Single position, prone oblique lateral interbody fusion (OLIF)-case illustration and technical considerations.

Oblique lateral interbody fusion (OLIF) is a powerful method to treat various spinal conditions and is frequently combined with posterior instrumentation. This is traditionally performed in dual positions, with the patient first in lateral then turned prone. Single position lateral surgery (SPS-L) has been studied in a bid to improve surgical efficiency and reduce operative costs, but various limitations have been identified. More recently, the single position prone surgery (SPS-P) has been described as an alternative to address some of these limitations. This case illustrates a patient who underwent SPS-P using an OLIF corridor with subsequent posterior decompression and instrumentation. The benefits and limitations of this procedure compared to the conventional techniques are highlighted in this case. We present the case of a 75-year-old female presenting with thoracic myelopathy over T11/12 and concurrent L2-4 spinal stenosis. She underwent OLIF of L2/3 and L3/4, posterior decompression of T11/12 and L2/3, and posterior instrumented fusion from T10-L4 via a single prone position. We aim to describe the advantages of this approach and the challenges encountered through our experience. SPS-P offers numerous benefits compared to the already powerful SPS-L. In the upper levels of the lumbar spine, a pre-psoas approach may also be feasible. However, the prone lateral technique does not replace all patients suited for a lateral interbody fusion but should be seen as a viable option for selected cases such as those with previous fusion at the L5/S1 with adjacent degeneration requiring extension and posterior fixation.

The Evolution of Lateral Lumbar Interbody Fusion: A Journey from Past to Present.

Lumbar interbody fusion procedures have seen a significant evolution over the years, with various approaches being developed to address spinal pathologies and instability, including posterior lumbar interbody fusion (PLIF), transforaminal lumbar interbody fusion (TLIF), anterior lumbar interbody fusion (ALIF), and lateral lumbar interbody fusion (LLIF). LLIF, a pivotal technique in the field, initially emerged as extreme/direct lateral interbody fusion (XLIF/DLIF) before the development of oblique lumbar interbody fusion (OLIF). To ensure comprehensive circumferential stability, LLIF procedures are often combined with posterior stabilization (PS) using pedicle screws. However, achieving this required repositioning of the patient during the surgical procedure. The advent of single-position surgery (SPS) has revolutionized the procedure by eliminating the need for patient repositioning. With SPS, LLIF along with PS can be performed either in the lateral or prone position, resulting in significantly reduced operative time. Ongoing research endeavors are dedicated to further enhancing LLIF procedures making them even safer and easier. Notably, the integration of robotic technology into SPS has emerged as a game-changer, simplifying surgical processes and positioning itself as a vital asset for the future of spinal fusion surgery. This literature review aims to provide a succinct summary of the evolutionary trajectory of lumbar interbody fusion techniques, with a specific emphasis on its recent advancements.

Single-Position Robotic-Assisted Prone Lateral Fusion: Technical Description and Feasibility.

Single-position lateral interbody fusion surgery has gained traction over the years because of reduced surgical time and improved operating theater workflow. With the introduction of robotics in spine surgery, surgeons can place pedicle screws with a high degree of accuracy and efficiency; moreover, the robot allows us to localize the disk space and perform endplate preparation accurately with minimal radiation. In this study, we discuss the potential synergistic benefits of integrating robotic-assisted spine surgery and singleposition prone lateral surgery. We share our technique and provide the operative nuances of using the Mazor X Stealth Edition system (Medtronic, Minneapolis, MN, USA). We highlighted the potential synergistic benefits of integrating both the prone lateral and robotic-assisted surgical techniques, including the challenges encountered. This approach is not meant to replace other techniques or be used in all patients. Instead, it adds to our arsenal for managing spine fusion.

Frequency and predictors of implant-related complications after posterior cervical fusion.

