Degeneration of paraspinal and gluteus medius muscles in nonspecific chronic low back pain: a quantitative MRI study.

PURPOSE: Nonspecific chronic low back pain (NCLBP) is highly prevalent, yet its underlying musculoskeletal alterations remain incompletely characterized. This study aimed to quantitatively assess paraspinal muscles, gluteus medius (GM), subcutaneous fat tissue thickness (SFTT), vertebral bone marrow fat fraction (BMFF), and sagittal spinal parameters in NCLBP using a 3D 6-echo q-Dixon MRI technique. METHODS: This retrospective study included twenty-two patients with NCLBP and twenty controls who underwent lumbar MRI including 3D q-Dixon sequences. Cross-sectional area (CSA) and fat infiltration (FI) of the psoas major, multifidus, erector spinae, and GM were measured. SFTT, BMFF (L1–L5), lumbar lordosis (LL), and sacral slope (SS) were also evaluated. Group differences were analyzed using t-tests or Mann–Whitney U tests, with Cohen’s d used to estimate effect sizes. RESULTS: FI was significantly higher in the paraspinal muscles at multiple lumbar levels in the NCLBP group (p < 0.05, d > 0.6), whereas CSA showed no consistent differences except for the right erector spinae at L5/S1 (p = 0.047; d = 0.66, 95% CI 0.03 to 1.28). GM demonstrated bilateral FI elevation (both p < 0.05; right d =0.68, 95% CI 0.09 to 1.37; left d = 0.72, 95% CI 0.18 to 1.34) with only right CSA reduction (p < 0.05; d = 0.61, 95% CI 0.05 to 1.33). No significant group differences were observed in SFTT, BMFF, LL, or SS (all p > 0.05). CONCLUSION: Using quantitative 3D q-Dixon MRI, patients with NCLBP showed increased muscle FI in paraspinal and GM muscles, whereas muscle CSA exhibited no consistent differences. These findings suggest that muscle FI may be a more sensitive imaging marker of early muscle degeneration in NCLBP.