A Quantitative Study Of Positive Buttress Reduction And Development Of A New Plate Based On Pauwels Classification Of Femoral Neck Fracture

Femoral neck fracture is one of the most common hip fractures in clinical practice.Because of the reason of blood supply,fracture nonunion and femoral head necrosis are easy to occur.Especially the treatment of the young and middle-aged patients has been a difficult problem,because of their special hip preservation need and the high rate of femoral head necrosis.Effective reduction and stable internal fixation are the keys to reduce complications.For young and middle-aged femoral neck fractures with high energy injuries,some experts believe that the Pauwels classification based on biomechanics can better refl ect the severity of such fractures,so the study of reduction and internal fixation based on Pauwels classification is very important in clinical treatment.Anatomic reduction is the goal of clinical closed reduction,but it is difficult to achieve anatomic reduction for some refractory femoral neck fractures,and repeated traction reduction will damage the remaining femoral head blood supply.In 2013,Gotfried et al proposed a concept of positive buttress reduction for femoral neck fracture,which can also achieve better clinical efficacy.When closed anatomical reduction is difficult to achieve,positive buttress reduction is acceptable,while negative buttress should be avoided as much as possible.But at present there are lack of biomechanical evaluation and quantitative standard research of positive buttress reduction for femoral neck fractures,so a quantitative study of positive buttress reduction for femoral neck fractures with three Pauwels classification(Pauwels Ⅰ,Ⅱ and Ⅲ)is very important in clinical treatment.And the internal fixation research based on Pauwels classification has always been a hot issue.As the Pauwels Angle increases,more stable internal fixation is required,especially different internal fixation and new development of internal fixation for Pauwels Ⅲfemoral neck fracture has been important research direction.This subject aims at a quantitative study of positive buttress reduction based on Pauwels classification of femoral neck fracture and the development of a new plate based on the characteristics of PauwelsⅢ femoral neck fracture.Part Ⅰ Clinical and experimental study of positive buttress reduction for femoral neck fractureSection oneClinical efficacy of Gotfried positive and negative buttress reduction in treatment of femoral neck fractureObjective:We aimed to compare the clinical efficacy between Gotfried positive and negative buttress reduction in treatment of femoral neck fracture.Methods:We conducted a retrospective review of fifty-five patients with femoral neck fractures treated with positive buttress reduction and negative buttress reduction from October 2011 to March 2016.Twenty-nine patients were treated by Gotfried positive buttress reduction,including 16 males and 13 females,with an average age of 43.45±8.23 years old.Twenty-six patients were treated by Gotfried negative buttress reduction,including 14 males and 12 females,with an average age of 41.96±8.69 years old.The degree of femoral neck shortening,nonunion,fixation failure,avascular necrosis of femoral head and Harris score of hip joint were measured postoperatively.Results:All patients were followed up more than 18 months.In Gotfried positive buttress reduction group,there were no cases of bone nonunion,fixation failure and avascular necrosis of femoral head.In Gotfried negative buttress reduction group,1 case occurred bone nonunion,3 cases supervened early fixation failure,1 case presented avascular necrosis,and 5 cases(19.23%)finally received joint replacement surgery.The average length of shortening were 4.07±1.98mm and 8.08±3.54mm in the vertical plane.And the average length of shortening in the horizontal plane were 3.90±1.57mm and 7.77±3.31mm(P<0.05).Harris score of the hip joint was higher in Gotfried positive buttress reduction group at last follow-up(P<0.05).Conclusion:The positive buttress reduction has a higher success rate in surgery,and can significantly prevent femoral neck shortening and improve hip joint function.Therefore,negative buttress reduction should be avoided as far as possible for displaced femoral neck fractures.Section twoBiomechanical experimental evaluation of positive buttress reduction for femoral neck fractureObjective:In this study,we evaluated the biomechanical effects of positive,negative and anatomic buttress reduction for Pauwels Ⅰ femoral neck fractures.Methods:The 24 cases of the fourth-generation synthetic composite femur were divided into 3 groups on average.According to the Pauwels 30°Angle osteotomy,femoral neck fractures were formed.According to different reduction criteria,they were divided into positive buttress reduction group,anatomical reduction group and negative buttress reduction group.All fracture models were fixed by three parallel cannulated screws with inverted triangle.Biomechanical methods(axial loading test,ultimate load test)were used to evaluate the samples,including