空心螺钉固定Sanders ⅡB型跟骨骨折的有限元研究

Fixation of Sanders type ⅡB calcaneal fractures with hollow screws:a finite element analysis

目的通过有限元分析研究不同空心螺钉内固定方式在Sanders ⅡB型跟骨骨折的生物力学稳定性。方法在一名志愿者(男性,26岁,身高173 cm,体重70 kg)跟骨CT基础上,通过Mimics 22.0、Geomagic12.0、Solidworks2019、ANSYS Workbench 2022等数字医学软件建立跟骨三维有限元模型,建立Sandres ⅡB型跟骨骨折模型。螺钉分为以下3种:①纵螺钉:自跟骨结节向前部;②横螺钉:自跟骨外侧壁向载距突;③垂直螺钉:自跟骨底部向丘部,垂直于后关节面。螺钉配置方案如下:纵螺钉自跟骨结节上方、中部、下方为进钉点分为上方组、中部组、下方组,再依据双横螺钉+单垂直螺钉、单横螺钉+单垂直螺钉、双横螺钉+无垂直螺钉和单横螺钉+无垂直螺钉的配置方式进一步分为4个亚组,最终得到12个模型(a、b、c、d、e、f、g、h、i、j、k、l模型)。在后距关节面和中距关节面分别施加420 N和200 N载荷模拟成人单足站立时跟骨受力,分析各个模型的总形变位移,丘部、前部、关节面骨折裂缝相对位移,骨折断端、螺钉的应力峰值。结果i、j模型的总形变位移最低,k、l模型的形变位移最高;其余模型的最大形变位移变化幅度较小。丘部骨折裂缝平均相对位移在上方组最低(0.27 mm),下方组相对较高,其中k、l模型的变异最大;前部骨折裂缝平均相对位移在下方组最小(0.16 mm),其中i、k模型表现最佳;关节面骨折裂缝相对位移在所有模型中均保持在较低水平。上方组模型骨折断端平均应力峰值最低(60.20 MPa),中部组和下方组接近(分别为103.88 MPa和99.76 MPa)。上方组的螺钉平均应力峰值最小(222.77 MPa),下方组k、l模型的平均应力峰值最高,分别达到331.48、349.82 MPa。结论i模型(下置纵螺钉+双横螺钉+单垂直螺钉)在降低总形变位移和前部骨折裂缝相对位移方面具有优势,值得推荐。纵螺钉、垂直螺钉和横螺钉在跟骨骨折固定中承担着不同作用,医生可根据患者需求选择适宜的螺钉配置。

ObjectiveTo investigate the biomechanical stabilities of different internal screw fixations for Sanders type ⅡB calcaneal fractures using finite element analysis.MethodsBased on the CT scan data of a male volunteer's calcaneus(26 years old,173 cm tall,weighing 70 kg),a three-dimensional finite element model of the calcaneus was established using digital medical software such as Mimics 22.0,Geomagic 12.0,Solidworks 2019,and ANSYS Workbench 2022.A three-dimensional finite element model of Sanders type ⅡB calcaneal fracture was also established.The following 3 kinds of screws were used:①longitudinal screws:from the calcaneal tuberosity to the anterior part;②transverse screws:from the lateral wall of the calcaneus to the sustentaculum tali;③vertical screws:from the base of the calcaneus to the talar dome,perpendicular to the posterior articular surface.The scheme of screw configuration was as follows:the longitudinal screws were divided into the upper,middle,and lower groups based on their entry points from the upper,middle,and lower parts of the calcaneal tuberosity.Based on different configurations(double transverse screws+single vertical screw,single transverse screw+single vertical screw,double transverse screws without a vertical screw,and single transverse screw without a vertical screw)4 subgroups were further subdivided,resulting in a total of 12 models(a,b,c,d,e,f,g,h,i,j,k,l).Forces of 420 N and 200 N were applied to the posterior and middle subtalar joints,respectively,to simulate the load on the calcaneus during single-leg standing in adults.In each model,total deformation displacement,relative displacement of the sustentaculum tali fracture gap,relative displacement of the anterior fracture gap,relative displacement of the articular surface fracture gap,peak stress at the fracture ends and peak screw stress were analyzed.ResultsThe total deformation displacement was the lowest in models i and j,while models k and l exhibited the highest deformation displacement.The maximum deformation values in the remaining models varied only slightly.The average relative displacement of the sustentaculum tali fracture gap was the lowest in the upper group(0.27 mm)and relatively higher in the lower group,with the greatest variation seen in models k and l.The average relative displacement of the anterior fracture gap was the smallest in the lower group(0.16 mm),with models i and k performing the best.The relative displacement of the articular surface fracture gap remained at a low level across all models.The upper group had the lowest average peak stress at the fracture ends(60.20 MPa),while the middle and lower groups had similar values(103.88 MPa and 99.76 MPa,respectively).The upper group had the lowest average screw stress peak value(222.77 MPa),whereas models k and l in the lower group had the highest stress peaks,reaching 331.48 MPa and 349.82 MPa,respectively.ConclusionsModel i(inferior longitudinal screw+double transverse screws+single vertical screw)can be recommended in clinic because it demonstrates balanced performance in displacement and stress and a notable advantage in reducing overall deformation displacement and anterior fracture gap displacement.As longitudinal,vertical,and transverse screws each play their distinct role in calcaneal fracture fixation,surgeons should select an appropriate screw configuration based on the patient's needs.