Effect of Durotomy versus Myelotomy on Tissue Sparing and Functional Outcome after Spinal Cord Injury

Quantifying injury expansion in the cervical spinal cord with intravital ultrafast contrast-enhanced ultrasound imaging

Spinal cord injury is characterized by hemodynamic disruption at the injury epicenter and hypoperfusion in the penumbra, resulting in progressive ischemia and cell death. This degenerative secondary injury process has been well-described, though mostly using ex vivo or depth-limited optical imaging techniques. Intravital contrast-enhanced ultrasound enables longitudinal, quantitative evaluation of anatomical and hemodynamic changes in vivo through the entire spinal parenchyma. Here, we used ultrasound imaging to visualize and quantify subacute injury expansion (through 72 h post-injury) in a rodent cervical contusion model. Significant intraparenchymal hematoma expansion was observed through 72 h post-injury (1.86 ± 0.17-fold change from acute, p < 0.05), while the volume of the ischemic deficit largely increased within 24 h post-injury (2.24 ± 0.27-fold, p < 0.05). Histology corroborated these findings; increased apoptosis, tissue and vessel loss, and sustained tissue hypoxia were observed at 72 h post-injury. Vascular resistance was significantly elevated in the remaining perfused tissue, likely due in part to deformation of the central sulcal artery nearest to the lesion site. In conjunction, substantial hyperemia was observed in all perilesional areas examined except the ipsilesional gray matter. This study demonstrates the utility of longitudinal ultrasound imaging as a quantitative tool for tracking injury progression in vivo.

Spinal decompression surgery may alleviate vasopressor-induced spinal hemorrhage and extravasation during acute cervical spinal cord injury in rats

BACKGROUND

Cervical spinal injury often disrupts the supraspinal vasomotor pathways projecting to the thoracic sympathetic preganglionic neurons, leading to cardiovascular dysfunction. The current guideline is to maintain the mean arterial blood pressure at 85 to 90 mmHg using a vasopressor during the first week of the injury. Some studies have demonstrated that this treatment might be beneficial to alleviate secondary injury and improve neurological outcomes; however, elevation of blood pressure may exacerbate spinal hemorrhage, extravasation, and edema, exacerbating the initial injury.

PURPOSE

The present study was designed to (1) examine whether vasopressor administration exacerbates spinal hemorrhage and extravasation; (2) evaluate whether spinal decompression surgery relieves vasopressor-induced spinal hemorrhage and extravasation.

STUDY DESIGN

In vivo animal study.

METHODS

Animals received a saline solution or a vasopressor (phenylephrine hydrochloride, 500 or 1000 μg/kg, 7 mL/kg/h) after mid-cervical contusion with or without spinal decompression (ie, incision of the dura and arachnoid mater). Spinal cord hemorrhage and extravasation were examined by expression of Evans blue within the spinal cord section.

RESULTS

The results demonstrated that cervical spinal contusion significantly reduced the mean arterial blood pressure and induced spinal hemorrhage and extravasation. Phenylephrine infusion significantly elevated the mean arterial blood pressure to the preinjury level within 15 to 60 minutes postcontusion; however, spinal hemorrhage and extravasation were more extensive in animals that received phenylephrine than in those that received saline. Notably, spinal decompression mitigated spinal hemorrhage and extravasation in contused rats who received phenylephrine.

CONCLUSIONS

These data indicate that, although phenylephrine can prevent hypotension after cervical spinal injury, it also causes excess spinal hemorrhage and extravasation.

CLINICAL SIGNIFICANCE

Spinal decompressive surgery seemed to minimize the side effect of phenylephrine as vasopressor treatment during acute spinal cord injury.

Randomized Controlled Trial of Durotomy as an Adjunct to Routine Decompressive Surgery for Dogs With Severe Acute Spinal Cord Injury

Although many interventions for acute spinal cord injury (SCI) appear promising in experimental models, translation directly from experimental animals to human patients is a large step that can be problematic. Acute SCI occurs frequently in companion dogs and may provide a model to ease translation. Recently, incision of the dura has been highlighted in both research animals and human patients as a means of reducing intraspinal pressure, with a view to improving perfusion of the injured tissue and enhancing functional recovery. Observational clinical data in humans and dogs support the notion that it may also improve functional outcome. Here, we report the results of a multi-center randomized controlled trial of durotomy as an adjunct to traditional decompressive surgery for treatment of severe thoracolumbar SCI caused by acute intervertebral disc herniation in dogs. Sample-size calculation was based on the proportion of dogs recovering ambulation improving from an expected 55% in the traditional surgery group to 70% in the durotomy group. Over a 3.5-year period, we enrolled 140 dogs, of which 128 had appropriate duration of follow-up. Overall, 65 (51%) dogs recovered ambulation. Recovery in the traditional decompression group was 35 of 62 (56%) dogs, and in the durotomy group 30 of 66 (45%) dogs, associated with an odds ratio of 0.643 (95% confidence interval: 0.320-1.292) and z-score of -1.24. This z-score indicates trial futility to reach the target 15% improvement over traditional surgery, and the trial was terminated at this stage. We conclude that durotomy is ineffective in improving functional outcome for severe acute thoracolumbar SCI in dogs. In the future, these data can be compared with similar data from clinical trials on duraplasty in human patients and will aid in determining the predictive validity of the "companion dog model" of acute SCI.