structural stiffness,maximum fracture displacement(horizontal and vertical displacement)and ultimate load,and the results were compared by analysis of variance(P<0.05).Results:The results showed that the structural stiffness,maximum fracture displacement and ultimate load of the positive buttress reduction group were similar to those of the anatomical reduction group(P>0.05).The structural stiffness and ultimate load of the two groups were much higher than that of the negative buttress reduction group,while the maximum displacement of fractures were much lower than that of the negative buttress reduction group(P<0.01).Conclusion:Compared with the negative buttress reduction,the positive buttress reduction and anatomical reduction had better biomechanical strength,and the positive buttress model group had similar biomechanical strength with the anatomical reduction model group.Part Ⅱ A quantitative study of positive buttress reduction based on Pauwels classification of femoral neck fracture:a finite element analysisSection oneEstablishment and validation of femur finite element modelObjective:Finite element model of femur was established based on CT data of normal human femur,and its validity was verified.Methods:The femur CT data of a volunteer was collected.Mimics 17.0,Hypermesh 12.0 and other software were used to construct the femur solid model and mesh division,and then Abaqus 6.9 was used for finite element analysis.Axial loading test was carried out under the stress of 1400N.Eight equal points were marked in the middle part of the femoral neck,and the von Mises stress values and the variation pattern of the points were compared between finite element analysis and cadaveric bone loading.Results:The von Mises stress values of eight points were close to each other between finite element analysis and cadaveric bone loading,and the variation pattern of the two data were similar.This variation pattern is basically consistent with that provided in previous literature.Conclusion:The femur finite element model was established and verified to be valid.The model could be used for subsequent finite element analysis tests.Section twoA quantitative biomechanical study of positive buttress reduction for femoral neck fractures of different Pauwels classification:a finite element analysisObjective:In this study,we evaluated the biomechanical effects of anatomic,negative,and positive buttress with various degrees of displacement in three Pauwels types of femoral neck fractures by a finite element analysis in order to quantitatively investigate positive buttress reduction.Methods:Five reduction models of three Pauwels types of femoral neck fractures(Pauwels 30°,Pauwels 50° and Pauwels 70°)were established using the Mimics 17.0 and Hypermesh 12.0 software.According to the degree of fracture displacement,there were three models of positive buttress(2mm,3mm,4mm),an anatomic reduction model,and a negative 2 mm reduction model.Three parallel cannulated screws of inverted triangle configuration were assembled for fixation,and a total of 15 finite element models were obtained.Finite element analysis was conducted using the Abaqus 6.9 software.The von Mises stress distribution and the stress peak of internal fixation in different models,the displacement between fracture blocks,and the principal strain of the femoral neck cancellous bone model were recorded under the axial stress of 2100 N.Results:In Pauwels Ⅰ and Pauwels Ⅱ femoral neck fracture model,the peak von Mises stress of internal fixation and the maximal displacement between fracture blocks from big to small in turn were positive 4mm,negative 2mm,positive 3mm,positive 2mm and anatomical reduction model respectively.The peak von Mises stress of internal fixation and the maximal displacement in negative 2mm model were involved between positive 3mm model and positive 4mm model.In Pauwels Ⅲ femoral neck fracture model,the peak von Mises stress of internal fixation and the maximal displacement between negative 2mm and positve 3mm model were relatively close,and positive 2mm is better than negative 2mm model.Among all models,the strain area of the proximal femoral neck cancellous bone were mainly concentrated around the screw hole,and the yield strain area increased with the increase of Pauwels angle.The area around the screw hole could be easily cut.Moreover,with the increase of Pauwels angle,the peak von Mises stress and the maximal displacement increased significantly.Conclusion:Compared with negative buttress for femoral neck fracture,positive buttress can provide better biomechanical stability.According to the results,the positive buttress reduction was quantitatively graded,including grade Ⅰ(displacement≤2mm),grade Ⅱ(2mm<displacement≤3mm),grade Ⅲ(3mm<displacement≤4mm)and grade Ⅳ(displacement>4mm).In Pauwels Ⅰ and Ⅱ femoral neck fractures,grade Ⅰ can also maintain relatively stable biomechanical effects,grade Ⅱ is also relatively acceptable,while grade Ⅲ and Ⅳ should be avoided as much as possible.In Pauwels Ⅲ femoral neck fractures,the positive buttress should be controlled at grade Ⅰ as much as possible.There are