Euler Simon A, Petri Maximilian, Venderley Melanie B, Dornan Grant J, Schmoelz Werner, Turnbull Travis Lee, Plecko Michael, Kralinger Franz S, Millett Peter J
Department of Trauma Surgery and Sports Traumatology, Medical University Innsbruck, Anichstr. 35, 6020, Innsbruck, Austria.
The Steadman Clinic, 181 West Meadow Drive, Suite 400, Vail, CO, 81657, USA.
Int Orthop. 2017 Sep;41(9):1715-1721. doi: 10.1007/s00264-017-3498-y. Epub 2017 May 11.
Varus failure is one of the most common failure modes following surgical treatment of proximal humeral fractures. Straight antegrade nails (SAN) theoretically provide increased stability by anchoring to the densest zone of the proximal humerus (subchondral zone) with the end of the nail. The aim of this study was to biomechanically investigate the characteristics of this "proximal anchoring point" (PAP). We hypothesized that the PAP would improve stability compared to the same construct without the PAP.
Straight antegrade humeral nailing was performed in 20 matched pairs of human cadaveric humeri for a simulated unstable two-part fracture.
Biomechanical testing, with stepwise increasing cyclic axial loading (50-N increments each 100 cycles) at an angle of 20° abduction revealed significantly higher median loads to failure for SAN constructs with the PAP (median, 450 N; range, 200-1.000 N) compared to those without the PAP (median, 325 N; range, 100-500 N; p = 0.009). SAN constructs with press-fit proximal extensions (endcaps) showed similar median loads to failure (median, 400 N; range, 200-650 N), when compared to the undersized, commercially available SAN endcaps (median, 450 N; range, 200-600 N; p = 0.240).
The PAP provided significantly increased stability in SAN constructs compared to the same setup without this additional proximal anchoring point. Varus-displacing forces to the humeral head were superiorly reduced in this setting. This study provides biomechanical evidence for the "proximal anchoring point's" rationale. Straight antegrade humeral nailing may be beneficial for patients undergoing surgical treatment for unstable proximal humeral fractures to decrease secondary varus displacement and thus potentially reduce revision rates.
内翻失败是肱骨近端骨折手术治疗后最常见的失败模式之一。直形顺行髓内钉（SAN）理论上通过钉的末端锚固到肱骨近端最致密区域（软骨下区域）来提供更高的稳定性。本研究的目的是对这个“近端锚固点”（PAP）的特性进行生物力学研究。我们假设与没有PAP的相同结构相比，PAP能提高稳定性。
对20对匹配的人类尸体肱骨进行直形顺行肱骨髓内钉固定，模拟不稳定的两部分骨折。
生物力学测试中，在20°外展角度下逐步增加循环轴向载荷（每100个循环增加50 N），结果显示有PAP的SAN结构的中位失效载荷（中位值450 N；范围200 - 1000 N）显著高于没有PAP的结构（中位值325 N；范围100 - 500 N；p = 0.009）。与尺寸过小的市售SAN端帽相比，带有压配近端延伸部分（端帽）的SAN结构显示出相似的中位失效载荷（中位值400 N；范围200 - 650 N）（中位值450 N；范围200 - 600 N；p = 0.240）。
与没有这个额外近端锚固点的相同设置相比，PAP在SAN结构中显著提高了稳定性。在这种情况下，肱骨头的内翻移位力得到了更好的降低。本研究为“近端锚固点”的原理提供了生物力学证据。对于接受不稳定肱骨近端骨折手术治疗的患者，直形顺行肱骨髓内钉固定可能有助于减少继发性内翻移位，从而可能降低翻修率。
