What’s New in Spine Surgery (2019)

A review of articles in the area of spinal conditions over the past year, mostly high-quality, peer-reviewed manuscripts, revealed advances in our understanding of cervical deformity, cervical myelopathy, patient satisfaction, predictive analytics, and other topics in spine care. Cervical Deformity Cervical spinal deformity in the setting of concurrent thoracolumbar deformity is difficult to define. Correction of the thoracolumbar deformity can lead to a reciprocal change in cervical sagittal malalignment; however, this reciprocal change is not universal. Similar to the relationship between lumbar lordosis and pelvic incidence1,2, the relationship between T1 slope and cervical lordosis may be useful in predicting primary cervical deformity. In a study by Protopsaltis et al., a mismatch of <17° for T1 slope minus cervical lordosis (reciprocal compensation) was associated with improved cervical alignment following correction of thoracolumbar deformity. In the cohort with a mismatch of >17° in T1 slope minus cervical lordosis (lacking the compensatory mechanism), the cervical deformity progressed after correction of the thoracolumbar deformity3. Cervical Myelopathy As discussed in a recent report by Rao and colleagues, diffusion tensor imaging (DTI) uses the diffusion pattern of water molecules in biological tissues to reveal microscopic tissue architecture4. Using fractional anisotropy (FA), which measures the degree of connectivity in neuronal tissue, microstructural changes in the central nervous system can be appreciated. FA is a scalar measure, ranging from 0 to 1, with lower values indicating isotropic diffusion (i.e., unrestricted diffusion in all directions) and higher values indicating greater spatial asymmetry of diffusion (i.e., diffusion occurring mainly in one direction)4. In a prospective study of 44 patients with cervical spondylotic myelopathy who underwent decompressive surgery, Rao et al. observed that a lower preoperative FA value (<0.55) was associated with greater likelihood of an increase in the modified Japanese Orthopaedic Association (mJOA) score postoperatively. Conversely, a higher preoperative FA value at the level of maximal compression was associated with less functional improvement after decompressive surgery. DTI could serve as an objective proxy for functional status and as a tool to aid in clinical decision-making regarding surgery and calibrating patients’ expectations of functional recovery after surgery4. Proinflammatory cytokine concentrations have been shown to be elevated in compressive lesions of the spinal cord. Specifically, interleukin-1 beta (IL-1β), IL-6, interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α) have demonstrated prognostic value in animal models of spinal cord injury5. In a single-center study that included 40 patients with degenerative cervical myelopathy, serum levels of IL-6 were significantly elevated among the patients in this cohort compared with normal controls, and the concentration of IL-6 was correlated with the severity of myelopathy6. Spinal Cord Injury The inflammatory cascade initiated after an acute spinal cord injury involves the caspase-1-mediated release of IL-1β and IL-18 under the control of an intracellular multiprotein complex called inflammasome. In the setting of an acute spinal cord injury, most inflammasome components (IL-1β, IL-18, apoptosis-associated speck-like protein containing a CARD [ASC]) are upregulated. Furthermore, 17-estradiol (E2) has been shown to be a neuroprotective hormone with high anti-inflammatory properties. In a preclinical study, Zendedel et al. demonstrated that subcutaneous administration of E2 every 12 hours for 3 days post-spinal cord injury was associated with an attenuated expression of some inflammasome components and increased functional improvement in treated animals7. These findings support the neuroprotective function of 17-estradiol (E2) and its potential for use in treating patients with acute spinal cord injuries. The enzyme Rho is activated by growth-inhibitory factors after spinal cord injury. Overactivation of Rho leads to a cascade of events culminating in the collapse of axonal growth cones, neuronal loss, and failure of injured axons to regenerate, contributing to failure of sensorimotor and functional recovery. In in vitro rat cortical neuron models, the inhibition of Rho kinase (a downstream effector of Rho) led to decreased neuronal injury and represented a potential treatment for spinal cord injuries8. VX-210 is a cell-permeable derivative of C3 transferase that inhibits Rho activity by blocking the Rho-mediated collapse of axonal growth cones and inhibiting post-spinal cord injury neuronal apoptosis. In preclinical rodent models, VX-210 administered within 24 hours post-injury led to a significant improvement in the open-field locomotor rating scale compared with the control group 16 days post-injury9. A multicenter, phase-2b/3, randomized double-blinded, placebo-controlled human investigational clinical trial to evaluate the