Department of Otorhinolaryngology, Jena University Hospital, Jena.
Department of Otolaryngology - Head and Neck Surgery, Hearing Research Center, University of Tübingen Medical Center, Tübingen.
Otol Neurotol. 2022 Feb 1;43(2):e174-e180. doi: 10.1097/MAO.0000000000003413.
Despite the complete embodiment of the stapedius muscle (SM) into the pyramidal eminence, it is possible to safely gain access to the SM belly via a retrofacial approach. This presents a novel approach to directly measure the electrically evoked stapedius reflex threshold (eSRT).
Objective fitting of maximum comfortable loudness levels for cochlear implant users can improve the benefit introduced by the device. Sensing SM activity via direct surgical access represents a potential tool for objective eSRT fitting.
Eighteen human temporal bones (TBs) were used. Micro-computed tomography was performed for six TBs. Standard computed tomography for six TBs. Manual 3D-segmentation of the relevant middle and inner ear anatomy was performed on 12 TBs. Mastoidectomy and posterior tympanotomy allowed the access to middle ear of all 18 the TBs. Once identified the mastoidal segment of the facial nerve (FN), the retrofacial access to the SM was drilled.
The total access rate was 72.2%. Only in the first three cases the posterior semi-circular canal was hit. The SM access was identified posterior to the FN at a 4 ± 0.78 mm distance from the stapes' head, almost halfway to the chorda tympani's branching point along the FN direction. The drilling depth to access the SM posterior to the external surface of FN on average was 2 ± 0.30 mm. The exposure took on average of 5 to 8 minutes.
The retrofacial approach seems to offer a feasible and reproducible access to the SM belly opening an avenue to electromyographic sensing of eSRT.
尽管镫骨肌（SM）完全嵌入锥体隆起，但通过后路入路安全地进入 SM 腹部是可能的。这为直接测量电诱发镫骨肌反射阈值（eSRT）提供了一种新方法。
为耳蜗植入用户进行最大舒适响度级别的客观拟合可以提高设备带来的益处。通过直接手术获得 SM 活动的感知代表了客观 eSRT 拟合的潜在工具。
使用了 18 个人颞骨（TB）。对 6 个 TB 进行了微计算机断层扫描。对 6 个 TB 进行了标准计算机断层扫描。对 12 个 TB 进行了相关中耳和内耳解剖结构的手动 3D 分割。乳突切除术和后鼓室切开术允许进入所有 18 个 TB 的中耳。一旦确定面神经（FN）的乳突段，就会对 SM 进行后路入路。
总进入率为 72.2%。仅在前三个病例中，后半规管受到撞击。SM 进入点位于 FN 后 4±0.78mm 处，距离镫骨头几乎有 FN 方向上的鼓索分支点的一半。沿 FN 方向向后路进入 FN 外表面后平均需钻深 2±0.30mm 以到达 SM。暴露平均需要 5 到 8 分钟。
后路入路似乎提供了一种可行且可重复的进入 SM 腹部的方法，为 eSRT 的肌电图感应开辟了途径。
