Biomechanical Analysis Of Percutaneous Compression Plate And Femoral Neck System In Pauwels Type Ⅲ Femoral Neck Fractures

Background and objective:Femoral neck fractures in young adults(Pauwels type III classification)are frequently accounted for high-energy trauma and mainly associated with multiple injuries.Its treatment is very challenging because the fracture line is usually close to the vertical shear direction,and the fracture site bears greater shear force,which increases the risk of complications,such as nonunion,malunion,avascular necrosis of the femoral head,internal fixation failure,and etc.At present,the majority of patients with femoral neck fractures require surgical treatments.Timely anatomical reduction and stable internal fixation can help relieve the distortion of proximal femoral blood vessels,and save the blood supply to the femoral head to the greatest extent.The internal fixation devices also create an appropriate biomechanical environment for fracture healing,achieving angiogenesis and osteogenesis at the fracture site.There has been a debate about the choice of internal fixation methods for femoral neck fractures in young adults.The common internal fixation devices included inverted triangular cannulated cancellous screws(ICCS)and dynamic hip screws(DHS).In recent years,some novel internal fixation devices such as femoral neck system(FNS)and percutaneous compression plate(PCCP)have achieved good clinical efficacy in the treatment of femoral neck fractures.However,there are few studies comparing their biomechanical properties in the femoral neck fracture fixation.The aim of this study was to examinate and compare the biomechanical properties of these two novel internal fixation devices(PCCP and FNS)and traditional ICCS in Pauwels type III femoral neck fractures by using the Sawbone artificial synthetic femoral models,in order to provide a biomechanical basis and clinical options for the treatment of unstable femoral neck fractures.Methods:Eighteen Sawbone femoral models were used to establish Pauwels type Ⅲ femoral neck fractures,and they were randomly divided into three groups: ICCS,FNS,and PCCP.Each group was fixed with corresponding internal fixation devices subsequently.After the completion of internal fixation,biomechanical tests in each group were performed to record the vertical subsidence displacement of the femoral head under different loads,the ultimate load value,and the torque of the fracture site at different torsion angles.Finally,the biomechanical properties of each group were compared.Results:The results of the vertical subsidence displacement of the femoral head under different loads showed that under the vertical loads of 200 N and 400 N,the vertical displacement of the femoral head in the FNS group and the PCCP group was significantly lower than that in the ICCS group(P<0.05),and the vertical displacement of the femoral head in the PCCP group was slightly less than that in the FNS group(P>0.05).When the loads were 600 N,800N,and 1000 N,the vertical displacement of the femoral head in the FNS and PCCP group was significantly lower than that in the ICCS group,and the vertical displacement of the femoral head in the PCCP group was significantly lower than that in the FNS group.Subsequently,the axial stiffness of each group was calculated,and the results indicated that PCCP had a higher axial stiffness than FNS(529.98±23.08N/mm vs.415.03±27.10N/mm,P<0.001),and FNS had a higher axial stiffness than FNS(415.03±27.10N/mm vs.244.86±2.84N/mm,P<0.001).Therefore,PCCP exhibited the greatest axial stiffness,followed by FNS and finally ICCS,for Pauwels type III femoral neck fractures.Moreover,under the ultimate load test,the ultimate load value of the FNS and PCCP group was significantly higher than that of ICCS group,and PCCP showed higher resistance to ultimate loads than FNS(P=0.03).For the torsional torque test,when the torsion angles were 2°,4°,and 6°,the torque of the PCCP group was obviously higher than that of the FNS and ICCS group,and there was no significant difference between FNS and ICCS(P>0.05).This result demonstrated that PCCP required a larger torsional moment than FNS and ICCS to achieve the same torsion angle,indicating that PCCP had better anti-rotation ability than FNS and ICCS.Conclusion:Different internal fixation methods have different biomechanical characteristics for Pauwels type III femoral neck fractures.Compared with the conventional ICCS,the novel internal fixation devices(FNS and PCCP)have stronger axial stiffness and ultimate load resistance,and their good mechanical properties are more eligible for Pauwels type III femoral neck fractures.Moreover,PCCP showed better anti-rotational performance compared with FNS,and reduced fracture rotation.