Clinical Laboratory for Bionic Extremity Reconstruction, Department of Plastic, Reconstructive and Aesthetic Surgery, Medical University of Vienna, Vienna, Austria.
BG Trauma Clinic, Eberhard Karls University, Department for Plastic and Reconstructive Surgery, Tübingen, Germany.
Clin Orthop Relat Res. 2022 Jun 1;480(6):1191-1204. doi: 10.1097/CORR.0000000000002135. Epub 2022 Feb 23.
Currently used prosthetic solutions in upper extremity amputation have limited functionality, owing to low information transfer rates of neuromuscular interfacing. Although surgical innovations have expanded the functional potential of the residual limb, available interfaces are inefficacious in translating this potential into improved prosthetic control. There is currently no implantable solution for functional interfacing in extremity amputation which offers long-term stability, high information transfer rates, and is applicable for all levels of limb loss. In this study, we presented a novel neuromuscular implant, the the Myoelectric Implantable Recording Array (MIRA). To our knowledge, it is the first fully implantable system for prosthetic interfacing with a large channel count, comprising 32 intramuscular electrodes.
QUESTIONS/PURPOSES: The purpose of this study was to evaluate the MIRA in terms of biocompatibility, functionality, and feasibility of implantation to lay the foundations for clinical application. This was achieved through small- and large-animal studies as well as test surgeries in a human cadaver.
We evaluated the biocompatibility of the system's intramuscular electromyography (EMG) leads in a rabbit model. Ten leads as well as 10 pieces of a biologically inert control material were implanted into the paravertebral muscles of four animals. After a 3-month implantation, tissue samples were taken and histopathological assessment performed. The probes were scored according to a protocol for the assessment of the foreign body response, with primary endpoints being inflammation score, tissue response score, and capsule thickness in µm. In a second study, chronic functionality of the full system was evaluated in large animals. The MIRA was implanted into the shoulder region of six dogs and three sheep, with intramuscular leads distributed across agonist and antagonist muscles of shoulder flexion. During the observation period, regular EMG measurements were performed. The implants were removed after 5 to 6 months except for one animal, which retained the implant for prolonged observation. Primary endpoints of the large-animal study were mechanical stability, telemetric capability, and EMG signal quality. A final study involved the development of test surgeries in a fresh human cadaver, with the goal to determine feasibility to implant relevant target muscles for prosthetic control at all levels of major upper limb amputation.
Evaluation of the foreign body reaction revealed favorable biocompatibility and a low-grade tissue response in the rabbit study. No differences regarding inflammation score (EMG 4.60 ± 0.97 [95% CI 4.00 to 5.20] versus control 4.20 ± 1.48 [95% CI 3.29 to 5.11]; p = 0.51), tissue response score (EMG 4.00 ± 0.82 [95% CI 3.49 to 4.51] versus control 4.00 ± 0.94 [95% CI 3.42 to 4.58]; p > 0.99), or thickness of capsule (EMG 19.00 ± 8.76 µm [95% CI 13.57 to 24.43] versus control 29.00 ± 23.31 µm [95% CI 14.55 to 43.45]; p = 0.29) were found compared with the inert control article (high-density polyethylene) after 3 months of intramuscular implantation. Throughout long-term implantation of the MIRA in large animals, telemetric communication remained unrestricted in all specimens. Further, the implants retained the ability to record and transmit intramuscular EMG data in all animals except for two sheep where the implants became dislocated shortly after implantation. Electrode impedances remained stable and below 5 kΩ. Regarding EMG signal quality, there was little crosstalk between muscles and overall average signal-to-noise ratio was 22.2 ± 6.2 dB. During the test surgeries, we found that it was possible to implant the MIRA at all major amputation levels of the upper limb in a human cadaver (the transradial, transhumeral, and glenohumeral levels). For each level, it was possible to place the central unit in a biomechanically stable environment to provide unhindered telemetry, while reaching the relevant target muscles for prosthetic control. At only the glenohumeral level, it was not possible to reach the teres major and latissimus dorsi muscles, which would require longer lead lengths.
As assessed in a combination of animal model and cadaver research, the MIRA shows promise for clinical research in patients with limb amputation, where it may be employed for all levels of major upper limb amputation to provide long-term stable intramuscular EMG transmission.
