| Objective To evaluate the biomechanical performance of femoral neck system(FNS)fixation for three Pauwels classification of femoral neck fractures and the clinical efficacy in the treatment for femoral neck fractures.MethodsPart 1:Biomechanical study of FNS for femoral neck fractures: A three-dimensional finite element analysisOne left fourth-generation artificial composite femur was selected and CT data was obtained.At the same time,the data obtained after scanning FNS and three CS physical products were used to establish three Pauwels classification of femoral neck fractures and Three-dimensional finite element models of two internal fixtures.FNS and three CSs were used to simulate the surgical fixation process,and three Pauwels classification fracture internal fixation models were established.Referring to the literature,each model was subjected to restraint loading under three loads.Under three different working conditions,the femoral displacement distribution and peak value,the displacement distribution and peak value of the proximal femur in different directions,the femoral stress distribution and peak value,and the distributions and peaks of stress and displacement of internal fixation were recorded.Part 2 : Biomechanical evaluation of FNS for femoral neck fractures: an in vitro mechanical test of artificial composite bonesThirty-six artificial composite femurs were randomly divided into 3 groups,and three Pauwels classification femoral neck fracture models were made.FNS and three CS were used to fix each Pauwels classification of fracture models.They were divided into group A(FNS)and group B(CS),with 6 models in each group of fracture models of each Pauwels classification.Quasi-static non-destructive twisting around the neck,A-P bending,and axial compression tests were performed to examine stiffness.The global deformation of the model was evaluated after a simulated load-bearing cyclic compression,and the local deformation of the model was evaluated by measuring the implant tunnel.Part 3:Finite element analysis of FNS inserted in different positions to stabilize femoral neck fracturesThe three-dimensional finite element model of femoral neck fracture and the FNS finite element model of the three established Pauwels classifications were used to simulate the process of FNS surgical fixation of the fracture.Three positions of the center of the femoral head and neck in the coronal plane,the lower 1/3 of the femoral neck,and the lowermost position of the femoral neck were selected to place the bolt,and each model was subjected to restraint loading under three loads.Under three different working conditions,the femoral displacement distribution and peak value,the displacement distribution and peak value of the proximal femur in different directions,the femoral stress distribution and peak value,and the internal fixation stress and displacement distribution and peak value were recorded.Trends in fracture stability were compared between the three placement positions.Part 4:Clinical application of FNS for the treatment of femoral neck fracturesSixty-five patients(31 males and 34 females)with femoral neck fractures treated with internal fixation in our hospital from November 2019 to October 2020 were recruited.Among them,group A included 34 patients with a mean age of 43.5 years(range 20 to 61 years)with FNS fixation;group B included 31 patients with a mean age of 40.0 years(21 to 62 years)with CS fixation.Baseline data of both groups,perioperative outcomes(including operation time,reduction quality,blood loss,incision length,number of fluoroscopy,hospital stay,hospitalization cost),and various indicators during postoperative follow-up,including Visual Analog Scale(VAS),Hip Harris Score(HHS),Radiographic Hip Score(RUSH)at 6 months,time to full weight bearing,shortening of the femoral neck,and postoperative complications(including infection,delayed or nonunion of fractures,femoral head necrosis,incidence,internal fixation failure)were recorded.All patients were followed up for no less than 12 months.ResultsPart 1:Biomechanical study of FNS for femoral neck fractures: A three-dimensional finite element analysisFor the three Pauwels classification of femoral neck fractures,under the three working conditions,the peak femoral displacement of the two internal fixation models was centralized in the proximal femoral head,and the peak displacement after FNS fixation was smaller than that of CS;The peak displacement of the axis was centralized at the fracture end of the superior side of the femoral neck,the peak displacement of the Y axis was centralized at the proximal end of the femoral head,and the peak displacement of the Z axis was centralized at the force of the femoral head.The peak displacement in three directions after fixed by FNS was smaller than that of CS;the peak stress of femur was concentrated in Adams’ s arc,and the peak stress of FNS after fixation was smaller than that of CS;the peak stress of FNS was concentrated at the junction of the bolt and the locking plate around the fracture end,and the stress of CS was shared by three screws mainly concentrated near the fracture end of the middle part of the