A Review of Strategies Associated with Surgical Decompression in Traumatic Spinal Cord Injury

Traumatic spinal cord injury (TSCI) is frequent. Timely diagnosis and treatment have reduced the mortality, but the long-term recovery of neurologic functions remains ominous. After TSCI, tissue bleeding, edema, and adhesions lead to an increase in the intraspinal pressure, further causing the pathophysiologic processes of ischemia and hypoxia and eventually accelerating the cascade of secondary spinal cord injury. Timely surgery with appropriate decompression strategies can reduce that secondary injury. However, disagreement about the safety and effectiveness of decompression surgery and the timing of surgery still exists. The level and severity of spinal cord injury do have an impact on the timing of surgery; therefore, TSCI subpopulations may benefit from early surgery. Early surgery perhaps has little effect on recovery from complete TSCI but might be of benefit in patients with incomplete injury. Early decompression should be considered in patients with incomplete cervical TSCI. Patient age should not be used as an exclusion criterion for early surgery. The best time point for early surgery is although influenced by the shortest duration to thoroughly examine the patient's condition and stabilize the patient's state. After the patient's condition is fully evaluated, we can perform the surgical modality of emergency myelotomy and decompression. Therefore, a number of conditions should be considered, such as standardized decompression methods, indications and operation timing to ensure the effectiveness and safety of early surgical intervention, and promotion of the functional recovery of residual nerve tissue.

Composite Fibrin/Carbon Microfiber Implants for Bridging Spinal Cord Injury: A Translational Approach in Pigs

Biomaterials may enhance neural repair after spinal cord injury (SCI) and testing their functionality in large animals is essential to achieve successful clinical translation. This work developed a porcine contusion/compression SCI model to investigate the consequences of myelotomy and implantation of fibrin gel containing biofunctionalized carbon microfibers (MFs). Fourteen pigs were distributed in SCI, SCI/myelotomy, and SCI/myelotomy/implant groups. An automated device was used for SCI. A dorsal myelotomy was performed on the lesion site at 1 day post-injury for removing cloths and devitalized tissue. Bundles of MFs coated with a conducting polymer and cell adhesion molecules were embedded in fibrin gel and used to bridge the spinal cord cavity. Reproducible lesions of about 1 cm in length were obtained. Myelotomy and lesion debridement caused no further neural damage compared to SCI alone but had little positive effect on neural regrowth. The MFs/fibrin gel implant facilitated axonal sprouting, elongation, and alignment within the lesion. However, the implant also increased lesion volume and was ineffective in preventing fibrosis, thus precluding functional neural regeneration. Our results indicate that myelotomy and lesion debridement can be advantageously used for implanting MF-based scaffolds. However, the implants need refinement and pharmaceuticals will be necessary to limit scarring.

Spinal cord injury: molecular mechanisms and therapeutic interventions

Spinal cord injury (SCI) remains a severe condition with an extremely high disability rate. The challenges of SCI repair include its complex pathological mechanisms and the difficulties of neural regeneration in the central nervous system. In the past few decades, researchers have attempted to completely elucidate the pathological mechanism of SCI and identify effective strategies to promote axon regeneration and neural circuit remodeling, but the results have not been ideal. Recently, new pathological mechanisms of SCI, especially the interactions between immune and neural cell responses, have been revealed by single-cell sequencing and spatial transcriptome analysis. With the development of bioactive materials and stem cells, more attention has been focused on forming intermediate neural networks to promote neural regeneration and neural circuit reconstruction than on promoting axonal regeneration in the corticospinal tract. Furthermore, technologies to control physical parameters such as electricity, magnetism and ultrasound have been constantly innovated and applied in neural cell fate regulation. Among these advanced novel strategies and technologies, stem cell therapy, biomaterial transplantation, and electromagnetic stimulation have entered into the stage of clinical trials, and some of them have already been applied in clinical treatment. In this review, we outline the overall epidemiology and pathophysiology of SCI, expound on the latest research progress related to neural regeneration and circuit reconstruction in detail, and propose future directions for SCI repair and clinical applications.

