Outcome of Surgery for Sciatica - a Comparison of Data From Three National Quality Registries
Condition: Intervertebral Disc Displacement; Sciatica
MeSH terms: Intervertebral Disc Displacement; Sciatica
Study type: Observational [Patient Registry]

Summary: 
      Purpose: The incidence of surgery for lumbar disc hernia varies. According to the national
      spine registries in Sweden, Norway and Denmark, there is a 30-60% difference in surgical
      incidence between these countries. The cause for this difference is not known. It may reflect
      a difference in incidence of lumbar disc hernia, but with a similar socio-economic and
      ethnical background in these countries, it is more likely that the differences are due to
      varying surgical indications. Comparing indications for surgery, patient reported outcome and
      factors predictive for outcome after surgery for lumbar disc hernia in these countries could
      provide information about optimal indications for surgery.

      Hypotheses: (i) there are no differences in patient-reported outcome after surgery between
      these countries, (ii) there are no differences in indications for surgery between these
      countries and (iii), factors that predict outcome are similar in these countries.

      Method of research: By using data from three Nordic national spine registers, we will compare
      baseline data, indications for surgery and patient reported outcome one year after surgery
      for lumbar disc herniation. Register based studies have advantages such as large sample
      sizes, reflecting real life, but they also have limitations such as lower follow-up rates
      than clinical trials. A non-response analysis will be performed to take this into account.
    

Detailed description: 
      This is an observational register based study, with prospective data registration and a
      retrospective study design. Included are individuals treated surgically for a lumbar disc
      herniation between the ages of 18 through 65 years, without a history of previous lumbar
      spine surgery. Surgery has been performed in Denmark, Norway or Sweden during 2011, 2012 or
      2013. Data will be presented according to the STROBE criteria.

      The registers

      All registries have the aim of studying outcome after spine surgery. All departments and
      patients participate voluntarily. At the time of admission, the patient reports data
      consisting of information on social factors, comorbidity and previous surgery. After surgery,
      the surgeon records diagnosis and type of surgery performed.

      The Swespine Register has included individuals treated with surgery for lumbar disc
      herniation since 1993. During the last decade, the number of departments participating in the
      registry has varied between 35 and 41 of the 42 to 45 departments providing spinal surgery
      services in Sweden. Coverage is approximately 90%. The completeness (number of patients
      reported to Swespine at the time of surgery) is approximately 80%.

      The Norwegian Spine register, NORspine, is based on experiences from the Swespine register
      and previous validation studies from a local clinical registry, and was founded in 2007. In
      total 36 of 40 centers performing lumbar spine surgery in Norway report to NORspine. Coverage
      is approximately 90%. The completeness is approximately 65%.

      The Danish spine register, DaneSpine, is based on Swespine and was acquired by the Danish
      Spine Society from the Swedish Society of Spinal Surgeons in 2009 and has successively been
      implemented. In total 17 of 19 centers performing lumbar spine surgery in Denmark report to
      DaneSpine. Coverage is approximately 90%. The completeness is approximately 60%.

      Quality assurance

      As for all studies, there is a risk that loss to follow-up may bias the results. Solberg et
      al. (2011) studied 633 patients, who were operated on for degenerative disorders of the
      lumbar spine in Norway, and found that a loss to follow-up of 22% would not bias conclusions
      about overall treatment effects. There were no indications of worse outcomes in the
      non-responders group. In a similar one-center study of the DaneSpine. Højmark et al. (2016)
      found that a loss to follow-up of 12% at did not seem to bias the conclusions that can be
      drawn from DaneSpine at that center. Preliminary data indicates that predictors of outcome
      after lumbar disc herniation surgery are comparable with data in a study with a very high
      follow-up rate and with the Swespine register.

      Data handling

      Anonymized individual level data from all three registers will be pooled in one database. The
      cohort will be divided by country for comparisons.

      Missing data and out of range data

      In case of missing data case exclusion analysis by analysis, will be used. Out of range data
      will be deleted.

      Analysis

      The data will be cleaned by excluding patients with missing or incorrect date of surgery,
      missing date for follow-up, previous lumbar spine surgery and surgery other than discectomy
      only.

      After data cleaning, we aim to perform blinded statistical analyses, in which the independent
      statistician performing the analyses is unaware of group belonging (i.e. country). The code
      will not be broken until the analyses and interpretations have been performed.

      Comparisons of indications for surgery

      Analysis of baseline data will include age at surgery, sex, anthropometrics, number of
      smokers, Oswestry Disability Index, numeric rating scale leg pain, numeric rating scale back
      pain, EQ-5D, number on sick leave, employment status, and duration of leg and back pain and
      presented as mean (SD), mean (95% confidence interval), or number (%).

      Variables will be analyzed by analysis of variance, Chi-square or logistic regression tests.
      Data will be presented as crude (unadjusted) data to elucidate any differences between the
      countries.

      Comparisons of outcome

      Comparisons of the change of the outcome variables from baseline to 1 year, as well as
      comparisons of the actual value at 1 year will be performed. Analysis of covariance (ANCOVA),
      Chi-square or logistic regression tests will be used and the crude (unadjusted) data will be
      presented.

      The baseline variables will be used as covariates in the ANCOVA and the adjusted data
      presented. Additionally, the results from the ANCOVA will be compared with results from
      propensity score matching or ANCOVA with the propensity score as a covariate.

      Non-response analysis

      A non-response analysis will be performed comparing all available baseline variables between
      those that responded to the 1 year follow-up with those that did not respond.

      Sample size

      A study of similar character has never been performed before. Due to the nature of the study,
      the sample size is not formulated in the guise of power, risk level, or clinical difference.
      The number of patients participating in the study is estimated to 7500. The sample is so
      large that differences in the Oswestry Disability Index of as low as 2 points may be detected
      (power 90%, significance level 5%), but in the interpretation the minimal important
      difference of 10-15 points in the Oswestry Disability Index often referred to has to be taken
      into account.
    

Intervention name(s): Lumbar disc hernia surgery
Intervention type(s): Procedure
Other intervention name(s): Surgery for sciatica due to lumbar disc herniation
Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        This is an observational register based study, with prospective data registration and with
        a retrospective study design. Individuals treated surgically for lumbar disc herniation in
        Denmark, Norway and Sweden during 2011, 2012 and 2013 are included.