• Lyndsay A Alexander, Elizabeth Hancock, Ioannis Agouris, Francis W Smith, and Alasdair MacSween.
• School of Health Sciences, Faculty of Health and Social Care, Robert Gordon University, Garthdee Road, Aberdeen, AB10 7QG, UK. l.a.alexander@rgu.ac.uk
• Spine. 2007 Jun 15; 32 (14): 1508-12.

Study DesignAsymptomatic volunteers underwent magnetic resonance imaging to investigate how different positions affect lumbar intervertebral discs.ObjectiveTo quantify sagittal migration of the lumbar nucleus pulposus in 6 functional positions.Summary Of Background DataPrevious studies of the intervertebral disc response in the sagittal plane were limited to imaging of recumbent positions. Developments of upright magnetic resonance imaging permit investigation of functional weight-bearing positions.MethodsT2-weighted sagittal scans of the L1-L2 to L5-S1 discs were taken of 11 volunteers in standing, sitting (upright, flexed, and in extension), supine, and prone extension. Sagittal migration of the nucleus pulposus was measured (mm) as distance from anterior disc boundary to peak pixel intensity. Lumbar lordosis (Cobb angle) was measured in each position.ResultsFifteen comparisons between positions showed significant positional effects (14 at L4-L5, L5-S1, the most mobile segments). Prone extension and supine lying induced significantly less posterior migration than sitting. Flexed and upright sitting, significantly more than standing at L4-L5, as did flexed sitting compared with extended.ConclusionThese results support for the first time the validity of clinical assumptions about disc behavior in functional positions: sitting postures may increase risk of posterior derangement, and prone and supine may be therapeutic for symptoms caused by posterior disc displacement.

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