The Effect of Paravertebral Muscle on the Maintenance of Upright Posture in Patients With Adult Spinal Deformity

Objective We investigated the relationship between cross-sectional area (CSA) of paravertebral muscle and trunk tilt at standing and walking in adult spinal deformity (ASD) surgery. Summary of Background Data Although the importance of back muscles for the development of spinal kyphosis was well described, the influence on maintaining the sagittal balance was unclear. Methods Forty-five female patients (mean age, 68.8 years) with ASD were studied. We measured sagittal vertical axis [SVA], pelvic tilt [PT], and pelvic incidence–lumbar lordosis [PI-LL]) by lateral spine radiograph. For the assessment of trunk tilt standing-trunk tilt angle (STA) by lateral standing radiograph, gait-trunk tilt angle (GTA) by lateral gait images, and the increasing trunk tilt angle (ITA) by subtracting the STA from the GTA were calculated. Using L1/2 and L4/5 axial MRI, the CSAs of bilateral multifidus muscles (MF) and elector spinae (ES) removed fat by Image J software were calculated. We examined the correlation between trunk tilt angle (STA, GTA, and ITA) and spinopelvic parameters (SVA, PT, and PI minus LL) and also the correlation among muscle CSA, trunk tilt angle (STA, GTA, and ITA), and Oswestry Disability Index (ODI). Results The mean STA, GTA, and ITA were 4.2°, 13.0°, and 8.8°, respectively. The CSAs of back muscles were 278 mm 2 at L1/2 MF, 1,687 mm 2 at L1/2 ES, 636 mm 2 at L4/5 MF, and 1,355 mm 2 at L4/5 ES, respectively. Trunk tilt angle had significant relations with spinopelvic parameters. Concerning about muscle CSA, significant correlations were observed between STA and L4/5 MF (r = −0.517), GTA and L1/2 ES (r = −0.461) and L4/5 MF (r = −0.476), and ITA and L1/2 ES(r = −0.429). ODI showed significant correlation with STA and GTA. Conclusions Paravertebral muscles were crucial to keep upright posture during walking as well as standing.