Background

Screw fixation in osteoporotic bone is clinically challenging. Screw failure rates are growing due to an increasing prevalence of osteoporosis. To address this, biomechanical models are needed to recreate the bone clinically encountered alongside the development of new operative techniques. The first aim of this study was to test whether the use of a smaller than recommended pilot-hole diameter improved pull-out strength for cancellous screws, with the second aim to create a model of low-density porcine bone for biomechanical testing.

Methods

Thirty porcine tibiae were cut into transverse metaphyseal sections of 20 mm thickness. Bone density was altered using 0.15 M Hydrochloric acid, and measured and pre- and post-demineralisation using HRμCT. Seventy-two screw areas were randomised to either 2.5 mm or 1.5 mm pilot holes and to either be normal or reduced density. Maximum axial pull-out strength was measured.

Findings

Demineralisation reduced bone density by 12% (p < 0.0001) and 11% (p < 0.0001) for 2.5 mm and 1.5 mm pilot hole diameters respectively. Pull-out strength reduced by 50% (p = 0.0001) and 44% (p < 0.0001) following demineralisation for both 2.5 mm and 1.5 mm pilot hole diameters. Pull-out strength increased by 51% (p = 0.0008) when inserting screws into 1.5 mm pilot holes in low density bone, and by 28% (p = 0.027) in normal bone.

Interpretation

Porcine bone can be demineralised to model low density cancellous bone. This novel model showed that pullout force is significantly reduced in lower density screw holes, but that this reduction can be mitigated by reducing pilot hole diameter for cancellous screws.

中文翻译：

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导向孔直径在密度降低的动物骨骼模型中的松质螺钉固定中的影响。

背景

骨质疏松性骨的螺钉固定在临床上具有挑战性。由于骨质疏松症患病率的增加，螺钉的失败率正在增加。为了解决这个问题，除了新的手术技术的发展，还需要生物力学模型来重建临床上遇到的骨骼。这项研究的第一个目标是测试是否使用比建议的孔直径小的建议来改善松质螺钉的拔出强度，第二个目标是创建用于生物力学测试的低密度猪骨模型。

方法

将30只猪胫骨切成20mm厚的干transverse端部分。使用0.15 M盐酸改变骨密度，并使用HRμCT进行去矿化前后的测量。将72个螺钉区域随机分配到2.5毫米或1.5毫米的导向孔中，并按正常或减小的密度进行分配。测量最大轴向拉出强度。

发现

 对于2.5 mm和1.5 mm的导向孔直径，去矿质可分别将骨密度降低12％（p  <0.0001）和11％（p <0.0001）。 对于2.5 mm和1.5 mm的导向孔直径脱盐后，抗拉强度分别降低了50％（p  = 0.0001）和44％（p <0.0001）。 将螺钉插入低密度骨的1.5 mm导向孔中时，拉出强度提高了51％（p = 0.0008），而 在正常骨中则提高了28％（p = 0.027）。

解释

猪骨可以脱矿质以模拟低密度松质骨。这种新颖的模型表明，在密度较低的螺孔中拔出力显着减小，但是可以通过减小松质螺钉的导向孔直径来减轻这种减小。