Comparison of cross-sectional area for paraspinal muscles in patients with lumbar spinal stenosis with and without lumbar segmental instability: A retrospective cross-sectional study

Background Lumbar spinal stenosis (LSS) causes nerve compression with low back pain and neurogenic claudication. Paraspinal muscles maintain lumbar stability, and coexisting lumbar segmental instability (LSI) may be associated with altered muscle morphology. Objective To compare paraspinal muscle cross-sectional area (CSA) (psoas major, multifidus, erector spinae) in LSS patients with and without LSI. Methods This retrospective cross-sectional study analyzed 97 patients with LSS. LSI was determined from flexion–extension radiographs; 43 patients met LSI criteria. Paraspinal muscle CSA was measured at L4–L5 using MRI. Independent t-tests or Mann-Whitney U tests compared CSA and pain characteristics including pain intensity (Numerical Rating Scale [NRS]) and pain duration (months). Multiplicity was controlled using Benjamini–Hochberg false discovery rate (BH-FDR). Results Psoas major CSA was smaller in the LSI group bilaterally (right: mean difference −166.50 mm 2 , 95% CI −301.42 to −31.58, p = 0.016, d = 0.49; left: p = 0.040, d = 0.43). Multifidus CSA was also smaller (right: mean difference −53.61 mm 2 , 95% CI −104.27 to −2.94, p = 0.038, d = 0.43; left: p = 0.033, d = 0.44). However, there were no significant differences in the CSA of the erector spinae muscles and pain characteristics between groups ( p > 0.05). Conclusions LSS patients with concurrent LSI demonstrated significantly smaller CSA in local stabilizers (psoas major and multifidus) but not in global mobilizers (erector spinae). Pain characteristics did not differ between groups. These findings suggest that LSI has selective effects on paraspinal muscle morphology in LSS patients, supporting the importance of muscle morphological assessment in the clinical evaluation of patients with suspected segmental instability.