In our study, the MIRA provided high-bandwidth prosthetic interfacing through intramuscular electrode sites. Its high number of individual EMG channels may be combined with signal decoding algorithms for accessing spinal motor neuron activity after targeted muscle reinnervation, thus providing numerous degrees of freedom. Together with recent innovations in amputation surgery, the MIRA might enable improved control approaches for upper limb amputees, particularly for patients with above-elbow amputation where the mismatch between available control signals and necessary degrees of freedom for prosthetic control is highest.
目前在上肢截肢中使用的假肢解决方案，由于神经肌肉接口的信息传输率较低，其功能有限。尽管手术创新扩大了残肢的功能潜力，但现有的接口在将这种潜力转化为改善假肢控制方面效果不佳。目前，在肢体截肢的功能接口方面，还没有一种可植入的解决方案能够提供长期稳定性、高信息传输率，并适用于所有截肢水平。在这项研究中，我们提出了一种新型的神经肌肉植入物，即肌电植入式记录阵列（MIRA）。据我们所知，这是第一个具有大容量通道的完全可植入系统，包含 32 个肌内电极。
问题/目的：本研究的目的是评估 MIRA 的生物相容性、功能和植入的可行性，为临床应用奠定基础。这是通过小动物和大动物研究以及人体尸体测试手术来实现的。
我们在兔模型中评估了系统的肌内电描记术（EMG）导丝的生物相容性。将 10 个导丝和 10 个生物惰性对照材料植入 4 只动物的椎旁肌。植入 3 个月后，取出组织样本进行组织病理学评估。探针根据异物反应评估方案进行评分，主要终点为炎症评分、组织反应评分和厚度以µm 为单位。在第二项研究中，在大动物中评估了完整系统的慢性功能。将 MIRA 植入 6 只狗和 3 只羊的肩部区域，肌内导丝分布在肩屈伸的主动肌和拮抗肌上。在观察期间，定期进行 EMG 测量。除了一只动物因长期观察而保留植入物外，其余动物在 5 至 6 个月后取出植入物。大动物研究的主要终点是机械稳定性、遥测能力和 EMG 信号质量。最后一项研究涉及在新鲜人体尸体上进行测试手术，目的是确定在所有主要上肢截肢水平上为假肢控制植入相关目标肌肉的可行性。
在兔研究中，对异物反应的评估显示出良好的生物相容性和低等级的组织反应。炎症评分（EMG 4.60 ± 0.97 [95%CI 4.00 至 5.20] 与对照组 4.20 ± 1.48 [95%CI 3.29 至 5.11]；p = 0.51）、组织反应评分（EMG 4.00 ± 0.82 [95%CI 3.49 至 4.51] 与对照组 4.00 ± 0.94 [95%CI 3.42 至 4.58]；p > 0.99）或胶囊厚度（EMG 19.00 ± 8.76 µm [95%CI 13.57 至 24.43] 与对照组 29.00 ± 23.31 µm [95%CI 14.55 至 43.45]；p = 0.29）与惰性对照物（高密度聚乙烯）相比，在 3 个月的肌内植入后无差异。在大动物中长时间植入 MIRA 期间，遥测通信在所有标本中均不受限制。此外，除了两只羊在植入后不久植入物移位外，所有动物的植入物都保留了记录和传输肌内 EMG 数据的能力。电极阻抗保持稳定且低于 5 kΩ。关于 EMG 信号质量，肌肉之间的串扰很小，总体平均信噪比为 22.2 ± 6.2 dB。在测试手术中，我们发现可以在人体尸体的所有上肢主要截肢水平（桡骨、肱骨和肩胛盂水平）植入 MIRA。对于每个水平，可以将中央单元放置在生物力学稳定的环境中，以提供不受阻碍的遥测，同时到达用于假肢控制的相关目标肌肉。仅在肩胛盂水平，无法到达胸大肌和背阔肌，这需要更长的导丝长度。
如动物模型和尸体研究相结合所评估的，MIRA 有望在肢体截肢患者的临床研究中得到应用，它可以用于所有主要上肢截肢水平，以提供长期稳定的肌内 EMG 传输。
在我们的研究中，MIRA 通过肌内电极部位提供了高带宽的假肢接口。其大量的单个 EMG 通道可以与信号解码算法结合使用，以访问靶向肌肉再支配后的脊髓运动神经元活动，从而提供多个自由度。结合最近的截肢手术创新，MIRA 可能为上肢截肢患者提供更好的控制方法，特别是对于那些以上肢截肢的患者，因为在这些患者中，可用的控制信号与假肢控制所需的自由度之间的不匹配最高。