STUDY DESIGN: Retrospective, observational study. PURPOSE: To determine the frequency and predictors of implant-related complications in adults after posterior cervical fusion. OVERVIEW OF LITERATURE: Published literature on lumbosacral fusion suggest that implant-related complications are not uncommon. Although posterior cervical fusion is a common operation, data on frequency and predictors of implant-related complications after posterior cervical fusion is still scarce. METHODS: 86 patients (with 740 screws) who underwent posterior cervical fusion were included. Implant-related complications were identified by the presence of: (1) halo sign, (2) screw pull-out/breakage (3) post-operative kyphosis and (4) implant-related complications requiring revision surgery. These were stratified into two groups: (a) minor - isolated halo sign or screw pull-out/breakage (b) major - post-operative kyphosis > 10 degrees, and revision surgery. Demographic, operative and radiological data was collected. Rates of implant-related complications were determined and associated risk factors identified. RESULTS: 33 (38.4%) patients had signs of implant-related complications. Of these, 29 (87.9%) had minor complications and 4 (12.1%) had major complications. Charlson Comorbidity Index (CCI) (p = 0.03179) and pre-op C2-C7 sagittal vertical alignment (SVA) (p = 0.02449) were the only significant risk factors for all-cause implant-related complications during multivariate logistic regression. Other intraoperative parameters (type of screw, length of fusion, levels decompressed, and extension of fusion beyond the levels decompressed) were not significantly associated with implant-related complications. CONCLUSIONS: Implant-related complications are not uncommon but rarely require revision surgery. Higher pre-operative SVA and CCI were significant risk factors; length of construct and extent of decompression were not. These findings may assist clinicians when deciding the extent of fusion and in selecting patients for closer follow-up.

We assessed the frequency and predictors of implant-related complications in adults after posterior cervical fusion. Implant-related complications (halo sign, screw pull-out/breakage, post-operative kyphosis) are not uncommon but rarely require revision surgery. Higher pre-operative SVA and CCI were significant risk factors; length of construct and extent of decompression were not.

Return to Driving Is Safe 6 Weeks After Anterior Cervical Surgery for Symptomatic Cervical Degenerative Disc Disease.

STUDY DESIGN: Prospective Cohort Study. OBJECTIVES: This study aims to determine the timing and clinical parameters for a safe return to driving. SUMMARY OF BACKGROUND DATE: Returning to driving after cervical spine surgery remains a controversial topic, with no clear consensus on how to best assess a patient's fitness to drive. Previous studies using brake reaction time or subjective questionnaires recommend a return to driving 6 weeks after surgery. METHODS: Patients above 18 years of age who underwent anterior cervical spine surgery for symptomatic cervical degenerative disk disease and possessed a valid motorcar driving license were recruited from 2018 to 2020. Neck Disability Index (NDI), modified Japanese Orthopaedic Association (mJOA) scores, range of motion, and functional strength of the cervical spine were collected preoperatively and at 2-, 4-, 6- and 12 weeks postsurgery. Patients underwent a standard functional driving assessment protocol at the institution to determine their fitness to drive. This comprised of a clinic-based off-road screening tests and on-road driving test in a real-world environment. RESULTS: Twenty-one patients were recruited. The mean age was 56.6±8.9 years. Eighty-one percent of the patients passed the on-road driving assessment at 6 weeks. Patients who passed the driving assessment had lower mean NDI scores, 3.4±3.1 versus 10.8±8.0 ( P =0.006), and higher mean mJOA scores 16.1±0.6 versus 15.0±1.8 ( P =0.045). Patients who passed the driving assessment also had higher functional cervical flexor strength, 21.1s±5.8s versus 13.0s±10.2s ( P =0.042) in a supine position but not correlated with a range of motion of the spine in all directions. CONCLUSION: Most patients undergoing single or dual-level anterior cervical surgery for symptomatic cervical degenerative disk disease demonstrate the ability to pass a standardized driving assessment and are safe to return to driving more than 6 weeks after surgery. Driving ability appears to be correlated with NDI scores ≤3 ( P =0.006), mJOA scores ≥16 ( P =0.045), and cervical flexion endurance of ≥21s ( P =0.042). LEVEL OF EVIDENCE: Level II.

