Category: Spine

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Not Just an Anchor: The Human Filum Terminale Contains Stretch Sensitive and Nociceptive Nerve Endings and Responds to Electrical Stimulation With Paraspinal Muscle Activation

Neurosurgery 91:618–624, 2022

Neural components of the fibrous filum terminale (FT) are well known but are considered as embryonic remnants without functionality.

OBJECTIVE: To investigate the ultrastructure of human FT specimens for sensory nerve endings and record paraspinal muscle activity on electrostimulation of the FT. METHODS: We prospectively investigated a cohort of 53 patients who underwent excision of the FT for the treatment of tethered cord syndrome. Surgical FT specimens were investigated by light and transmission electron microscopy. Intraoperative electrophysiological routine monitoring was extended by recording paraspinal muscles above and below the laminotomy level.

RESULTS: Light microscopy revealed tiny peripheral nerves piercing the pia mater of the FT and entering its fibrous core. Transmission electron microscopy unveiled within the fibrous core of the FT myelinated nerve structures in 8 of the 53 patients and unmyelinated ones in 10 of the 53 patients. Both nerve endings encapsulated in fibrous tissue or unencapsulated nonmyelinated Schwann cell nerve bundles, that is, Remak cells, were found. Those nerve endings resembled mechanoreceptor and nociceptive receptor structures found in human skin, muscle tendons, and skeletal ligaments. Specifically, we found Ruffini mechanoreceptors and in addition nerve endings which resembled nociceptive glioneural structures of the skin. Bipolar electrostimulation of the FT was associated with paraspinal muscle activity above and below the spinal segment at which the FT was stimulated.

CONCLUSION: Morphological and electrophysiological results indicate the presence of functional sensory nerve endings in the FT. Like other spine ligaments, the FT may serve as a proprioceptive element but may also contribute to back pain in spine disorders.

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Assessing the differences in operative and patient-reported outcomes between lateral approaches for lumbar fusion: a systematic review and indirect meta-analysis

 

J Neurosurg Spine 37:498–514, 2022

Anterior-to-psoas lumbar interbody fusion (ATP-LIF), more commonly referred to as oblique lateral interbody fusion, and lateral transpsoas lumbar interbody fusion (LTP-LIF), also known as extreme lateral interbody fusion, are the two commonly used lateral approaches for performing a lumbar fusion procedure. These approaches help overcome some of the technical challenges associated with traditional approaches for lumbar fusion. In this systematic review and indirect meta-analysis, the authors compared operative and patient-reported outcomes between these two select approaches using available studies.

METHODS Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) approach, the authors conducted an electronic search using the PubMed, EMBASE, and Scopus databases for studies published before May 1, 2019. Indirect meta-analysis was conducted on fusion rate, cage movement (subsidence plus migration), permanent deficits, and transient deficits; results were depicted as forest plots of proportions (effect size [ES]).

RESULTS A total of 63 studies were included in this review after applying the exclusion criteria, of which 26 studies investigated the outcomes of ATP-LIF, while 37 studied the outcomes of LTP-LIF. The average fusion rate was found to be similar between the two groups (ES 0.97, 95% CI 0.84–1.00 vs ES 0.94, 95% CI 0.91–0.97; p = 0.561). The mean incidence of cage movement was significantly higher in the ATP-LIF group compared with the LTP-LIF group (stand-alone: ES 0.15, 95% CI 0.06–0.27 vs ES 0.09, 95% CI 0.04–0.16 [p = 0.317]; combined: ES 0.18, 95% CI 0.07–0.32 vs ES 0.02, 95% CI 0.00–0.05 [p = 0.002]). The mean incidence of reoperations was significantly higher in patients undergoing ATPLIF than in those undergoing LTP-LIF (ES 0.02, 95% CI 0.01–0.03 vs ES 0.04, 95% CI 0.02–0.07; p = 0.012). The mean incidence of permanent deficits was similar between the two groups (stand-alone: ES 0.03, 95% CI 0.01–0.06 vs ES 0.05, 95% CI 0.01–0.12 [p = 0.204]; combined: ES 0.03, 95% CI 0.01–0.06 vs ES 0.03, 95% CI 0.00–0.08 [p = 0.595]). The postoperative changes in visual analog scale (VAS) and Oswestry Disability Index (ODI) scores were both found to be higher for ATP-LIF relative to LTP-LIF (VAS: weighted average 4.11 [SD 2.03] vs weighted average 3.75 [SD 1.94] [p = 0.004]; ODI: weighted average 28.3 [SD 5.33] vs weighted average 24.3 [SD 4.94] [p < 0.001]).

CONCLUSIONS These analyses indicate that while both approaches are associated with similar fusion rates, ATP-LIF may be related to higher odds of cage movement and reoperations as compared with LTP-LIF. Furthermore, there is no difference in rates of permanent deficits between the two procedures.

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Prognostic factors for surgically managed intramedullary spinal cord tumours: a single‑centre case series

Acta Neurochirurgica (2022) 164:2605–2622

Intramedullary spinal cord tumours (IMSCTs) are comparatively rare neoplasms. We present a single-centre clinical case series of adult patients with surgically managed IMSCTs.

Methods We performed a retrospective analysis of electronic patient records in the time period spanning July 2010 to July 2021. All adult patients that had undergone surgical management for IMSCTs were eligible for inclusion. Baseline and postoperative clinical and radiological characteristics, along with follow-up data, were assessed. We also performed a literature review with a focus on surgical outcomes for IMSCTs.

