Tallman Madeline G, Patel Akshar H, Anderson Ronald C, Medvedev Gleb
Department of Biomedical Engineering, Tulane University, New Orleans, LA.
Department of Orthopaedic Surgery, Tulane University School of Medicine, New Orleans, LA.
J Hand Surg Glob Online. 2023 Feb 1;5(2):159-163. doi: 10.1016/j.jhsg.2023.01.004. eCollection 2023 Mar.
To investigate the changes in biomechanical fixation of an initial and replacement headless compression screw by quantifying interfragmentary compression and shear displacement.
A bone model was created with 2 blocks of rigid polyurethane foam to simulate a fracture site. A 24-mm headless compression screw was inserted into the model at a perpendicular or oblique angle, removed, and replaced with the 22-mm screw. The 22-mm screw replaced the 24-mm screw in either the same or reverse direction of initial insertion. All 4 methods of initial and replacement screw fixation were trialed 15 times for a total of 60 trials. Two button load cells measured compression. A digital microscope recorded shear displacement. Statistical analysis was performed to determine the differences in compression and sheer between the initial and replacement screw for each angle and screw insertion group with a 2-sided paired Student test.
In comparison with the average compression force achieved by placement of the primary screw, there was a significant loss of average compression force when the secondary screw was placed in the same direction and perpendicular to the fracture plane (50 N, < .001), in the reverse direction and perpendicular to the fracture plane (9 N, = .049), and in the same direction and 60º to the fracture plane (11 N, < .001). A significantly greater average shear displacement was noted for initial screw insertion at oblique compared with perpendicular orientations (0.03 mm, < .001).
This study demonstrates loss of compression when replacing screws despite varying orientations. Additionally, shear displacement in obliquely placed screws increased compared with perpendicularly placed screws.
This study provided quantitative evidence to support the importance of establishing the correct screw length initially to avoid compression loss caused by replacing a primary screw.
通过量化骨折块间的压缩力和剪切位移，研究初次使用及更换无头加压螺钉时生物力学固定的变化。
用两块硬质聚氨酯泡沫制作骨模型以模拟骨折部位。将一枚24毫米的无头加压螺钉以垂直或倾斜角度插入模型，取出后用22毫米的螺钉替换。22毫米的螺钉沿初次插入的相同或相反方向替换24毫米的螺钉。初次和更换螺钉固定的所有4种方法均进行15次试验，共60次试验。两个纽扣式测力传感器测量压缩力。一台数字显微镜记录剪切位移。采用双侧配对t检验进行统计分析，以确定每个角度和螺钉插入组初次和更换螺钉时压缩力和剪切力的差异。
与初次置入螺钉时所获得的平均压缩力相比，二次螺钉沿相同方向且垂直于骨折平面置入时，平均压缩力显著降低（50牛，P<0.001）；沿相反方向且垂直于骨折平面置入时，平均压缩力显著降低（9牛，P = 0.049）；沿相同方向且与骨折平面呈60°角置入时，平均压缩力显著降低（11牛，P<0.001）。与垂直方向相比，初次螺钉倾斜插入时平均剪切位移显著更大（0.03毫米，P<0.001）。
本研究表明尽管螺钉置入方向不同，但更换螺钉时压缩力会降低。此外，与垂直放置的螺钉相比，倾斜放置的螺钉剪切位移增加。
本研究提供了定量证据，支持了最初确定正确螺钉长度以避免更换初次螺钉导致压缩力损失的重要性。