Post-surgical thoracic spinal cord herniation following an unrepaired dural defect: a rare complication.

Surgery for ossification of the ligamentum flavum (OLF) comes with a relatively high risk of dural tear. We report a 50-year-old woman, who presented with symptomatic spinal stenosis from OLF at T11-T12 and lower lumbar spondylosis for which a single stage posterior decompression and instrumented fusion of both sites was done. Removal of the OLF resulted in a small dural tear with intact arachanoid which was covered using a fibrin sealant. In the first post-operative day, the patient's neurology started deteriorating. An MR scan was done to look for hematoma. It showed the spinal cord herniating out of the thecal sac at the operated level. Emergency re-operation was done to reduce the herniation and the dural defect was repaired. The patient gradually recovered to her best functional status. Based on this experience, we advise primary repair of inadvertent durotomies.

Equipoise for Lateral Access Surgery.

OBJECTIVE: To investigate the use of lateral access surgery among surgeons from the Asia-Pacific region to determine equipoise for areas of contentious use. METHODS: A questionnaire was distributed to members of the Asia Pacific Spine Society. Surgeons were asked about their past experiences with lateral access surgery, including their advantages and disadvantages, specific surgical strategies, choices in implant-related factors, order of levels to operate on in multilevel reconstruction surgery, and postoperative complications. RESULTS: A total of 69 of 102 surgeons (67.6%) had performed lateral access surgery previously. In total, 56 participating surgeons (54.9%) agreed that anterior column reconstruction via lateral access is most of time superior to transforaminal lumbar interbody fusion and other techniques. Surgeons would consider laminectomy instead of indirect decompression in the presence of severe central or lateral recess stenosis, thickened ligamentum flavum, and facet joint hypertrophy. For the order of levels to operate on in multiple level reconstruction for deformity, where 1 stands for L3-L4 or higher, 2 stands for L4-L5, and 3 stands for L5-S1, 2-1-3 (28/95, 29.5%) was most common, followed by 1-2-3 (26/95, 27.4%), and 3-2-1 (21/95, 22.1%). CONCLUSIONS: Lateral access surgery is seeing greater use in the Asia-Pacific region, especially in upper middle- to high-income countries, whereas keenness of surgeons who practice in lower middle- to low-income countries can be improved by more training, resources, and reasonable cost. A high percentage of surgeons do not consider indirect decompression for spinal stenosis. There was no consensus on the order of levels in multiple level reconstruction for deformity.

Traumatic intradural disc herniation following a cervical facet dislocation: a case report.

We report a unique case of a patient who sustained an intradural disc herniation from a left C5-6 unilateral facet dislocation after a fall. This was not easily identified on pre-operative imaging. We explain the details of our surgical approach in this case report. A 65-year-old male fell into a 2 m drain and sustained a left C5/6 unilateral facet dislocation. He then sustained an American Spinal Injury Association (ASIA) B cord injury. His power was 0/5 from C8 downwards bilaterally but sensation was intact throughout. Magnetic resonance imaging (MRI) showed severe compression at C5/6 but no overt intradural disc herniation. This patient subsequently underwent a closed reduction in the operating theatre followed by a combined anterior and posterior approach for the disc herniation. Cerebral spinal fluid (CSF) leakage was noted upon completion of the C5/6 discectomy and it was discovered that there was a traumatic dural tear from the traumatic disc herniation. The decision was made not to repair the dural tear due to the friable nature of the dura and the potential for adhesive glue to propagate through the spinal cord. An anterior drain was placed for 3 days and then removed, he subsequently underwent rehabilitation and was able to regain power in the affected myotomes. Intradural disc herniations can be easily missed on MRI in the setting of cervical spinal trauma. Hence, the anterior approach is an increasingly acceptable approach to tackle disc herniations in unilateral cervical facet dislocations (CFD) surgery.

Early Postoperative Loss of Disc Height Following Transforaminal and Lateral Lumbar Interbody Fusion: A Radiographic Analysis.

