Analysis of unfused adjacent segment lordosis in standing and sitting positions for patients with short-segments lumbar fusion

English Keywords:Lumbar fusion  Standing  Natural sitting  Sagittal alignment

English Abstract:

  【Abstract】 Objectives: This study aimed to investigate the differences in spinopelvic sagittal alignment of patients with posterior lumbar fusion among different functional postures. The variation of spinopelvic sagittal alignment, especially the unfused adjacent segments lordosis in sitting position will be fully studied. Methods: This was a radiological analysis using full-spine standing, erect and natural sitting lateral radiographs of patients with posterior lumbar fusion before surgery and in final follow-up. A total of 63 patients who received lumbar fusions with short segments between September 2010 and February 2012(30 males, 33 females; mean age 61.6±11.0 years; mean follow-up duration time 82.0±7.3 months) were enrolled. 39 patients had lumbosacral fusion, including 3 patients with L5-S1 fusion, 20 patients with L4-S1 fusion, 15 patients with L3-S1 fusion, and 1 patient with L2-S1 fusion. 24 patients had lumbar floating fusion, including 13 patients with L3-L5 fusion, 5 patients with L4-L5 fusion, and 6 patients with L2-L5 fusion. Pelvic and spinal parameters were measured, including pelvic incidence(PI), pelvic tilt(PT), sacral slope(SS), lumbar lordosis(LL), fusion segment lordosis(FSL), upper residual lordosis(URL), lower residual lordosis(LRL), thoracic kyphosis(TK) and T1-pelvic angle(TPA). Using one-way ANOVA, the parameters were compared between standing and erect sitting posture, erect and natural sitting posture. The changes of sagittal alignment in different postures were discussed. Using Pearson′s correlation test, relationships between residual lordosis and other parameters were discussed according to different positions. Results: When moving from standing to sitting position, sagittal parameters were changed significantly. For patients with lumbar floating fusions, when changing from standing to erect sitting, increased TPA and decreased LL were observed(P<0.05). When changing to natural sitting, increasing TPA and decreasing LL were further observed(P<0.05), SS, URL and LRL were significantly decreased(P<0.05), and PT was significantly increased(P<0.05). For patients with lumbosacral fusions, when changing from standing to erect sitting, increased TPA, decreased LL and URL were observed(P<0.05). When changing to natural sitting, increasing TPA and decreasing LL and URL were further observed(P<0.05), SS was significantly decreased(P<0.05), and PT was significantly increased(P<0.05). In standing position, the correlations between URL-PI and URL-FSL existed(P<0.05). But in natural sitting position, the correlation in URL-FSL was lost(P=0.388), URL had close relationship with TK(P<0.05). Correlations between LRL-SS, LRL-PT and LRL-LL existed(P<0.05). Conclusions: In a natural sitting posture, the total spine becomes kyphotic comprising the thoracic, the unfused lumbar and fused lumbar spine. The unfused lumbar segments are more straightened in sitting position. In natural sitting position, the URL depends more on the adjustment of TK. The characteristics of unfused segments lordosis in natural sitting position may provide information for one of the possible causes of proximal and distal junctional failure or adjacent segment degeneration.