Intra subject repeatability of intervertebral motion parameters for clinical studies.

Authors: Breen, A., Breen, A.C. and Mellor, F.

Start date: 12 September 2017

Intra subject repeatability of intervertebral motion parameters for clinical studies Alexander Breen, Fiona Mellor, Alan Breen Background Change in Intervertebral motion is sometimes a central consideration in the treatment of chronic non-specific low back pain (CNSLBP) in primary care. There has also been an increase in the number of motion parameters that can be measured in vivo due to the emergence of fluoroscopic video technologies. Each parameter addresses the preservation of different mechanical norms and therefore has potential uses as moderators, mediators or outcome measures in clinical studies. The main intervertebral motion parameters are: IV-RoM, sagittal plane translation, sagittal plane disc height, laxity, motion share inequality (MSI) and motion share variability (MSV). These have all been used in pathomechanical studies of patients. All reflect constraint between vertebrae and/or control of intervertebral motion during various tasks.

We assessed the intra subject repeatability of these 6 variables over 6 weeks in order to determine their suitability for distinguishing between individuals and detecting change.

Methods Seventy-four healthy people with no back pain in the previous year had active controlled weight bearing and controlled passive recumbent quantitative fluoroscopy (QF) examinations of their lumbar spine motion 6 weeks apart. Half performed coronal plane motion and the other half sagittal plane. The above motion parameters were calculated for vertebral levels L2-5 in the coronal plane and L2-S1 in the sagittal plane. The results for all intervertebral levels for each parameter in each direction and configuration were pooled.

Reference ranges (95% CI) were calculated for baseline assessments and repeatability was determined using standard errors of measurement, MDC95 and intraclass correlation coefficients (ICC 2,1). Bland Altman plots and 95% limits of agreement between baseline and 6 week measurements were also obtained.

Results Between 99 and 111 levels were accessed for each intervertebral parameter. Reference ranges for IV-RoM and sagittal plane translation and disc height were comparable to published studies. ICCs were above 0.7 for 12/20 passive recumbent studies (median 0.82, range 0.71- 0.85) and 10/20 weight bearing studies (median 0.77, range 0.70-0.85). ICCs were particularly high for IV-RoM, laxity and motion share inequality (MSI) and particularly poor for sagittal translation and motion share variability (MSV). MDC95 was never below 55% of baseline (iV-RoM right recumbent) and were only below 100% in 10/20 recumbent and 5/20 weight bearing ones. In weight bearing flexion, IV-RoM in controlled motion to 60o of trunk bending had better reliability (ICC 0.82, 0.73-0.88) and %MDC (73% of baseline) than maximum voluntary bending angle (MVBA) in the same participants (ICC 0.74, 0.61-0.83 and %MDC 94% of baseline).

Discussion and conclusion Although the majority of motion measures had reasonable reliability over a 6 week period, large changes will need to be observed to be confident of avoiding a Type 1 error. Reliability was generally higher and MDC95 generally lower in passive recumbent studies. Controlled flexion was superior to MVBA in weight bearing flexion studies for IV-RoM. This study provides the basis for selection of intervertebral motion parameters for follow-up clinical studies. Larger samples with normal distributions will be needed to estimate the number of subjects necessary to compare changes in clinical trials.

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