STUDY DESIGN: Retrospective comparative radiological study. PURPOSE: To analyze the difference in early disc height loss following transforaminal and lateral lumbar interbody fusion (TLIF and LLIF). OVERVIEW OF LITERATURE: Minimal disc height loss facilitated by the polyaxial screw heads can occur naturally due to mechanical loading following lumbar fusion procedures. This loss does not usually cause any significant foraminal narrowing. However, when there is concomitant cage subsidence, symptomatic foraminal compromise could occur, especially when posterior decompression is not performed. It is not known whether the type of procedure, TLIF or LLIF, could influence this phenomenon. METHODS: Retrospectively, patients who underwent TLIF and LLIF for various degenerative conditions were shortlisted. Each of their fused levels with the cage in situ was analyzed independently, and the preoperative, postoperative, and follow-up disc height measurements were compared between the groups. In addition, the total disc height loss since surgery was calculated at final follow-up and was compared between the groups. RESULTS: Forty-six patients (age, 64.1±8.9 years) with 70 cage levels, 35 in each group, were selected. Age, sex, construct length, preoperative disc height, cage height, and immediate postoperative disc height were similar between the groups. By 3 months, disc height of the TLIF group was significantly less and continued to decrease over time, unlike in the LLIF group. By 1 year, the TLIF group demonstrated greater disc height loss (2.30±1.3 mm) than the LLIF group (0.89±1.1 mm). However, none of the patients in either group had any symptomatic complications throughout follow-up. CONCLUSIONS: Although our study highlights the biomechanical advantage of LLIF over TLIF in maintaining disc height, none of the patients in our cohort had symptomatic complications or implant-related failures. Hence, TLIF, as it incorporates posterior decompression, remains a safe and reliable technique despite the potential for greater disc height loss.

Postoperative Urinary Retention Following Thoracolumbosacral Spinal Fusion: Prevalence, Risk Factors, and Outcomes.

Objective Postoperative urinary retention (POUR) is an often-underestimated common complication following spine surgery, and it is essential to avoid its untoward long-term consequences. Besides, a dilemma exists regarding the appropriate timing for the postoperative removal of indwelling catheter (IDC). Hence, we aim to describe the prevalence, risk factors, and outcomes of POUR and also come up with recommendations for the removal of IDC. Methods Electronic records of patients who underwent elective thoracolumbosacral spinal fusion surgery from January 2017 to December 2019 were retrospectively reviewed. Excluded were those who underwent fusion for indications such as trauma, cauda equina syndrome, infection, and malignancy. Both surgery-related and patient-related risk factors were tabulated, and their association with the likely development of POUR was assessed by univariate and multivariate analysis. Results One hundred sixty-eight patients (median age=64.1 years; 58.9% female) were included, with the incidence of POUR being 7.8%. Our findings suggest surgery-related factors, both intra- and postoperative, including operating time (p=0.008), anesthetic time (p=0.005), number of fusion levels (p<0.001), mobilization status prior to trial off catheter (TOC; p=0.021), and TOC timing (p=0.029) may have an association with POUR. In addition, patient-related factors, including the use of beta-blockers (p=0.020) and pre-operative mobility status (p<0.001), may also be associated with the likely development of POUR. Conclusion POUR seems to be a frequent complication following thoracolumbosacral spinal fusion surgery, which was found to have an association with some surgery-related and patient-related factors. While most of these factors are non-modifiable, certain modifiable risk factors provide the surgeon an opportunity to prevent POUR. Considering these factors, we recommend appropriate and timely mobilization of the patient prior to removal of IDC, which is to be performed preferably in the daytime.

Intracerebral haemorrhage following spine surgery: a word of caution on the use of suction drains.