Results Sixty-six patients matched our selection criteria, with a median age of 42 years (range 23–85). Thirty-four ependymomas, 17 haemangioblastomas, 12 astrocytomas, 2 lymphomas and 1 teratoma were included. Statistical analysis yielded several significant findings: IMSCTs spanning a greater number of vertebral levels are significantly associated with poor McCormick outcomes (p = 0.03), presence of gait disturbance before surgery is significantly associated with poor outcome for both postoperative McCormick and Nurick scores (p = 0.007), and radicular pain present pre-operatively is significantly associated with a good post-operative McCormick score (p = 0.045). Haemangioblastomas are significantly more likely to have a clear intraoperative dissection plane compared to ependymomas and astrocytomas (p = 0.009). However, astrocytomas have a significantly higher prevalence of good McCormick outcomes compared to ependymomas and haemangioblastomas (p = 0.03). Conclusion Histological diagnosis, cranio-caudal extent of the tumour and the presence or absence of baseline deficits—such as gait impairment and radicular pain—are significant in determining neurological outcomes after surgery for IMSCTs.

Keywords Intramedullary spinal cord tumours · Spinal ependymomas · Spinal astrocytomas · Spinal oncology · Surgical outcomes

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Characteristics of patients undergoing revision surgery for proximal junctional failure after adult spinal deformity surgery

J Neurosurg Spine 37:402–409, 2022

Score on the proximal junctional kyphosis severity scale (PJKSS) has been validated to show good correlations with likelihood of revision surgery for proximal junctional failure (PJF) after surgical treatment of adult spinal deformity (ASD). However, if the patient has progressive neurological deterioration, revision surgery should be considered regardless of severity based on PJKSS score. This study aimed to revalidate the correlation of PJKSS score with likelihood of revision surgery in patients with PJF but without neurological deficit. In addition, the authors provide the cutoff score on PJKSS that indicates need for revision surgery.

METHODS A retrospective study was performed. Among 360 patients who underwent fusion of more than 4 segments including the sacrum, 83 patients who developed PJF without acute neurological deficit were included. Thirty patients underwent revision surgery (R group) and 53 patients did not undergo revision surgery (NR group). All components of PJKSS and variables other than those included in PJKSS were compared between groups. The cutoff score on PJKSS that indicated need for revision surgery was calculated with receiver operating characteristic curve analysis. Multivariate analysis with logistic regression was performed to identify which variables were most predictive of revision surgery.

RESULTS The mean patient age at the time of index surgery was 69.4 years, and the mean fusion length was 6.1 segments. All components of PJKSS, such as focal pain, instrumentation problem, change in kyphosis, fracture at the uppermost instrumented vertebra (UIV)/UIV+1, and level of UIV, were significantly different between groups. The average total PJKSS score was significantly greater in the R group than in the NR group (6.0 vs 3.9, p < 0.001). The calculated cutoff score was 4.5, with 70% sensitivity and specificity. There were no significant between-group differences in patient, surgical, and radiographic factors (other than the PJKSS components). Three factors were significantly associated with revision surgery on multivariate analysis: instrumentation problem (OR 8.160, p = 0.004), change in kyphosis (OR 4.809, p = 0.026), and UIV/UIV+1 fracture (OR 6.462, p = 0.002).

CONCLUSIONS PJKSS score positively predicted need for revision surgery in patients with PJF who were neurologically intact. The calculated cutoff score on PJKSS that indicated need for revision surgery was 4.5, with 70% sensitivity and specificity. The factor most responsible for revision surgery was bony failure with > 20° focal kyphotic deformity. Therefore, early revision surgery should be considered for these patients even in the absence of neurological deficit.

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Early mobilization versus bed rest for incidental durotomy

J Neurosurg Spine 37:460–465, 2022

The aim of this study was to assess whether flat bed rest for > 24 hours after an incidental durotomy improves patient outcome or is a risk factor for medical and wound complications and longer hospital stay.

METHODS Medical records of consecutive patients undergoing thoracic and lumbar decompression procedures from 2010 to 2020 were reviewed. Operative notes and progress notes were reviewed and searched to identify patients in whom incidental durotomies occurred. The need for revision surgery related to CSF leak or wound infection was recorded. The duration of bed rest, length of hospital stay, and complications (pulmonary, gastrointestinal, urinary, and wound) were recorded. The rates of complications were compared with regard to the duration of bed rest (≤ 24 hours vs > 24 hours).

RESULTS A total of 420 incidental durotomies were identified, indicating a rate of 6.7% in the patient population. Of the 420 patients, 361 underwent primary repair of the dura; 254 patients were prescribed bed rest ≤ 24 hours, and 107 patients were prescribed bed rest > 24 hours. There was no statistically significant difference in the need for revision surgery (7.87% vs 8.41%, p = 0.86) between the two groups, but wound complications were increased in the prolonged bed rest group (8.66% vs 15.89%, p = 0.043). The average length of stay for patients with bed rest ≤ 24 hours was 4.47 ± 3.64 days versus 7.24 ± 4.23 days for patients with bed rest > 24 hours (p < 0.0001). There was a statistically significant increase in the frequency of ileus, urinary retention, urinary tract infections, pulmonary issues, and altered mental status in the group with prolonged bed rest after an incidental durotomy. The relative risk of complications in the group with bed rest ≤ 24 hours was 50% less than the group with > 24 hours of bed rest (RR 0.5, 95% CI 0.39–0.62; p < 0.0001).

