Trends in hospital admissions and surgical procedures for degenerative lumbar spine disease in England: a 15 year time-series For peer review only

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1 Trends in hospital admissions and surgical procedures for degenerative lumbar spine disease in England: a year time-series Journal: Manuscript ID: bmjopen Article Type: Research Date Submitted by the Author: 0-Jun-0 Complete List of Authors: Sivasubramaniam, Vinothan; St George's Hospital, Department of Neurosurgery Patel, Hitesh; Royal Brompton & Harefield NHS Foundation Trust, Department of Cardiology Ozdemir, Baris; St George's Hospital, London United Kingdon, Department of Vascular surgery Papadopoulos, Marios; St George's Hospital, Department of Neurosurgery <b>primary Subject Heading</b>: Public health Secondary Subject Heading: Health policy, Epidemiology, Health economics, Surgery Keywords: Neurosurgery < SURGERY, NEUROSURGERY, Spine < ORTHOPAEDIC & TRAUMA SURGERY, Back pain < ORTHOPAEDIC & TRAUMA SURGERY : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

2 Page of Research Paper Trends in hospital admissions and surgical procedures for degenerative lumbar spine disease in England: a year time-series Authors Vinothan Sivasubramaniam, BSc (Hons) MRCS Hitesh C Patel, BSc (Hons) MRCP Baris A Ozdemir, BSc (Hons) MB BS MRCS Marios C Papadopoulos, MA MD FRCS(SN) Affiliations Department of Neurosurgery, Atkinson Morley Wing, St George's Hospital, Blackshaw Road, London SW 0QT, United Kingdom. Department of Cardiology The Royal Brompton & Harefield NHS Foundation Trust, Sydney Street, London SW NP, United Kingdom. Department of Vascular Surgery St George's Hospital, Blackshaw Road, London SW 0QT London Deanery Surgical Rotation, United Kingdom. Corresponding author's details: Vinothan Sivasubramaniam Department of Neurosurgery, St George's Hospital, Blackshaw road, Tooting, London SW 0QT Tel No vino.siva@nhs.net Keywords: low back pain, degenerative lumbar spine disease, hospital trends Word count: words (excluding title page, abstract, references and figures) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

3 Page of ABSTRACT Objectives Low back pain (LBP), from degenerative lumbar spine disease, represents a significant burden on healthcare resources. Studies worldwide report trends attributable to their country's specific demographics and healthcare system. Considering England's specific medico-socioeconomic conditions, we investigate recent trends in hospital admissions and procedures for LBP, and discuss the implications for the allocation of healthcare resources. Design Retrospective cohort study using Hospital Episode Statistics (HES) data relating to degenerative lumbar spine disease in England, between and 0. Regression models were used to analyse trends. Outcome measures Trends in the number of admissions and procedures for LBP, mean patient age, gender and length of stay. Results Hospital admissions and procedures have increased significantly over the study period, from.0 to. and from. to. per 00,000, respectively(p<0.00). The increase was most marked in the oldest age groups with a. and. fold increase in admissions for patients aged 0- and years respectively, and a. fold increase in procedures for those aged 0 years. Trends in hospital admissions were characterised by a widening gender gap, increasing mean patient age, and decreasing mean hospital stay (P<0.00).Trends in procedures were characterised by a narrowing gender gap, increasing mean patient age (p=0.0) and decreasing mean hospital stay (p<0.00). Linear regression models estimate that each hospital admission translates to 0. procedures, per 00,000 (%CI , r 0.,p<0.00). Hospital admissions are increasing at. times the rate of surgical procedures (regression gradient:. versus. per 00,000/year). Conclusions LBP represents a significant and increasing workload for hospitals in England. These trends demonstrate an increasing demand for specialists involved in the surgical and non-surgical management of this disease, and highlight the need for services capable of dealing with the increased co-morbidity burden associated with an ageing patient group. - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

4 Page of STRENGTHS AND LIMITATIONS OF THIS STUDY The use of routinely collected national administrative data allowed for the analysis of trends in admissions and surgical procedures for LBP throughout England, for a prolonged time period. As Hospital Episode Statistics (HES) is collected independently of this study, it is not subject to study-related bias or affected by factors that may have influenced hospital trends in LBP. This study provides important England-specific population-level data about longitudinal trends, associations, and patterns of care for LBP. Limitations inherent to using aggregate administrative data include coding errors relating to inaccurate representation of admissions and procedures, data duplication and inter-hospital variability. - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

5 Page of INTRODUCTION Low back pain (LBP), from degenerative lumbar spine disease, is one of the most prevalent non-fatal conditions worldwide, and a significant cause of long-term disability.[,] In England, it is one of the leading causes of physician attendances, hospitalisation, and utilisation of social care services.[] It confers a significant economic burden in terms of funding of health resources, disability benefits, and effect on industry from sick leave.[] Several studies in other countries, using national and medical insurance databases, have identified interesting trends in hospitalisation for degenerative lumbar spine disease. These trends have been attributed to the country's specific healthcare system, demographics, medical technological advances, and profitability of treatment modalities.[-] There is sparse data on trends in hospitalisation for this disease in England. The aim of this study is to investigate the longitudinal trends in hospital admissions and surgical procedures for degenerative lumbar spine disease in England, between and 0. Considering England's specific medico-socioeconomic conditions, which includes the existence of a health service free at the point of delivery, we evaluate whether it follows trends seen in other countries, and discuss the implications for allocation of healthcare resources. - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

