Spatial distribution of fat infiltration within the paraspinal muscles: implications for chronic low back pain.

PURPOSE: Fat infiltration (FI) of the paraspinal muscles (PSMs) measured using MRI is an aspect of muscle quality and is considered to be worse in chronic low back pain (cLBP) patients. However, there is not a clear association between paraspinal muscle FI and cLBP, leaving the clinical importance of paraspinal muscle composition unestablished. The spatial distribution of FI in the PSMs may inform mechanistic understanding of non-specific cLBP as it relates to degenerative intervertebral disc (IVD) pathology. We hypothesized that paraspinal muscle fat-mapping would reveal distinct FI distribution patterns in relation to cLBP symptoms and proximity to symptomatic IVD degeneration. METHODS: From advanced-sequence water-fat MRI of 40 axial cLBP patients and 21 controls, we examined the spatial distribution of paraspinal muscle FI in relation to the center of rotation at the L4L5 disc. Using statistical parametric mapping, we compared FI patterns for multifidus (MF), erector spinae (ES), and psoas between patients and controls, and to the presence and severity of adjacent degenerative IVD pathology. RESULTS: The spatial distribution of PSMs FI differs between PSMs and according to symptoms and the adjacent degenerative IVD pathology. Furthermore, the region of MF closest to the disc center of rotation appears most susceptible to FI in the presence of symptomatic IVD degeneration. CONCLUSION: Our study identified spatial distribution patterns of FI in the PSMs as a potential diagnostic biomarker that may also provide granular mechanistic insights into spine biomechanics related to cLBP, as well as advancing the use of prior summary measures limited to overall muscle FI.

The Relationship Between Endplate Pathology and Patient-reported Symptoms for Chronic Low Back Pain Depends on Lumbar Paraspinal Muscle Quality.

STUDY DESIGN: Cross-sectional cohort study of chronic low back pain (CLBP) patients and matched controls. OBJECTIVE: To explore the interplay between vertebral endplate damage and adjacent paraspinal muscle (PSM) quality, and to test their association in a cohort of patients with CLBP and matched controls. SUMMARY OF BACKGROUND DATA: Nonspecific CLBP is challenging to diagnose, in part, due to uncertainty regarding the source of pain. Delineating interactions among potential CLBP mechanisms may enhance diagnosis and treatment customization. METHODS: We collected advanced MRI imaging on 52 adult subjects, including 38 CLBP patients and 14 age- and sex-matched asymptomatic control subjects. Mean multifidus and erector spinae fat fraction (FF) was measured throughout the spine using an IDEAL MRI sequence. Presence of cartilage endplate (CEP) defects was determined at each disc level using UTE MRI. Logistic regression was used to test association of PSM FF, CEP defects, modic changes (MC), disc degeneration, and their interplay. RESULTS: We observed that CEP defects were the strongest predictor of nonspecific CLBP (OR: 14.1, P < 0.01) even after adjusting for MC and disc degeneration (OR: 26.1, P = 0.04). PSM quality did not independently distinguish patient and control groups, except for patients with high self-reported disability.At specifically L4L5, CEP damage was most prevalent and CEP damage was significantly associated with CLBP (OR: 3.7, 95% CI: 1.2-21.5, P = 0.03). CEP damage at L4L5 was predictive of CLBP when adjacent to PSMs with greater FF (MF, OR 14.7, P = 0.04; ES, OR: 17.3, P = 0.03), but not when PSM FF was lower and comparable to values in control, asymptomatic subjects. CONCLUSION: These results demonstrate the clinically important reciprocity between passive and dynamic spinal stabilizers, and support the notion that therapies targeting the PSMs may provide clinical benefit even in the presence of other spinal pathologies. LEVEL OF EVIDENCE: 4.