Utilization of a mechanical hinge-powered operative table in thoracic spinal cord decompression and fusion: a report of two cases

Introduction

Prior literature demonstrates the utility of motorized-hinged operative tables (ProAxis) in sagittal plane corrections (1,2). Martin et al. (1) used ProAxis to achieve bilateral facetectomy and osteotomy closure during 2-level transforaminal lumbar interbody fusion (TLIF). The authors report decompression in 10-degrees flexion, with subsequent fusion in 10-degrees extension, achieving 30-degree postoperative lordosis improvement. Jones et al. (2) report controlled closure of an L4 pedicle subtraction osteotomy (PSO) using ProAxis. Decompression and osteotomy were performed in 20-degrees flexion. Extension was sequentially performed in 5-degree increments to 10-degrees extension for controlled PSO closure. Differential alignment improved ease of decompression, interbody insertion, and controlled osteotomy closure, avoiding excessive compressive force on instrumentation. To the best of the authors knowledge, no previous literature has described the utility of ProAxis to maintain patient preoperative thoracic alignment to aid in surgical decompression prior to fusion. The current case study identifies an alternative use of ProAxis during thoracic cord decompression prior to final stabilization. We present the following two cases of thoracic cord compression with progressive neurologic decline associated with patient positioning during advanced imaging acquisition and intraoperatively, with a solution to intraoperative neurologic deterioration. We present this article in accordance with the CARE reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-25-36/rc).

Case presentation

Case 1

A 59-year-old female presented to outpatient clinic with severe midback pain, and progressive bilateral lower extremity (BLE) weakness. The patient was previously treated for degenerative scoliosis and degenerative spondylolisthesis at L4–5 with anterior lumbar interbody fusion at L4–5 and L5–S1 and T11-pelvis posterior instrumented fusion in September 2022. She presented 8 months postoperatively with increasing midback and BLE pain. Plain radiographs and magnetic resonance imaging (MRI) were obtained demonstrating proximal junctional failure with focal kyphosis at the upper instrumented level and wedging of T11 vertebra with a superimposed central disc herniation at T10–T11 causing severe stenosis without spinal cord edema. The patient was indicated for T9–T11 posterior spinal decompression and extension of fusion to T4.

The patient was taken to the operating room on May 8, 2023. General endotracheal anesthesia was induced and baseline supine neuromonitoring signals were obtained. At baseline, somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) were intact in bilateral upper and lower extremities. The patient was placed in cranial traction, repositioned prone on an open Jackson table. Prior to operative timeout, loss of SSEPs were reported. Standard neuromonitoring signal loss protocol was performed including confirmation of adequate blood pressure and mean arterial pressure (MAP), adequate temperature, no confounding anesthetic agent, confirmation of appropriate neutral alignment in gross positioning, and cranial traction removed. Upper extremity MEPs remained good quality. Lower extremity MEPs and SSEPs remained absent. As no incision had been made, the patient was placed supine and Stagnara Wake Up test was performed. The hospital and surgeon policy for performance of a Stagnara Wake Up test is dependent on the stage of surgery, however, a threshold of greater than 50% loss of MEPs and/or greater than 50% reduction in SSEP amplitude or 10% increase in SSEP latency, not otherwise explained by a mechanical event or corrective maneuver warrants further evaluation.

Anesthesia was lightened until lower extremity movement was confirmed. In the setting of acute neurologic change, the patient was fully awakened, extubated, and transported directly to MRI for emergent re-imaging. She had return of BLE neurologic function prior to MRI. During MRI, the patient experienced significant pain when positioned supine and required sedation to reduce motion artifact. Throughout imaging, intravenous steroids were provided and MAPs were maintained >85 mmHg. Once MRI was complete, neurologic examination identified BLE weakness: right lower extremity with 2/5 proximally and 3/5 distally; left lower extremity with 4/5 throughout. MRI demonstrated T10–T11 cord edema (Figure 1A-1C). The patient was maintained in 30-degrees flexion and steroids continued until she regained full BLE function on day 2. On May 10, 2023 she underwent T9–T11 laminectomy and fusion extension to T4 as indicated on ProAxis. With normal strength in flexion/thoracic kyphosis posture, the initial thoracic decompression was completed with ProAxis flexed to 30-degrees and slowly extended, 10-degrees sequentially with continuous neuromonitoring. During this time, the patient had spinal implants placed while flattening ProAxis to neutral position. No MEP or SSEP neuromonitoring changes were identified throughout the procedure. The patient awoke with full motor strength in her BLE.