Intracranial haemorrhage (ICH) is a rare but devastating complication post spinal surgery. We present three cases of post spine surgery ICH that were associated with high drain outputs postoperatively. The first patient underwent C1-C6 instrumented fusion and C4-C6 decompression. 950 mls hemoserous fluid was drained via suction drain immediately postoperatively. He suffered cerebral hemorrhage with tonsillar herniation and was brain dead on the same night. The second patient underwent C1-T1 instrumented fusion with C3-C4 decompression. 400 mls hemoserous fluid was drained via suction drain shortly after skin closure. He suffered subdural hemorrhage, subarachnoid hemorrhage and intraventricular hemorrhage, with persistent neurologic deficits and required long-term institutionalised care. The third patient underwent L2-L4 decompression and instrumented fusion. 480 mls hemoserous fluid was drained via suction drain 2 hours postoperatively. He suffered subdural haemorrhage but eventually recovered fully. An excessive drain output, especially within first few minutes to hours postoperatively, may signify a CSFleak. Suction drains should be used with caution in these cases as negative suction in the presence of a dura tear increases risk of post spine surgery ICH. In these cases, the use of non-suction drains should be considered.

The Feasibility of Anterior Spinal Access: The Vascular Corridor at the L5-S1 Level for Anterior Lumbar Interbody Fusion.

STUDY DESIGN: Cross-sectional study. OBJECTIVE: To analyze the feasibility of anterior spinal access to the vascular corridor at the L5-S1 junction, by evaluating three crucial anatomical landmarks. This provides a framework for risk-stratification for the clinician during preoperative evaluation. SUMMARY OF BACKGROUND DATA: The anterior lumbar interbody fusion (ALIF) offers many advantages for fusion at the L5-S1 junction. However, the variant iliac vasculature may preclude safe anterior access. METHODS: Five hundred magnetic resonance imaging (MRI) images of the L5-S1 level were identified, with 379 meeting inclusion criteria. We graded the anterior access into three grades, namely, easy, advanced, or difficult by looking at three important anatomical landmarks-the vascular corridor (narrow if ≤25 mm, medium if 25-35 mm [inclusive], and wide if >35 mm), the left common iliac vein (LCIV) location (grades A-D based on the relative position of the LCIV to the L5-S1 disc space), and the presence or absence of a fat plane. RESULTS: Our results showed that 43.27% of the patients had wide corridor for the anterior access, 19.26% of patients had no fat plane, and 7.65% had a LCIV that extended past the midline of the disc (Grade C, D: >50%). By combining these three factors, 37.20% would have easy anterior access, while a minority (1.85%) would have a difficult anterior access. CONCLUSION: The ALIF at L5-S1 offers significant benefits to the patient. The surgeon should be aware of the dangers in an anterior access by looking at three crucial factors to determine whether the access is easy, advanced, or difficult. Patients with a difficult access should be attempted by experts, vascular access surgeons, or consider an alternative approach to L5-S1.Level of Evidence: 3.

Correction of degenerative lumbar coronal deformity using asymmetrical interbody cages: Surgical technique and case report.

In adult degenerative spondylosis, much emphasis has been placed upon recognizing the sagittal plane deformity and techniques to restore this alignment. However, the coronal plane deformity has not received much attention and, if left uncorrected, may lead to poorer outcomes. Here, we present a case of degenerative lumbar scoliosis with a rigid coronal malalignment secondary to a dysplastic sacrum. We performed staged T11-pelvis lateral and posterior approach to address this deformity. For the first stage, a lateral lumbar interbody fusion was performed at the concavity of the curve from L3 to L5. For the second stage, through posterior approach, a long-segment instrumentation from T11 to pelvis was done along with bilateral asymmetrical posterior lumbar interbody fusion of L5-S1 to level the L5 vertebra at the hemi-curve, thereby leveling the coronal deformity. We propose, for cases with a rigid coronal deformity due to bony dysplasia, correction through the disc space using asymmetrical interbody cages as in this case offers the surgeon an option to achieve a desired correction, without the need for vertebral osteotomy.

Morphological Parameters of the Thoracic Pedicle in an Asian Population: A Magnetic Resonance Imaging-Based Study of 3324 Pedicles.

