Association of L4–5 Segmental Instability Parameters With Paraspinal Muscle CSA in Lumbar Spinal Stenosis: An MRI-Based Study

Background: Lumbar segmental instability is commonly assessed using sagittal translation (ST) and segmental angulation (SA) on flexion-extension radiographs, but their associations with paraspinal muscle morphology in lumbar spinal stenosis (LSS) remain unclear.Objects: To examine the associations between continuous ST/SA measurements, left-right paraspinal muscle cross-sectional area (CSA) asymmetry and total CSA at L4-5 in patients with LSS, controlling for age, sex, and body mass index (BMI).Methods: Eighty-five patients with LSS were included.The ST (mm) and SA (°) at L4-5 were measured from flexion and extension views.CSA of the paraspinal muscle was measured on magnetic resonance imaging at the L4-5 mid-disc level.CSA asymmetry was defined as right -left and total CSA as right + left.Partial correlations between ST/SA and CSA were calculated after controlling for age, sex, and BMI.Results: Forty-seven female and 38 male were included.The mean ST and SA were 2.15 ± 1.58 mm and 8.80° ± 5.51°, respectively.ST was weakly correlated with SA (partial r = 0.260, p < 0.05).ST showed a weak positive correlation with erector spinae (ES) CSA asymmetry (partial r = 0.223, p < 0.05) but was not associated with psoas major or multifidus asymmetry or total CSA in any muscle.SA was not associated with CSA asymmetry or the total CSA. Conclusion:In patients with LSS, ST at L4-5 was weakly but significantly correlated with ES CSA asymmetry after controlling for age, sex, and BMI.In contrast, SA showed no significant association with paraspinal muscle CSA asymmetry or total CSA, and neither ST nor SA was significantly associated with the total CSA of the paraspinal muscles.ST and SA were weakly correlated, suggesting that translational and angular motions represent partly distinct components of segmental motion in this cohort.