Disorders of consciousness (DoC) represent a wide spectrum of neurological conditions, which include coma, vegetative state/unresponsive wakefulness state (VS/UWS), and minimally conscious state (MCS), posing profound challenges to medical management and patient rehabilitation (Eapen et al., 2017; Giacino et al., 2018). These conditions result from significant brain injuries and are characterized by varied levels of wakefulness and awareness (Edlow et al., 2021). Traditional treatment modalities are often limited in their effectiveness, and only amantadine is considered as an effective drug through randomized controlled trial (Giacino et al., 2012; Ruhl et al., 2022). Thus, clinicians are seeking alternative therapeutic avenues to promote the recovery of patients with disorders of consciousness. Among these, neuromodulation techniques offer a novel approach to facilitating changes in the patients’ brain activity patterns in hopes of restoring consciousness (Vanhoecke and Hariz, 2017; Wu et al., 2023). This method represents an emerging frontier in the treatment of disorders of consciousness, attempting to bridge the gap between the damaged neuronal pathways and the complex network that governs wakefulness and awareness (Raguz et al., 2021; Cao et al., 2023).

Spinal cord stimulation (SCS) is an innovative therapeutic intervention for DoC that targets the neural structures implicated in arousal and awakening by delivering electrical impulses directly to the spinal cord (Martens et al., 2017; Yamamoto et al., 2017). This modality of treatment demonstrates potential not only for transient cognitive improvements but also for facilitating long-term recovery in brain function (Yang et al., 2022). Recently, percutaneous short-term SCS has been reported to may be useful in the treatment of DoC (Yang et al., 2022; Huang et al., 2023). This minimally invasive approach affords clinicians the ability to directly engage with neuronal circuits that may be responsible for the modulation of conscious states (Zhuang et al., 2023). This treatment method implants electrodes into the body for a short time and is currently mainly used for diagnostic treatment. Therefore, this requires the electrode to be effective within a short period of time, so the requirement for full effectiveness is more important. However, whether anatomical-related factors will affect the effectiveness of percutaneous short-term SCS in patients with DoC to restore consciousness remain unknown.

Recognizing the importance of these issues, the present study aims to investigate the effectiveness of percutaneous short-term SCS in treating DoC and the possible anatomical factors related to electrode shift which could affect patients’ outcome. Through a meticulous analysis of various anatomical parameters and their relationship to electrode shift, this research seeks to provide valuable insights into improving the stability of SCS implantation process and, ultimately, the outcomes of patients with DoC.

The findings from this study underscore the critical issue of electrode shift in the cervical region when performing percutaneous short-term SCS in patients with DoC, which has a direct and adverse impact on the short-term therapeutic efficacy of SCS in patients with disorders of consciousness. Despite our initial hypothesis, anatomical factors such as the actual length of the cervical spine, spinal canal diameter, spinal canal transverse diameter, and the height of the C2 vertebral body were not associated with the length of electrode shift. Interestingly, we found a significant linear correlation between the length of electrode shift with the outcome in patients with DoC. The data suggests that the greater the extent of electrode shift, the worse the outcome in the patients, potentially due to decreased stimulation efficacy or increased interval of therapy disruption. This finding indicates that securing the electrode optimally is of paramount importance to improving patient outcomes.

By modulating neural activity and possibly promoting neuroplasticity, spinal cord stimulation emerges as a complementary approach capable of augmenting the limited therapeutic options currently available for patients with disorders of consciousness. Evoked compound action potentials (ECAPs) are generated when electric stimuli are applied to the dorsal columns of the spinal cord, which predominantly consist of sensory fibers that conduct information toward the brain. These action potentials propagate along the ascending sensory pathways and are thought to facilitate the activation of various subcortical structures, including the thalamus and reticular formation, which play crucial roles in modulating consciousness. The stimulation of these pathways is believed to enhance the synaptic efficacy and promote neuroplasticity, potentially leading to improvements in the neural circuits involved in consciousness. Such theoretical and empirical frameworks provide a basis for understanding how SCS might contribute to the restoration of awareness in patients with disorders of consciousness, offering hope for augmenting their responsive states. Currently, non-surgical treatments include drug treatments such as amantadine, levodopa, baclofen, and zolpidem, as well as treatments including hyperbaric oxygen therapy, repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS), midline nerve stimulation (MNS), and transcutaneous vagus nerve stimulation (taVNS) (Gosseries et al., 2014; Edlow et al., 2021; Ruhl et al., 2022; Somaa et al., 2022; Vitello et al., 2023; Marino, 2024). It is also pertinent to consider the emerging evidence surrounding invasive neuromodulation techniques, notably deep brain stimulation (DBS). DBS involves the placement of electrodes in specific brain regions, which, when stimulated, can modulate neural activity at deeper levels. Studies targeting nuclei such as the thalamus, basal ganglia, and limbic structures have shown promising results in altering the state of consciousness and promoting cognitive function in DoC patients. For instance, research indicates that thalamic stimulation may help in ‘reactivating’ neural networks that are crucial for consciousness, potentially leading to significant clinical improvements in responsiveness in some patients (Yang et al., 2023). These findings underscore the potential utility of DBS alongside other methods like SCS in managing complex conditions like DoC, suggesting a multimodal approach might be the most effective in modulating the intricate neural pathways implicated in consciousness. SCS implants the stimulating electrode into the C2-C4 cervical spinal cord segment. The stimulation signal is transmitted downward from the neural network to the effect muscle group, producing an action potential, while activating the reticular structure, thalamus, dopamine, and norepinephrine nerve nuclei upward to increase cerebral blood flow and improve brain function to increase consciousness level (Mazzone et al., 1995; Visocchi et al., 2001; McDonagh et al., 2007; Liu et al., 2008; Yamamoto et al., 2012). Through the strategic placement of electrodes along the cervical spinal column, SCS plays a pivotal role in regulating wakefulness and attention. Its role in clinical practice may provide a gateway to enhanced rehabilitation strategies and improved quality of life for individuals who have suffered severe brain injuries.

