Chronic low back pain is a leading cause of disability worldwide, and in a large share of sufferers the pain is attributed to the myofascial system, the complex of muscle and fascia whose smooth gliding allows the spine to move without strain. Yet despite the enormous burden of this condition, clinicians still diagnose myofascial pain largely by palpation and by what patients report, because objective, quantitative tools for measuring the mechanical properties of these tissues have been lacking. A new study published in European Radiology Experimental reports that a magnetic resonance elastography-based technique called slip interface imaging can fill part of that gap, detecting measurably reduced sliding between lumbar muscles in patients with chronic low back pain with myofascial pain features.

The research, led by Emi Hojo and colleagues at Mayo Clinic in Rochester, Minnesota, set out to evaluate whether the technique, abbreviated SII, could reliably quantify mobility at the interfaces between adjacent lumbar muscles. The team recruited 61 participants between October 2022 and August 2025: 20 patients with chronic low back pain with myofascial pain features and 41 healthy volunteers. All participants were scanned on a 3.0-Tesla MRI system, with mechanical vibrations at 30 hertz transmitted to the lower back through a customized belt driver positioned over the L4–L5 region while participants lay supine with a knee bolster to keep lumbar positioning consistent.

Slip interface imaging builds on magnetic resonance elastography, which uses the applied vibrations to map cyclic tissue displacement throughout the scanned volume. The technique extracts a measure called the maximal normalized displacement discontinuity, or Dnorm, which captures how sharply displacement changes across a boundary between two tissue layers. Where adjacent muscles glide freely against one another during vibration, Dnorm maps show bright, high-intensity lines tracing the interface; where sliding is restricted, the boundary fades and displacement on either side of the interface becomes similar. By sampling Dnorm values along manually segmented interfaces and averaging them, the researchers computed a single unitless mobility index for each interface region, with higher values indicating greater relative motion between the muscle layers.

The study focused on two clinically relevant interfaces at the L3 and L4 vertebral levels: the boundary between the quadratus lumborum and erector spinae, and the boundary between the erector spinae and multifidus. These mid-lumbar sites were chosen because they are commonly affected in chronic low back pain and because standardizing the field of view at L3–L4 improves measurement reproducibility relative to the belt driver position. Before any group comparisons could be meaningful, however, the team first needed to establish that the measurements themselves were trustworthy.

Repeatability testing was carried out in a subset of 18 healthy volunteers who underwent three scanning sessions: two on the same day, separated by a break during which the belt was removed and repositioned, and a third approximately two weeks later. The results were striking. The within-subject coefficient of variation, a standard measure of test–retest variability, averaged below 10 percent for every interface, side, and vertebral level, both within and between days, a threshold the authors had predefined as indicating excellent repeatability. Bland–Altman analysis showed negligible bias, with within-day bias ranging from −0.006 to 0.020 and between-day bias from −0.022 to 0.008, and no consistent directional drift across sessions. Inter-rater reproducibility was similarly strong, with coefficients of variation below 5 percent when a second rater independently segmented the muscles.

In the healthy volunteers, the technique also revealed normal anatomical variability. Repeated-measures analysis of variance showed significant effects of interface and vertebral level on mobility, with generally greater mobility at the quadratus lumborum–erector spinae interface than at the erector spinae–multifidus interface, and greater mobility at L3 than L4 on the right erector spinae–multifidus boundary. Mobility was bilaterally symmetric, and, notably, showed no significant associations with age, sex, or body mass index in either unadjusted or multivariable analyses, apart from a small association at the L3 quadratus lumborum–erector spinae interface. This suggests that demographic factors explain little of the variability in lumbar intermuscular mobility, strengthening the interpretation that differences observed in patients reflect something other than normal biological variation.