6 Page of METHODS Annual aggregate data for all hospital admissions and procedures in England, from to 0, were retrieved from Hospital Episode Statistics (HES),available from the Health and Social Care Information Centre (HSCIC). In this study, the term LBP refers to degenerative disease resulting in low back pain with or without radicular or neurogenic claudicant symptoms. This encompasses a variety of underlying processes including herniated disc disease, isthaemic/degenerative spondylolisthesis, spinal stenosis, and nonspecific LBP (back pain not attributable to spinal instability or associated with radicular symptoms). Surgical procedures refer to surgery for degenerative lumbar spine disease, and do not include surgery for non-degenerative pathology such as trauma or malignancy. The HES dataset groups primary diagnoses according to the World Health Organisation's 0th revision of the International Classification of Diseases (ICD-0).The codes relevant to our study were M., M.,M., and M., referring to admissions with the primary diagnosis of radiculopathy, sciatica, lumbago with sciatica, and low back pain respectively. Finished consultant episodes, representative of hospital admissions, were analysed with respect to gender and four different age groups (0-, -, 0-, and years). Primary procedures, defined as the most resource intensive procedure performed during the hospital episode, were identified using to the th version of the Office of Population Censuses and Surveys Classification of Interventions and Procedures (OPCS-). Codes representing surgical procedures relevant to degenerative lumbar spine disease (Appendix) were aggregated and analysed to produce admission trends stratified by age and gender. The data for was excluded from our analysis of surgical interventions as only the less detailed -character procedure codes were available, deemed insufficient for this study. Mid-year estimates of English population denominators grouped by age and gender were obtained from the Office of National Statistics (ONS). Annual hospital admissions and surgical interventions are reported per 00,000 of the population, and further stratified by broad age groups and gender. Time trends were investigated using linear regression models with the gradient expressed as β values with % confidence intervals (CI), per 00,000 of the population. Correlation is represented by Pearson's correlation coefficient (r). Continuous variables were compared using the independent samples T-test. A p value of <0.0 was chosen to imply statistical significance. Statistical Package for the Social Sciences (SPSS) was used to perform data analysis. - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

7 Page of RESULTS Trends in hospital admissions for LBP: Overall hospital admissions. Over the year period from to 0, there was a significant rise in the overall hospital admissions for LBP, increasing from.0 in to. in 0, per 00,000 population (Fig ). This represents a. fold increase or an annual increase of. per 00,000 (β.[ci:.-.0],r=0., p<0.00). Gender. Hospital admissions for both men and women increased over the year period (β:.[.-.] and 0.[.-.] respectively, r=0. for both, p<0.00), with admissions being significantly greater in women than in men (p <0.00) (Fig ).Hospital admission rates for women increased at approximately twice the rate of men's, resulting in a widening gender gap over the year period (p<0.00). Mean age of patients at admission. Age at admission increased from. years in to. years in 0, representing an estimated 0. year increase in the average patient age per annum, over the years (β0.[ci: 0.-0.], r=0., p<0.00). Age categories. The data demonstrates a significant increase in hospital admissions for each of the four age groups over the study period (p<0.00) (Fig ). The greatest increase is seen in those aged 0- and years, evident by a. and. fold increases respectively (from. to., and from 0. to.0,per 00,000, respectively). Hospital admissions for those aged 0- years increased from. to. per 00,000, representing a. fold increase in a paediatric population, and from 0. to 00. per 00,000 for patients aged - years, over the years. The older the age group the greater was the observed annual rate of increase in hospital admissions (p<0.00) (Fig ). Mean hospital stay. The average length of hospital stay decreased from. days in to. days in 0, representing a % decrease or a fall of 0. years per study year (β0.[ ], r=0., p<0.00). - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

8 Page of Trends in surgical procedures for degenerative lumbar spine disease: Overall surgical procedures. Over the study period, there was a significant increase in the overall number of surgical procedures performed for degenerative lumbar spine disease(fig ), Recorded procedures almost doubled from. to. per 00,000, with an estimated. per 00,000 increase each year (β.[ci.-.], r=0.,p<0.00). Association between hospital admissions and the number of surgical procedures. There was a strong positive linear correlation between hospital admissions and procedures, with every incremental admission translating to an estimated 0./00,000 increase in surgical interventions (β0.[ ],r=0., p<0.00). Gender. There was a significant increase in surgical procedures for both genders over the study period (p<0.00). There was a statistically significant difference between genders for the early years only (000-0, p=0.0), but not for the latter years (0-, p=0.), suggesting a narrowing of any early gender gap. Mean patient age. This increased from. in 000 to. years in 0 (p=0.0), with an estimated increase in mean patient age of 0. years per annum, over the study period (β0.0[0.- 0.], r=0.,p<0.00). Age categories. With the exception of patients aged 0-years, there was a significant increase in the uptake of surgery for all age groups (-, 0- and years, p<0.00) (Fig ). The most significant increases were seen in the oldest age groups, with a. fold increase in both those aged 0- and years over the study period (from. to. and from. to 0, per 00,000, respectively). In contrast, those aged - years demonstrated a. fold increase (0. to 0. per 00,000). There was a fall in the number of surgical procedures recorded for those aged 0- years, from 0. in 000 to 0. in 0 per 00,000 (p=0.00). The rate of increase was greatest for patients aged 0 years, with patients aged 0- years demonstrating a slowly falling trend (0- years: β-0.0[ ],r=-0.; -years: β.[.-.],r=0.; 0-years: β.[.-.],r=0.; years: β.[.-.], r=0.; p<0.0 for all groups) (Fig ). Mean hospital stay. The mean hospital stay for those undergoing surgery decreased from. to. days over the study period, representing a % decrease or a fall of 0.days per study year (β- 0.[ ], r=-0., p<0.00). - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

