R Adams Cowley Shock Trauma Center, Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
J Orthop Trauma. 2013 Feb;27(2):e25-30. doi: 10.1097/BOT.0b013e3182511ed7.
External fixator pins are thought to have improved pullout strength if inserted into both cortices and if pilot holes are drilled. We tested these hypotheses and investigated effects of osteoporosis and pin location on pin pullout strength.
Self-drilling external fixator pins were inserted using 4 techniques: 1) predrilled bicortically inserted, 2) not predrilled bicortically inserted, 3) not predrilled unicortically inserted, and 4) technique 2 with far cortex disengaged to test holding power of near cortex in isolation. Ninety-six samples were tested from four locations in 12 matched pairs of cadaveric femora [6 pairs osteoporotic (T ≤ -2.5), six pairs nonosteoporotic (T > -2.5)]. Pullout force was tested on materials testing system until failure of pin-bone interface.
Bicortical pin placement and location within femur had substantial effects on the holding power of the pins. Osteoporosis had statistically significant effect but with smaller effect size (P = 0.05). No significant difference in holding power was observed between predrilling and no predrilling techniques (P = 0.27). We observed only a trend toward "stripping effect" in near cortex with technique 4. Bicortical placement rendered 69% greater holding power than unicortical. Proximal placement rendered 56% greater holding power than distal. Osteoporotic samples had 15% less holding power than nonosteoporotic samples.
Single-cortex pin placement, osteoporotic bone, and more distal pin location decreased pin pullout strength. We did not observe a significant mechanical advantage of predrilling for modern external fixator pins. The near cortex of a pin inserted into 2 cortices without predrilling did not exhibit substantial stripping effect.
人们认为，如果将外固定器钉插入双皮质并钻导孔，钉的拔出强度会提高。我们检验了这些假设，并研究了骨质疏松症和钉位置对钉拔出强度的影响。
使用 4 种技术将自钻外固定器钉插入：1）预钻孔双皮质插入，2）未预钻孔双皮质插入，3）未预钻孔单皮质插入，4）第 2 种技术，远皮质分离以单独测试近皮质的固位力。从 12 对配对的尸体股骨的 4 个部位（6 对骨质疏松症（T ≤-2.5），6 对非骨质疏松症（T＞-2.5））测试了 96 个样本。在材料测试系统上测试拔出力，直到钉-骨界面失效。
双皮质钉的放置和股骨内的位置对钉的固位力有很大影响。骨质疏松症有统计学意义，但影响较小（P = 0.05）。预钻孔和未预钻孔技术之间的固位力无显著差异（P = 0.27）。我们仅观察到第 4 种技术中近皮质有“剥离效应”的趋势。双皮质放置使固位力提高 69%，而单皮质放置使固位力提高 56%。近端放置比远端放置的固位力大 56%。骨质疏松症样本的固位力比非骨质疏松症样本低 15%。
单皮质钉放置、骨质疏松症骨和更远端的钉位置降低了钉的拔出强度。我们没有观察到预钻孔对现代外固定器钉有显著的力学优势。未预钻孔插入双皮质的近皮质没有明显的剥离效应。
