THORACOLUMBAR FUSION IN THE UNIFIED HEALTH SYSTEM: PRE-COVID-19 TEMPORAL TEMPORAL TRENDSARTRODESIS TEMPORAL COVID-19

Objective: To evaluate the temporal trends of thoracolumbar fusion procedures performed by the United Health System in Brazil from 2009 to 2019. Methods: This was an observational ecological study based on data collected from the information systems under the aegis of DATASUS, especially the Hospital Information System, which manages the Hospital Admission Authorizations (Autorizações de Internação Hospitalar - AIHs). All patients who had undergone the procedures of interest, that is, elective and emergency short and long thoracolumbar arthrodeses, were included. The temporal trends of the procedures performed in Brazil and in its five regions were calculated using polynomial regression. Results: The temporal trend of elective thoracolumbar arthrodesis decreased, while that of emergency arthrodesis increased, with the peak in 2015, followed by a marked decline. Short fusions were more frequent in both elective and emergency modalities, and the South and Central-West Regions had the highest indices of procedures per million inhabitants during the entire 2009 to 2019 period. Conclusions: The temporal trends of thoracolumbar fusions performed by SUS have decreased over the last decade, a phenomenon which may be explained by the growing criticism of indications of the procedure in the current literature. Level of evidence III; Retrospective Comparative Study.


INTRODUCTION
Arthrodesis of the thoracolumbar spine is defined as the fusion of two or more vertebral bodies, and is described as short, when the fusion involves up to three segments, or long, when it involves more than three segments. 1 Spinal fusion can be performed in orthopedic/neurological emergencies and as elective procedures. 2 The main indication for lumbar arthrodesis is to treat degenerative spine diseases, which include conditions such as degenerative symptomatic spondylolisthesis, degenerative disc disease with chronic low back pain refractory to conservative treatment, foraminal stenosis with nerve root compression, lumbar canal stenosis, and degenerative scoliosis. 3 Outside the core of degenerative etiologies, it is indicated for the treatment of conditions such as infectious diseases of the spine, vertebral fractures, traumatic and isthmic spondylolistheses, traumatic extruded herniations, recurring disc herniations, post-discectomy collapse, post-laminectomy instability, and after spinal tumor resections. 3 Other indications are pseudoarthrosis and adjacent segment disease. 3 With the advent of the Unified Health System (SUS), Brazil became the largest country to have a public health system, and it is estimated that 80% of the Brazilian population is SUS-dependent for health care. 4 Thus, the present study was conducted with the aim of filling a knowledge gap and producing information to assist in the reformulation of policies and the elaboration of strategies to implement surgical assistance in Brazil. For this, the annual frequency of thoracolumbar spinal fusions by SUS and its evolution from 2009 to 2019 in the regions of Brazil were evaluated.

METHODS
This was an observational ecological study based on secondary data. The medical records of patients over 18 years of age who underwent thoracolumbar fusion surgery during the period from 2009 to 2019 in public, philanthropic, or private hospitals in Brazil, and whose procedures were financed by SUS, were evaluated. The data were collected from information systems under the aegis of DATASUS (via the link http://datasus.saude.gov.br), especially from the Hospital Information System, which manages the AIHs (Hospital Admission Authorizations).
Using the "Procedures" option, we obtained the types of surgical procedures available during the period January 2009 and December 2019. All the patients (census) who underwent the following procedures by SUS were included in the study: POSTERIOR/ POSTERO-LATERAL INTERBODY FUSION OF ONE, TWO, THREE, OR FOUR  LEVELS; POSTERIOR THORACO-LUMBAR-SACRAL FUSION OF  ONE, TWO, THREE The proposed study was based on the ethical terms of National Health Council Resolution 466/12. Because the study data was obtained from secondary sources, without identification of the study subjects and available in the public domain, the review by the Institutional Review Board and the Informed Consent Form requirements were waived.
The data were tabulated using MS-Excel software and analyzed by the Statistical Package for the Social Sciences (SPSS) program, version 20.0. The qualitative data were presented as frequencies (absolute and proportional) and the quantitative data as measures of central tendency (mean or median) and their respective measures of variability/dispersion (standard deviation). The temporal trend analysis was conducted using polynomial regression models, given that they have high statistical power and are easier to formulate and interpret. The coefficient of determination (R 2 ), the βeta (mean annual variation of the time series from Pearson's simple linear regression), and the p-value from the variance analysis (ANOVA) were used for the temporal analyses.

RESULTS
Between 2009 and 2019, 79,529 thoracolumbar arthrodeses were performed in Brazil by SUS, 38,835 of which were elective and 40,694 were emergency procedures. In this period, the temporal trend of the elective thoracolumbar arthrodeses was decreasing, with a seasonal increase up until 2014, followed by a decline, as shown in Figure 1. The trends of the regions of Brazil are also found in Figure 1, and it is noteworthy that only the Central-West Region had an upward trend during that period. Regarding the emergency thoracolumbar arthrodeses, there was an upward temporal trend in the period, with a peak in 2015 and a downtrend since then, as shown in