A decrease in the neuroprotective effects of acute spinal cord decompression according to injury severity: introducing the concept of a ceiling effect

OBJECTIVE

Acute traumatic spinal cord injury (tSCI) is followed by a prolonged period of secondary neuroglial cell death. Neuroprotective interventions, such as surgical spinal cord decompression, aim to mitigate secondary injury. In this study, the authors explore whether the effect size of posttraumatic neuroprotective spinal cord decompression varies with injury severity.

METHODS

Seventy-one adult female Long Evans rats were subjected to a thoracic tSCI using a third-generation spinal contusion device. Moderate and severe tSCI were defined by recorded impact force delivered to the spinal cord. Immediately after injury (< 15 minutes), treatment cohorts underwent either a decompressive durotomy or myelotomy. Functional recovery was documented using the Basso, Beattie, and Bresnahan locomotor scale, and tissue sparing was documented using histological analysis.

RESULTS

Moderate and severe injuries were separated at a cutoff point of 231.8 kdyn peak impact force based on locomotor recovery at 8 weeks after injury. Durotomy improved hindlimb locomotor recovery 8 weeks after moderate trauma (p < 0.01), but not after severe trauma (p > 0.05). Myelotomy led to increased tissue sparing (p < 0.0001) and a significantly higher number of spared motor neurons (p < 0.05) in moderate trauma, but no such effect was noted in severely injured rats (p > 0.05). Within the moderate injury group, myelotomy also resulted in significantly more spared tissue when compared with durotomy-only animals (p < 0.01).

CONCLUSIONS

These results suggest that the neuroprotective effects of surgical spinal cord decompression decrease with increasing injury severity in a rodent tSCI model.

Clinical Trials Targeting Secondary Damage after Traumatic Spinal Cord Injury

Spinal cord injury (SCI) often causes loss of sensory and motor function resulting in a significant reduction in quality of life for patients. Currently, no therapies are available that can repair spinal cord tissue. After the primary SCI, an acute inflammatory response induces further tissue damage in a process known as secondary injury. Targeting secondary injury to prevent additional tissue damage during the acute and subacute phases of SCI represents a promising strategy to improve patient outcomes. Here, we review clinical trials of neuroprotective therapeutics expected to mitigate secondary injury, focusing primarily on those in the last decade. The strategies discussed are broadly categorized as acute-phase procedural/surgical interventions, systemically delivered pharmacological agents, and cell-based therapies. In addition, we summarize the potential for combinatorial therapies and considerations.

Incidence, prevalence and disability of spinal cord injury in China from 1990 to 2019: a systematic analysis of the Global Burden of Disease Study 2019

PURPOSE

We aimed to estimate the incidence, prevalence and years lived with disability (YLDs) of spinal cord injury (SCI) in China in 2019 and temporal trends from 1990 to 2019.

METHODS

The Global Burden of Disease Study 2019 was used to obtain data. Outcome measures included age-standardized incidence rate (ASIR), prevalence rate (ASPR) and YLDs rate (ASYR). A Bayesian meta-regression tool, DisMod-MR 2.1, was used to produce the estimates of each value after adjustments.

RESULTS

In 2019, there were 234.19 [95% uncertainty interval (UI) 171.84-312.87] thousand incident cases of SCI in China, with an ASIR of 13.87 (95% UI 10.15-18.66) per 100,000. ASIR and ASYR increased by 40.81% (95% UI 32.92-49.14%) and 11.44% (95% UI 5.16-17.29%) compared with 1990, individually. Males had higher ASIR and ASYR in each year from 1990 to 2019, but the incidence and YLDs rates of females exceeded males after 70 years old. Incidence and YLDs rates both ascended with age. SCI at neck level had slightly higher incidence rate but much higher YLDs rate than that below neck level. The average incidence age increased from 38.97 in 1990 to 54.59 in 2019. Falls were the leading cause of SCI.

CONCLUSION

The incidence and burden of SCI in China increased significantly during the past three decades. The age structure of SCI patients showed a shift from the young to the elderly as population aging. Urgent efforts are needed to relieve the health pressure from SCI.

