INTRODUCTION: Degenerative lumbar diseases cause degeneration in various spinal structures, including trunk muscles such as the paravertebral muscles (PVM) and psoas major (PM). While computed tomography (CT) and magnetic resonance imaging (MRI) are traditionally used to evaluate muscle size and fat infiltration, these methods lack standardized quantitative measures. MRI T2 mapping, which can assess collagen arrangement and water content in tissues, offers potential for quantitative evaluation of muscle degeneration. This study aimed to evaluate trunk muscle degeneration using T2 mapping and investigate its relationships with various clinical and radiological parameters.
METHODS: We analyzed 60 patients (30 males; mean age 70.0 years) who underwent surgery for lumbar degenerative diseases. MRI T2 mapping was performed to measure T2 relaxation times of PVM and PM at the L4/5 level. CT images were analyzed for muscle CT numbers and cross-sectional area (CSA). Body composition parameters, including skeletal muscle mass and phase angle (PhA), were assessed using bioelectrical impedance analysis. Clinical symptoms were evaluated using visual analog scale (VAS) for low back pain, leg pain, and numbness, Japanese Orthopedic Association (JOA) score, Oswestry Disability Index (ODI), and Roland-Morris Disability Questionnaire (RDQ). Correlations between T2 relaxation times and these parameters were statistically analyzed.
RESULTS: Mean T2 relaxation times were 68.4±12.5 ms for PVM and 56.8±6.6 ms for PM, showing significant correlation between both muscles (r=0.591, p<0.01). T2 relaxation times showed positive correlations with age (PVM: r=0.523, PM: r=0.365, p<0.01) and negative correlations with CT numbers (PVM: r=-0.840, PM: r=-0.512, p<0.01). PVM T2 relaxation times negatively correlated with CSA (r=-0.315, p=0.014) and skeletal muscle mass (r=-0.437, p<0.01), while showing significant negative correlations with PhA, particularly in the lower limbs (r=-0.549, p<0.01). PVM T2 relaxation times demonstrated significant negative correlations with improvements in leg pain VAS (r=-0.407), leg numbness VAS (r=-0.454), and JOA scores (r=-0.381, all p<0.01) after surgery. In contrast, PM T2 relaxation times showed no significant correlations with CSA, skeletal muscle mass, or any postoperative clinical outcomes (p>0.05).
DISCUSSION: This study demonstrates that MRI T2 mapping effectively quantifies age-related trunk muscle degeneration, particularly in the PVM, with prolonged T2 relaxation times indicating muscle degeneration. The significant correlations between PVM T2 relaxation times and various parameters, including skeletal muscle mass and PhA, suggest its association with systemic muscle degeneration. Additionally, the correlation between PVM T2 relaxation times and surgical outcomes indicates its potential value in predicting postoperative improvement. These findings establish T2 mapping as a valuable tool for evaluating trunk muscle degeneration in patients with lumbar degenerative diseases.