CONCLUSIONS In this retrospective study, the rate of revision surgery was not higher in patients with durotomy who underwent immediate mobilization, and medical complications were significantly decreased. Flat bed rest > 24 hours following incidental durotomy was associated with increased length of stay and increased rate of medical complications. After primary repair of an incidental durotomy, flat bed rest may not be necessary and appears to be associated with higher costs and complications.

 

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Comparison of local and regional radiographic outcomes in minimally invasive and open TLIF

J Neurosurg Spine 37:384–394, 2022

Local and regional radiographic outcomes following minimally invasive (MI) transforaminal lumbar interbody fusion (TLIF) versus open TLIF remain unclear. The purpose of this study was to provide a comprehensive assessment of local and regional radiographic parameters following MI-TLIF and open TLIF. The authors hypothesized that open TLIF provides greater segmental and global lordosis correction than MI-TLIF.

METHODS A single-center retrospective cohort study of consecutive patients undergoing MI- or open TLIF for grade I degenerative spondylolisthesis was performed. One-to-one nearest-neighbor propensity score matching (PSM) was used to match patients who underwent open TLIF to those who underwent MI-TLIF. Sagittal segmental radiographic measures included segmental lordosis (SL), anterior disc height (ADH), posterior disc height (PDH), foraminal height (FH), percent spondylolisthesis, and cage position. Lumbopelvic radiographic parameters included overall lumbar lordosis (LL), pelvic incidence (PI)–lumbar lordosis (PI-LL) mismatch, sacral slope (SS), and pelvic tilt (PT). Change in segmental or overall lordosis after surgery was considered “lordosing” if the change was > 0° and “kyphosing” if it was ≤ 0°. Student t-tests or Wilcoxon rank-sum tests were used to compare outcomes between MI-TLIF and open-TLIF groups.

RESULTS A total of 267 patients were included in the study, 114 (43%) who underwent MI-TLIF and 153 (57%) who underwent open TLIF, with an average follow-up of 56.6 weeks (SD 23.5 weeks). After PSM, there were 75 patients in each group. At the latest follow-up both MI- and open-TLIF patients experienced significant improvements in assessment scores obtained with the Oswestry Disability Index (ODI) and the numeric rating scale for low-back pain (NRS-BP), without significant differences between groups (p > 0.05). Both MI- and open-TLIF patients experienced significant improvements in SL, ADH, and percent corrected spondylolisthesis compared to baseline (p < 0.001). However, the MI-TLIF group experienced significantly larger magnitudes of correction with respect to these metrics (ΔSL 4.14° ± 4.35° vs 1.15° ± 3.88°, p < 0.001; ΔADH 4.25 ± 3.68 vs 1.41 ± 3.77 mm, p < 0.001; percent corrected spondylolisthesis: −10.82% ± 6.47% vs −5.87% ± 8.32%, p < 0.001). In the MI-TLIF group, LL improved in 44% (0.3° ± 8.5°) of the cases, compared to 48% (0.9° ± 6.4°) of the cases in the open-TLIF group (p > 0.05). Stratification by operative technique (unilateral vs bilateral facetectomy) and by interbody device (static vs expandable) did not yield statistically significant differences (p > 0.05).

CONCLUSIONS Both MI- and open-TLIF patients experienced significant improvements in patient-reported outcome (PRO) measures and local radiographic parameters, with neutral effects on regional alignment. Surprisingly, in our cohort, change in SL was significantly greater in MI-TLIF patients, perhaps reflecting the effect of operative techniques, technological innovations, and the preservation of the posterior tension band. Taking these results together, no significant overall differences in LL between groups were demonstrated, which suggests that MI-TLIF is comparable to open approaches in providing radiographic correction after surgery. These findings suggest that alignment targets can be achieved by either MI- or open-TLIF approaches, highlighting the importance of surgeon attention to these variables.

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Do the newly proposed realignment targets for C2 and T1 slope bridge the gap between radiographic and clinical success in corrective surgery for adult cervical deformity?

J Neurosurg Spine 37:368–375, 2022

Surgical correction of cervical deformity (CD) has been associated with superior alignment and functional outcomes. It has not yet been determined whether baseline or postoperative T1 slope (T1S) and C2 slope (C2S) correlate with health-related quality-of-life (HRQoL) metrics and radiographic complications, such as distal junctional kyphosis (DJK) and distal junctional failure (DJF). The objective of this study was to determine the impact of T1S and C2S deformity severity on HRQoL metrics and DJF development in patients with CD who underwent a cervical fusion procedure.

