Impact of Fatigue on Maintenance of Upright Posture

Study Design. Retrospective analysis of prospectively collected data. Objective. To assess global and regional spinal sagittal radiographic parameters in adults with loss of lumbar lordosis (''flatback'') before and after walking 10 minutes. Summary of Background Data. While routine activities of daily living may exacerbate functional disability of spinal sagittal-plane deformity, there is limited understanding of how sagittal parameters and compensatory mechanisms are affected by activity. Methods. Consecutive adults with ''flatback'' at a single institution who previously had full-length standing spinal radiographs before and after walking 10 minutes were reviewed. Changes in spinal deformity sagittal parameters before and after walking were evaluated for two groups: Compensated Sagittal Deformity (''Compensated'': sagittal vertical axis [SVA] <= 4cm and pelvic tilt [PT] > 20 degrees) and Decompensated Sagittal Deformity (''Decompensated'': SVA>4cm and PT>208). Intra-group radiographic comparisons were performed with paired Student t tests. Results. One hundred fifty-seven patients (143 females, 14 males; average age 67.9 +/- 5.9 yr) met inclusion criteria. Initial average SVA was 1.7 +/- 1.2cm for ''Compensated'' and 11.5 +/- 6.4cm for `` Decompensated.'' After walking 10 minutes, significant deteriorations in average SVA were observed for all ''Decompensated'' patients and 84.6% of '' Compensated'' patients. For both groups, this was accompanied by significant decreases in PT and LL and increases in PI- LL (P<0.01). Thoracic kyphosis increased after walking for only ''Decompensated'' (P<0.01). For ''Compensated,'' the change in SVA was determined by decreases in PT and LL, while changes in SVA for ''Decompensated'' were correlated to worsening of all sagittal parameters. Conclusion. After walking, compensatory mechanisms to maintain sagittal balance in adults with spinal deformity are less pronounced than when the patient initially presents. This results in significant sagittal decompensation, irrespective of the initial SVA. As we postulate that loss of compensatory mechanisms is due to fatigue on pelvic and spinal extensor muscles, sagittal parameters can be re-evaluated with radiographs obtained after patients walk 10 minutes to unmask a hidden sagittal imbalance in compensated deformities.