Epigenetic and Molecular Biomarkers in Chronic Low Back Pain and Modic Changes

Overview

In the present study the investigators aim to examine the presence of bacteria in the disc and Modic Changes (MCs) (bone). A prospective study with 1-year follow-up of two patient populations undergoing elective spinal surgery (spinal fusion or disc herniation surgery) will be conducted. Patients previously operated on at index level will also be included, and evaluated as sub-groups. The following tissues are collected: dermis, sub-fascial tissue, nucleus pulposus, annulus fibrosus, and endplates. Endplate biopsies are only performed in patients undergoing fusion surgery. All tissue samples undergoing culturing should be processed within 4 hours of sampling. The time for sampling and culture processing are noted for each sample. Details are available in a published Method article. For each tissue sample, bacterial growth is recorded and identified at species level. Initially, the microbiologist grades the plates as "no growth", "possible contamination", and "significant growth". Possible contamination means that the bacteria may be derived from the environment and can be introduced at any step from the sample is taken to the analyses in the laboratory. The investigators will perform direct 16S rDNA Sanger sequencing on all frozen tissue samples. Other broad metagenomic methods will also be considered, e.g., nanopore or Illumina sequencing. Since C. acnes is considered the main pathogen in this setting, the investigators will also use a specific quantitative PCR on all samples. The investigators will also use whole genome sequencing on C. acnes isolates for phylogenetic analyses to compare isolates found in samples from the same patient. Based on cultivation alone, many samples will be clearly graded as "significant growth" or "no growth". Before unblinding, sensitivity analyses will be done after such "possible contamination" has been re-categorized as "significant growth" or "no growth" based on PCR and histological findings". Microbiologists,the pathologist and clinicians are blinded until end of study. Blood-samples are collected to characterize gene expression patterns and related markers.

Planned analyses Primary analyses: MC1 vs. control (significant growth from disc, yes/no) MC2 vs. control (significant growth from disc, yes/no) Exploratory subgroup analyses: MC1 and MC2 in previously operated vs. control (significant growth from disc, yes/no) Large MCs vs. control (significant growth from disc, yes/no). Large MCs are defined as MCs with volume ≥ 25 % of vertebral body volume or height \> 50 % of vertebral body height. MC1 and MC2 vs. control in fusion group (significant growth from vertebral body biopsy, yes/no). Vertebral body biopsies are not performed in the disc herniation group. Statistics and power: The main aim of this study is to investigate if the proportions of patients with significant bacterial growth from perioperative disc biopsies differ between cases (MC1 patients or MC2 patients) vs controls without MCs. The null hypothesis is that there is no difference between cases and controls. The alternative hypothesis is that there is a difference. The sample size calculation is based on previously published data and a pre-specified relevant difference in proportions of bacterial growth among cases vs. controls The investigators calculated the sample size using a two-sided Pearson's chi-squared test. For the primary analysis, with two primary endpoints, the investigators aim to achieve 80 % power to detect a difference in bacterial growth in 25 % of cases with MC1 or MC2 vs. 5% of controls. Due to multiple testing the investigators use Bonferroni correction (alfa 0.025). The investigators therefore plan to analyze at least 60 cases with MC1, 60 cases with MC2 and 60 controls. The MC2 sample is likely to become larger than n = 60, since the investigators recruit MC1 and MC2 patients consecutively and MC2 is more common than MC1. The investigators will consider performing statistical sensitivity analysis where samples with possible contamination and positive PCR ("possible significant growth") are recategorized as positive bacterial growth. The investigators will also consider sensitivity analyses with categorization of patients (positive/negative bacterial growth) depending on results from endplate, dermis and subfascia. The primary endpoint will be analyzed with a logistic regression model with bacterial growth (positive/negative) as the outcome and group (MC1 or MC2 vs. control) as the main explanatory variable. After fitting the model, the model-predicted marginal probabilities of positive bacterial findings will be estimated for both groups. The effect measure will be the difference between the two probabilities, and will be reported with a 95 % confidence interval and a P-value for the null hypothesis of a zero difference. The standard error of the difference will be estimated using the delta method. The exploratory and sensitivity analyses will be carried out with the same model, after replacing outcome and main explanatory variable as appropriate. The subgroup analysis of previously operated will be carried out by adding previously operated as an interaction term between groups, and previously operated as covariates in the logistic model. A significant coefficient for the interaction term will indicate a subgroup effect.