METHODS All operative CD patients with upper instrumented vertebra above C7 and preoperative (baseline) and up to 2-year postoperative radiographic and HRQoL data were included. CD was defined as meeting at least one of the following radiographic parameters: C2–7 lordosis < −15°, TS1–cervical lordosis mismatch > 35°, segmental cervical kyphosis > 15° across any 3 vertebrae between C2 and T1, C2–7 sagittal vertical axis > 4 cm, McGregor’s slope > 20°, or chin-brow vertical angle > 25°. Spearman’s rank-order correlation and linear regression analysis assessed the impact of T1S and C2S on HRQoL metrics (Neck Disability Index [NDI], modified Japanese Orthopaedic Association [mJOA] scale, EuroQOL 5-Dimension Questionnaire [EQ-5D] visual analog scale [VAS] score, and numeric rating scale [NRS]–neck) and complications (DJK, DJF, reoperation). Logistic regression and a conditional inference tree (CIT) were used to determine radiographic thresholds for achieving optimal clinical outcome, defined as meeting good clinical outcome criteria (≥ 2 of the following: NDI < 20 or meeting minimal clinically important difference, mild myelopathy [mJOA score ≥ 14], and NRS-neck ≤ 5 or improved by ≥ 2 points), not undergoing reoperation, or developing DJF or mechanical complication by 2 years.

RESULTS One hundred five patients with CD met inclusion criteria. By surgical approach, 14.7% underwent an anterioronly approach, 46.1% a posterior-only approach, and 39.2% combined anterior and posterior approaches. The mean baseline radiographic parameters were T1S 28.3° ± 14.5° and C2S 25.9° ± 17.5°. Significant associations were found between 3-month C2S and mJOA score (r = −0.248, p = 0.034), NDI (r = 0.399, p = 0.001), EQ-5D VAS (r = −0.532, p < 0.001), NRS-neck (r = 0.239, p = 0.040), and NRS-back (r = 0.264, p = 0.021), while significant correlation was also found between 3-month T1S and mJOA score (r = −0.314, p = 0.026), NDI (r = 0.445, p = 0.001), EQ-5D VAS (r = −0.347, p = 0.018), and NRS-neck (r = 0.269, p = 0.049). A significant correlation was also found between development of DJF and 3-month C2S (odds ratio [OR] 1.1, 95% confidence interval [CI] 1.01–1.1, p = 0.015) as well as for T1S (OR 1.1, 95% CI 1.01–1.1, p = 0.023). Logistic regression with CIT identified thresholds for optimal outcome by 2 years: optimal 3-month T1S < 26° (OR 5.6) and C2S < 10° (OR 10.4), severe 3-month T1S < 45.5° (OR 0.2) and C2S < 38.0° (no patient above this threshold achieved optimal outcome; all p < 0.05). Patients below both optimal thresholds achieved rates of 0% for DJK and DJF, and 100% met optimal outcome.

CONCLUSIONS The severity of CD, defined by T1S and C2S at baseline and especially at 3 months, can be predictive of postoperative functional improvement and occurrence of worrisome complications in patients with CD, necessitating the use of thresholds in surgical planning to achieve optimal outcomes.

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Surgery for degenerative cervical myelopathy in the elderly: a nationwide registry‐based observational study with patient‐reported outcomes

Acta Neurochirurgica (2022) 164:2317–2326

The aim of this study was to investigate whether clinical outcomes in patients aged ≥ 70 undergoing decompressive surgery for degenerative cervical myelopathy (DCM) differ from those of younger patients (50–70 years) at 1 year.

Methods Data were obtained from the Norwegian Registry for Spine Surgery (NORspine). Among 651 patients included, 177 (27.2%) were ≥ 70 years old. The primary outcome was change in the Neck Disability Index (NDI). Secondary outcomes were changes in the European Myelopathy Score (EMS), quality of life (EuroQoL EQ-5D), numeric rating scales (NRS) for headache, neck pain, and arm pain, and complications.

Results Significant improvements in all patient-reported outcomes (PROMs) were detected for both age cohorts at 1 year. For the two age cohorts combined, there was a statistically significant improvement in the NDI score (mean 9.2, 95% CI 7.7 to 10.6, P < 0.001). There were no differences between age cohorts in mean change of NDI (− 8.9 vs. − 10.1, P = 0.48), EQ-5D (0.13 vs. 0.17, P = 0.37), or NRS pain scores, but elderly patients experienced a larger improvement in EMS (0.7 vs. 1.3, P = 0.02). A total of 74 patients (15.6%) in the younger cohort and 43 patients (24.3%) in the older cohort experienced complications or adverse effects within 3 months of surgery, mainly urinary and respiratory tract infections.

Conclusion Surgery for DCM was associated with significant improvement across a wide range of PROMs for both younger and elderly patients. Surgery for DCM should not be denied based on age alone.

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Perioperative outcomes and survival after surgery for intramedullary spinal cord tumors: a single-institution series of 302 patients

J Neurosurg Spine 37:252–262, 2022

Intramedullary spinal cord tumors (IMSCTs) are rare neoplasms whose treatment is often technically challenging. Given the low volume seen at most centers, perioperative outcomes have been reported infrequently. Here, the authors present the largest single-institution series of IMSCTs, focusing on the clinical presentation, histological makeup, perioperative outcomes, and long-term survival of surgically treated patients.

METHODS A cohort of patients operated on for primary IMSCTs at a comprehensive cancer center between June 2002 and May 2020 was retrospectively identified. Data on patient demographics, tumor histology, neuraxial location, baseline neurological status, functional deficits, and operative characteristics were collected. Perioperative outcomes of interest included length of stay, postoperative complications, readmission, reoperation, and discharge disposition. Data were compared across tumor histologies using the Kruskal-Wallis H test, chi-square test, and Fisher exact test. Pairwise comparisons were conducted using Tukey’s honest significant difference test, chi-square test, and Fisher exact test. Long-term survival was assessed across tumor categories and histological subtype using the log-rank test.