Quantitative tissue perfusion imaging using nonlinear ultrasound localization microscopy

Ultrasound localization microscopy (ULM) is a recent advancement in ultrasound imaging that uses microbubble contrast agents to yield vascular images that break the classical diffraction limit on spatial resolution. Current approaches cannot image blood flow at the tissue perfusion level since they rely solely on differences in velocity to separate tissue and microbubble signals; lower velocity microbubble echoes are removed during high pass wall filtering. To visualize blood flow in the entire vascular tree, we have developed nonlinear ULM, which combines nonlinear pulsing sequences with plane-wave imaging to segment microbubble signals independent of their velocity. Bubble localization and inter-frame tracking produces super-resolved images and, with parameters derived from the bubble tracks, a rich quantitative feature set that can describe the relative quality of microcirculatory flow. Using the rat spinal cord as a model system, we showed that nonlinear ULM better resolves some smaller branching vasculature compared to conventional ULM. Following contusion injury, both gold-standard histological techniques and nonlinear ULM depicted reduced in-plane vessel length between the penumbra and contralateral gray matter (-16.7% vs. -20.5%, respectively). Here, we demonstrate that nonlinear ULM uniquely enables investigation and potential quantification of tissue perfusion, arguably the most important component of blood flow.

Elevated intraspinal pressure drives edema progression after acute compression spinal cord injury in rabbits

Elevated intraspinal pressure (ISP) following traumatic spinal cord injury (tSCI) can be an important factor for secondary SCI that may result in greater tissue damage and functional deficits. Our present study aimed to investigate the dynamic changes in ISP after different degrees of acute compression SCI in rabbits with closed canals and explore its influence on spinal cord pathophysiology. Closed balloon compression injuries were induced with different inflated volumes (40 μl, 50 μl or no inflation) at the T7/8 level in rabbits. ISP was monitored by a SOPHYSA probe at the epicenter within 7 days post-SCI. Edema progression, spinal cord perfusion and damage severity were evaluated by serial multisequence MRI scans, somatosensory evoked potentials (SEPs) and behavioral scores. Histological and blood spinal cord barrier (BSCB) permeability results were subsequently analyzed. The results showed that the ISP waveforms comprised three peaks, significantly increased after tSCI, peaked at 72 h (21.86 ± 3.13 mmHg) in the moderate group or 48 h (31.71 ± 6.02 mmHg) in the severe group and exhibited "slow elevated and fast decreased" or "fast elevated and slow decreased" dynamic changes in both injured groups. Elevated ISP after injury was correlated with spinal cord perfusion and edema progression, leading to secondary lesion enlargement. The secondary damage aggravation can be visualized by diffusion tensor tractography (DTT). Moreover, the BSCB permeability was significantly increased at the epicenter and rostrocaudal segments at 72 h after SCI; by 14 days, notable permeability was still observed at the caudal segment in the severely injured rabbits. Our results suggest that the ISP of rabbits with closed canals increased after acute compression SCI and exhibited different dynamic change patterns in moderately and severely injured rabbits. Elevated ISP exacerbated spinal cord perfusion, drove edema progression and led to secondary lesion enlargement that was strongly associated with BSCB disruption. For severe tSCI, early intervention targeting elevated ISP may be an indispensable choice to rescue spinal cord function.

Elevated intraspinal pressure in traumatic spinal cord injury is a promising therapeutic target

The currently recommended management for acute traumatic spinal cord injury aims to reduce the incidence of secondary injury and promote functional recovery. Elevated intraspinal pressure (ISP) likely plays an important role in the processes involved in secondary spinal cord injury, and should not be overlooked. However, the factors and detailed time course contributing to elevated ISP and its impact on pathophysiology after traumatic spinal cord injury have not been reviewed in the literature. Here, we review the etiology and progression of elevated ISP, as well as potential therapeutic measures that target elevated ISP. Elevated ISP is a time-dependent process that is mainly caused by hemorrhage, edema, and blood-spinal cord barrier destruction and peaks at 3 days after traumatic spinal cord injury. Duraplasty and hypertonic saline may be promising treatments for reducing ISP within this time window. Other potential treatments such as decompression, spinal cord incision, hemostasis, and methylprednisolone treatment require further validation.

Acute Traumatic Spinal Cord Injury in Humans, Dogs, and Other Mammals: The Under-appreciated Role of the Dura

We review human and animal studies to determine whether, after severe spinal cord injury (SCI), the cord swells against the inelastic dura. Evidence from rodent models suggests that the cord swells because of edema and intraparenchymal hemorrhage and because the pia becomes damaged and does not restrict cord expansion. Human cohort studies based on serial MRIs and measurements of elevated intraspinal pressure at the injury site also suggest that the swollen cord is compressed against dura. In dogs, SCI commonly results from intervertebral disc herniation with evidence that durotomy provides additional functional benefit to conventional (extradural) decompressive surgery. Investigations utilizing rodent and pig models of SCI report that the cord swells after injury and that durotomy is beneficial by reducing cord pressure, cord inflammation, and syrinx formation. A human MRI study concluded that, after extensive bony decompression, cord compression against the dura may only occur in a small number of patients. We conclude that the benefit of routinely opening the dura after SCI is only supported by animal and level III human studies. Two randomized, controlled trials, one in humans and one in dogs, are being set up to provide Level I evidence.