Yamaguchi Kent T, Telfer Scott, Iannuzzi Nicholas, Hoang Don, Huang Jerry I
Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, WA.
J Hand Surg Glob Online. 2023 Jan 5;5(2):189-195. doi: 10.1016/j.jhsg.2022.12.002. eCollection 2023 Mar.
This biomechanical study evaluated the effect of intramedullary screw diameter and length relative to 3-point bending force and torsional force when used to stabilize metacarpal shaft fractures.
Transverse osteotomies were made in the proximal metacarpal shaft in 36 middle finger metacarpal fourth-generation composite Sawbones. To compare screw diameters, antegrade intramedullary screws of 30-mm length were placed in 6 metacarpals, which included 4.7-mm Acutrak 2, Standard Acutrak 2 (4.0 mm), and Mini-Acutrak 2 (3.5 mm) screws. To compare screw lengths, metacarpals were fixated with Standard Acutrak 2 screws of 26, 30, or 34 mm in length, with screw tips bypassing the osteotomy by 6, 10, or 14 mm, respectively. A 6 degrees of freedom robot was used for torsional and 3-point bending testing.
Increasing screw diameter demonstrated significant differences in both 3-point bending and torsional strengths. Maximum torsional loads were 69 Ncm (4.7-mm Acutrak 2), 45 Ncm (Standard Acutrak 2), and 27 Ncm (Mini-Acutrak 2) ( < .05). Loads to failure in the 3-point bending tests were 916 N (4.7-mm Acutrak 2), 713 N (Standard Acutrak 2), and 284 N (Mini-Acutrak 2) ( < .05). Differing screw lengths demonstrated significant differences with maximum torsional loads when comparing the 26-mm screws (22 Ncm) with 30- and 34-mm screws (45 and 55 Ncm, respectively) ( < .05). The 3-point dorsal bending strengths were significantly different between the 26-mm screws (320 N) and 30- and 34-mm screws (713 N and 702 N, respectively) ( < .05).
The results demonstrated significantly higher torsional strength and resistance to 3-point bending with larger intramedullary screw diameters. Further, when selecting the intramedullary screw length, the screw tip should pass at least 10 mm beyond the fracture.
This study provided biomechanical evidence to guide surgeons in selecting intramedullary screw diameter and length for treating metacarpal fractures.
本生物力学研究评估了用于稳定掌骨干骨折的髓内螺钉直径和长度相对于三点弯曲力和扭转力的影响。
在36根中指掌骨第四代复合Sawbones的近端掌骨干处进行横向截骨。为比较螺钉直径，将长度为30 mm的顺行髓内螺钉置入6根掌骨中，其中包括4.7 mm的Acutrak 2螺钉、标准Acutrak 2螺钉（4.0 mm）和微型Acutrak 2螺钉（3.5 mm）。为比较螺钉长度，用长度为26、30或34 mm的标准Acutrak 2螺钉固定掌骨，螺钉尖端分别超过截骨处6、10或14 mm。使用六自由度机器人进行扭转和三点弯曲测试。
增加螺钉直径在三点弯曲强度和扭转强度方面均显示出显著差异。最大扭转载荷分别为69 N·cm（4.7 mm Acutrak 2螺钉）、45 N·cm（标准Acutrak 2螺钉）和27 N·cm（微型Acutrak 2螺钉）（P<0.05）。三点弯曲试验中的破坏载荷分别为916 N（4.7 mm Acutrak 2螺钉）、713 N（标准Acutrak 2螺钉）和284 N（微型Acutrak 2螺钉）（P<0.05）。比较26 mm螺钉（22 N·cm）与30 mm和34 mm螺钉（分别为45 N·cm和55 N·cm）时，不同螺钉长度在最大扭转载荷方面显示出显著差异（P<0.05）。26 mm螺钉（320 N）与30 mm和34 mm螺钉（分别为713 N和702 N）之间的三点背侧弯曲强度存在显著差异（P<0.05）。
结果表明，较大直径的髓内螺钉具有显著更高的扭转强度和抗三点弯曲能力。此外，在选择髓内螺钉长度时，螺钉尖端应至少超过骨折处10 mm。
本研究提供了生物力学证据，以指导外科医生选择治疗掌骨骨折的髓内螺钉直径和长度。