RESULTS Three hundred two patients were included in the study (mean age 34.9 ± 19 years, 77% white, 57% male). The most common tumors were ependymomas (47%), astrocytomas (31%), and hemangioblastomas (11%). Ependymomas and hemangioblastomas disproportionately localized to the cervical cord (54% and 59%, respectively), whereas astrocytomas were distributed almost equally between the cervical cord (36%) and thoracic cord (38%). Clinical presentation, extent of functional dependence, and postoperative 30-day outcomes were largely independent of underlying tumor pathology, although tumors of the thoracic cord had worse American Spinal Injury Association (ASIA) grades than cervical tumors. Rates of gross-total resection were lower for astrocytomas than for ependymomas (54% vs 84%, p < 0.01) and hemangioblastomas (54% vs 100%, p < 0.01). Additionally, 30-day readmission rates were significantly higher for astrocytomas than ependymomas (14% vs 6%, p = 0.02). Overall survival was significantly affected by the underlying pathology, with astrocytomas having poorer associated prognoses (40% at 15 years) than ependymomas (81%) and hemangioblastomas (66%; p < 0.01) and patients with high-grade ependymomas and astrocytomas having poorer longterm survival than those with low-grade lesions (p < 0.01).

CONCLUSIONS The neuraxial location of IMSCTs, extent of resection, and postoperative survival differed significantly across tumor pathologies. However, perioperative outcomes did not vary significantly across tumor cohorts, suggesting that operative details, rather than pathology, may have a stronger influence on the short-term clinical course, whereas pathology appears to have a stronger impact on long-term survival.

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Robot-assisted and augmented reality–assisted spinal instrumentation

J Neurosurg Spine 37:299–314, 2022

The use of technology-enhanced methods in spine surgery has increased immensely over the past decade. Here, the authors present the largest systematic review and meta-analysis to date that specifically addresses patient-centered outcomes, including the risk of inaccurate screw placement and perioperative outcomes in spinal surgeries using robotic instrumentation and/or augmented reality surgical navigation (ARSN).

METHODS A systematic review of the literature in the PubMed, EMBASE, Web of Science, and Cochrane Library databases spanning the last decade (January 2011–November 2021) was performed to present all clinical studies comparing robot-assisted instrumentation and ARSN with conventional instrumentation techniques in lumbar spine surgery. The authors compared these two technologies as they relate to screw accuracy, estimated blood loss (EBL), intraoperative time, length of stay (LOS), perioperative complications, radiation dose and time, and the rate of reoperation.

RESULTS A total of 64 studies were analyzed that included 11,113 patients receiving 20,547 screws. Robot-assisted instrumentation was associated with less risk of inaccurate screw placement (p < 0.0001) regardless of control arm approach (freehand, fluoroscopy guided, or navigation guided), fewer reoperations (p < 0.0001), fewer perioperative complications (p < 0.0001), lower EBL (p = 0.0005), decreased LOS (p < 0.0001), and increased intraoperative time (p = 0.0003). ARSN was associated with decreased radiation exposure compared with robotic instrumentation (p = 0.0091) and fluoroscopy-guided (p < 0.0001) techniques.

CONCLUSIONS Altogether, the pooled data suggest that technology-enhanced thoracolumbar instrumentation is advantageous for both patients and surgeons. As the technology progresses and indications expand, it remains essential to continue investigations of both robotic instrumentation and ARSN to validate meaningful benefit over conventional instrumentation techniques in spine surgery.

Systematic review registration no.: CRD42021283631 (https://www.crd.york.ac.uk/prospero/)

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Fifty years later: the “rule of Spence” is finally ready for retirement

J Neurosurg Spine 37:149–156, 2022

Determination of the optimal approach to traumatic atlas fractures with or without transverse atlantal ligament (TAL) injury requires a nuanced understanding of the biomechanics of the atlantoaxial complex. The “rule of Spence” (ROS) was created in 1970 in a landmark effort to streamline management of burst-type atlas fractures. The ROS states that radiographic evidence of lateral mass displacement (LMD) (i.e., the distance that the C1 lateral masses extend beyond the C2 superior articular processes) greater than 6.9 mm may indicate both a torn TAL and need for surgical management. Since then, the ROS has become ubiquitous in the spine literature about atlas injuries. However, in the decades since the original paper by Spence et al., modern research efforts and imaging advancements have revealed that the ROS is inaccurate on both fronts: it neither accurately predicts a TAL injury nor does it inform surgical decision-making.

The purpose of this review was to delineate the history of the ROS, demonstrate its limitations, present findings in the existing literature on ROS and LMD thresholds, and discuss the current landscape of management techniques for TAL injuries, including parameters such as the atlantodental interval and type of injury according to the Dickman classification system and AO Spine upper cervical injury classification system. The ROS was revolutionary for initially investigating and later propelling the biomechanical and clinical understanding of atlas fractures and TAL injuries; however, it is time to retire its legacy as a rule.

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Predictors of subsidence after lateral lumbar interbody fusion

J Neurosurg Spine 37:183–187, 2022

Lateral lumbar interbody fusion (LLIF) facilitates the restoration of disc height and the indirect decompression of neural elements. However, these benefits are lost when the graft subsides into the adjacent endplates. The factors leading to subsidence after LLIF are poorly understood. This article presents a case series of patients who underwent LLIF and reports factors correlating with subsidence.

