Sagittal Radiographic Parameters of the Spine in Three Physiological Postures Characterized Using a Slot Scanner and Their Potential Implications on Spinal Weight-Bearing Properties

Abstract

To compare and understand the load-bearing properties of each functional spinal unit (FSU) using three commonly assumed, physiological, spinal postures, namely, the flexed (slump sitting), erect (standing) and extended (backward bending) postures. Overview of Literature: Sagittal spinal alignment is posture-dependent and influences the load-bearing properties of the spine. The routine placement of intervertebral cages "as anterior as possible" to correct deformity may compromise the load-bearing capabilities of the spine, leading to complications. Methods: We recruited young patients with nonspecific low back pain for <3 months, who were otherwise healthy. Each patient had EOS images taken in the flexed, erect and extended positions, in random order, as well as magnetic resonance imaging to assess for disk degeneration. Angular and disk height measurements were performed and compared in all three postures using paired t-tests. Changes in disk height relative to the erect posture were caclulated to determine the alignment-specific load-bearing area of each FSU. Results: Eighty-three patients (415 lumbar intervertebral disks) were studied. Significant alignment changes were found between all three postures at L1/2, and only between erect and flexion at the other FSUs. Disk height measurements showed that the neutral axis of the spine, marked by zones where disk heights did not change, varied between postures and was level specific. The load-bearing areas were also found to be more anterior in flexion and more posterior in extension, with the erect spine resembling the extended spine to a greater extent. Conclusions: Load-bearing areas of the lumbar spine are sagittal alignment-specific and level-specific. This may imply that, depending on the surgical realignment strategy, attention should be paid not just to placing an intervertebral cage "as anterior as possible" for generating lordosis, but also on optimizing load-bearing in the lumbar spine.

Prevalence and Risk Factors of Degenerative Spondylolisthesis and Retrolisthesis in the Thoracolumbar and Lumbar Spine – An EOS Study Using Updated Radiographic Parameters

“…A forward-directed nett force should lead to spondylolisthesis and a backward-directed nett force retrolisthesis. Determinants of these forces include the posture and activities of the patient 40,[48][49][50] , which in turn influences the force magnitude on each lumbar vertebra. In our study, the higher prevalence of spondylolisthesis from L3/4 to L5/S1 levels and retrolisthesis from L1/2 to L3/4 further substantiates this point.…”