Relationship Between Paralumbar Muscle Assessment Methods and Spinal Alignment in Adult Spinal Deformity

Study designRetrospective cross-sectional study.ObjectivesParalumbar muscle degeneration is closely linked to adult spinal deformity (ASD). However, assessment methods vary widely, including quality via fat infiltration (FI) and quantity through paraspinal total cross-sectional area (PTCSA), psoas vertebral body index (PVBI), and normalized total psoas area (NTPA). This study aimed to determine which parameter best correlates with spinal alignment in ASD.Methods116 ASD patients were analyzed. Spinal alignment was evaluated using standard preoperative spinopelvic parameters. Paralumbar muscle was evaluated by preoperative MRI, using FI for quality, and PTCSA, PVBI, and NTPA for quantity. Correlations between these metrics and spinopelvic alignment were analyzed. Subgroup analyses assessed associations between alignment and FI or PVBI levels. Age-stratified analyses explored these associations in patients under and over 70.ResultsFI and PVBI demonstrated significant correlations with multiple sagittal alignment parameters, including lumbar lordosis (LL), sacral slope (SS), pelvic incidence (PI)-LL, pelvic tilt (PT), L1 pelvic angle (L1PA) deviation from normal, T4 pelvic angle (T4PA), and T4-L1PA mismatch while PTCSA and NTPA only exhibited weak correlations (r < .30) with few alignment measures. Higher FI and lower PVBI were associated with reduced LL and SS, and increased PT, PI-LL, T4PA, and T4-L1PA mismatch. In patients ≥70, FI showed moderate correlations with LL and SS, while PVBI had limited relevance. In those <70, both FI and PVBI were associated with sagittal alignment.ConclusionsFI and PVBI are the most relevant metrics for evaluating paralumbar muscle in ASD. FI appears more correlated in elderly patients.