• Noor Shaikh, Honglin Zhang, Brown Stephen H M SHM Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Canada., Jason R Shewchuk, Zakariya Vawda, Hanbing Zhou, John Street, David R Wilson, and Thomas R Oxland.
• School of Biomedical Engineering, University of British Columbia, Vancouver, Canada.
• Eur Spine J. 2020 Sep 1; 29 (9): 2306-2318.

PurposeTo assess the effect of upright, seated, and supine postures on lumbar muscle morphometry at multiple spinal levels and for multiple muscles.MethodsSix asymptomatic volunteers were imaged (0.5 T upright open MRI) in 7 postures (standing, standing holding 8 kg, standing 45° flexion, seated 45° flexion, seated upright, seated 45° extension, and supine), with scans at L3/L4, L4/L5, and L5/S1. Muscle cross-sectional area (CSA) and muscle position with respect to the vertebral body centroid (radius and angle) were measured for the multifidus/erector spinae combined and psoas major muscles.ResultsPosture significantly affected the multifidus/erector spinae CSA with decreasing CSA from straight postures (standing and supine) to seated and flexed postures (up to 19%). Psoas major CSA significantly varied with vertebral level with opposite trends due to posture at L3/L4 (increasing CSA, up to 36%) and L5/S1 (decreasing CSA, up to 40%) with sitting/flexion. For both muscle groups, radius and angle followed similar trends with decreasing radius (up to 5%) and increasing angle (up to 12%) with seated/flexed postures. CSA and lumbar lordosis had some correlation (multifidus/erector spinae L4/L5 and L5/S1, r = 0.37-0.45; PS L3/L4 left, r =  - 0.51). There was generally good repeatability (average ICC(3, 1): posture = 0.81, intra = 0.89, inter = 0.82).ConclusionChanges in multifidus/erector spinae muscle CSA likely represent muscles stretching between upright and seated/flexed postures. For the psoas major, the differential level effect suggests that changing three-dimensional muscle morphometry with flexion is not uniform along the muscle length. The muscle and spinal level-dependent effects of posture and spinal curvature correlation, including muscle CSA and position, highlight considering measured muscle morphometry from different postures in spine models.

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