舟骨骨折螺钉固定的生物力学研究

目的：对于腰部斜形舟骨骨折，通过生物力学试验评价舟骨骨折螺位置居中性与垂直性对螺钉固定强度的影响。方法将32例外形、材质相同的舟骨Sawbone骨根据螺钉的位置在舟骨内是否居中、与骨折面是否垂直分4组：居中并且垂直，居中但不垂直，不居中但垂直，不居中不垂直，每组8例，在舟骨腰部作截骨模拟骨折，用螺钉固定。对其中的1例Sawbone进行CT扫描，利用术前设计与手术模拟软件设计骨折模拟平面、螺钉导针位置，用以确定在生物力学实验中骨折平面及螺钉的位置。将螺钉固定后的舟骨置于生物力学试验机平台，测量并比较不同试验组标本固定失效时的最大负荷及位移。结果当螺钉在舟骨内居中且与骨折线垂直时（A组）的最大负荷及位移均值（398.5N，2.8mm）与螺钉在舟骨内居中固定但与骨折线不垂直时的（B组）（393.1N，2.9mm）变化均不大，差异无统计学意义（P＞0.5）；螺钉在舟骨内偏心固定且与骨折线垂直时（C组）的最大负荷及位移均值（348.25N，3.6mm）与螺钉在舟骨内偏心固定且与骨折线不垂直时（D组）的（342.50N，3.8mm）的变化均不大，差异无统计学意义（ P＞0.5）。这说明螺钉固定强度与螺钉是否与骨折面垂直无关。而舟骨骨折螺钉位置居中性的A、B组的最大负荷值均较偏心固定的C、D组大，且差异均有统计学意义（P＜0.001）；A、B组的最大位移值均较C、D组小，且差异有统计学意义（P＜0.001）。结论对于舟骨斜形不稳定骨折，将螺钉在舟骨内居中放置可以提供更高的固定强度，与螺钉是否与骨折面垂直无关。

A biomechanical test study of screw fixation for scaphoid fractures

Objective To evaluate the effects of the middle and vertical positions of the screw on the ifxation stability in the treatment of oblique scaphoid fractures using biomechanical testing. Methods Oblique osteotomies for 32 sawbone scaphoids that were identical in the shape and texture were designed, and each specimen was ifxed with a screw. According to the positions of the screw and the fracture plane, sawbone scaphoids were divided into 4 groups. In group A, the screw was perpendicular to the fracture plane and was central in the scaphoid. In group B, the screw was not perpendicular to the fracture plane and was central in the scaphoid. In group C, the screw was perpendicular to the fracture plane and was eccentric in the scaphoid. In group D, the screw was neither perpendicular to the fracture plane nor central in the scaphoid. There were 8 cases in each group. The Computed Tomography （ CT ） scan was performed on 1 specimen, and the positions of the osteotomy plane and the screw guide pin were designed in biomechanical testing using the preoperative planning and the surgery simulation software. The specimen was placed under the increasing load of a pneumatically driven plunger to measure and compare the maximum load and displacement at fixation failure among the study groups. Results The average maximum load and displacement were （ 398.5 N, 2.8 mm ） in group A, （ 393.1 N, 2.9 mm ） in group B, （ 348.25 N, 3.6 mm ） in group C and （ 342.50 N, 3.8 mm ） in group D, and the differences both between group A and Group B, group C and group D were not statistically different （ P＆gt;0.5 ）. It was illustrated that whether the screw was perpendicular to the fracture plane or not was irrelevant to the stability of the screw ifxation. The maximum load in group A and group B was greater than that in group C and group D, and the differences between them was statistically different （ P＆lt;0.001 ）. The maximum displacement in group A and group B was smaller than that in group C and group D, and the differences between them was statistically different （ P＆lt;0.001 ）. Conclusions In this biomechanical test study of unstable oblique scaphoid fractures, it is shown that higher stability of ifxation can be achieved with the screw placed centrally in the scaphoid, and the stability has nothing to do with whether the screw is perpendicular to the fracture plane or not.