Figure 1 Preoperative magnetic resonance image and postoperative radiographs following posterior spinal instrumented fusion. (A) Preoperative sagittal T2 magnetic resonance image demonstrating increased signal within the T10–T11 disc space, posterior disc herniation with severe spinal stenosis and cord signal change, (B) preoperative axial T2 magnetic resonance image demonstrating T10–11 posterior disc herniation resulting in severe spinal stenosis and cord signal change, and (C) preoperative sagittal STIR magnetic resonance image demonstrating increased signal within the T10–T11 disc space, posterior disc herniation with severe spinal stenosis and cord signal change, postoperative standing (D) AP and (E) lateral full length spinal radiographs demonstrating T4-pelvis posterior spinal instrumented fusion. AP, anteroposterior; STIR, short tau inversion recovery.

The patient had an uneventful postoperative hospitalization, with some persistent numbness in both legs/feet. She was discharged on May 15, 2023 (postoperative day 5) without complication. Figure 1D,1E demonstrate standing anteroposterior (AP) and lateral full length radiographs at her initial postoperative visit. One year after surgery, she had mild persistent back pain and required a walker for ambulation, but all motor/sensory symptoms in her BLE had resolved. Unfortunately, she developed proximal junctional kyphosis with worsening back pain, and underwent extension of fusion to T1 with T3/4 Ponte osteotomies on October 1, 2024. She has been seen in clinic since that surgery with improved back pain and reduced reliance on her walker.

Case 2

A 68-year-old male diagnosed with prostate adenocarcinoma in 2019 and treated with 3 months of local radiation, April to July 2019, presented to the emergency department, December 2023, with acute midback pain and BLE weakness. Over the prior week, he experienced BLE numbness, gait imbalance, and paresthesias below the umbilicus. The night prior to presentation, he stood to use the bathroom at 02:00 and fell due to increasing BLE weakness with acute midback and radiating pain to bilateral scapula and lateral rib cage.

On presentation, he reported development of urinary incontinence at the time of fall. Notably, the patient was preferentially positioned in nearly 20-degrees midthoracic flexion on the hospital stretcher. Initial examination revealed BLE strength 2/5 except bilateral hip flexion graded 1/5, and normal rectal tone.

The patient was emergently taken for computed tomography (CT) and MRI and positioned supine during image acquisition. Following imaging, repeat examination reported diminished BLE strength graded 0/5 in all major muscle groups. Subjectively, the patient reported loss of function following imaging studies. The patient was subsequently transferred to the operative hospital.

Imaging demonstrated an expansile lesion consistent with metastasis involving the T6 and T7 vertebral bodies and pedicles causing high grade epidural spinal cord compression (ESCC) and thoracic stenosis (Figure 2A-2C). Examination on arrival to the operative hospital confirmed absent BLE strength, T7 sensory level, and American Spinal Injury Association (ASIA) B impairment rating (3,4). Based on the spinal instability neoplastic score (SINS) and high grade ESCC with ASIA B neurologic rating, separation surgery and stabilization was recommended (5,6). The patient was indicated for T5–T7 posterior and transpedicular thoracic decompression, T4–T9 posterior instrumented fusion.

