term bone ingrowth.