After the stimulator is implanted at the ideal position of the spinal cord segment, a pulse is generated at the black dot mark to activate the dorsal column of the spinal cord and produce electrically evoked compound action potentials (ECAPs) (Foreman and Linderoth, 2012; Dietz et al., 2022). The ECAP is transmitted back through the side branch of primary Aβ input to stimulate interneurons and ultimately trigger action potentials of muscle effectors. After the stimulation electrode is turned on, if the implantation position is shifted, the generated stimulation electric field may be decreased.

There are three main aspects of complications of SCS surgery: implant-related complications, biological complications, and program or treatment-related complications. Electrode shift is the most common and serious complication associated with implant-related complications. Existing literature reports that the rate of electrode shift in surgery for failed back surgery syndrome (FBSS) and complex regional pain syndrome (CRPS) is 2.1 to 27% (Fiume et al., 1995; Kumar et al., 2006; Klase et al., 2009). When the electrode is shifted, minor adjustments to the program parameters may be required, and major adjustments may require surgical fine-tuning. Patients with severe shift may even need to have the electrode re-implanted (Eldabe et al., 2016). There are currently no reports of electrode shift in SCS surgery for patients with DoC. For SCS implantation for pain relief, the probability of electrode shift can be reduced by intraoperative awakening of patients to relieve pain (Hwang et al., 2019). However, for patients with DoC, long-term maintenance of tracheotomy and bed rest lead to impaired ventilation and gas exchange function, and intraoperative awakening seems to be impossible. Moreover, patients with DoC lack subjective expression, and clinical manifestations will be affected by abnormal muscle tone and muscle capacity of patients. Therefore, the accuracy and precision are not high.

In this study, we found percutaneous short-term SCS may be promising for patients with DoC. By stimulating specific neural pathways, there is the potential to not only awaken cognitive functions in these individuals but also to ameliorate a variety of motor and respiratory impairments, refine muscle tone, and address other related complications. This could dramatically improve the quality of life for affected patients and provide a cornerstone for longer-term rehabilitation strategies. Surgeons, neurologists, and rehabilitation specialists should take cognizance of the linear correlation between electrode loss and patient prognosis, as it underscores the critical need for secure electrode placement and monitoring to prevent electrode shift.

Despite the insights provided by this research, there are several limitations that need to be addressed. The study’s retrospective design is inherently limited by the quality and completeness of recorded data. Prospective studies are warranted to more accurately assessing the relationship between electrode shift and outcomes. Meanwhile, a non-shift group may provide further informative results, which was not included in this study. The study measured several anatomical parameters, other potential anatomical or biomechanical factors influencing electrode stability (like neck muscle tone, ligament integrity) were not analyzed. Enhancing future research with these considerations in mind could provide deeper insights and help in fine-tuning therapeutic strategies for patients undergoing SCS for DoC.

The study showed the importance of electrode stability in SCS for patients with DoC, and the electrode shift may lead to worse outcome in those patients. While anatomical dimensions do not seem to play a decisive role in electrode shift, the actual length of the cervical spine and its relationship to shift could present a new avenue of investigation in achieving improved patient outcomes.

The data supporting the conclusions of this article will be made available by the corresponding author, upon reasonable request.

The studies involving humans were approved by IRB of Beijing Tiantan Hospital. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

QH: Conceptualization, Writing – original draft, Writing – review & editing. CY: Formal analysis, Writing – review & editing. YX: Data curation, Writing – review & editing. HN: Data curation, Writing – review & editing. HW: Data curation, Writing – review & editing. HH: Data curation, Writing – review & editing. XC: Data curation, Writing – review & editing. TC: Data curation, Writing – review & editing. NW: Data curation, Writing – review & editing. PW: Writing – review & editing. JH: Supervision, Writing – review & editing. YY: Funding acquisition, Project administration, Supervision, Validation, Writing – review & editing. JZ: Supervision, Writing – review & editing.