9 Page of DISCUSSION This study identified significant increases in hospital admissions and procedures for degenerative lumbar spine disease in England, between and 0. The findings are, in general, concordant with studies from other countries.[-] The results reveal a widening gender gap, with women accounting for an increasingly greater proportion of hospital admissions. Interestingly, this has not translated to a similar trend in surgical procedures, where any gender gap in the early years is decreasing, in direct contrast to studies from other countries.[] This suggests that although more women are admitted for LBP, they appear to be managed nonsurgically. It is also possible that the gender gap may be related to gender-specific coding inconsistencies: for example, gynaecological flank pain incorrectly coded as lumbago or low back pain. Considering that this data mirrors trends identified in other countries, this is less likely. Further investigation into trends in specific surgical procedures may identify procedure-specific gender gaps not revealed when analysing aggregate surgical procedures. As with other surgical trends in England, in the context of an ageing population, there has been a shift in the burden of this disease to the oldest population groups (0- and ), resulting in an increase in the mean patient age for both hospital admissions and surgical interventions.[0,] Unexpectedly, over the same period, the average hospital stay has halved. Although the data does not allow us to address the underlying reasons for this, it may be attributable to improved peri-operative care (such as high risk anaesthetic clinics optimising patients prior to surgery), and improved post-operative therapy and social care, allowing for earlier patient mobilisation and discharge; or possibly, the result of the recent paradigm shift towards moving care into the community with better community services for chronic conditions. Our observation of an ageing patient group and falling mean hospital stay is well established in the international literature.[,,] There is, however, a well described increase in the burden of comorbidities associated with increased rates of postoperative complications and mortality in older patients.[,,] Further analysis of trends in age-specific mortality and morbidity for lumbar spine surgery in England may better reflect the true burden of this disease on hospital resources, as the significantly shorter stay by younger patients may have skewed the data. An advancing mean patient age has important implications for provision of critical care resources, and demand for medical specialties involved in managing the increased co-morbidity burden. The data identifies an under-appreciated trend in increasing hospital admissions for patients aged 0- years. Although the data cannot identify the underlying reasons, it may be attributable to the rising obesity levels in children.[] LBP is less well recognised in this age group, and consequently, health resources are relatively suboptimal.[] The data suggests growing demand and indicate the need for provision of paediatric services to manage the underlying causes in an effort to attenuate current trends. This study estimates that for every 00 patients being admitted with LBP, approximately undergo surgical intervention (β0.[0.-0.0], r=0., p<0.00). Regression models looking at hospital admissions and surgical procedures separately (Figure & ), illustrate that admissions are increasing at. times the rate of surgical interventions (β values of. versus. respectively). This highlights a disproportionate growth in demand for those involved in the non-surgical management of LBP, such as therapists and pain specialists, and indicates that more funding might be needed in the future for these services. It is possible that a proportion of this difference may be - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

10 Page of due to a lack of surgical capacity to deal with the increasing workload. Further analysis of waiting lists and mean waiting times may elucidate the factors accounting for this observation. Limitations inherent to using aggregate administrative data include coding errors relating to inaccurate representation of admissions and procedures (for example, lumbar fixation for trauma being incorrectly counted in the codes selected for this study), inter-hospital variability, data duplication, and discrepancy between finished consultant episodes and admissions. Considering the size of the dataset and duration of this study, any systematic error is likely to have evened out, especially when investigating trends rather than absolute values. Furthermore, systematic reviews have demonstrated good correlation between reported and actual validated data, reporting coding accuracies between -%, which is sufficient for use in this study.[,] Finally, the trends identified in this study not only reflect those found in other countries, but also mirror patterns seen in other surgical pathologies in England that have been subject to similar changing demographics, surgical innovation, and changes in health guidelines.[-, -] Although this data does not directly address the underlying reasons for the observed trends, over the last years, there have been numerous factors that may have influenced hospital trends for degenerative lumbar spine disease in England. These include demographic changes such as an ageing population, rise in obesity, sedentary lifestyles, public health factors such as changes in health guidelines, and surgical factors such as advancements in diagnostic imaging and proliferation of spinal instrumentation and implant systems.[,0] - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

11 Page 0 of CONCLUSION LBP, from degenerative lumbar spine disease, represents a significant and increasing workload for hospitals in England. The strong trends and associations identified in this study demonstrate an increasing demand for specialists involved in the surgical and non-surgical management of this condition. It highlights the need for the provision of services capable of dealing with the increased co-morbidity burden associated with an ageing patient group. An under-appreciated trend in increasing admissions for patients aged 0-years is identified, prompting the need for research into underlying causes, and the provision of appropriate paediatric services to attenuate this adverse finding : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

12 Page of FIGURE LEGENDS Figure Hospital admissions for low back pain in England, -0. Solid line-admissions per 00,000 population, dashed line- linear regression model. Figure Male and female hospital admissions for low back pain, -0. Solid lines - admissions per 00,000 population, dashed lines- linear regression model. Figure Hospital admissions for low back pain in England by age groups, -0. Figure Age specific annual rate of increase in hospital admissions and procedures, -0. Values correspond to each age group's β coefficient with their respective % confidence intervals represented as error bars. Figure The number of surgical procedures performed for degenerative lumbar spine disease, solid line- number of procedures per 00,000 population. Dashed line- linear regression model Figure Number of surgical procedures for degenerative lumbar spine disease by age groups, : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

13 Page of FOOTNOTES Contributors VS conceived and designed the study, analysed and interpreted the data, drafted the article, and approved the final version of the manuscript. HP provided statistical analysis, and critically reviewed and revised the original draft. BAO critically reviewed and revised the manuscript. MCP is the guarantor. Funding This research received no specific grant from any funding agency in the public, commercial or not-forprofit sectors. Competing interests None. Ethical approval This study is exempt from UK National Ethics Committee approval as it analyses freely available anonymised aggregate data used for administrative purposes. Data sharing statement No additional data are available. - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

