A Follow-up Of Femoral Head Osteonecrosis After Internal Fixation Of Femoral Neck Fractures And Related Research Of Biomechanics

Object:(1)Describe the preoperative displacements and postoperative reduction quality quantitatively by three-dimensional reconstruction technique,and reveal the limitations evaluation method based on two-dimensional X-ray film.Investigate the rate of femoral head necrosis after internal fixation of femoral neck fractures,and explore the relationship among femoral head necrosis,the preoperative displacements and residual displacements postoperatively.(2)Make the models of femoral neck fracture with different degrees of posterior-inferior bone defect,and explore the biomechanical changes of proximal femur with posterior-inferior bone defect.Compare the biomechanical effect of hollow screws with different mounts and configurations in treatment of adductive femoral neck fractures.Method:(1)More than 1000 patients with femoral neck fractures were collected from January 2010 to December 2013 in Tianjin Hospital.The clinical data of 163 patients who met the criterias were analysed retrospectively.There were 61 males and 102 females.Age ranged from 45 to 78 years old,and the average age was(55.7±7.9)years old.According to Garden classification,20 patients were type Ⅰ;30 patients were type Ⅱ;57 patients were type Ⅲ;56 patients were type IV.Duration of follow-up ranged from 2.5 to 5.4 years,and the average duration of follow-up was 3.1 years.Assess hip function and living quality by OHS score and BI index.The primitive CT data of proximal femur were collected and imported to Mimics 10.01 software.Match bilateral femurs to measure the preoperative displacements and residual displacements postoperatively,included the central displacement,lowest displacement at the dimple and spatial deflection angle.Univariate χ2 analysis and logistic regression analysis were conducted to explore risk factors of femoral head necrosis.(2)CT scans performed on proximal femur of a healthy adult male volunteer and exported the DICOM original data.MIMICS 10.01 software and Rhino3 D NURBS software were used to make the model of femoral neck fracture with different degrees of posterior-inferior bone defect and hollow screws with different amounts and configurations.Loads were applied on each model to simulate normal walking status.And changes in stress distributions of each proximal femur model were observed and analyzed.The average stress peak value of femoral head,femoral neck pressure side and tension side,hollow screw tail were compared among the models with different amounts and configurations.Result:(1)Until June 2015,33 patients presented femoral head necrosis,and the rate were 20.2%.Femoral head necrosis were found at about(1.9±0.6)years postoperatively.The OHS score and BI index of necrosis group were lower than non-necrosis group.The preoperative displacements and residual displacements postoperatively of necrosis group were higher than non-necrosis group,and shift parameter included the central displacement,lowest displacement at the dimple and spatial deflection angle.Univariate χ2 analysis revealed that the Garden type were the related factors of femoral head necrosis.Logistic regression analysis revealed that the Garden type,preoperative displacements and residual displacements postoperatively were the related factors of femoral head necrosis.(2)The inner side of the femoral neck was subjected to compressive stress,and the lateral bearing was tensile stress for the non-defect model,and the stress distribution of the femoral head is more uniform.With the increase of the degrees of posterior-inferior bone defect,the average stress peak value of femoral head,femoral neck pressure side and tension side,hollow screw tail were increased gradually.For unstable and adductive femoral neck fractures,especially for the cases with bone defect,the pressure side stress and the tension side stress of four screws group were lower than those of inverted triangle and regular triangle group(P<0.05).For medium and large defect model,average peak stress of femoral head of four screws group were lower than those of inverted triangle and regular triangle group(P<0.05),while there had no significant difference between inverted triangle and regular triangle group(P>0.05).For the femoral neck fracture with bone defect,the hollow screw tail stress of four screws group were lower than the other two groups,while the hollow screw tail stress of inverted triangle were higher than those of the other two groups(P<0.05).Conclusion:(1)We could observe the severity of fracture and reduction quality comprehensively by three-dimensional reconstruction technique,and describe the preoperative displacements and postoperative residual displacements quantitatively.The Garden type,preoperative displacements and residual displacements postoperatively were the major risk factors for the incidence of femoral head necrosis.(2)Posterior-inferior bone defect could affect the biomechanical properties of the proximal femur significantly.It could cause the uneven stress distribution,and trigger the stress concentration.For unstable and adductive femoral neck fractures,especially for the cases with bone defect,the biomechanical properties of four screws group were superior than those of inverted triangle and regular triangle group.