Department of Orthopedic Surgery, University of California, Davis, Sacramento, California 95817, USA.
J Trauma Acute Care Surg. 2012 Mar;72(3):751-4. doi: 10.1097/TA.0b013e31823b8b9f.
This study qualified and evaluated the mechanical properties of three different screw orientations used for fixation of vertical shear fractures of the medial malleolus.
Identical vertical osteotomies were created in synthetic distal tibiae using a jig. The specimens were assigned to one of the three fixation groups (n = 8 per group): (1) parallel: two 40 mm length, 4.0 mm diameter screws placed parallel to each other in the transverse plane; (2) convergent: two 40 mm length, 4.0 mm diameter screws placed 25 degree convergent to each other in the transverse plane; and (3) divergent: two 40 mm length, 4.0 mm diameter screws placed 15 degree divergent to each other in the transverse plane. The specimens were tested using offset axial loading at 1 mm/s until 2 mm of displacement.
The average stiffness was 102 N/mm ± 51 N/mm for the parallel group, 109 N/mm ± 37 N/mm for the convergent group, and 185 N/mm ± 73 N/mm for the divergent group. The average stiffness of the divergent group was significantly greater than either the parallel (p < 0.05) or convergent (p < 0.05) groups. The divergent group was 81.4% more stiff than the parallel group and 69.7% more stiff than the convergent group. The average load at 2 mm of displacement was 324 N ± 87 N for the parallel group, 373 N ± 95 N for the convergent group, and 512 N ± 170 N for the divergent group. The average load at failure of the divergent group was significantly (p < 0.05) greater than the parallel groups. The divergent group was required 58.0% more force at 2 mm of displacement than the parallel group and 37.3% more force at 2 mm of displacement than the convergent group.
The use of a divergent screw pattern resulted in a stiffer fixation construct that requires more force for 2 mm of displacement when used to stabilize an osteotomy model of vertical shear medial malleolus fractures.
本研究对用于固定内踝垂直剪切骨折的三种不同螺钉方向的力学性能进行了定性和评估。
使用夹具在合成胫骨远端创建相同的垂直截骨术。将标本分为三组固定组（每组 8 个标本）：（1）平行：两个 40mm 长、4.0mm 直径的螺钉在横平面上彼此平行放置；（2）会聚：两个 40mm 长、4.0mm 直径的螺钉在横平面上以 25 度会聚放置；和（3）发散：两个 40mm 长、4.0mm 直径的螺钉在横平面上以 15 度发散放置。标本以 1mm/s 的偏移轴向加载至 2mm 位移。
平行组的平均刚度为 102N/mm±51N/mm，会聚组为 109N/mm±37N/mm，发散组为 185N/mm±73N/mm。发散组的平均刚度明显大于平行组（p<0.05）或会聚组（p<0.05）。发散组比平行组僵硬 81.4%，比会聚组僵硬 69.7%。平行组 2mm 位移时的平均载荷为 324N±87N，会聚组为 373N±95N，发散组为 512N±170N。发散组的失效载荷平均值明显大于平行组（p<0.05）。发散组在 2mm 位移时需要的力比平行组多 58.0%，比会聚组多 37.3%。
使用发散式螺钉模式可固定更坚固的结构，在稳定垂直剪切内踝骨折模型时，在 2mm 位移处需要更大的力。
