Morphological Changes Of Femur During Medial Compartment Knee Osteoarthritis And Its Influence On Decision-making And Curative Effect Of Osteotomy By Three-dimensional Finite Element Analysis

Knee osteoarthritis(KOA)is a degenerative disease of bone and joint.Its pathogenesis includes immunity,strain,metabolism,biomechanics and other factors.According to the location of the lesion,it can be divided into medial compartment type,lateral compartment type,patellofemoral type and total joint type,among which medial compartment type is the most common type of KOA,often accompanied with varying degrees of knee varus deformity.According to the theory of"nonuniform settlement",the collapse of the medial tibial plateau is due to the low bone hardness and the high stress of the tibial plateau.The collapse will occur under long-term and high load.The collapse will cause the force line of the lower limbs to move to the medial side to further increase the compliance of the medial plateau.The above process is mutual cause and effect,ultimately accelerating the wear of the medial compartment,and forming the medial compartment KOA.This theory explains the causes of KOA from the perspective of biomechanics.Based on this theory,high tibial osteotomy(HTO),proximal fibular osteotomy and other operations are aimed at correcting the wrong mechanical alignment at the distal of the knee joint,and finally to restore the normal alignment of the lower limbs.HTO has been widely used in young and middle-aged patients with moderate KOA,and has achieved good clinical results.Due to the simple operation,low cost and good clinical effect of HTO,it is almost the only operation for the treatment of medial compartment KOA.Considering that the knee joint is composed of femur and tibia,the medial condyle of femur is in direct contact with the medial platform of tibia,and the stress of the medial platform of tibia also reacts on the medial condyle of femur,that is,the medial condyle of femur bears more than the lateral condyle of femur.Based on the theory of microfracture and bone remodeling,the large stress side should undergo morphological changes,but there is no relevant data to support this view.With the development of X-ray film technology,the full-length X-ray film of the lower extremity is more and more used,especially in the surgical planning of the lower extremity with osteoarthritis prepared for total knee arthroplasty(TKA).Because the goal of TKA is to recover the lower extremity alignment,the preoperative surgical planning is to accurately find the insertion point and angle of the intramedullary positioning rod during the operation,and select the suitable prosthesis.It has been reported that distal femoral osteotomy(DFO)is used to treat genu varus caused by femur,but the vast majority of DFO is used to treat genu valgus.Whether there is femoral mechanical axis varus in medial compartment KOA,and whether there is universality is a blind area.The mechanical alignment of the femur can also be measured from the full-length X-ray of the lower limb.In this study,the incidence and distribution of the femoral varus in the medial compartment KOA were obtained through the measurement of the total length X-ray of the lower limb of a large number of patients with different degrees of genu vara,and the specific bone morphological changes of the femoral mechanical axis varus were explored.The theory of "nonuniform settlement"has pointed out that the collapse of the tibial plateau makes the alignment move medially and aggravates the burden of the medial plateau.A large number of biomechanical experiments were also carried out to verify the stress changes in the knee joint when the tibial plateau collapsed.But the biomechanical experiment mostly uses the joint specimen which cuts the femur and tibia.The application of stress on this specimen is far from the starting and ending point of the force line under physiological state and the position passing through the knee joint level,which can not represent the true stress state very well.Moreover,even if the full-length specimen of the lower limb is obtained,it is difficult to preserve,and the too long height is difficult to assemble on most biomechanical machines.Therefore,the biomechanical experiment of knee joint is in an awkward state.With the development of digital technology,finite element(FE)analysis of biomechanics has been widely used in the field of biological science.Compared with traditional biomechanical experiments,FE has good operability and is not constrained by experimental equipment and experimental conditions.As long as the model is established accurately,the data obtained by the operation has high stability,and as long as the settings are made before the operation,the data of multiple effect indicators can be obtained at the same time.These characteristics of finite element can