efficacy of VX-210 (SPinal Cord Injury Rho INhibition InvestiGation [SPRING] trial)10 was launched in 2016; however, this trial was terminated early (at intermediate follow-up) because of lack of efficacy. Patient Satisfaction In a Level-IV retrospective analysis of data from a multicenter database, Yang and colleagues used latent class analysis to identify homogenous clusters of patients on the basis of their responses to the Oswestry Disability Index (ODI) and Scoliosis Research Society (SRS)-22r questionnaire11. Latent class analysis is a modeling technique used to classify subjects into groups on the basis of responses to questions for a set of categorical variables. This technique possibly facilitates a more granular understanding of functional limitations at the patient level given the heterogeneity of current health-related quality-of-life (HRQoL) measurement tools. In the study by Yang et al., which included 430 patients who underwent corrective surgery for adult spinal deformity, the authors identified 4 classes of patients: the “worsened-condition” class (1.4% of patients), the “remained-same” class (13% of patients), the “mild-improved” class (40.2% of patients), and the “most-improved” class (45.3% of patients). When comparing the mild and most-improved classes with the remained-same and worsened-condition classes, the odds of a patient being satisfied with surgery were higher in the mild and most-improved classes (odds ratio [OR], 3.91 and 16.99, respectively). Furthermore, the authors demonstrated that improvement in the ability to stand, social life, and employment are the most important determinants of patient satisfaction after surgery, while lifting and sitting ability, personal care, sleeping, and traveling appeared to be of less importance11. Costs and Value in Spine Care In a study of 1 and 2-level anterior cervical discectomy and fusion (ACDF) procedures, Schroeder and colleagues used time-driven activity-based costing (TDABC) to assess the true cost of surgery12. In this Level-III study, 27 prospectively enrolled patients were included in the analysis; the patients were followed by a research assistant through the entire episode of care, to prevent recall bias. A process map consisting of 7 stages was designed for each patient, with the stages including the preoperative surgical visit; preadmission testing; preoperative care on the day of surgery; intraoperative care, including the surgical procedure; postoperative care, including the post-anesthesia care unit (PACU) and postoperative observation unit; the first postoperative visit, ∼2 to 3 weeks after surgery; and the second postoperative visit, ∼8 weeks after surgery12. The authors found that the mean total cost (and standard deviation) for a single-level ACDF 90-day episode of care was $27,558 ± $2,654, with hospital disposable resource charges ($15,309 ± $2,195) being the largest contributor to the total cost, followed by intraoperative personnel charges ($4,491 ± $1,052). The total 90-day cost for a 2-level ACDF procedure was $30,566 ± $5,534, with hospital disposable resource charges ($15,841 ± $5,411) representing the largest cost items, followed by intraoperative personnel charges ($6,672 ± $1,255). The smallest cost items for both 1 and 2-level ACDF procedures was the PACU personnel costs, averaging $125 ± $14. The authors concluded that reimbursement for 1 or 2-level ACDFs in bundled care should be no less than $29,299 to cover the true costs of care for the entire care cycle12. Predictive Analytics for Lumbar and Adult Deformity Conditions Using prospective registry data of 422 patients who underwent a microdiscectomy for symptomatic lumbar disc herniation, Staartjes et al. demonstrated the feasibility of generating personalized, robust, deep learning-based analytics for outcome prediction with limited surgeon and center-specific data13. The authors trained deep neural network-based and logistic regression-based prediction models on patient-reported outcome measures (PROMs). Compared with logistic regression-based models, the deep neural network-based models predicted achievement of the minimum clinically important difference (MCID) for leg pain, with a high area under the curve (AUC) of 0.87 and with an accuracy, sensitivity, and specificity of 85%. Similarly, the attainment of the MCID for functional disability (measured as change in the ODI) and improvement in back pain were predicted, with a higher AUC and accuracy by the deep-learning compared with logistic regression models13. In a Level-IV, statewide, multicenter analysis, Khor et al. developed and validated a predictive model for improvement in pain and functional outcomes after lumbar spine surgery14. The patient sample was obtained from the Spine Surgical Care and Outcomes Assessment Program (SCOAP) in Washington State, representing approximately 75% of eligible spine fusion procedures in the state over the study period. The primary outcomes of interest were a reduction of ≥15 points from baseline in the ODI score and improvement in back pain and leg