STUDY DESIGN: A cross-sectional magnetic resonance imaging (MRI)-based anatomical study. OBJECTIVES: Instrumentation of the thoracic spine may be challenging due to the unique pedicle morphology and the proximity of vital structures. As prior morphological studies have mostly been done in Caucasians, our study aims to determine the optimal pedicle screw size for transpedicular fixation in an Asian population. METHODS: A retrospective analysis of 400 patients who had undergone MRI of the thoracic spine was performed. A total of 3324 pedicles were included. Pedicle morphology was graded qualitatively based on the size of its cancellous channel, and quantitatively with the following parameters: pedicle transverse diameter, pedicle screw path length, and pedicle angle. Subgroup analysis based on gender was performed. RESULTS: Mean pedicle transverse diameter was the narrowest at the T4 (2.9 ± 1 mm) and T5 (3.1 ± 1.1 mm) level. The mean pedicle screw path length progressively increased from T1 (34 ± 4.6 mm) to T12 (47 ± 4.6 mm). The mean pedicle angle was the largest at T1 (34° ± 7.9°) and decreased caudally, to 9.4° ± 3.8° at the T12 level. Females had significantly lower mean pedicle diameter and screw path length than males at every vertebral level; however, they had a larger pedicle angle at T8 to T10. The most common size of the pedicle cancellous channel was more than 4 mm. CONCLUSION: Morphological differences in the Asian pedicle suggest that caution needs to be taken during thoracic spine instrumentation, particularly in Asian females who have significantly smaller pedicles. In such cases, the use of alternative techniques or intraoperative navigation may be useful.

Spinal Navigation for Cervical Pedicle Screws: Surgical Pearls and Pitfalls.

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: We intend to evaluate the accuracy and safety of cervical pedicle screw (CPS) insertion under O-arm-based 3-dimensional (3D) navigation guidance. METHODS: This is a retrospective study of patients who underwent CPS insertion under intraoperative O-arm-based 3D navigation during the years 2009 to 2018. The radiological accuracy of CPS placement was evaluated using their intraoperative scans. RESULTS: A total of 297 CPSs were inserted under navigation. According to Gertzbein classification, 229 screws (77.1%) were placed without any pedicle breach (grade 0). Of the screws that did breach the pedicle, 51 screws (17.2%) had a minor breach of less than 2 mm (grade 1), 13 screws (4.4%) had a breach of between 2 and 4 mm (grade 2), and 4 screws (1.3%) had a complete breach of 4 mm or more (grade 3). Six screws were revised intraoperatively. There was no incidence of neurovascular injury in this series of patients. 59 of the 68 breaches (86.8%) were found to perforate laterally, and the remaining 9 (13.2%) medially. It was noted that the C5 cervical level had the highest breach rate of 33.3%. CONCLUSIONS: O-arm-based 3D navigation can improve the accuracy and safety of CPS insertion. The overall breach rate in this study was 22.9%. Despite these breaches, there was no incidence of neurovascular injury or need for revision surgery for screw malposition.

Accuracy of Thoracolumbar Pedicle Screw Insertion Based on Routine Use of Intraoperative Imaging and Navigation.

STUDY DESIGN: Retrospective review. PURPOSE: To determine the accuracy of thoracolumbar pedicle screw insertion with the routine use of three-dimensional (3D) intraoperative imaging and navigation over a large series of screws in an Asian population. OVERVIEW OF LITERATURE: The use of 3D intraoperative imaging and navigation in spinal surgery is aimed at improving the accuracy of pedicle screw insertion. This study analyzed 2,240 pedicle screws inserted with the routine use of intraoperative navigation. It is one of very few studies done on an Asian population with a large series of screws. METHODS: Patients who had undergone thoracolumbar pedicle screws insertion using intraoperative imaging and navigation between 2009 and 2017 were retrospectively analyzed. Computed tomography (CT) images acquired after the insertion of pedicle screws were analyzed for breach of the pedicle wall. The pedicle screw breaches were graded according to the Gertzbein classification. The breach rate and revision rate were subsequently calculated. RESULTS: A total of 2,240 thoracolumbar pedicle screws inserted under the guidance of intraoperative navigation were analyzed, and the accuracy of the insertion was 97.41%. The overall breach rate was 2.59%, the major breach rate was 0.94%, and the intraoperative screw revision rate was 0.7%. There was no incidence of return to the operating theater for revision of screws. CONCLUSIONS: The routine use of 3D navigation and intraoperative CT imaging resulted in consistently accurate pedicle screw placement. This improved the safety of spinal instrumentation and helped in avoiding revision surgery for malpositioned screws.