make up for the defects of biomechanical experiment.For the biomechanical experiment of knee joint,FE analysis is an ideal method.In this experiment,the standard three-dimensional model of the full-length of the lower limbs and the three-dimensional model of the full-length of the lower limbs with different degrees of femoral varus were established by image collection and relevant image processing software.The model was analyzed in the FE method to study the impact of the femoral varus on the biomechanics of the knee joint,so as to provide effective data support and theoretical basis for knee-salvage treatment.Part 1 The influence of femoral mechanical axis varus on the alignment compartment knee osteoarthritis based on bone morphologyObjective:Through the measurement of a large number of X-ray films of the full length of the lower limbs of the knee joint with varus of different degrees,the distribution of the femoral mechanical axis varus in the medial compartment KOA was counted;the influence of the femoral mechanical axis varus on the genu varus was discussed;the image classification based on the bone morphology of the medial compartment KOA was carried out to provide the theory basis and data supportfor the diagnosis and treatment of the medial compartment KOA.Methods:X-ray films were collected from patients with non-traumatic knee joint pain from January to July 2017 according to the inclusion exclusion criteria.The measurement indexes were:the distal mechanical medial angle of the femoral axis(m MDFA),the medial proximal tibial angle(MPTA),the joint line converting angle(JLCA),KL classification.Based on femoral varus,tibia varus and JLCA,the collected lower limbs were divided into four types,and the incidence of femoral varus,tibia varus and JLCA augmentation in the lower limbs of genu varus and the constituent ratio of various types of deformities were counted respectively,the incidence of genu varus of four types and the constituent ratio in different degrees of KL classification were counted,and the physical constituent factors of genu varus were analyzed.Results:The incidence of femur varus in genu varus was 24.77%in males and 24.57%in females,that of tibial varus was 97.21%in males and95.54%in females.Among the four types,type I(single tibia varus)accounted for the majority,73.07%in males,72.16%in females,that of type?(tibia varus+femur varus)was 24.15%in males and 23.38%in females.Regression analysis showed that m MDFA,MPTA and JLCA together affected HKA by 78.2%(?was-0.491,0.487 and-0.463,respectively,P<0.01)in males,and 81.2%(?was-0.464,0.560 and-0.450,respectively,P<0.01)in females.Conclusion:Femur varus is an important morphological component of genu varus,but its incidence is low,the diagnosis is complex(it needs to be measured on the full length X-ray of the lower extremity),and the degree of varus is small,which has not been paid enough attention in clinical.The image classification system based on the morphological changes of the lower limbs considers the changes of femur varus,tibia varus and joint space comprehensively,which has a clear guiding significance for the operation strategy selection of knee-salvage treatment.Part 2 The dynamic deformation of femur in medial compartment knee osteoarthritisObjective:To find and discriminate the specific deformation of the femur that can cause the femoral mechanical axis to turn medially through the measurement of X-ray film of the lower extremity;to analyze the relationship between the deformation,age and gender;to explore the dynamic deformation law of the femur,so as to provide theoretical basis and data support for the diagnosis and treatment of the medial compartment KOA.Methods:Full-length X-ray films of the lower limbs were used and selected according to the inclusion and exclusion criteria.The measurement indexes were hip knee ankle angle(HKA),m MDFA,neck shaft angle(NSA),femur bending angle(FBA),anatomical medial angle of distal femoral axis(a MDFA).The measurements were divided into three groups of<40,40-60,and>60 according to different age groups.The data of the three groups were compared.Regression analysis was performed with m MDFA was used as the dependent variable,and NSA,FBA,a MDFA were as independent variables.Results:In females,age was significantly correlated with m MDFA,FBA and a MDFA(r=-0.076,0.253,0.141,respectively,P<0.01),FBA was significantly correlated with NSA and a MDFA(r=0.312,0.233,P<0.01).A negative correlation(r=-0.065,P<0.05)was found when FBA was the controlling factor,partial correlation analysis was made between age and NSA.However,in males,there was no significant correlation between age and all variables.The morphological components of femoral mechanical axis varus(m MDFA decrease)in females are NSA,FBA and a MDFA.When m MDFA was used as the dependent variable,and NSA,FBA,a MDFA were as the independent