Figure 2 Preoperative pre- and post-contrast magnetic resonance image and postoperative radiographs demonstrating posterior spinal instrumented fusion. (A) Preoperative sagittal T2 magnetic resonance image demonstrating expansile metastatic lesion involving the T6 and T7 vertebral bodies resulting in high grade epidural spinal cord compression, (B) preoperative axial T2 magnetic resonance image demonstrating expansile metastatic lesion involving bilateral pedicles, left greater than right, and (C) preoperative sagittal T1 post-contrast magnetic resonance image demonstrating expansile metastatic lesion involving the T6 and T7 vertebral bodies with post contrast enhancement resulting in high grade epidural spinal cord compression. Postoperative standing (D) AP and (E) lateral radiographs demonstrating T4–T9 posterior spinal instrumented fusion. AP, anteroposterior.

The patient was taken to the operating room within 24 hours of weakness onset and 3 hours after MRI. At baseline, BLE SSEPs were reduced, MEPs were present in upper extremities and reduced in the BLE. Post-positioning signals remained at baseline.

Intraoperatively, T4–T9 instrumentation and T5–T7 dorsal decompression was performed with patient in 20-degrees ProAxis flexion to accommodate preoperative thoracic flexion. The thecal sac above and below compression was normal and decompressed to aid in ventral and transpedicular decompression performed at bilateral T6 and left T7. Figure 2D,2E demonstrates standing 5-month postoperative radiographs.

Postoperatively, the patient was admitted to the intensive care unit for neuromonitoring and blood pressure maintenance. MAP goal of 85 mmHg was maintained for 5 days and 48 hours of 4 mg dexamethasone given every 4 hours (7). On postoperative day 1 the patient had improved 4−/5 extensor hallucis longus (EHL) motor function. He progressed throughout hospitalization to near full strength in BLE and discharged to acute spinal cord injury rehabilitation on postoperative day 8.

By 6 months postoperatively, he had near complete BLE strength recovery, with continued improvement in sensation and proprioception.

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patients for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

We present two cases of thoracic spinal cord compression with progressive neurologic decline associated with positioning during advanced imaging acquisition and intraoperatively. The ProAxis was used to maintain patient alignment during decompression at a degree associated with preoperative neurologic function with resultant restoration of postoperative neurologic function.

The advantage of controlled alignment in thoracic decompression relates to dynamic spinal stenosis. Prior literature demonstrates positional volumetric changes in cervical and lumbar spines (8-14). In the cervical spine, flexion-extension radiographs and MRIs have been used to quantify degree of cervical stenosis. Kolcun et al. (8) published a systematic review of 19 studies evaluating dynamic MRI in diagnosis of cervical spondylotic myelopathy. The authors review canal dimension, cord dimension, cervical range of motion (ROM) and disc changes in dynamic MRI and conclude dynamic MRI are beneficial to assess dynamic compression incompletely characterized on standard advanced imaging modalities. Utilizing dynamic supine MRI, Lee et al. (11) evaluate 92 patients with cervical radiculopathy or myelopathy in which neutral MRI did not identify a clear symptom generator. The authors calculated a cumulative cervical spinal stenosis score via novel scoring system and demonstrate the degree of spinal stenosis increased from flexion to extension postures. In 66 patients with neck pain, Jha et al. (9) demonstrated a 10–23% reduction in sagittal cervical spinal canal diameter from flexion to extension on dynamic MRI (9). These findings suggest dynamic imaging may be beneficial in evaluating the effect of motion on spinal stenosis and cord compression. Additionally, dynamic imaging confirms variable stenosis by position and further emphasizes the role of differential positioning during decompression and fusion.