14 Page of REFERENCES [] Hoy D, March L, Brooks P, et al. The global burden of low back pain: estimates from the Global Burden of Disease 00 study. Ann Rheum Dis 0; : -. [] Vos T, Flaxman AD, Naghavi M, et al. Years lived with disability (YLDs) for 0 sequelae of diseases and injuries 0-00: a systematic analysis for the Global Burden of Disease Study 00. Lancet 0; 0: -. [] Maniadakis N, Gray A. The economic burden of back pain in the UK. Pain 000; : -0. [] Deyo RA, Mirza SK. Trends and variations in the use of spine surgery. Clin Orthop Relat Res 00; : -. [] Pumberger M, Chiu YL, Ma Y, et al. National in-hospital morbidity and mortality trends after lumbar fusion surgery between and 00. J Bone Joint Surg Br 0; : -. [] Rajaee SS, Bae HW, Kanim LE, et al. Spinal fusion in the United States: analysis of trends from to 00. Spine (Phila Pa ) 0; : -. [] Kim P, Kurokawa R, Itoki K. Technical advancements and utilization of spine surgery-- international disparities in trend-dynamics between Japan, Korea, and the USA. Neurol Med Chir (Tokyo) 00; 0: -. [] Weinstein JN, Lurie JD, Olson PR, et al. United States' trends and regional variations in lumbar spine surgery: -00. Spine (Phila Pa ) 00; : 0-. [] Yoshihara H, Yoneoka D. National trends in the surgical treatment for lumbar degenerative disc disease: United States, 000 to 00. Spine J 0; : -. [0] Evans LM, Owens D, Scott-Coombes DM, at al. A decade of change in the uptake of parathyroidectomy in England and Wales. Ann R Coll Surg Engl 0; : -. [] von Allmen RS, Anjum A, Powell JT. Incidence of descending aortic pathology and evaluation of the impact of thoracic endovascular aortic repair: a population-based study in England and Wales from to 00. Eur J Vasc Endovasc Surg 0; : -. [] von Allmen RS, Anjum A, Powell JT, et al. Hospital trends of admissions and procedures for acute leg ischaemia in England, Ann R Coll Surg Engl 0; : -. [] Peul WC, Bredenoord AL, Jacobs WC. Avoid surgery as first line treatment for non-specific low back pain. BMJ 0; : g. [] Ma Y, Passias P, Gaber-Baylis LK, et al. Comparative in-hospital morbidity and mortality after revision versus primary thoracic and lumbar spine fusion. Spine J 00; 0: -. [] Shen Y, Silverstein JC, Roth S. In-hospital complications and mortality after elective spinal fusion surgery in the united states: a study of the nationwide inpatient sample from 00 to 00. J Neurosurg Anesthesiol 00; : -0. [] Stamatakis E, Zaninotto P, Falaschetti E, at al. Time trends in childhood and adolescent obesity in England from to 00 and projections of prevalence to 0. J Epidemiol Community Health 00; : -. [] Michaleff ZA, Kamper SJ, Maher CG, et al. Low back pain in children and adolescents: a systematic review and meta-analysis evaluating the effectiveness of conservative interventions. Eur Spine J 0; : 0-0. [] Burns EM, Rigby E, Mamidanna R, et al. Systematic review of discharge coding accuracy. J Public Health (Oxf) 0; : -. [] Campbell SE, Campbell MK, Grimshaw JM, et al. A systematic review of discharge coding accuracy. J Public Health Med 00; : 0-. [0] Sperrin M, Marshall AD, Higgins V, et al. Slowing down of adult body mass index trend increases in England: a latent class analysis of cross-sectional surveys (-00). Int J Obes (Lond) 0; : : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

15 Page of Figure Hospital admissions for low back pain in England, -0. Solid line-admissions per 00,000 population, dashed line- linear regression model. xmm ( x DPI) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

16 Page of Figure Male and female hospital admissions for low back pain, -0. Solid lines - admissions per 00,000 population, dashed lines- linear regression model. xmm ( x DPI) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

17 Page of Figure Hospital admissions for low back pain in England by age groups, -0. xmm ( x DPI) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

18 Page of Figure Age specific annual rate of increase in hospital admissions and procedures, -0. Values correspond to each age group's β coefficient with their respective % confidence intervals represented as error bars. xmm ( x DPI) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

19 Page of Figure The number of surgical procedures performed for degenerative lumbar spine disease, solid line- number of procedures per 00,000 population. Dashed line- linear regression model xmm ( x DPI) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

20 Page of Figure Number of surgical procedures for degenerative lumbar spine disease by age groups, xmm ( x DPI) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

21 Page 0 of APPENDIX Office of Population Censuses and Surveys Classification of Interventions and Procedures version (OPCS-) codes representing surgical procedures relevant to degenerative lumbar spine disease: V. Primary extended decompression of lumbar spinal cord and intertransverse fusion of joint of lumbar spine V. Primary extended decompression of lumbar spinal cord NEC V. Primary posterior decompression of lumbar spinal cord and intertransverse fusion of joint of lumbar spine V. Primary posterior laminectomy decompression of lumbar spinal cord V. Primary posterior decompression of lumbar spinal cord NEC V. Other specified primary decompression operations on lumbar spine V. Unspecified primary decompression operations on lumbar spine V. Primary laminectomy excision of lumbar intervertebral disc V. Primary fenestration excision of lumbar intervertebral disc V. Primary anterior excision of lumbar intervertebral disc and interbody fusion of joint of lumbar spine V. Primary anterior excision of lumbar intervertebral disc and posterior graft fusion of joint of lumbar spine V. Primary anterior excision of lumbar intervertebral disc and posterior instrumentation of lumbar spine V. Other specified primary excision of lumbar intervertebral disc V. Unspecified primary excision of lumbar intervertebral disc V. Revisional laminectomy excision of lumbar intervertebral disc V. Primary posterior interlaminar fusion of joint of lumbar spine V. Primary posterior fusion of joint of lumbar spine NEC V. Primary intertransverse fusion of joint of lumbar spine NEC V. Primary posterior interbody fusion of joint of lumbar spine V. Primary transforaminal interbody fusion of joint of lumbar spine V0. Posterior instrumented fusion of lumbar spine NEC - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

22 Page of Section/Topic Item # STROBE 00 (v) Statement Checklist of items that should be included in reports of cohort studies Recommendation Reported on page # Title and abstract (a) Indicate the study s design with a commonly used term in the title or the abstract Introduction (b) Provide in the abstract an informative and balanced summary of what was done and what was found Background/rationale Explain the scientific background and rationale for the investigation being reported Objectives State specific objectives, including any prespecified hypotheses Methods Study design Present key elements of study design early in the paper Setting Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection Participants (a) Give the eligibility criteria, and the sources and methods of selection of participants. Describe methods of follow-up (b) For matched studies, give matching criteria and number of exposed and unexposed Variables Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if Data sources/ measurement applicable * For each variable of interest, give sources of data and details of methods of assessment (measurement). Describe comparability of assessment methods if there is more than one group Bias Describe any efforts to address potential sources of bias Study size 0 Explain how the study size was arrived at Quantitative variables Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and why Statistical methods (a) Describe all statistical methods, including those used to control for confounding Results on March 0 by guest. Protected by copyright. (b) Describe any methods used to examine subgroups and interactions (c) Explain how missing data were addressed (d) If applicable, explain how loss to follow-up was addressed (e) Describe any sensitivity analyses - : first published as 0./bmjopen on December 0. Downloaded from n/a n/a n/a n/a