variables,the regression analysis was made,the adjusted R-square was 0.722,and the standardized beta values were NSA 0.071,FBA-0.528,and a MDFA 0.803,respectively.Conclusion:During medial compartment KOA,there is dynamic deformation of femur in females.The deformation includes the changes of NSA,FBA and a MDFA.The superposition of these changes will eventually lead to the femoral mechanical axis varus.Moreover,the deformation of the femur involves the change of the whole femur rather than the local part.The bending of the femur will lead to the corresponding deformation of the proximal and distal ends of the femur.The deformation of male femur is not obvious.Part 3 The finite element analysis of the effect of femoral varus on thebiomechanics of knee joint in medial compartment osteoarthritis Objective:To establish the standard FE model of the whole knee joint;to establish the model of femur varus 0°,5°,10°,15°,tibia varus 0°,5°,10°,15°,20°,25°,and to form 24 kinds of varus FE models of the lower limbs in different situations;to do the biomechanical experiment on the human lower limb specimens to get the bone strain value to verify the validity of the FE model;to analyzes the influence of the different combinations of femur varus and tibia varus on osteoarthritis induced factors such as knee joint stress and contact area,so as to explore the role of femoral varus in the occurrence and development of KOA.Methods:An embalmed specimen of adult male full-length lower limb was used(less than 1 month).After being wrapped and fixed with thermoplastic film,X-ray,CT and MRI were performed,and the documents were saved in DICOM format.The specimens were fixed on the BOSE biomechanical testing machine.Five sites were found on the tension side and another five on the pressure side.Strain gauges were pasted and the strain values of 10 points were recorded with digital strain gauges under the vertical load of 100N?200N?300N?400N?500N.The three-dimensional FE models of the whole lower limbs were established by using the software of Mimics,Geographic Studio,Unigraphics NX and Abaqus,as well as 24three-dimensional FE models with different degrees of femoral varus and different combinations of tibia varus.The effects of femoral varus on the maximum Von Mises stress,the joint contact area and the area of joint"abnormal stress"were analyzed.Results:the regression equation y=1.025x+0.025,R~2=0.969,which showed that the model was effective.On the basis of the same tibia varus,the greater the femur varus,the greater the maximum Mises stress in the joint,the smaller the joint contact area,and the area of"abnormal stress"is on the rise.The regression analysis of the degree of varus of femur and tibia with the maximum Mises stress,the joint contact area and the area of"abnormal stress"was carried out.The beta values were 0.789 and 0.556,-0.776 and-0.406,0.388 and 0.713,respectively(P<0.05).Conclusion:The FE model can simulate the biomechanical characteristics of the knee joint of normal lower extremity very well.Femur varus can further increase the maximum von Mises stress of knee joint,reduce the joint contact area and increase the area of"abnormal stress"on the basis of the original tibia varus,and its influence is as important as tibial varus.Part 4 The finite element analysis of the impact of femur varus on the biomechanics of knee joint after high tibial osteotomyObjective:To establish three kinds of full-length FE models of lower limbs with mixed varus of femur and tibia after double osteotomy of femur and tibia,undercorrection of HTO and overcorrection of HTO;to analyze and compare the differences of knee joint stress,joint contact area and other related indexes of osteoarthritis after three kinds of osteotomy,and to explore the effect of femoral varus on HTO.Methods:Using the FE model of the whole knee joint of the lower extremity established before,three kinds of FE models of the whole knee joint of the lower extremity were established:after the double osteotomy of the femur and tibia,undercorrection of HTO and overcorrection of HTO,the maximum Von Mises stress,the contact area and the"abnormal stress"area of the joint were analyzed under the vertical load of 500N,the maximum Von Mises stress on the collateral ligament,and the maximum Von Mises stress on the steel plate.Conclusion:The presence of femoral varus can lead to two kinds of situations of HTO:undercorrection and overcorrection.The influence on the biomechanical index of the joint will increase with the increase of the degree of femur varus.Femur varus can accelerate the wear of the joint after HTO,increase the area of possible wear and lead to joint relaxation.Therefore,for patients with medial compartment KOA with mixed varus of femur and tibia,DFO and HTO should be performed to obtain the best postoperative treatment effect and reduce the possibility of failure.