The key patient finding emerged at the L4 erector spinae–multifidus interface. Patients were stratified by their score on the pain, enjoyment, and general activity scale, a 0-to-10 measure of pain intensity and functional interference, into mild pain (score of 4 or less) and moderate-to-severe pain (score above 4). One-way analysis of variance across the three groups, mild pain, moderate-to-severe pain, and matched healthy volunteers, showed a significant group effect at this interface. Patients with moderate-to-severe pain had significantly lower mobility than those with mild pain and than healthy volunteers, with large effect sizes. Within the patient cohort, L4 erector spinae–multifidus mobility correlated moderately and negatively with the pain scale score, with a Pearson correlation coefficient of −0.51. No other interfaces or vertebral levels showed consistent group differences, pointing to a region-specific rather than global restriction.

The correlation with pain severity did not extend to other clinical measures. Mobility at the L4 erector spinae–multifidus interface showed no significant association with pain duration, pain catastrophizing, sleep disturbance, physical function, or the widespread pain index. The authors suggest this selectivity makes sense: the pain scale captures pain intensity and activity interference, dimensions that may be more closely tied to movement-associated mechanical factors, whereas pain duration and psychosocial measures may reflect other aspects of the pain experience. Because the L4–L5 segment bears high mechanical loads and the multifidus and erector spinae play complementary roles in segmental stabilization and torque generation, impaired gliding between them could plausibly alter local mechanical coupling and contribute to activity-related pain, although the cross-sectional design cannot determine whether restricted mobility causes pain or results from it.

Fibromyalgia, which frequently coexists with localized myofascial pain, added heterogeneity to the cohort. In exploratory analyses stratified by fibromyalgia status, patients with comorbid fibromyalgia also showed significantly reduced L4 erector spinae–multifidus mobility compared with healthy volunteers, and they tended to have higher pain scores and lower mobility. The authors emphasize, however, that these subgroup analyses involved small samples and should be regarded as descriptive and exploratory rather than confirmatory. They note that focal mechanical alterations at this interface may coexist with broader central pain modulation processes, and that larger, well-phenotyped cohorts will be needed to disentangle peripheral mechanical contributors from centralized pain mechanisms.

The study has several limitations that the authors acknowledge. Repeatability was assessed only in healthy volunteers with a body mass index of 30 or below, and reproducibility in more diverse patient populations remains to be established. The segmentation workflow, while highly reproducible between trained raters, is not yet automated. The design was cross-sectional and single-center, precluding causal inference and external validation, and subgroup sizes were modest. The authors also stress that Dnorm should be interpreted as an imaging-based indicator of relative intermuscular mobility differences rather than a standalone diagnostic criterion, since clinically meaningful cutoffs and diagnostic thresholds remain undefined. Even so, the combination of excellent repeatability, anatomical sensitivity, and a pain-related, site-specific reduction in mobility supports slip interface imaging as an early-stage quantitative biomarker candidate, one that could enable objective phenotyping of myofascial mechanics and guide larger multicenter and longitudinal studies in chronic low back pain.

Subject of Research: Quantifying lumbar intermuscular myofascial mobility in chronic low back pain using MR elastography-based slip interface imaging

Article Title: Reduced lumbar myofascial mobility in chronic low back pain quantified using MR elastography-based slip interface imaging

Article References: Hojo, E., Ito, D., Sui, Y., Shan, X., Rossman, P., Manduca, A., Powell, G. M., An, K.-N., Ehman, R. L., Nanda, S., Bauer, B. A., & Yin, Z. (2026). Reduced lumbar myofascial mobility in chronic low back pain quantified using MR elastography-based slip interface imaging. European Radiology Experimental, 10(1), Article 148. https://doi.org/10.1186/s41747-026-00812-0

Image Credits: AI Generated

DOI: 10.1186/s41747-026-00812-0

Keywords: chronic low back pain, myofascial pain, magnetic resonance elastography, slip interface imaging, lumbar spine, erector spinae, multifidus, quadratus lumborum, biomarker, repeatability, pain severity, fascia