There remains a relative inability to extrapolate learned concepts from dynamic cervical and lumbar stenosis to the thoracic spine due to biomechanical differences. The biomechanics of the thoracic spine differ resulting from the additional stability conferred by the thoracic rib and sternal articulations. With the exception of floating ribs, the thoracic vertebrae are anchored to the sternum through costovertebral and costotransverse articulations. Few studies have evaluated thoracic biomechanical ROM (15-18). Watkins et al. (15) evaluated the stability of the thoracic spine conferred by the sternum and rib cage. The authors performed a biomechanical cadaveric analysis and determined the rib cage provides significant stability, responsible for 77% reduction in thoracic ROM (15,18). Burgos et al. (16) evaluated the relative motion of thoracic vertebrae during inspiration and expiration by radiography. The authors identified a greater ROM within the lower thoracic spine with the maximal mobility between T7 and T10, responsible for nearly 75% of global sagittal thoracic ROM (16). The authors report thoracic mobility is expected due to the rib articulations. True ribs, T1–T7, articulate directly to the sternum with a small cartilage attachment. False ribs, T8–T10, articulate with the sternum via longer cartilaginous attachments, and the floating ribs, T11–T12, have the greatest mobility without sternal attachment. These findings would suggest upper thoracic stability is relatively maintained. However, the lower thoracic false and floating rib segments, there remains relative motion. Alterations in stabilizing attachments such as rib resection, compression or pathologic fracture could result in instability and subsequent dynamic cord compression. Similarly, in the setting of prior thoracolumbar fusion, a construct with upper instrumented level within the floating rib segments may result in greater risk of thoracic adjacent segment degeneration, and the resultant stress in a comparatively mobile segment may result in progressive instability and dynamic cord compression.

Uncommonly, flexion and extension thoracic MRIs have been performed. Braileanu et al. (10) performed dynamic MRI in two patients with thoracic ligamentous laxity with clinical appearance similar to Hirayama disease, resulting in anterior migration of the thecal sac and spinal cord with increased prominence of the dorsal epidural venous plexus. The authors placed an emphasis on the utility of dynamic advanced imaging to appropriately diagnose and treat uncommon dynamic thoracic pathology (10).

Preferred flexion posture is described in cases of cervical and lumbar stenosis as a protective mechanism to improve canal diameter and reduce neurologic compression. Dynamic stenosis is accentuated by loading or patient positioning and alignment (19). Intuitively, owing to thoracic kyphosis, a preferred extension would result in posterior drift of the thoracic cord, additional space available for the cord, and a relative reduction in thoracic stenosis. Few studies have evaluated the cross sectional volume and space available for the cord of the thoracic vertebral segments (20-22).

Morita et al. (20) and Machino et al. (21), of the same research group, evaluated the effect of passive thoracic flexion-extension via CT myelogram in 50 patients with cervical and lumbar disease. The authors hypothesized AP diameter, cross-sectional area of the dural sac and spinal cord, and occupancy ratio at each thoracic disc level would be smaller in flexion as a result of thoracic kyphosis. Morita et al. (20) report above T8–9, the AP diameter of the spinal canal was larger in flexion, and cross sectional area of thecal sac and spinal cord was smaller in flexion. Contrastingly, below T8–9, the AP diameter of spinal canal and cross-sectional area of dural sac was larger in flexion. The authors suggest below T8–9, the thoracic spine may experience dynamic changes comparable to the lumbar spine. Machino et al. (21) then corroborated the AP diameter of dural sac was larger in flexion, while the AP diameter of the cord, and cross sectional area of the thecal sac and spinal cord were smaller in flexion, and report the spinal cord occupancy rate of the thecal sac was also smaller in flexion. Counterintuitively, the authors report the thoracic spinal cord was lengthened and expanded in flexion, and shortened and narrowed in extension. These findings and discussion are counterintuitive and a focused re-evaluation of results would be recommended.

Paholpak et al. (22) evaluate the change in intervertebral disc and space available for the spinal cord in 105 patients with kinematic MRI. The authors report disc bulging was greatest in flexion and smallest in extension. Intuitively, they report the space available for the thoracic cord trended towards widest with extension and narrowest with flexion, however, there was no statistical difference in volume with the exception of the T5–6 disc space. Although results from these studies vary, it is intuitive that thoracic flexion posture would result in further disc bulging, reduced space available for the spinal cord, with intrinsic cord lengthening on further flexion and thinning or narrowing of the thoracic cord volume.

