Study design
This study was a retrospective cross-sectional observational study.
Patient population
All participants were above the age of 18 and had neck pain with or without arm pain. They had all attended the same publicly funded outpatient spine clinic (The Spine Centre of Southern Denmark) where they had been referred to from the primary care chiropractors and general practitioners for a multidisciplinary evaluation.
Data collection
Clinical data are routinely collected at the spine clinic using an electronically based standardised questionnaire ‘SpineData’ which is an internet-based, multiuser registry designed to capture patient data electronically at the point of clinical contact [17]. A list of patients > 18 years with neck and with or without arm pain, who had attended the spine clinic between January 1, 2011 and December 31, 2014, was extracted from the SpineData registry and the listed patients were assessed for eligibility. Patients who had filled out the questionnaire at the first visit and at 12-months follow-up, and also had an MRI of the cervical spine from the radiology department of the hospitals in either Middelfart or Vejle, were included. The narrative radiologists’ reports were collected and evaluated. Patients were excluded if one or more of the following pathoanatomies were identified: recent acute vertebral fractures, surgical fusions, spinal infections, tumors, inflammatory spondyloarthropathy or other serious pathology. A summary of the data collection is presented in Fig. 1.
Imaging
Only MRIs from the hospital’s radiology departments of Middelfart and Vejle were included in order to ensure homogeneity in the MRI scan and MRI evaluation protocols. The MRI protocol included the following sequences: one localiser, a sagittal short-tau inversion recovery (STIR), a sagittal T1-weighted turbo spin-echo (TSE), a sagittal T2-weighted Volume Isotropic Turbo spin echo Acquisition (VISTA) and axial T2 weighted TSE of the three lower cervical segmental levels with supplement of segmental levels suspicious of pathology. In addition, the radiologists use reconstructed semi-coronal series from the VISTA sequence, as part of their standardised evaluation, for visualisation of the neural foramina. The majority of MRIs were performed with a 1.0 Tesla (Philips Panorama, Best, The Netherlands) or 1.5 Tesla unit (Philips Achieva and Philips Ingenia, Best, The Netherlands) MRI system or, although rarely, with a 0.2 Tesla unit.
The narrative reports were retrieved from this hospitals Picture Archiving and Communication System (PACS) EasyViz archive (Medical Insight, Valby, Denmark).
Variables of interest
Ten MRI findings were chosen for this study as they were considered relatively common and relevant to the research context of this study; Modic changes type 1 and type 2, disc degeneration, disc herniation, disc bulge, nerve root compromise, foraminal stenosis, central stenosis, facet joint arthrosis and uncovertebral arthrosis.
Descriptive clinical data on age, sex, sick leave, neck and arm pain as measured on an 11-point numeric rating scale [18] and physical function measured with the Neck Disability Index (NDI) [19] were available from the SpineData registry.
Coding of MRI narrative reports
Coding of the narrative reports was modified for the cervical spine from the process previously described by Kent et al. [13]. A set of coding rules was developed to record the presence or absence of an MRI finding on each of the cervical segmental levels from C2/C3 to C7/Th1. A segmental level was defined as the inferior endplate of the top vertebra to the superior endplate of the vertebra below including the inter-vertebral space (e.g. inferior endplate of C2 to the superior endplate of C3).
The reviewers of the narrative reports were six second-year chiropractic master students who had finished their imaging course of 16 ECTS points (European Credit Transfer and Accumulation System). The data collection was part of their pre-graduate Master Thesis project which they had chosen from a catalogue of research projects suitable for a Master Thesis. The subject was chosen out of availability and interest. The students described the coding rules for identifying each of the MRI findings based on i) previous work in the department [16], ii) a consensus document from the radiological department and iii) by consulting senior researchers. In-person meetings were conducted first between the groups of students and later with the attendance of a senior researcher to review and refine the final set of coding rules. An additional file shows the final set of coding rules (see Additional file 1).
Reliability testing
The reliability study was done in two steps. One study was performed to test the inter-rater reliability between four of the six chiropractic master students for data extraction of disc degeneration, disc herniation, disc bulge, nerve root compromise, foraminal stenosis, central stenosis, facet joint arthrosis and uncovertebral arthrosis. The study was based on six cervical segmental levels in 59 patients (354 levels). Another study investigated the reliability of the data extraction of Modic changes type 1 and type 2 on six levels in 50 patients (300 segmental levels) between the remaining two students. Each finding from the MRI radiologists’ reports was registered in spread sheets developed for this purpose (Microsoft Excel 2010, Microsoft Corp, Redmond, WA, USA). To ensure blinding the observers were allocated to different rooms and filled in the spread sheets independently. Each observer then delivered the data to one of the senior researchers who merged the data and performed the analysis.
Statistics
Unweighted Kappa statistics including 95% confidence intervals (CI) were used to quantify the inter-rater reliability. The interpretation of the Kappa coefficient (κ) was based on Landis and Koch for strength of agreement: values lower than 0.20 indicated slight agreement; 0.21–0.40, fair agreement; 0.41–0.60 moderate agreement; 0.61–0.80 substantial agreement; and 0.81–1.00 almost perfect agreement [20]. The prevalence of the MRI findings for each segmental level and per person was calculated in percentage. The age of the participants was divided into decades. The minimum and maximum age group were merged with nearest age group if < 10 per group. STATA 14 (Stata Corp, College Station, Texas, USA) was used for all data management. The prevalence of MRI findings was calculated by disc level (C2/C3 to C7/Th1), by patient level and by age (18–30, 31–40, 41–50, 51–60, 61–70 and 70+ years of age).