Neuromonitoring in Cervical Spine Surgery: When Is a Signal Drop Clinically Significant?

STUDY DESIGN: Retrospective cohort study. PURPOSE: To identify the clinical significance of different patterns of intraoperative neuromonitoring (IONM) signal alerts. OVERVIEW OF LITERATURE: IONM is a long-established valuable adjunct to complex spine surgeries. IONM for cervical spine surgery is in the form of somatosensory evoked potential (SSEP) and motor evoked potential (MEP). The efficacy of both modalities (individually or in combination) to detect clinically significant neurological compromise is constantly being debated and requires conclusive suggestions. METHODS: Clinical and neuromonitoring data of 207 consecutive adult patients who underwent cervical spine surgeries at multiple surgical centers using bimodal IONM were analyzed. Signal changes were divided into three groups. Group 0 had transient signal changes in either MEPs or SSEPs, group 1 had sustained unimodal changes, and group 2 had sustained changes in both MEPs and SSEPs. The incidences of true neurological deficits in each group were recorded. RESULTS: A total of 25% (52/207) had IONM signal alerts. Out of these signal drops, 96% (50/52) were considered to be false positives. Groups 0 and 1 had no incidence of neurological deficits, while group 2 had a 29% (2/7) rate of true neurological deficits. The sensitivities of both MEP and SSEP were 100%. SSEP had a specificity of 96.6%, while MEP had a lower specificity at 76.6%. C5 palsy rate was 6%, and there was no correlation with IONM signal alerts (p=0.73). CONCLUSIONS: This study shows that we can better predict its clinical significance by dividing IONM signal drops into three groups. A sustained, bimodal (MEP and SSEP) signal drop had the highest risk of true neurological deficits and warrants a high level of caution. There were no clear risk factors for false-positive alerts but there was a trend toward patients with cervical myelopathy.

Orthostatic Hypotension Following Cervical Spine Surgery: Prevalence and Risk Factors.

STUDY DESIGN: Retrospective case series. OBJECTIVES: This study aims to determine the prevalence and risk factors for orthostatic hypotension (OH) in patients undergoing cervical spine surgery. METHODS: Data was collected from records of 190 consecutive patients who underwent cervical spine procedures at our center over 24 months. Statistical comparison was made between patients who developed postoperative OH and those who did not by analyzing characteristics such as age, gender, premorbid medical comorbidities, functional status, mechanism of spinal cord injury, preoperative neurological function, surgical approach, estimated blood loss, and length of stay. RESULTS: Twenty-two of 190 patients (11.6%) developed OH postoperatively. No significant differences in age, gender, medical comorbidities, or premorbid functional status were observed. Based on univariate comparisons, traumatic mechanism of injury (P = .002), poor ASIA (American Spinal Injury Association) grades (A, B, or C) (P < .001), and posterior surgical approach (P = .045) were found to significantly influence occurrence of OH. Among the significant variables, after adjusting for mechanism of injury and surgical approach, only ASIA grade was found to be an independent predictor. Having an ASIA grade of A, B, or C increased the likelihood of developing OH by approximately 5.978 times (P = .003). CONCLUSION: Our study highlights that OH is not an uncommon manifestation following cervical spine surgery. Patients with poorer ASIA grades A, B, or C were more likely to have OH when compared with those with ASIA grades D or E (43.5% vs 7.2%). Hence, we suggest that postural blood pressure should be routinely monitored in this group of patients so that early intervention can be initiated.