Differences in standing and sitting spinopelvic sagittal alignment for patients with posterior lumbar fusion: important considerations for the changes of unfused adjacent segments lordosis

Abstract

Objective This study aimed to describe the changes in spinopelvic sagittal alignment in the sitting position after posterior lumbar fusion, and to identify the factors influencing unfused adjacent segment lordosis. Methods Consecutive patients with lumbar degenerative disease who underwent posterior lumbar interbody fusion between December 2010 and April 2012 were recruited. Lateral full spine radiographs were obtained in the standing, erect sitting, and natural sitting positions. Spinopelvic parameters were measured preoperatively and at the final follow-up. Results The data of 63 patients were analyzed in this study. The average age was 61.6 ± 11.0 years. When changing from standing to sitting at the final follow-up, all spinopelvic sagittal parameters with the exceptions of pelvic incidence and thoracic kyphosis were significantly altered. The most noticeable changes occurred in the natural sitting position, with the spine slumped toward achieving a C-shaped sagittal profile. Multiple linear regression analysis revealed that when changing to a natural sitting position, age and fusion levels reflected the changes in lumbar lordosis (ΔLL), age and lumbosacral fusion reflected the changes in upper residual lordosis (ΔURL). Conclusion The most noticeable changes in spinopelvic sagittal alignment occurred in the natural sitting position after lumbar fusion. Age, fusion levels, and lumbosacral fusion significantly influenced the differences in LL and URL between the standing and natural sitting position. These characteristics should be fully considered when planning spinal realignment surgery and investigating the etiological factors of junctional complications.

The sitting vs standing spine

“…There were significant differences with a TK decrease by 30%, LL decrease by 50%, SS by 40%, PT increase by 53% and the thoracolumbar junctional angle tended to become less kyphotic and more lordotic. Although these observations are consistent with the ones on healthy individuals, a slight reduction in SS decrease (9%) and in PT increase (8%) was observed [30] , implying that patients undergone lumbar fusion are more likely to have residual lordosis, particularly at the lower lumber spine, in natural sitting position [17] .…”

“…All the studies, apart from Moon et al 2018 [16] evaluated subjects on a common natural sitting position comparing it with conventional standing lateral and/or sagittal radiographies. Few studies included more seated position variants in their analysis; namely erect sitting [17], floor sitting [16,18], sitting on a kneeling chair, sitting on a chair with back support, sitting on 90° angled chair, sitting on chair with anterior support, sitting on stool, sitting cross-legged [19], kneel sitting [16],…”

“…2018 [16] evaluated subjects on a common natural sitting position comparing it with conventional standing lateral and/or sagittal radiographies. Few studies included more seated position variants in their analysis; namely erect sitting [17] , floor sitting [16 , 18] , sitting on a kneeling chair, sitting on a chair with back support, sitting on 90° angled chair, sitting on chair with anterior support, sitting on stool, sitting cross-legged [19] , kneel sitting [16] , anteflexed sitting [20] , upright sitting [20 , 21] , seated flexion [21 , 22] , seated right and left axial rotation [21] , reclined and forward inclined sitting [23] . An overview of the included studies' and subjects' characteristics is presented in Table 1 .…”

Sagittal balance in sitting and standing positions: A systematic review of radiographic measures

“…There is a paucity in the literature regarding normal parameters in the sitting position, especially among non-ambulatory patients. The impact on lumbar alignment and pelvic compensation in sagittal balance has not been fully defined [ [16] , [17] , [18] , [19] ]. For example, there is spinal straightening and pelvic retroversion upon sitting [ 20 , 21 ] owing to a general decrease in LL and an increase in PT [ 22 , 23 ].…”

Changes in Spinopelvic Parameters Between Standing and Sitting Postures

“…8,9 However, numerous disparities between the standing and sitting sagittal spinal parameters have been previously reported which cast doubt on conventional realignment strategies that reference solely to the standing posture. [10][11][12] As the spine is a mobile structure, reinstating the normal sagittal alignment of the spine in standing inevitably creates a deformity when sitting 10,11,13 and vice versa. Increased mechanical stresses within the construct and at junctional areas resulting from this generated deformity in sitting likely explain why rod breakages and junctional failures are highly prevalent.…”