METHODS A retrospective review of a consecutive, prospectively collected, single-institution database of patients who underwent LLIF over a 29-month period was performed. The degree of subsidence was measured on the basis of postoperative imaging. The timing of postoperative subsidence was determined, and intraoperative fluoroscopic images were reviewed to determine whether subsidence occurred as a result of endplate violation. The association of subsidence with age, sex, cage size and type, bone density, and posterior instrumentation was investigated.

RESULTS One hundred thirty-one patients underwent LLIF at a total of 204 levels. Subsidence was observed at 23 (11.3%) operated levels. True subsidence, attributable to postoperative cage settling, occurred for 12 (5.9%) of the levels; for the remaining 11 (5.4%) levels, subsidence was associated with intraoperative endplate violation noted on fluoroscopy during cage placement. All subsidence occurred within 12 weeks of surgery. Univariate analysis showed that the prevalence of true subsidence was significantly lower among patients with titanium implants (0 of 55; 0%) than among patients with polyetheretherketone cages (12 of 149; 8.1%) (p = 0.04). In addition, the mean ratio of graft area to inferior endplate area was significantly lower among the subsidence levels (0.34) than among the nonsubsidence levels (0.42) (p < 0.01). Finally, subsidence among levels with posterior fixation (4.4% [6/135]) was not significantly different than among those without posterior fixation (8.7% [6/69]) (p = 0.23). Multivariate analysis results showed that the ratio of cage to inferior endplate area was the only significant predictor of subsidence in this study (p < 0.01); increasing ratios were associated with a decreased likelihood of subsidence.

CONCLUSIONS Overall, the prevalence of subsidence after LLIF was low in this clinical series. Titanium cages were associated with a lower prevalence of observed subsidence on univariate analysis; however, multivariate analysis demonstrated that this effect may be attributable to the increased surface area of these cages relative to the inferior endplate area.

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Artificial intelligence in predicting early‑onset adjacent segment degeneration following anterior cervical discectomy and fusion

European Spine Journal (2022) 31:2104–2114

Anterior cervical discectomy and fusion (ACDF) is a common surgical treatment for degenerative disease in the cervical spine. However, resultant biomechanical alterations may predispose to early-onset adjacent segment degeneration (EO-ASD), which may become symptomatic and require reoperation. This study aimed to develop and validate a machine learning (ML) model to predict EO-ASD following ACDF.

Methods Retrospective review of prospectively collected data of patients undergoing ACDF at a quaternary referral medical center was performed. Patients > 18 years of age with > 6 months of follow-up and complete pre- and postoperative X-ray and MRI imaging were included. An ML-based algorithm was developed to predict EO-ASD based on preoperative demographic, clinical, and radiographic parameters, and model performance was evaluated according to discrimination and overall performance.

Results In total, 366 ACDF patients were included (50.8% male, mean age 51.4 ± 11.1 years). Over 18.7 ± 20.9 months of follow-up, 97 (26.5%) patients developed EO-ASD. The model demonstrated good discrimination and overall performance according to precision (EO-ASD: 0.70, non-ASD: 0.88), recall (EO-ASD: 0.73, non-ASD: 0.87), accuracy (0.82), F1-score (0.79), Brier score (0.203), and AUC (0.794), with C4/C5 posterior disc bulge, C4/C5 anterior disc bulge, C6 posterior superior osteophyte, presence of osteophytes, and C6/C7 anterior disc bulge identified as the most important predictive features.

Conclusions Through an ML approach, the model identified risk factors and predicted development of EO-ASD following ACDF with good discrimination and overall performance. By addressing the shortcomings of traditional statistics, ML techniques can support discovery, clinical decision-making, and precision-based spine care.

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Can artificial intelligence support or even replace physicians in measuring sagittal balance?

European Spine Journal (2022) 31:1943–1951

Sagittal balance (SB) plays an important role in the surgical treatment of spinal disorders. The aim of this research study is to provide a detailed evaluation of a new, fully automated algorithm based on artificial intelligence (AI) for the determination of SB parameters on a large number of patients with and without instrumentation.

Methods Pre- and postoperative sagittal full body radiographs of 170 patients were measured by two human raters, twice by one rater and by the AI algorithm which determined: pelvic incidence, pelvic tilt, sacral slope, L1-S1 lordosis, T4-T12 thoracic kyphosis (TK) and the spino-sacral angle (SSA). To evaluate the agreement between human raters and AI, the mean error (95% confidence interval (CI)), standard deviation and an intra- and inter-rater reliability was conducted using intra-class correlation (ICC) coefficients.

Results ICC values for the assessment of the intra- (range: 0.88–0.97) and inter-rater (0.86–0.97) reliability of human raters are excellent. The algorithm is able to determine all parameters in 95% of all pre- and in 91% of all postoperative images with excellent ICC values (PreOP-range: 0.83–0.91, PostOP: 0.72–0.89). Mean errors are smallest for the SSA (PreOP: −0.1° (95%-CI: −0.9°–0.6°); PostOP: −0.5° (−1.4°–0.4°)) and largest for TK (7.0° (6.1°–7.8°); 7.1° (6.1°–8.1°)).