23 Page of Participants * (a) Report numbers of individuals at each stage of study eg numbers potentially eligible, examined for eligibility, confirmed n/a eligible, included in the study, completing follow-up, and analysed (b) Give reasons for non-participation at each stage n/a Descriptive data (c) Consider use of a flow diagram * (a) Give characteristics of study participants (eg demographic, clinical, social) and information on exposures and potential confounders (b) Indicate number of participants with missing data for each variable of interest (c) Summarise follow-up time (eg, average and total amount) Outcome data * Report numbers of outcome events or summary measures over time - Main results (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (eg, % confidence - interval). Make clear which confounders were adjusted for and why they were included (b) Report category boundaries when continuous variables were categorized (c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period Other analyses Report other analyses done eg analyses of subgroups and interactions, and sensitivity analyses n/a Discussion Key results Summarise key results with reference to study objectives Limitations Interpretation 0 Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence Generalisability Discuss the generalisability (external validity) of the study results - Other information Funding Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on which the present article is based *Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies. Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at Annals of Internal Medicine at and Epidemiology at Information on the STROBE Initiative is available at : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

24 Trends in hospital admissions and surgical procedures for degenerative lumbar spine disease in England: a year time-series Journal: Manuscript ID bmjopen r Article Type: Research Date Submitted by the Author: 0-Oct-0 Complete List of Authors: Sivasubramaniam, Vinothan; St George's Hospital, Department of Neurosurgery Patel, Hitesh; Royal Brompton & Harefield NHS Foundation Trust, Department of Cardiology Ozdemir, Baris; St George's Hospital, London United Kingdon, Department of Vascular surgery Papadopoulos, Marios; St George's Hospital, Department of Neurosurgery <b>primary Subject Heading</b>: Public health Secondary Subject Heading: Health policy, Epidemiology, Health economics, Surgery Keywords: Neurosurgery < SURGERY, NEUROSURGERY, Spine < ORTHOPAEDIC & TRAUMA SURGERY, Back pain < ORTHOPAEDIC & TRAUMA SURGERY : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

25 Page of Research Paper Trends in hospital admissions and surgical procedures for degenerative lumbar spine disease in England: a year time-series Authors Vinothan Sivasubramaniam, BSc (Hons) MRCS Hitesh C Patel, BSc (Hons) MRCP Baris A Ozdemir, BSc (Hons) MB BS MRCS Marios C Papadopoulos, MA MD FRCS(SN) Affiliations Department of Neurosurgery, Atkinson Morley Wing, St George's Hospital, Blackshaw Road, London SW 0QT, United Kingdom. Department of Cardiology The Royal Brompton & Harefield NHS Foundation Trust, Sydney Street, London SW NP, United Kingdom. Department of Vascular Surgery St George's Hospital, Blackshaw Road, London SW 0QT London Deanery Surgical Rotation, United Kingdom. Corresponding author's details: Vinothan Sivasubramaniam Department of Neurosurgery, St George's Hospital, Blackshaw road, Tooting, London SW 0QT Tel No vino.siva@nhs.net Keywords: low back pain, degenerative lumbar spine disease, hospital trends Word count: words (excluding title page, abstract, references and figures) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

26 Page of ABSTRACT Objectives Low back pain (LBP), from degenerative lumbar spine disease, represents a significant burden on healthcare resources. Studies worldwide report trends attributable to their country's specific demographics and healthcare system. Considering England's specific medico-socioeconomic conditions, we investigate recent trends in hospital admissions and procedures for LBP, and discuss the implications for the allocation of healthcare resources. Design Retrospective cohort study using Hospital Episode Statistics (HES) data relating to degenerative lumbar spine disease in England, between and 0. Regression models were used to analyse trends. Outcome measures Trends in the number of admissions and procedures for LBP, mean patient age, gender and length of stay. Results Hospital admissions and procedures have increased significantly over the study period, from.0 to. and from. to. per 00,000, respectively(p<0.00). The increase was most marked in the oldest age groups with a. and. fold increase in admissions for patients aged 0- and years respectively, and a. fold increase in procedures for those aged 0 years. Trends in hospital admissions were characterised by a widening gender gap, increasing mean patient age, and decreasing mean hospital stay (P<0.00).Trends in procedures were characterised by a narrowing gender gap, increasing mean patient age (p=0.0) and decreasing mean hospital stay (p<0.00). Linear regression models estimate that each hospital admission translates to 0. procedures, per 00,000 (%CI , r 0.,p<0.00). Hospital admissions are increasing at. times the rate of surgical procedures (regression gradient:. versus. per 00,000/year). Conclusions LBP represents a significant and increasing workload for hospitals in England. These trends demonstrate an increasing demand for specialists involved in the surgical and non-surgical management of this disease, and highlight the need for services capable of dealing with the increased co-morbidity burden associated with an ageing patient group. - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

27 Page of STRENGTHS AND LIMITATIONS OF THIS STUDY The use of routinely collected national administrative data allowed for the analysis of trends in admissions and surgical procedures for LBP throughout England, for a prolonged time period. As Hospital Episode Statistics (HES) is collected independently of this study, it is not subject to study-related bias or affected by factors that may have influenced hospital trends in LBP. This study provides important England-specific population-level data about longitudinal trends, associations, and patterns of care for LBP. Limitations inherent to using aggregate administrative data include coding errors relating to inaccurate representation of admissions and procedures, data duplication and inter-hospital variability. - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

28 Page of INTRODUCTION Low back pain (LBP), from degenerative lumbar spine disease, is one of the most prevalent non-fatal conditions worldwide, and a significant cause of long-term disability.[,] In England, it is one of the leading causes of physician attendances, hospitalisation, and utilisation of social care services.[] It confers a significant economic burden in terms of funding of health resources, disability benefits, and effect on industry from sick leave.[] Several studies in other countries, using national and medical insurance databases, have identified interesting trends in hospitalisation for degenerative lumbar spine disease. These trends have been attributed to the country's specific healthcare system, demographics, medical technological advances, and profitability of treatment modalities.[-] There is sparse data on trends in hospitalisation for this disease in England. The aim of this study is to investigate the longitudinal trends in hospital admissions and surgical procedures for degenerative lumbar spine disease in England, between and 0. Considering England's specific medico-socioeconomic conditions, which includes the existence of a health service free at the point of delivery, we evaluate whether it follows trends seen in other countries, and discuss the implications for allocation of healthcare resources. - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

