Low Back Pain and Paraspinal Muscles: Clinical and Instrumental Characteristics Across Different Age Groups

BACKGROUND. The reduction in mass and function of paraspinal muscles and its contribution to axial instability and the development of back pain has become an active area of research. However, current diagnostic criteria for sarcopenia have limitations when applied to spinal sarcopenia. The condition of the spinal muscular system in patients with chronic back pain and degenerative spine disorders is of interest not only for treatment but also for disease prevention.

OBJECTIVE. To assess the paraspinal muscle mass in patients with low back pain across different age groups using magnetic resonance imaging (MRI). MATERIALS AND METHODS. A total of 93 patients with low back pain were included in the study: young adults (n = 35, Me: 36.00 [30.00–42.00]), middle-aged (n = 30, Me: 50.00 [46.50–56.25]), and elderly patients (n = 28, Me: 66.00 [62.50–71.00]). Back pain intensity was measured using a Visual Analogue Scale (VAS, mm), and spinal function was assessed using the Backache Index (BAI). Intervertebral disc (IVD) degeneration was evaluated via MRI according to the Pfirrmann classification (2001). The cross-sectional areas of paraspinal muscles (psoas major, erector spinae, quadratus lumborum) were measured on axial MRI slices at the level of the third lumbar vertebra (L3). The muscle-to-vertebral index (MVI) was calculated by dividing the total cross-sectional area of the three paired muscles (Sm, cm2) by the crosssectional area of the L3 vertebral body at its superior endplate (Sv, cm²):  MVI = (Smdextra + sinistra) / Sv. The anterior-posterior body dimension was also measured on sagittal slices at the upper edge of L3.

RESULTS. Chronic back pain was reported in 80%, 83.3%, and 86.7% of the young, middle-aged, and elderly groups, respectively. The BAI scores indicating significant spinal dysfunction (0.80 [0.47–0.90], 0.67 [0.50–0.77], and 0.80 [0.65–1.00] respectively) positively correlated with VAS pain intensity across all subjects (r = 0.55, p < 0.0001). Obesity was twice as prevalent among elderly patients compared to younger and middle-aged individuals (30.0% vs. 14.3% and 16.7%, respectively). The mass of the paraspinal muscles according to the average MVI values in the groups was statistically lower in middleaged (p = 0.025) and elderly (p = 0.0001) individuals. Asymmetry of the quadratus lumborum muscle (right side larger than left) was identified in all patients (p < 0.05). An age-related increase in the cross-sectional area of the L3 vertebral body endplate was also found (p = 0.0003). A positive correlation was observed between the anterior-posterior torso dimension and the stage of IVD degeneration at L5–S1 (р = 0.054; r = 0.29).

CONCLUSION. Paraspinal muscle mass in patients with back pain and degenerative spine disease decreases with age (p < 0.05), as reflected by reduced MVI values on MRI. The MVI is an effective tool for evaluating paraspinal muscle loss. Altered motor patterns lead to chronic imbalance and asymmetry of the quadratus lumborum muscle in all age groups studied. The increase in the vertebral body’s endplate area may reflect adaptive changes aimed at maintaining axial spinal stability. The positive correlation between the anterior-posterior body dimension and IVD degeneration suggests a contribution of the musculoskeletal-visceral component to the condition of the lumbar spinal motion segment.

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