screw,and the peak stress of FNS was smaller than that of CS;the peak displacement of internal fixation was mainly concentrated at the tip,and the peak displacement of FNS was smaller than that of CS.The observed indexes of the two models after internal fixation increased with the increase of the Pauwels angle and the applied load,showing a similar change trends.Part 2 : Biomechanical evaluation of FNS for femoral neck fractures: an in vitro mechanical test of artificial composite bonesAfter the static test of the Pauwels type I femoral neck fracture model,the axial compression stiffness,A-P bending stiffness and rotational stiffness of group A were higher than those of group B(P<0.05).After the cycle test,the overall deformation and local deformation of group A were significantly lower than those of group B(P<0.05).After the static test of the Pauwels II femoral neck fracture model,the axial compression stiffness,A-P bending stiffness and rotational stiffness of group A were higher than those of group B(P<0.05).After the cyclic test,the overall deformation and local channel deformation of the model were significantly higher in group B than in group A(P<0.05).The Pauwels III femoral neck fracture model showed a similar trend after static test and cyclic test.The axial compression stiffness,AP bending stiffness and anti-rotation stiffness of group A were higher than those of group B(P<0.05).The deformation was significantly lower than that of B(P<0.05).With the increase of the Pauwels angle,the axial compression stiffness,A-P bending stiffness and anti-rotation stiffness of the two internal fixations all decreased,the overall deformation and local deformation increased,and the stability decreased.In the three Pauwels classification femoral neck fracture models,the stiffness of the three different loading directions showed a significant positive correlation(P < 0.05);the two deformations were negatively correlated with the axial stiffness(P < 0.05);While the two deformation,there was a significant positive correlation between them(P<0.05).Part 3:Finite element analysis of FNS inserted in different positions to stabilize femoral neck fracturesThe femoral displacement and stress distribution,proximal femoral displacement distribution,and internal fixation stress and displacement distribution of FNS were similar among the three Pauwels-typed femoral neck fracture models at the three placement positions.Compared with the FNS placed in the central axis of the femoral head and neck,the peak displacement and stress of the femur,the peak displacement of the proximal femur on the X and Y axes of the local coordinate system,and the peak internal fixation stress and displacement increased after the FNS was placed in the other two positions,among which the peak value of each observation index was the highest when FNS was placed at the bottom of the femoral neck,indicating the worst fracture stability.In the Pauwels type I and II femoral neck fracture models,when FNS was placed in the lower 1/3 of the femoral neck,the peak displacement of the proximal femur in the Z axis was smaller than that in the other two placement positions;but in the Pauwels type III femoral neck fracture model,the peak displacement of the proximal femur in the Z-axis was smallest when FNS was placed at the central axis of the femoral head and neck.In the models of the three placement positions,with the increase of the Pauwels angle and the applied load,the peak value of each observation index increased,the fracture stability decreased,and the fracture displacement and internal fixation fracture risk increased.Part 4:Clinical application of FNS for the treatment of femoral neck fracturesThe mean follow-up time of the included patients was 13.12±1.04 months in group A and13.58±1.39 months in group B.Baseline data of the two groups and perioperative outcomes(including reduction quality,intraoperative blood loss,surgical incision length,hospital stay),and postoperative follow-up indicators(including postoperative 3 months,6 months,and 12 months VAS,and 3 months HHS after surgery)had no statistical difference(P > 0.05).However,the operation time,fluoroscopy times,VAS 1 day after operation,full weight-bearing time,degree of femoral neck shortening and complication rate in group A were all lower than those in group B(P < 0.05).Besides,the hospitalization cost,the HSS of the postoperative 6 months and 12 months as well as the 6-month RUSH in group A were significantly higher than those in group B(P < 0.05).Conclusion FNS has shown excellent biomechanical performance for the treatment of three Pauwels classifications’ femoral neck fractures and can meet the mechanical environment required for femoral neck fracture healing,but the error tolerance of FNS is limited,the highest fracture stability could be obtained after placement in the central axis of the femoral head and neck.The clinical efficacy of FNS is affirmative,this internal fixation is characterized by its simple procedure,reduced trauma,faster recovery,and fewer complications.So,it can be used as a new choice for the treatment of femoral neck fractures. |
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