Supplementary Material for: Acoustic Emission Foreshocks and Aftershocks from Skull Fracture Caused by Surgical Clamping

Abstract Background and Objectives: The clamping force for surgical head immobilization must be sufficiently large enough to prevent slippage but not to induce fracturing. Motivated by an unmet need to detect skull fractures during surgery to trigger remedial action, we sought to demonstrate a method of viable measurement and interpretation of acoustic emissions (AE) generated by a fracturing skull prior, during, and after a fracture. Methods: Escalating clamping force via skull pins affixed in an Integra Life Sciences Mayfield® skull clamp was applied to a formalin-fixed cadaveric head. Variable and pathologic skull thickness was simulated by drilling the skull to reduce thickness at pin locations on the frontal or temporal bone. AE was monitored via an in-house developed device. Results: This method produced a mixture of “punch-out type” skull fractures with some occurrences of larger area “cave-in” type fractures. The recorded AE waveforms, amplitudes, and temporal patterns showed the skull can fail not only immediately upon application of clamping, but also in delayed manners seconds or minutes after force application. A stereotypical, escalating rate of event occurrence and amplitude was detectable prior to delayed fractures (foreshocks) up to a peak event correlating with macroscopic fracture. A stereotypical hyperbolic decay of event rates was detectable immediately post-fracture (aftershocks). Other acoustic sources like drilling were distinguishable. Conclusion: Skull fractures produce stereotypical AE, possibly identifiable intra-operatively. Detecting patterns indicative of impending or recent fracture may allow for immediate intervention, avoiding severe complications. This represents the first reported evidence of detectable foreshock and aftershock AE sequences from bone fracture and points to striking parallels with seismicity generated by earthquakes, thus enabling tools from geophysics to be applied to detect imminent and recent bone failure.

【摘要】背景与目标：手术中头部固定所用的夹持力需足够大以防止移位，但又不能过大导致颅骨骨折。鉴于目前术中检测颅骨骨折以启动补救措施的临床需求尚未得到满足，我们旨在开发一种可有效测量并解读颅骨骨折发生前、中、后所产生的声发射（Acoustic Emissions, AE）的方法。方法：使用固定于Integra Life Sciences Mayfield®颅骨固定夹的颅骨钉逐步增加夹持力，对福尔马林固定的尸体头颅开展实验。通过在额骨或颞骨的颅骨钉固定位点钻孔，模拟不同厚度及病理性颅骨厚度变化。采用自研设备监测声发射信号。结果：本实验方法诱导出了「凿穿型」颅骨骨折，同时也出现了部分大面积「塌陷型」颅骨骨折。记录到的声发射波形、幅值及时域模式显示，颅骨不仅可在施加夹持力的瞬间发生断裂，还可在施力后数秒至数分钟延迟断裂。在延迟性骨折发生前，可观测到典型的事件发生率与幅值逐步升高的模式（前震），直至出现与肉眼可见骨折对应的峰值事件。骨折发生后即刻可观测到典型的事件速率双曲线衰减模式（余震）。其他声源（如钻孔产生的声响）可被有效区分。结论：颅骨骨折会产生具有典型特征的声发射信号，有望在术中被识别。检测出预示即将发生或刚发生骨折的信号模式，可实现及时干预，避免严重并发症。本研究首次报道了可被检测到的骨折相关声发射前震与余震序列，其与地震产生的地震活动存在显著相似性，因此可将地球物理学领域的相关工具应用于检测即将发生或刚发生的骨组织断裂。