MRI-based lumbar cross-sectional indentation value is associated with spinopelvic sagittal balance in patients with degenerative kyphosis

Objective To investigate whether MRI-based paraspinal muscle morphology, assessed using the lumbar cross-sectional indentation value (LCIV), is associated with spinopelvic sagittal balance in patients with degenerative kyphosis (DK). Methods This retrospective case-control study included 81 patients with DK, defined as degenerative thoracolumbar kyphosis and/or loss of lumbar lordosis, and 60 surgical controls with symptomatic lumbar spinal stenosis but without degenerative spinal deformity. LCIV was measured from T12-L1 to L4-L5 on axial T2-weighted MRI, and the mean LCIV (mLCIV) was calculated. Spinopelvic sagittal balance in the DK group was evaluated using pelvic incidence minus lumbar lordosis (PI-LL) mismatch and pelvic tilt (PT). Associations among mLCIV, body mass index (BMI), thoracolumbar kyphosis, lumbar lordosis, and PT were also analysed. Results Patients with DK had a lower mLCIV than controls (7.2 ± 5.4 mm vs. 10.8 ± 3.5 mm, P < 0.001). In the DK group, mLCIV was positively correlated with lumbar lordosis and BMI, and lumbar lordosis showed the stronger association in multivariate analysis. Patients with preserved PI-LL matching had a greater mLCIV than those with PI-LL mismatch (9.4 ± 5.2 mm vs. 5.8 ± 5.0 mm, P = 0.005). Similarly, patients with lower PT had a greater mLCIV than those with increased PT (8.5 ± 5.0 mm vs. 5.7 ± 5.4 mm, P = 0.028). Conclusion Lower mLCIV was observed in patients with PI-LL mismatch and increased PT, suggesting that lower LCIV may accompany spinopelvic sagittal imbalance and compensatory pelvic retroversion in DK. LCIV may provide a simple MRI-based measure of posterior paraspinal muscle contour in sagittal balance evaluation.