Effect Of Morphological Characteristics Of Femoral Intertrochanteric Fracture On Internal Fixation

Objectives 1.To compare the clinical efficacy of existing intramedullary and extramedullary internal fixation devices in treating intertrochanteric fractures by systematic review and meta analysis to determine appropriate treatment options;2.To analyze the stress distribution of the whole model and the internal fixation under different stress loadings by establishing a three-dimensional finite element model of different fractures between the femoral trochanter,and discusse the significance of the main fracture line and medial cortical support on fracture stability,and further discuss the possible site of fixation failure in clinical treatment;3.To Investigate the relationship between the main fracture line,the integrity of the medial cortex and the stability of the internal fixation of the fracture under intramedullary and extramedullary fixation through in vitro biomechanical experiments,and to determine the maximum axial load that each model can withstand,and explore the choice of weight-bearing timing and degree after fixation in different fracture modes to guide functional exercise of postoperation.Methods 1.According to the literature search strategy,we searched the PubMed,Embase and Cochrane Central Register of Controlled Trials to compare the therapeutic effects and key effect indicators of intramedullary or extramedullary fixations for intertrochanteric fractures including functional measurements and differences in adverse events.Cochran’s Q test and I~2 test were used to assess the risk of bias,and a subgroup analysis of fracture stability in the study was conducted to explore the source of heterogeneity;2.The normal adult femur CT data were selected,and the femur 3D model was reconstructed by Mimics 17.0 software.The surface treatment,meshing and material property assignment were performed in turn,the internal fixation was reconstructed,and the femoral internal fixation was assembled by Abaqus software.Different fracture internal fixation models were constructed using SolidWorks 2014software.According to the main fracture line including lateral superior medial inferior(LSMI)and medial superior lateral inferior(MSLI),the integrity of the medial femoral cortex which including medial cortical bone intact(MI),medial cortical bone patial defect(MPD)and medial cortical bone complete defect(MCD),and the internal fixation contained extramedullary(EM)and intramedullary(IM),the models were divided into 12 groups:EM-LSMI-MI group,EM-LSMI-MPD group,EM-LSMI-MCD group,EM-MSLI-MI group,EM-MSLI-MPD group,EM-MSLI-MCD group,IM-LSMI-MI group,IM-LSMI-MPD group,IM-LSMI-MCD group,IM-MSLI-MI group,IM-MSLI-MPD group,IM-MSLI-MCD group.We chose proximal femoral locking compression plate(PFLCP)as an extramedullary fixator,and proximal femoral nail anti-rotation(PFNA)as an intramedullary fixation implant.The hip joint loads(300 N,600 N,1200 N,1800 N)and constraints were applied to each group of finite element models to cover the daily activities of the postoperative patients,and the effective stress distribution and peak value of each model and the maximum displacement distribution of the coronal plane were all observed.3.Thirty-six femur cadaver bones soaked in formalin were selected,and 3 femoral specimens in each group were sequentially subjected to soft tissue removal,internal fixation implantation,fracture line and medial cortical defect modeling,X-ray film,embedding,strain gauge pasted.Measured the value of tip-apex distance(TAD).The Bose ElectroForce 3510 dynamic mechanical test system was used to apply the axial loads of 300 N,600 N,1200 N and 1800 N to the 12 sets of models.The displacement-load curve was analyzed and the axial stiffness of the model was calculated.The different strains of each set of strain gauges were recorded.The changes of strain values under different loads of each strain gauge at each point were recorded,and the maximum load at each fixed failure was compared.The cyclic load was applied to the un-failed model under 1800 N loading,and the initial and final displacements were recorded.Results 1.In the systematic review,43 prospective randomized controlled trials were included,including 11 internal fixation treatments involving 6911 patients.The meta-analysis showed that the functional scores of Gamma nail and SHS were lower than those of PFNA.There was no significant difference in mortality between patients with intramedullary and extramedullary fixation in terms of adverse events(P>0.05).Compared with SHS or PFN,Gamma nails increased the risk of intraoperative fractures;Compared with SHS,Gamma nails had a higher risk of late fractures;Compared with PCCP,SHS fixation significantly increased the risk of embolization;There were no significant differences in adverse events such as cut-out in other comparisons(P>0.05).2.Three-dimensional finite element analysis showed that,regardless of intramedullary(IM)fixation or extramedullary(EM)fixation,the overall stress distribution was concentrated in the area around the fracture line and the medial lower cortex of the femoral shaft.The maximum stress value of the internal fixation increased with the increase of the load and the degree of the medial cortical defect.The maximum stress of the lateral superior medial inferior(LSMI)fracture line model group