Eu-Jin Cheah Andre, Behn Anthony W, Comer Garet, Yao Jeffrey
Robert A. Chase Hand and Upper Limb Center, Department of Orthopaedic Surgery, Stanford University Medical Center, Redwood City, CA; Department of Hand and Reconstructive Microsurgery, National University Hospital, National University Health System, Singapore.
Robert A. Chase Hand and Upper Limb Center, Department of Orthopaedic Surgery, Stanford University Medical Center, Redwood City, CA.
J Hand Surg Am. 2017 Dec;42(12):1033.e1-1033.e6. doi: 10.1016/j.jhsa.2017.07.018. Epub 2017 Sep 7.
Surgeons confronted with a long spiral metacarpal fracture may choose to fix it solely with lagged screws. A biomechanical analysis of a metacarpal spiral fracture model was performed to determine whether 3 1.5-mm screws or 2 2.0-mm screws provided more stability during bending and torsional loading.
Second and third metacarpals were harvested from 12 matched pairs of fresh-frozen cadaveric hands and spiral fractures were created. One specimen from each matched pair was fixed with 2 2.0-mm lagged screws whereas the other was fixed with 3 1.5-mm lagged screws. Nine pairs underwent combined cyclic cantilever bending and axial compressive loading followed by loading to failure. Nine additional pairs were subjected to cyclic external rotation while under a constant axial compressive load and were subsequently externally rotated to failure under a constant axial compressive load. Paired t tests were used to compare cyclic creep, stiffness, displacement, rotation, and peak load levels.
Average failure torque for all specimens was 7.2 ± 1.7 Nm. In cyclic torsional testing, the group with 2 screws exhibited significantly less rotational creep than the one with 3 screws. A single specimen in the group with 2 screws failed before cyclic bending tests were completed. No other significant differences were found between test groups during torsional or bending tests.
Both constructs were biomechanically similar except that the construct with 2 screws displayed significantly less loosening during torsional cyclic loading, although the difference was small and may not be clinically meaningful.
Because we found no obvious biomechanical advantage to using 3 1.5-mm lagged screws to fix long spiral metacarpal fractures, the time efficiency and decreased implant costs of using 2-2.0 mm lagged screws may be preferred.
面对长螺旋形掌骨骨折的外科医生可能会选择仅用拉力螺钉进行固定。对掌骨螺旋骨折模型进行生物力学分析，以确定3枚1.5毫米螺钉或2枚2.0毫米螺钉在弯曲和扭转载荷下是否能提供更高的稳定性。
从12对匹配的新鲜冷冻尸体手中获取第二和第三掌骨，并制造螺旋骨折。每对匹配标本中的一个用2枚2.0毫米拉力螺钉固定，另一个用3枚1.5毫米拉力螺钉固定。9对标本先进行联合循环悬臂弯曲和轴向压缩加载，然后加载至破坏。另外9对标本在恒定轴向压缩载荷下进行循环外旋，随后在恒定轴向压缩载荷下外旋至破坏。采用配对t检验比较循环蠕变、刚度、位移、旋转和峰值载荷水平。
所有标本的平均破坏扭矩为7.2±1.7牛米。在循环扭转试验中，2枚螺钉组的旋转蠕变明显低于3枚螺钉组。2枚螺钉组中有1个标本在循环弯曲试验完成前就发生了破坏。在扭转或弯曲试验中，各试验组之间未发现其他显著差异。
两种固定方式在生物力学上相似，只是2枚螺钉的固定方式在扭转循环加载过程中的松动明显较少，尽管差异较小，可能在临床上并无意义。
由于我们发现使用3枚1.5毫米拉力螺钉固定长螺旋形掌骨骨折并无明显的生物力学优势，因此使用2枚2.0毫米拉力螺钉的时间效率和降低的植入成本可能更受青睐。