29 Page of METHODS Annual aggregate data for all hospital admissions and procedures in England, from to 0, were retrieved from Hospital Episode Statistics (HES), available from the Health and Social Care Information Centre (HSCIC). In this study, the term LBP refers to degenerative disease resulting in low back pain with or without radicular or neurogenic claudicant symptoms. This encompasses a variety of underlying processes including herniated disc disease, isthaemic/degenerative spondylolisthesis, spinal stenosis, and nonspecific LBP (back pain not attributable to spinal instability or associated with radicular symptoms). Surgical procedures refer to surgery for degenerative lumbar spine disease, and do not include surgery for non-degenerative pathology such as trauma or malignancy. The HES dataset groups primary diagnoses according to the World Health Organisation's 0th revision of the International Classification of Diseases (ICD-0).The codes relevant to our study were M., M.,M., and M., referring to admissions with the primary diagnosis of radiculopathy, sciatica, lumbago with sciatica, and low back pain respectively. Finished consultant episodes, representative of hospital admissions, were analysed with respect to gender and four different age groups (0-, -, 0-, and years). Primary procedures, defined as the most resource intensive procedure performed during the hospital episode, were identified using to the th version of the Office of Population Censuses and Surveys Classification of Interventions and Procedures (OPCS-). Codes representing surgical procedures relevant to degenerative lumbar spine disease (Appendix) were aggregated and analysed to produce admission trends stratified by age and gender. The data for was excluded from our analysis of surgical interventions as only the less detailed -character procedure codes were available, deemed insufficient for this study. Mid-year estimates of English population denominators grouped by age and gender were obtained from the Office of National Statistics (ONS). Annual hospital admissions and surgical interventions are reported per 00,000 of the population, and further stratified by broad age groups and gender. Time trends were investigated using linear regression models with the gradient expressed as β values with % confidence intervals (CI), per 00,000 of the population. Correlation is represented by Pearson's correlation coefficient (r). Continuous variables were compared using the independent samples T-test. A p value of <0.0 was chosen to imply statistical significance. Statistical Package for the Social Sciences (SPSS) was used to perform data analysis. This study is exempt from UK National Ethics Committee approval as it analyses freely available anonymised aggregate data used for administrative purposes. - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

30 Page of RESULTS Trends in hospital admissions for LBP: Overall hospital admissions. Over the year period from to 0, there was a significant rise in the overall hospital admissions for LBP, increasing from.0 in to. in 0, per 00,000 population (Fig ). This represents a. fold increase or an annual increase of. per 00,000 (β.[ci:.-.0], r=0., p<0.00). Gender. Hospital admissions for both men and women increased over the year period (β:.[.-.] and 0.[.-.] respectively, r=0. for both, p<0.00), with admissions being significantly greater in women than in men (p <0.00) (Fig ).Hospital admission rates for women increased at approximately twice the rate of men's, resulting in a widening gender gap over the year period (p<0.00). Mean age of patients at admission. Age at admission increased from. years in to. years in 0, representing an estimated 0. year increase in the average patient age per annum, over the years (β0.[ci: 0.-0.], r=0., p<0.00). Age categories. The data demonstrates a significant increase in hospital admissions for each of the four age groups over the study period (p<0.00) (Fig ). The greatest increase is seen in those aged 0- and years, evident by a. and. fold increases respectively (from. to., and from 0. to.0,per 00,000, respectively). Hospital admissions for those aged 0- years increased from. to. per 00,000, representing a. fold increase in a paediatric population, and from 0. to 00. per 00,000 for patients aged - years, over the years. The older the age group the greater was the observed annual rate of increase in hospital admissions (p<0.00) (Fig ). Mean hospital stay. The average length of hospital stay decreased from. days in to. days in 0, representing a % decrease or a fall of 0. years per study year (β0.[ ], r=0., p<0.00). - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

31 Page of Trends in surgical procedures for degenerative lumbar spine disease: Overall surgical procedures. Over the study period, there was a significant increase in the overall number of surgical procedures performed for degenerative lumbar spine disease(fig ), Recorded procedures almost doubled from. to. per 00,000, with an estimated. per 00,000 increase each year (β.[ci.-.], r=0.,p<0.00). Association between hospital admissions and the number of surgical procedures. There was a strong positive linear correlation between hospital admissions and procedures, with every incremental admission translating to an estimated 0./00,000 increase in surgical interventions (β0.[ ],r=0., p<0.00). Gender. There was a significant increase in surgical procedures for both genders over the study period (p<0.00). There was a statistically significant difference between genders for the early years only (000-0, p=0.0), but not for the latter years (0-, p=0.), suggesting a narrowing of any early gender gap. Mean patient age. This increased from. in 000 to. years in 0 (p=0.0), with an estimated increase in mean patient age of 0. years per annum, over the study period (β0.0[0.- 0.], r=0.,p<0.00). Age categories. With the exception of patients aged 0-years, there was a significant increase in the uptake of surgery for all age groups (-, 0- and years, p<0.00) (Fig ). The most significant increases were seen in the oldest age groups, with a. fold increase in both those aged 0- and years over the study period (from. to. and from. to 0, per 00,000, respectively). In contrast, those aged - years demonstrated a. fold increase (0. to 0. per 00,000). There was a fall in the number of surgical procedures recorded for those aged 0- years, from 0. in 000 to 0. in 0 per 00,000 (p=0.00). The rate of increase was greatest for patients aged 0 years, with patients aged 0- years demonstrating a slowly falling trend (0- years: β-0.0[ ],r=-0.; -years: β.[.-.],r=0.; 0-years: β.[.-.],r=0.; years: β.[.-.], r=0.; p<0.0 for all groups) (Fig ). Mean hospital stay. The mean hospital stay for those undergoing surgery decreased from. to. days over the study period, representing a % decrease or a fall of 0.days per study year (β- 0.[ ], r=-0., p<0.00). - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