pain of ≥2 points on a numeric rating scale. In their model, the patient subgroups who were less likely to improve with lumbar fusion surgery included patients with lower preoperative disability scores, those with Medicaid or Workers’ Compensation as the primary insurance source, and current and previous smokers. The invasiveness of surgery, surgeon type, and hospital type had lower predictive value in the model, a recognition that the main factors associated with functional improvement were patient-level variables14. As discussed in a recent report by Ames and colleagues, statistical models identifying patients with adult spinal deformity who are likely to benefit from corrective surgery have centered largely on radiographic parameters15. Many preoperative data points likely to enhance predictive modeling are excluded because the ability to separate patient patterns manually on the basis of hundreds of data points is not practical for surgeons. Machine-based clustering using artificial intelligence-based hierarchical clustering may be a step toward the development of a classification scheme that optimizes quality, value, and safety for patients undergoing corrective surgery for adult spinal deformity15. In their Level-IV study, the authors used unsupervised hierarchical clustering to identify optimal groups of patients for surgery and data patterns that may supplement preoperative decision-making through the construction of a risk-benefit grid15. Opioid Consumption In a Level-IV, single-center, retrospective study of 138 patients who underwent surgery for degenerative (nontraumatic) spine disease, Dunn et al. found that high preoperative catastrophizing scores (defined as >30 points on the pain catastrophizing scale) were associated with high postoperative pain scores and opioid consumption16. In a retrospective study of 27,031 patients who underwent lumbar decompression with or without fusion, Schoenfeld et al. found that the majority of patients using prescription opioids discontinued these medications postoperatively; however, in the subset of patients with prolonged opioid use (>90 days after surgery), the duration of preoperative opioid use appeared to be the most important predictor of postoperative opioid use17. In a Level-III retrospective study of 24,610 patients who underwent lumbar arthrodesis, Jain et al. found that 22.3% of patients had documented opioid use prior to surgery, and 87.4% of these patients continued long-term use postoperatively18. Additionally, the authors found preoperative chronic opioid therapy to be associated with higher 90-day wound complication rates, emergency department visits, and readmission rates. Deformity Adult Spinal Deformity In a Level-II retrospective analysis, Kato et al. used a multicenter, prospectively collected database to assess the incidence and outcomes of major versus minor neurological decline after corrective surgery for adult spinal deformity19. The authors reported that 23% of 265 subjects experienced a neurological injury, and of these patients, 33% experienced a major neurological decline. Full recovery was observed in 24% of these subjects at 6 weeks and in 65% at 6 months; however, about one-third of the subjects experienced persistent neurological deficit at 24 months postoperatively. Of the subjects who experienced a minor neurological injury, 49% reported full recovery at 6 weeks, and this increased to 70% at 6 months. About one-quarter of the subjects who experienced a minor neurological deficit after surgery showed no improvement at 24 months19. In a Level-III retrospective study involving 839 patients with adult spinal deformity treated either operatively or nonoperatively, Kelly et al. investigated the minimum detectable measurement difference (MDMD) in the SRS-22r outcomes instrument20. Understanding the relationship between the MDMD and the MCID is important because the MCID must be greater than the MDMD to be considered relevant. The proposed MCID for the SRS-22r instrument in adult spinal deformity is 0.4. Using the SRS-22r instrument, the MDMD for pain was 0.6; self-image, 0.5; activity, 0.3; mental health, 0.3; and total score, 0.2. The authors concluded that the MCID of 0.4 for the SRS-22r instrument may not be the optimal threshold for clinically meaningful change, as the calculated MDMD for the pain and the are for the treatment of adult spinal deformity. have shown improvement in measures after surgical correction of deformity, have investigated the of thoracolumbar on of In a Level-III study including patients who underwent corrective surgery for adult spinal deformity, et al. the of surgery with to including and was a 70% of patient satisfaction with the surgical to of the patients reported with as and after surgery. as in the and and in to of the measures appeared to improve after surgery for the of patients treated for adult spinal deformity, of not to a is increased as a of persistent pain following thoracolumbar fusion for treatment of adult spinal deformity. 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