was higher than that of the medial superior lateral inferior(MSLI)fracture line model group.The maximum stress of PFNA was always higher than PFLCP model under the same conditions.When the fracture line was lateral superior medial inferior,the maximum stress value in IM-LSMI-MCD group(318.8 MPa)was 45.7 MPa higher than EM-LSMI-MCD(273.1 MPa).Regardless of the fracture line,the PFLCP stress distribution was mainly concentrated in the femoral neck nail and its interface with the steel plate,when the fracture line was lateral superior medial inferior,the stress distribution was also concentrated around the distal cortical screw;while the PFNA stress distribution was mainly concentrated at the junction of the femoral neck nail and the main nail,the stress distribution was concentrated at the distal static interlocking nail when the fracture line was lateral superior medial inferior.The coronal displacement of the model increased with the increase of axial load and the degree of medial cortical defect.When axially loaded with 1800 N stress,the maximum displacement occurred in the EM-LSMI-MCD group at 6.90 mm.3.In this biomechanical study,36 cadaveric femur specimens,with an average age of67.53±6.45 years,bone mineral density T values was from-2.05 to 1.12,mean-0.49±0.96,the average TAD was 23.05±2.16 mm.The displacement-load curves showed that the displacement of PFNA fixation was smaller than PFLCP fixation under the same axial load.In the same internal fixation,when the degree of medial cortical defect was also the same,the MSLI fracture line model had smaller axial displacement than the LSMI fracture line.In each model,the IM-MSLI-MI group had the largest axial stiffness of 678.90±26.64 N/mm,and the fixation was the most stable.The axial stiffness of the EM-LSMI-MCD group was 79.83±2.52 N/mm which was the smallest,and the fixation is the most unstable.When the medial cortex was intact,each group can be loaded to 1800 N.However,when the medial cortex was partially deficient,the maximum axial load that the IM-LSMI-MPD group,EM-MSLI-MPD group,and EM-LSMI-MPD group can withstand was 1552.28 N,1431.08 N and 1192.81 N.When the medial cortex was completely deficient,the maximum axial loads that the IM-LSMI-MCD group,the EM-MSLI-MCD group,and the EM-LSMI-MCD group could withstand were 1361.78 N,1283.64 N,and 986.50 N,respectively.After the 1800 N cycle of IM-MSLI-MCD specimens,the displacement changed 6.165 mm.The proximal end of the fracture showed varus sinking,the fracture space disappeared,and the fracture of the distal cortex and the proximal end of the fracture could not be restored to the initial position after unloading.Conclusions1.There was no significant difference in the clinical efficacy of intramedullary and extramedullary fixation for intertrochanteric fractures,and no internal fixation was significantly superior to others.2.The overall stress distribution of each group was mainly concentrated in the surrounding area of the main fracture line and the lateral cortical bone in the lower part of the femoral shaft whether intramedullary or extramedullary fixation.When the main fracture line was lateral superior medial inferior,the extramedullary system had obvious stress concentration areas in the femoral neck nail and the plate,and distributed in the femoral neck nail,nail plate junction area and distal cortical screw;The stress of the intramedullary system was mainly concentrated in the junction between the main nail and the femoral neck nail and the distal static interlocking nail.When the main fracture line was medial superior lateral inferior,regardless of the fixation method,the stress was mainly concentrated in the surrounding area of the main fracture line,that was,the border between the nail plate or the junction of the femoral neck nail and the main nail,however,the degree of stress concentration was significantly lower than that of lateral superior medial inferior fracture lines.3.Intramedullary fixation had a smaller overall displacement than extramedullary fixation under the same fracture model and axial stress loading,indicating that intramedullary fixation was better than extramedullary fixation against varus stress.4.The distal end of the fracture could fully exert the mechanical support effect on the proximal end when the main fracture line was medial superior lateral inferior,it could effectively block the proximal varus of the fracture and reduce the internal fixation failure.5.In the case of intact medial cortex,regardless of the direction of the main fracture line,extramedullary fixation and intramedullary fixation could both achieve stable fixation,which could meet the daily activities such as standing and walking during the weight-bearing process;but when there was a defect in the medial cortex,regardless of the major fracture line,intramedullary fixation could achieve better fracture stability and internal fixation effectiveness than extramedullary fixation.And the patient must avoid weight bearing walk when the medial cortex was complete defect.6.Regardless of the major fracture line,the extent of the medial cortical defect in the proximal femur,as long as there was partial support,or during the weight-bearing process,the defect gap can be eliminated by the axial load and re-implemented,then the internal fixation protection could be exerted,otherwise the fixator must fail.