Distinguishing chronic low back pain in young adults with mild to moderate pain and disability using trunk compliance

Abstract

Chronic low back pain (cLBP) rates among younger individuals are rising. Although pain and disability are often less severe, underlying changes in trunk behavior may be responsible for recurrence. We examine the biomarker capacity of a simple Trunk Compliance Index (TCI) to distinguish individuals with and without cLBP. A random subset (n = 49) of the RELIEF RCT were matched to healthy controls for sex, age, height and weight. We measured TCI (as displacement/ weight-normalized perturbation force) using anthropometrically-matched, suddenly-applied pulling perturbations to the trunk segment, randomized across three planes of motion (antero-posterior, medio-lateral, and rotational). Mean differences between cLBP, sex and perturbation direction were assessed with repeated-measures analysis of variance. Discriminatory accuracy of TCI was assessed using Receiver Operator Characteristic (ROC) analysis. Baseline characteristics between groups were equivalent (x̅ [range]): sex (57% female / group), age (23.0 [18-45], 22.8 [18-45]), height, cm (173.0 [156.5-205], 171.3 [121.2-197], weight, kg (71.8 [44.5-116.6], 71.7 [46.8-117.5]) with cLBP associated with significantly lower TCI for 5 of 6 directions (range mean difference, - 5.35: - 1.49, range 95% CI [- 6.46: - 2.18 to - 4.35: - 0.30]. Classification via ROC showed that composite TCI had high discriminatory potential (area under curve [95% CI], 0.90 [0.84-0.96]), driven by TCI from antero-posterior perturbations (area under curve [95% CI], 0.99 [0.97-1.00]). Consistent reductions in TCI suggests global changes in trunk mechanics that may go undetected in classic clinical examination. Evaluation of TCI in younger adults with mild pain and disability may serve as a biomarker for chronicity, leading to improved preventative measures in cLBP.Trial Registration and Funding RELIEF is registered with clinicaltrials.gov (NCT01854892) and funded by the NIH National Center for Complementary & Integrative Health (R01AT006978).

Conflict of interest statement

Dr. Stamenkovic reported no conflict during the conduct of this study. Dr. Clark reported receiving grants from the NIH during the conduct of this study and grants from the Osteopathic Heritage Foundations and the American Osteopathic Association outside the submitted work. Dr. Pidcoe reported no conflict during the conduct of this study. Dr. van der Veen reported no conflict during the conduct of this study. Dr. France reported receiving grants from the NIH during the conduct of this study. Dr. Russ reported receiving grants from the NIH during the conduct of this study. Dr. Kinser reported receiving grants from the NIH during the conduct of this study. Dr. Thomas reported receiving grants from the NIH during the conduct of this study.

Figures

Figure 1

Experimental schematic of perturbation device and average time series data for calculation of Trunk Compliance Index. (a) Schematic of perturbation puller system with examples of motor combinations to produce directional perturbations and example calculation of measures, displacement and perturbation load. BW, Body weight. (b) Average time series profile of perturbation load (top panels) and displacement (bottom panels) for an individual with chronic low back pain (left panels) and matched control (right panel). Perturbations reached peak loads within 100 ms and displacement was calculated at the zero crossing following peak perturbation.

Figure 2

Mean differences in Trunk Compliance Index across 6 directions of trunk position perturbation. (a) Comparisons were split by chronic low back pain (a, grey) and matched healthy controls (a, black). (b) Color comparisons were split by biological sex (females, red; males, blue). *P < 0.05 Bonferroni-adjusted; All individual values reported with bars representing mean + 95% confidence interval. Abbreviations: F, Flexion; E, Extension; LFR, Lateral Flexion (Right); LFL, Lateral Flexion (Left); AC, Anti-clockwise (rightward) rotation; C, Clockwise (leftward) rotation.

Figure 3

Receiver Operator Characteristic (ROC) curves for Trunk Compliance Index. Summary curves were produced for a Composite Trunk Compliance Index score (averaged across all perturbation directions, black), and individually for perturbations across each plane of motion (Flexion/Extension-grey; lateral flexion-blue; Rotation-brown). Area under the curve (AUC), and Youden’s index (Jmax) indicating optimal cut-points are shown for measures with good to excellent discriminatory capacity.