Conclusion A new, fully automated algorithm that determines SB parameters has excellent reliability and agreement with human raters, particularly on preoperative full spine images. The presented solution will relieve physicians from timeconsuming routine work of measuring SB parameters and allow the analysis of large databases efficiently.

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3D printing applications in spine surgery: an evidence‑based assessment toward personalized patient care

European Spine Journal (2022) 31:1682–1690

Spine surgery entails a wide spectrum of complicated pathologies. Over the years, numerous assistive tools have been introduced to the modern neurosurgeon’s armamentarium including neuronavigation and visualization technologies. In this review, we aimed to summarize the available data on 3D printing applications in spine surgery as well as an assessment of the future implications of 3D printing.

Methods We performed a comprehensive review of the literature on 3D printing applications in spine surgery.

Results Over the past decade, 3D printing and additive manufacturing applications, which allow for increased precision and customizability, have gained significant traction, particularly spine surgery. 3D printing applications in spine surgery were initially limited to preoperative visualization, as 3D printing had been primarily used to produce preoperative models of patient-specific deformities or spinal tumors. More recently, 3D printing has been used intraoperatively in the form of 3D customizable implants and personalized screw guides.

Conclusions Despite promising preliminary results, the applications of 3D printing are so recent that the available data regarding these new technologies in spine surgery remains scarce, especially data related to long-term outcomes.

 

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Change in sagittal alignment after decompression alone in patients with lumbar spinal stenosis without significant deformity

J Neurosurg Spine 37:57–63, 2022

The authors’ objective was to investigate whether sagittal balance improves in patients with spinal stenosis after decompression alone.

METHODS This prospective longitudinal cohort study compared preoperative and 6-month postoperative 36-inch full-length radiographs in patients aged older than 60 years. Patients underwent decompression alone for central lumbar spinal stenosis with either a minimally invasive bilateral laminotomy for central decompression, unilateral laminectomy as an over-the-top procedure for bilateral decompression, or traditional wide laminectomy with removal of the spinous processes on both sides. The following radiographic parameters were measured: sagittal vertical axis (SVA), lumbar lordosis (LL), pelvic tilt (PT), pelvic incidence (PI), PI-LL mismatch, coronal Cobb angle, and sacral slope (SS). Patient reported outcome measures (PROMs) were collected, including scores on the Oswestry Disability Index (ODI), visual analog scale (VAS) for leg and back pain, and EQ-5D.

RESULTS Forty-five patients (24 males) with a mean ± SD age of 71.8 ± 5.6 years were included. Sagittal balance showed statistically significant improvement, with the mean SVA decreasing from 52.3 mm preoperatively to 33.9 mm postoperatively (p = 0.0001). The authors found an increase in LL, from mean −41.5° preoperatively to −43.9° postoperatively, but this was not statistically significant (p = 0.055). A statistically significant decrease in PI-LL mismatch from mean 8.4° preoperatively to 5.8° postoperatively was found (p = 0.002). All PROM scores showed significant improvement after spinal decompression surgery. The correlations between SVA and all PROMs were statistically significant at both preoperative and postoperative time points, although most correlations were weak except for those between preoperative SVA and ODI (r = 0.55) and between SVA and VAS for leg pain (r = 0.58).

CONCLUSIONS Sagittal balance and PROMs show improvement at short-term follow-up evaluations in patients who have undergone decompression alone for lumbar spinal stenosis.

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Change in sagittal alignment after decompression alone in patients with lumbar spinal stenosis without significant deformity: a prospective cohort study

J Neurosurg Spine 37:57–63, 2022

OBJECTIVE The authors’ objective was to investigate whether sagittal balance improves in patients with spinal stenosis after decompression alone.

METHODS This prospective longitudinal cohort study compared preoperative and 6-month postoperative 36-inch full-length radiographs in patients aged older than 60 years. Patients underwent decompression alone for central lumbar spinal stenosis with either a minimally invasive bilateral laminotomy for central decompression, unilateral laminectomy as an over-the-top procedure for bilateral decompression, or traditional wide laminectomy with removal of the spinous processes on both sides. The following radiographic parameters were measured: sagittal vertical axis (SVA), lumbar lordosis (LL), pelvic tilt (PT), pelvic incidence (PI), PI-LL mismatch, coronal Cobb angle, and sacral slope (SS). Patient reported outcome measures (PROMs) were collected, including scores on the Oswestry Disability Index (ODI), visual analog scale (VAS) for leg and back pain, and EQ-5D.

RESULTS Forty-five patients (24 males) with a mean ± SD age of 71.8 ± 5.6 years were included. Sagittal balance showed statistically significant improvement, with the mean SVA decreasing from 52.3 mm preoperatively to 33.9 mm postoperatively (p = 0.0001). The authors found an increase in LL, from mean −41.5° preoperatively to −43.9° postoperatively, but this was not statistically significant (p = 0.055). A statistically significant decrease in PI-LL mismatch from mean 8.4° preoperatively to 5.8° postoperatively was found (p = 0.002). All PROM scores showed significant improvement after spinal decompression surgery. The correlations between SVA and all PROMs were statistically significant at both preoperative and postoperative time points, although most correlations were weak except for those between preoperative SVA and ODI (r = 0.55) and between SVA and VAS for leg pain (r = 0.58).

CONCLUSIONS Sagittal balance and PROMs show improvement at short-term follow-up evaluations in patients who have undergone decompression alone for lumbar spinal stenosis.