DISCUSSION
In Brazil, between 2009 and 2019, emergency thoracolumbar arthrodeses (40,694) were more frequent than elective ones (38,835), and both had a consistently downward temporal trend after 2015. The incidence of arthrodeses in Brazil was 34.9 procedures per million inhabitants in 2009 and 27.7 procedures per million inhabitants in 2019, representing a decrease of 20.63%. The rise followed by the decline is similar to the temporal trend observed in North America in the same period. 5 The first instrumented vertebral body fusion was performed in 1891 using silver wire for fixation. 6 During that period, it was mainly indicated for spinal trauma, severe scoliosis, and Pott's disease. 6 In 1929, Hibbs performed the first vertebral fusion with silver wire for degenerative diseases of the lumbar spine, which proved unsatisfactory due to the high degree of associated pseudarthrosis. 7 However, in the late 1940s the orthopedist King adapted the Hibbs technique incorporating the use of facet screws, 8,9 a device improved by Boucher in 1959. 10 Thus, after the advent of screws and the 1934 publication of the article by Mixter and Barr that advocated the addition of intervertebral fusion in disc herniation surgeries, 11 the first wave of thoracolumbar arthrodeses was observed in the United States.
Thus, the incidence of the procedure doubled between 1979 and 1990, and its rise substantially intensified after the advent and approval of interbody devices (cage) by the Food and Drug Administration (FDA) in 1996. 12 According to Deyo et al., during the period between 1990 and 2001 there was a 220% increase in the incidence of arthrodeses per 100,000 inhabitants in the United States. 13 Regarding elective thoracolumbar arthrodeses, the upward trend of intervertebral fusions observed at the end of the 20th century continued into the first decades of the 21st century, as demonstrated in the North American study by Martin et al., who observed an increase of 62.3% in the procedures in the period between 2004 and 2015. 5 However, regarding the incidence of elective arthrodeses by indication, Martin et al. observed a drop in procedures for disc herniations and disc degeneration around 2015. 5 This drop was attributed to the questionable and controversial level of evidence of the procedure for degenerative diseases of the lumbar spine, as well as spondylolistheses, 5 a factor which may also have contributed to the decline in elective thoracolumbar arthrodeses in Brazil after 2014 observed in our study. The recognition of non-drug treatment as the first line for chronic low back pain intensified after the publication of the American, 14 European, 15 and Danish 16 guidelines and can also be associated with the decline in intervertebral fusions. In addition, the role of thoracolumbar fusion for chronic low back pain without neurological involvement is considered uncertain in the article by Foster et al. published in The Lancet in 2018. 17 Regarding emergency thoracolumbar arthrodeses, the indication of conservative treatment for traumatic vertebral fractures rather than surgery is also in vogue in the current scientific scenario, 18 and may be associated with the decline in incidence observed in the present study after 2015. According to Spiegl et al., the conservative approach can be used in thoracolumbar fractures with <10º of scoliotic deformity, <15º of kyphotic deformity, without neurological deficit, without relevant disc damage, and in the A0, A1, and A2 fracture subtypes of the AOSpine Thoracolumbar Spine Injury Classification System. 18 All five regions had drops in the incidence of arthrodeses per million inhabitants during the period from 2009 to 2019. The North Region had the largest drop (38.53%), followed by the Northeast (29.22%), Central-West (23.12%), South (20.08%), and Southeast (18.27%) Regions. Only the Central-West Region had an upward trend for elective arthrodeses, with a peak in 2017 followed by constant decline. Only the South and Northeast Regions had upward trends for emergency fusions, with peaks in 2015 and 2016, respectively, followed by decline. In summary, all regions showed a decline in all fusion modalities in the final years of the period evaluated. Once again, the drop in the number of procedures performed can be attributed to the uncertain and controversial level of evidence of thoracolumbar arthrodesis in the contemporary literature. [14][15][16][17][18] The different seasonality of the peaks and declines among the regions can be explained by the multiple factors that motivate surgeons to perform intervertebral             thoracolumbar spinal fusions, such as patient characteristics, baseline diagnosis, personal experience, and the availability of special devices and imaging exams. 5 The higher proportions of both emergency and elective short arthrodeses performed may be justified by epidemiological issues and some surgical implications. Regarding epidemiology, diseases affecting the spine that require long fusions, such as neoplasms, deformities, and infectious diseases, are less common. 5 As for surgical implications, evidence suggests that in treating degenerative spinal diseases short arthrodesis, when indicated, has more benefits than long arthrodesis, due to lower costs, shorter intraoperative time, and a lower risk of complications, especially pulmonary ones. 19

CONCLUSIONS
In Brazil, between 2009 and 2019, there was a downward temporal trend for both elective and emergency arthrodeses after 2015. Downward trends were also observed in all regions in the final years of the period evaluated for both the short and long categories of elective and emergency fusions. Finally, a decline in the incidence of thoracolumbar fusion per million inhabitants was observed in Brazil and in each of the five regions.
All authors declare no potential conflict of interest related to this article.
CONTRIBUTIONS OF THE AUTHORS: LDR: Writing, review, and intellectual concept; active participation in the discussion of the results; approval of the definitive version of the work. HB: Active participation in the discussion of the results; approval of the definitive version of the work. KSK: Writing, review, and intellectual concept; active participation in the discussion of the results; approval of the definitive version of the work. PSM: Active participation in the discussion of the results; approval of the definitive version of the work. ROM: Active participation in the discussion of the results; approval of the definitive version of the work. MBN: Writing, review, and intellectual concept; active participation in the discussion of the results; approval of the definitive version of the work.