A novel subgrouping approach to low back pain: Exploring differences in lumbar muscle morphology and function - A cross-sectional study.

BackgroundClassifying low back pain (LBP) based solely on symptom duration may be insufficient to explain underlying paraspinal muscle degeneration and dysfunction in recurrent and chronic LBP cases.MethodsFifty-nine females (45 with non-specific low back pain, 14 pain-free controls) were categorized into subgroups using cluster analysis based on personal, pain-related, psychological, and functional characteristics. Lumbar paraspinal muscle structure was assessed using T1-weighted Dixon MRI to measure muscle cross-sectional area (CSA), fat CSA, and muscle fat index (MFI). Muscle function was evaluated using T2-weighted MRI to determine resting T2 values (T2-rest) and T2 shift following muscle activation (T2-shift) at three specific lumbar levels: upper L3 (UL L3), upper L4 (UL L4), and lower L4 (LL L4).ResultsFour new LBP subgroups were identified and compared to HC (healthy control (n = 14), 23.6%): Neutral (NT; n = 5, 8.5%), Personal and Pain Affected (PA; n = 9, 15.3%), Maladaptive cognition affected (MCA; n = 25, 42.4%), and Personal, Pain, Psychological, and Functional Affected (PPFA; n = 6, 10.2%). NT resembled HC indicating healthy lumbar muscle, PA subgroup showed with a higher fat CSA and MFI in paraspinals muscle. PA and MCA exhibited localized muscle hyperactivity. PPFA subgroups remained metabolically inactive.ConclusionsThis novel LBP subgrouping framework revealed distinct patterns of paraspinal muscle fatty infiltration and dysfunction. Fatty infiltration and hyperactivity were linked to BMI, chronicity, and cognitive traits; hypoactivity was found in those with broad psychosocial and functional impairments.