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A systematic review with meta‑analysis of the diagnostic test accuracy of pedicle screw electrical stimulation

European Spine Journal (2022) 31:1599–1610

Purpose To provide a systematic review with meta-analysis providing evidence of the current diagnostic test accuracy (DTA) of pedicle screw electrical stimulation.

Methods A systematic database search on PubMed, Scopus and Web of Science was performed according to the PRISMADTA guidelines, and eligibility criteria applied to reduce the results to: (1) only journal articles reporting electrical stimulation of the pedicle screw head, (2) screw position confirmation by imaging techniques, and (3) enough information allowing the calculation of a 2 × 2 contingency table. Sample characteristics, image confirmation method, electrical current threshold and stimulation results were retrieved and analyzed using according to appropriate DTA analysis methods, and allowing the calculation of specificity, sensitivity for pedicle screws insertion at the lumbar and thoracic levels.

Results Lumbar screw stimulation presents a higher sensitivity (0.586 [0.336, 0.798] and specificity (0.984 [0.958, 0.994]) than thoracic screws (sensitivity: 0.270 [0.096; 0.562]; specificity: 0.958 [0.931, 0.975]). The same is observed in terms of the diagnostic odds ratio for lumbar (88.32 [32.136, 242.962]) and thoracic (8.460 [2.139, 33.469]) levels. When performing a sub-group analysis, it is possible to divide the lumbar stimulation threshold as 8 and 10–12 mA, and the thoracic threshold as 6 and 9–12 mA. A threshold of 8 mA at the lumbar level provides higher sensitivity and specificity. Increasing the threshold results in higher specificity but not sensitivity. In fact, at the range of 10–12 mA, the diagnostic validity is too low to confer this technique any robust diagnostic validity. Similarly, at the thoracic level, lower threshold currents are associated with increased sensitivity, but their diagnostic validity is very low.

Conclusion Electrical stimulation of the pedicle screw can be used as an adequate diagnostic capability at the lumbar level with a threshold of 8 mA. However, thoracic stimulation is currently not reliable, with very low sensitivity and diagnostic validity at 6 mA or higher.

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Safe Electromyography Stimulation Thresholds Within Kambin’s Triangle During Endoscopic Transforaminal Lumbar Interbody Fusion

Neurosurgery 91:150–158, 2022

Transforaminal endoscopic approaches through Kambin’s triangle traditionally require surgery to be performed without general anesthesia to allow live patient feedback. No reliable intraoperative neuromonitoring method specific to the dorsal root ganglion (DRG), the structure most at risk during this approach, currently exists.

OBJECTIVE: To correlate evoked electromyography (EMG) thresholds within Kambin’s triangle with new postoperative pain or sensorimotor symptoms potentially resulting from DRG irritation.

METHODS: Data were prospectively collected for all patients undergoing endoscopic transforaminal lumbar interbody fusion (TLIF) under general anesthesia at a single institution. A stimulation probe was inserted into Kambin’s triangle under fluoroscopic and robotic guidance, before passage of endoscopic instruments. EMG thresholds required to elicit corresponding myotomal responses were measured. Postoperatively, any potential manifestations of DRG irritation were recorded.

RESULTS: Twenty-four patients underwent a total of 34 transforaminal lumbar interbody fusion levels during the study period, with symptoms of potential DRG irritation occurring in 5. The incidence of new onset symptoms increased with lower stimulation thresholds. Sensitivities for EMG thresholds of ≤4, ≤8, and ≤11 mA were 0.6, 0.8, and 1, respectively. Corresponding specificities were 0.90, 0.69, and 0.55, respectively.

CONCLUSION: We demonstrated for the first time the feasibility of direct intraoperative neuromonitoring within Kambin’s triangle in transforaminal endoscopic surgery. Eight milliampere seems to be a reasonable compromise between sensitivity and specificity for this monitoring technique. In the future, larger-scale studies are required to refine safe stimulation thresholds.

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A novel use of cone beam CT: flexion and extension weight‑bearing imaging to assess spinal stability

European Spine Journal (2022) 31:1667–1681

Purpose To assess spinal stability in different physiological positions whilst weight-bearing.

Methods A cone beam CT scanner (CBCT) was used to identify any abnormal motion in the spine in different physiological positions whilst weight-bearing. The lumbar spine was assessed in 6 different patients with a comfortable neutral standing position and standing flexion and extension images in selected patients. Seated, weight-bearing flexion and extension images of the cervical spine were obtained in a further patient. Clinical indications included stability assessment post-trauma, post-surgical fusion and back pain. The projection images were reconstructed using bone and soft tissue algorithms to give isotropic CT images which could be viewed as per conventional multi-detector CT images. The flexion and extension CBCT data were fused to give a representation of any spinal movement between the extremes of motion.

Results The flexion and extension weight-bearing images gave anatomical detail of the spine. Detail of the surgical constructs was possible. Dynamic structural information about spinal alignment, facet joints, exit foramina and paraspinal musculature was possible. The effective dose from the neutral position was equal to that of supine, multi-detector CT.

Conclusion CBCT can be used to image the lumbar and cervical spine in physiological weight-bearing positions and at different extremes of spinal motion. This novel application of an existing technology can be used to aid surgical decision making to assess spinal stability and to investigate occult back and leg pain. Its use should be limited to specific clinical indications, given the relatively high radiation dose.

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