In the current report, dynamic compression occurred with thoracic extension positioning during advanced imaging acquisition and likely resulted in neurologic deterioration observed. The ventral compression from tumor and pathologic burst fractures resulted in spinal stenosis at the involved segments, as a result, compensatory flexion to lengthen and reduce cord volume was attempted, however, forced extension for imaging acquisition, resulting in cord shortening and volumetric expansion resulting in additional compression and neurologic deterioration.

Intraoperatively, pre- and post-positioning neurophysiologic status monitoring is commonly performed for cases of myelopathy or cord compression in which intraoperative techniques may result in additional neurologic stretch or compression and subsequent neurologic deterioration (23). Reduced neuromonitoring potentials may result from many factors, including decreased intraoperative MAP, hypothermia, or anesthetic agents, especially inhaled agents (24,25). Although reduced potentials may be multifactorial, guideline recommendations dictate following an acute reduction in potentials with alignment maneuver or positioning change, restoration of a pre-positioning alignment be the first surgical corrective maneuver.

Intraoperative patient positioning utilizing ProAxis allowed for mimicry of the preferred preoperative patient positioning in alignment associated with known neurologic function without hindering surgical approach. In theory, the secondary decompensation during imaging acquisition could have been avoided with additional attention to patient positioning.

Improved attention and education for hospital staff involved in emergency department and imaging acquisition may present an opportunity to obtain postural CT and MRI scans and avoid secondary neurologic deterioration.

The current case report is not without limitations. The limited sample size of this case report may limit meaningful conclusions; however, the authors identify the current technique and table utilization as an alternative option to potentially improve patient outcomes and warrants further evaluation. Additionally, although no complications occurred resulting from use of a mechanical hinge table in the two presented cases, modification from conventional prone positioning could potentially increase the risk of alternative position-related complications including, but not limited to, compressive neuropathies, deep vein thromboses, and vision loss (26,27). As intraoperative mobilization results in alteration of patient positioning during surgery without direct visualization of the altered position underneath the surgical drapes, it is possible the patient’s body moves on the padding, increasing the risk of a compressive neuropathy. Without additional attention to patient Trendelenburg status, manipulation can result in a patient’s head positioned below the initial operative position and should be monitored. Finally, the current manuscript does not compare outcomes with conventional positioning. As described, use of a standard radiolucent Jackson operative table in Case 1 resulted in deterioration of the patient’s neurologic status and supine extension posture during image acquisition resulted in neurologic deterioration in Case 2. While the acute neurologic deterioration was felt to be due to an alteration from the patient’s preferential protective positioning, the patient’s postoperative neurologic recovery resulted from spinal cord decompression. Although it is possible that the acute neurologic recovery would have occurred with expedited spinal cord decompression on a standard operative table, confirmation of an acute alteration in neurologic status via intraoperative MEP and SSEP signal loss and subsequent maintenance of signals with the use of a mechanical hinge operative table indicate the preferential positioning was beneficial to the patient’s neurologic status.

Future studies could examine both short- and long-term postoperative outcomes in patients or animal models who are subjected to position-induced deficits. This would help determine the ramifications and impact of short duration preoperative or intraoperative positional change on the postoperative course and neurologic recovery.

Conclusions

The ProAxis has previously been described to aid in correction of sagittal plane deformity in the setting of posterior column and pedicle subtraction osteotomies. The current case study identifies an alternative use in the setting of pathologic thoracic cord compression to aid in decompression prior to final stabilization with instrumentation.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-25-36/rc

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-36/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-25-36/coif). C.J.D. receives IP royalties, consulting fees and stock options from Alphatec, IP royalities from Smaio, and sits on the editorial board of Journal of Spinal Disorders. These conflicts of interest do not pertain to the publication of this manuscript. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patients for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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