改良中空加压螺钉内固定治疗股骨颈骨折的有限元分析

目的建立中空加压螺钉固定股骨颈骨折的三维有限元模型,研究3枚中空加压螺钉的受力情况及改良螺钉内固定治疗股骨颈骨折时能否提供所需的力学强度。方法三维有限元模型采取三钉倒三角并与股骨干成127°的内固定方式,并模拟单腿站立时的受载情况;在Pauwels角分别为50°、60°、70°、80°时,计算3枚螺钉在不同位置(下面螺钉为1号,前上螺钉为2号,后上螺钉为3号)所受应力;选择受力最大的螺钉开侧孔,研究孔径大小、开孔方向对螺钉固定股骨颈骨折模型的影响。结果随着Pauwels角度的增加,每个中空加压螺钉上的应力增大;Pauwels角为80°时各个中空加压螺钉的应力达到最大值,1、2、3号螺钉所受应力分别为304、515、和154 MPa;当受力最大的2号螺钉开孔直径为1 mm,开孔方向避开150°～195°时,3枚螺钉所受应力均在安全范围内。结论从力学角度看,3枚螺钉受到不同应力,开侧孔设计的中空加压螺钉具有良好的生物力学性能,治疗股骨颈骨折手术安全可靠,而且可以通过中空和侧孔管道向骨折端注入药物,为促进股骨颈骨折愈合创造有利条件。

Finite element analysis on a modified cannulated screw for fixation of femoral neck fracture

Objective To establish the three-dimensional finite element model of the cannulated screws for fixing the femoral neck fracture, and investigate stress distributions on three cannulated screws as well as determine whether internal fixation by a modified cannulated screw can provide sufficient stiffness and strength for the fixation. Methods The 3D finite element model was internal-fixed at the angle of 127°with femoral shaft under the inverted triangle mode to simulate loading on single legged standing condition. Stresses on three screws (No 1: the underneath screw, No 2: the anterosuperior screw, No 3: the posterosuperior screw) were calculated at different Pauwels angle (50°, 60°, 70°, 80°), respectively. A bore was drilled in the screw with the largest stress to study the effect of bore size and bore direction on the femoral neck fracture model with screw fixation. Results The stresses of three screws increased with the Pauwels angle increasing and reached the maximum value at 80°. The maximum stresses on No.1, No.2 and No.3 screw were 304, 515 and 154 MPa, respectively. When the No 2 screw had an opening bore with 1 mm in diameter, and the direction of the bore was not between 150°and 195°, the stresses on three screws were all within the safe limits. Conclusions From the mechanical point of view, three screws are subject to different stresses. The cannulated screws with side bore have good biomechanical properties for fixing the femoral neck fracture with safety and reliability, which can provide advantages for accelerating fracture healing by injecting drugs through the central and side bore into the fracture side.