highest stress of internal fixation,maximum displacement between fracture blocks,and maximum yield strain area of the proximal femoral neck cancellous bone in Pauwels Ⅲ femoral neck fractures,so we need to use stronger internal fixation to maintain stability.Part Ⅲ The development and design of a new plate based on the characteristics of Pauwels Ⅲ femoral neck fractureObjective:We design and develop a new femoral neck plate in order to provide a new choice for treating Pauwels Ⅲ femoral neck fracture based on the characteristics of the fracture.Methods:Based on the anatomical parameters and anatomical characteristics of the upper femur provided by previous studies,combining the advantages of Pauwels screw structure and locking plate,we designed a new plate capable of both intraoperative vertical fracture line compression and resistance to strong shear stress,and simulated the operation after development and production.The new femoral neck plate comprises three femoral head screw holes and one femoral shaft locking hole.One screw on the top of the femoral head is an ordinary partially threaded cannulated screw with 7.3mm diameter,which can achieve intraoperative vertical fracture line compression.The other two femoral head screws are partially threaded cannulated locking screws with 7.3mm diameter,which can provide strong angular support for the femoral head at an angle of 135°.A locking hole is designed at the farthest end of the plate and the femur is connected to the plate by implanting a 5.0mm diameter locking screw.Results:The new femoral neck plate has a high anatomical consistency with the lateral wall of the trochanter and a good fit with the external wall of the femur.After implanting steel plate and screw according to the operation method,the fracture end can be compressed and tightened.Postoperative c-arm fluoroscopy is used to confirm that the fracture end position was well and the screws distribution were well.Conclusion:The new femoral neck plate may be a good treatment for Pauwels Ⅲfemoral neck fracture.Fart Ⅳ Biomechanical stability evaluation of new femoral neck plateSection oneBiomechanical experimental study of new femoral neck plate in the treatment of Pauwels Ⅲ femoral neck fractureObjective:In this study,we evaluated the biomechanical effects of the new femoral neck plate,dynamic hip screw augmented with one screw and Pauwels screw structure in the treatment of Pauwels Ⅲ femoral neck fracture.Methods:The 24 cases of the fourth-generation synthetic composite femur were divided into 3 groups on average.According to the Pauwels 70°Angle osteotomy,femoral neck fractures were formed.Each group were fixed with new femoral neck plate(group A),dynamic hip screw augmented with one screw(group B)and Pauwels screw structure(group C).Biomechanical methods(axial loading test,ultimate load test)were used to evaluate the samples,including structural stiffness,maximum fracture displacement(horizontal and vertical displacement)and ultimate load,and the results were compared by analysis of variance(P<0.05).Results:The results showed that the structural stiffness,maximum fracture displacement and ultimate load of group A were similar to those of group B(P>0.05).The structural stiffness and ultimate load of the two groups were much higher than that of group C,while the maximum displacement of the fractures were much lower than that of group C(P<0.001).Conclusion:The new femoral neck plate had similar biomechanical strength to the dynamic hip screw augmented with one screw,and was superior to the Pauwels screw structure.Section twoBiomechanics comparison of new femoral neck plate and Pauwels screw in multiple osteotomy models of Pauwels Ⅲ femoral neck fractures by finite element analysisObjective:In this study,the biomechanical stability of a new femoral neck plate(NFNP)and Pauwels screw structure in multiple osteotomy models of PauwelsⅢ femoral neck fracture were compared by finite element analysis.Methods:Using the Mimics 17.0 and Hypermesh 12.0 software,we constructed models of Pauwels Ⅲ femoral neck fractures with the angles of 50°、60°and 70°.Moreover,a new femoral neck plate fixation model and a Pauwels screw structure fixation model were developed and assembled.Under the axial load of 1400N and 2100 N,von Mises stress(VMS)distribution and peak VMS of internal fixation,displacement between fracture fragments,VMS distribution and peak VMS in cancellous bone of proximal femoral neck were recorded.Results:The peak VMS in the two models were mostly located near the fracture line,and the screw closest to the femoral calcar experienced maximum stress.At the Pauwels angle of 50°,60°and 70°,the peak VMS values of the NFNP were lower than those in Pauwels screw structure.The maximal displacement of fracture fragments in the NFNP were smaller than those in Pauwels screw structure.The peak VMS values of cancellous bone in the NFNP were also lower than those in Pauwels screw structure.Conclusion:Compared with Pauwels screw structure fixation group,the NFNP can provide stronger biomechanical stability for different osteotomy models of Pauwels Ⅲfemoral neck fractures.