32 Page of DISCUSSION This study identified significant increases in hospital admissions and procedures for degenerative lumbar spine disease in England, between and 0. The findings are, in general, concordant with studies from other countries.[-] The results reveal a widening gender gap, with women accounting for an increasingly greater proportion of hospital admissions. Interestingly, this has not translated to a similar trend in surgical procedures, where any gender gap in the early years is decreasing, in direct contrast to studies from other countries.[] This suggests that although more women are admitted for LBP, they appear to be managed nonsurgically. It is also possible that the gender gap may be related to gender-specific coding inconsistencies: for example, gynaecological flank pain incorrectly coded as lumbago or low back pain. Considering that this data mirrors trends identified in other countries, this is less likely. Further investigation into trends in specific surgical procedures may identify procedure-specific gender gaps not revealed when analysing aggregate surgical procedures. As with other surgical trends in England, in the context of an ageing population, there has been a shift in the burden of this disease to the oldest population groups (0- and ), resulting in an increase in the mean patient age for both hospital admissions and surgical interventions.[0-] Unexpectedly, over the same period, the average hospital stay has halved. Although the data does not allow us to address the underlying reasons for this, it may be attributable to improved peri-operative care (such as high risk anaesthetic clinics optimising patients prior to surgery), and improved post-operative therapy and social care, allowing for earlier patient mobilisation and discharge; or possibly, the result of the recent paradigm shift towards moving care into the community with better community services for chronic conditions. Our observation of an ageing patient group and falling mean hospital stay is well established in the international literature.[,,] There is, however, a well described increase in the burden of comorbidities associated with increased rates of postoperative complications and mortality in older patients.[,,] Further analysis of trends in age-specific mortality and morbidity for lumbar spine surgery in England may better reflect the true burden of this disease on hospital resources, as the significantly shorter stay by younger patients may have skewed the data. An advancing mean patient age has important implications for provision of critical care resources, and demand for medical specialties involved in managing the increased co-morbidity burden. The data identifies an under-appreciated trend in increasing hospital admissions for patients aged 0- years. Although the data cannot identify the underlying reasons, it may be attributable to the rising obesity levels in children.[] LBP is less well recognised in this age group, and consequently, health resources are relatively suboptimal.[] The data suggests growing demand and indicate the need for provision of paediatric services to manage the underlying causes in an effort to attenuate current trends. This study estimates that for every 00 patients being admitted with LBP, approximately undergo surgical intervention (β0.[0.-0.0], r=0., p<0.00). Regression models looking at hospital admissions and surgical procedures separately (Figure & ), illustrate that admissions are increasing at. times the rate of surgical interventions (β values of. versus. respectively). This highlights a disproportionate growth in demand for those involved in the non-surgical management of LBP, such as therapists and pain specialists, and indicates that more funding might be needed in the future for these services. It is possible that a proportion of this difference may be - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

33 Page of due to a lack of surgical capacity to deal with the increasing workload. Further analysis of waiting lists and mean waiting times may elucidate the factors accounting for this observation. Limitations inherent to using aggregate administrative data include coding errors relating to inaccurate representation of admissions and procedures (for example, lumbar fixation for trauma being incorrectly counted in the codes selected for this study), inter-hospital variability, data duplication, and discrepancy between finished consultant episodes and admissions. Considering the size of the dataset and duration of this study, any systematic error is likely to have evened out, especially when investigating trends rather than absolute values. Furthermore, systematic reviews have demonstrated good correlation between reported and actual validated data, reporting coding accuracies between -%, which is sufficient for use in this study.[,] Finally, the trends identified in this study not only reflect those found in other countries, but also mirror patterns seen in other surgical pathologies in England that have been subject to similar changing demographics, surgical innovation, and changes in health guidelines.[-, -] Although this data does not directly address the underlying reasons for the observed trends, over the last years, there have been numerous factors that may have influenced hospital trends for degenerative lumbar spine disease in England. These include demographic changes such as an ageing population, rise in obesity, sedentary lifestyles, public health factors such as changes in health guidelines, and surgical factors such as advancements in diagnostic imaging and proliferation of spinal instrumentation and implant systems.[,0] - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

34 Page 0 of CONCLUSION LBP, from degenerative lumbar spine disease, represents a significant and increasing workload for hospitals in England. The strong trends and associations identified in this study demonstrate an increasing demand for specialists involved in the surgical and non-surgical management of this condition. It highlights the need for the provision of services capable of dealing with the increased co-morbidity burden associated with an ageing patient group. An under-appreciated trend in increasing admissions for patients aged 0-years is identified, prompting the need for research into underlying causes, and the provision of appropriate paediatric services to attenuate this adverse finding : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

35 Page of FIGURE LEGENDS Figure Hospital admissions for low back pain in England, -0. Solid line-admissions per 00,000 population, dashed line- linear regression model. Figure Male and female hospital admissions for low back pain, -0. Solid lines - admissions per 00,000 population, dashed lines- linear regression model. Figure Hospital admissions for low back pain in England by age groups, -0. Figure Age specific annual rate of increase in hospital admissions and procedures, -0. Values correspond to each age group's β coefficient with their respective % confidence intervals represented as error bars. Figure The number of surgical procedures performed for degenerative lumbar spine disease, solid line- number of procedures per 00,000 population. Dashed line- linear regression model Figure Number of surgical procedures for degenerative lumbar spine disease by age groups, : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

36 Page of FOOTNOTES Contributors VS conceived and designed the study, analysed and interpreted the data, drafted the article, made appropriate revisions, and approved the final version of the manuscript. HP provided statistical analysis, and critically reviewed and revised the original draft, and approved the final version. BAO assisted in the interpretation of the data, critically reviewed and revised the manuscript, and approved the final version. MCP is the guarantor and assisted in the conception of the study, critically reviewed the manuscript, and approved the final version. All authors agree to be accountable for the study. Funding This research received no specific grant from any funding agency in the public, commercial or not-forprofit sectors. Competing interests No, there are no competing interests. Ethical approval This study is exempt from UK National Ethics Committee approval as it analyses freely available anonymised aggregate data used for administrative purposes. Data sharing statement No additional data are available. - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

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38 Page of Figure Hospital admissions for low back pain in England, -0. Solid line-admissions per 00,000 population, dashed line- linear regression model. xmm (00 x 00 DPI) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

39 Page of Figure Male and female hospital admissions for low back pain, -0. Solid lines - admissions per 00,000 population, dashed lines- linear regression model. xmm (00 x 00 DPI) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

40 Page of Figure Hospital admissions for low back pain in England by age groups, -0. 0xmm (00 x 00 DPI) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

41 Page of Figure Age specific annual rate of increase in hospital admissions and procedures, -0. Values correspond to each age group's β coefficient with their respective % confidence intervals represented as error bars. 0xmm (00 x 00 DPI) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

42 Page of Figure The number of surgical procedures performed for degenerative lumbar spine disease, solid line- number of procedures per 00,000 population. Dashed line- linear regression model xmm (00 x 00 DPI) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

43 Page of Figure Number of surgical procedures for degenerative lumbar spine disease by age groups, x0mm (00 x 00 DPI) - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

44 Page 0 of APPENDIX Office of Population Censuses and Surveys Classification of Interventions and Procedures version (OPCS-) codes representing surgical procedures relevant to degenerative lumbar spine disease: V. Primary extended decompression of lumbar spinal cord and intertransverse fusion of joint of lumbar spine V. Primary extended decompression of lumbar spinal cord NEC V. Primary posterior decompression of lumbar spinal cord and intertransverse fusion of joint of lumbar spine V. Primary posterior laminectomy decompression of lumbar spinal cord V. Primary posterior decompression of lumbar spinal cord NEC V. Other specified primary decompression operations on lumbar spine V. Unspecified primary decompression operations on lumbar spine V. Primary laminectomy excision of lumbar intervertebral disc V. Primary fenestration excision of lumbar intervertebral disc V. Primary anterior excision of lumbar intervertebral disc and interbody fusion of joint of lumbar spine V. Primary anterior excision of lumbar intervertebral disc and posterior graft fusion of joint of lumbar spine V. Primary anterior excision of lumbar intervertebral disc and posterior instrumentation of lumbar spine V. Other specified primary excision of lumbar intervertebral disc V. Unspecified primary excision of lumbar intervertebral disc V. Revisional laminectomy excision of lumbar intervertebral disc V. Primary posterior interlaminar fusion of joint of lumbar spine V. Primary posterior fusion of joint of lumbar spine NEC V. Primary intertransverse fusion of joint of lumbar spine NEC V. Primary posterior interbody fusion of joint of lumbar spine V. Primary transforaminal interbody fusion of joint of lumbar spine V0. Posterior instrumented fusion of lumbar spine NEC - : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.

45 Page of Section/Topic Item # STROBE 00 (v) Statement Checklist of items that should be included in reports of cohort studies Recommendation Reported on page # Title and abstract (a) Indicate the study s design with a commonly used term in the title or the abstract Introduction (b) Provide in the abstract an informative and balanced summary of what was done and what was found Background/rationale Explain the scientific background and rationale for the investigation being reported Objectives State specific objectives, including any prespecified hypotheses Methods Study design Present key elements of study design early in the paper Setting Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection Participants (a) Give the eligibility criteria, and the sources and methods of selection of participants. Describe methods of follow-up (b) For matched studies, give matching criteria and number of exposed and unexposed Variables Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if Data sources/ measurement applicable * For each variable of interest, give sources of data and details of methods of assessment (measurement). Describe comparability of assessment methods if there is more than one group Bias Describe any efforts to address potential sources of bias Study size 0 Explain how the study size was arrived at Quantitative variables Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and why Statistical methods (a) Describe all statistical methods, including those used to control for confounding Results on March 0 by guest. Protected by copyright. (b) Describe any methods used to examine subgroups and interactions (c) Explain how missing data were addressed (d) If applicable, explain how loss to follow-up was addressed (e) Describe any sensitivity analyses - : first published as 0./bmjopen on December 0. Downloaded from n/a n/a n/a n/a

46 Page of Participants * (a) Report numbers of individuals at each stage of study eg numbers potentially eligible, examined for eligibility, confirmed n/a eligible, included in the study, completing follow-up, and analysed (b) Give reasons for non-participation at each stage n/a Descriptive data (c) Consider use of a flow diagram * (a) Give characteristics of study participants (eg demographic, clinical, social) and information on exposures and potential confounders (b) Indicate number of participants with missing data for each variable of interest (c) Summarise follow-up time (eg, average and total amount) Outcome data * Report numbers of outcome events or summary measures over time - Main results (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (eg, % confidence - interval). Make clear which confounders were adjusted for and why they were included (b) Report category boundaries when continuous variables were categorized (c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period Other analyses Report other analyses done eg analyses of subgroups and interactions, and sensitivity analyses n/a Discussion Key results Summarise key results with reference to study objectives Limitations Interpretation 0 Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence Generalisability Discuss the generalisability (external validity) of the study results - Other information Funding Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on which the present article is based *Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies. Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at Annals of Internal Medicine at and Epidemiology at Information on the STROBE Initiative is available at : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright. - n/a

47 Trends in hospital admissions and surgical procedures for degenerative lumbar spine disease in England: a year time-series Journal: Manuscript ID bmjopen r Article Type: Research Date Submitted by the Author: 0-Nov-0 Complete List of Authors: Sivasubramaniam, Vinothan; St George's Hospital, Department of Neurosurgery Patel, Hitesh; Royal Brompton & Harefield NHS Foundation Trust, Department of Cardiology Ozdemir, Baris; St George's Hospital, London United Kingdon, Department of Vascular surgery Papadopoulos, Marios; St George's Hospital, Department of Neurosurgery <b>primary Subject Heading</b>: Public health Secondary Subject Heading: Health policy, Epidemiology, Health economics, Surgery Keywords: Neurosurgery < SURGERY, NEUROSURGERY, Spine < ORTHOPAEDIC & TRAUMA SURGERY, Back pain < ORTHOPAEDIC & TRAUMA SURGERY : first published as 0./bmjopen on December 0. Downloaded from on March 0 by guest. Protected by copyright.