Sagittal thoracic decompensation following long adult lumbar spinal instrumentation and fusion to L5 or S1: Causes, prevalence, and risk factor analysis

Study Design. Retrospective study. Objective. To analyze the causes, prevalence of, and risk factors for sagittal thoracic decompensation in adult lumbar spinal instrumentation and fusion (from distal thoracic or upper lumbar spine) to L5 or S1. Summary of Background Data. To our knowledge, no studies on sagittal thoracic decompensation following long adult lumbar spinal instrumentation and fusion (from distal thoracic or upper lumbar spine) to L5 or S1 have been published. Methods. A clinical and radiographic assessment of 99 patients with adult lumbar spinal deformity (average age 56.7 years) who underwent long (>= 4 vertebrae; range 4-10/ average 6.7) spinal instrumentation and fusion (from lower thoracic or upper lumbar spine to L5 or S1) at a single institution between 1985 and 2003 with a minimum 2-year follow-up (average 4.5 years) was performed. We defined sagittal thoracic decompensation as a progressive kyphotic deformity of the thoracic spine without pseudarthrosis after a long lumbar fusion, which subsequently resulted in a C7 plumb relative to the posterior aspect of the L5-S1 disc >= 8 cm. Results. The prevalence of sagittal thoracic decompensation after long adult lumbar spinal instrumentation and fusion (from distal thoracic or upper lumbar spine) to L5 or S1 was 23% (23/ 99 cases). The etiologies were 14 acute sharp angular kyphoses and 9 long sweeping kyphoses above the instrumented fusion. Of the 14 sharp angular kyphoses, 10 occurred from severe disc degeneration and 4 were caused by compression fractures at the uppermost instrumented vertebra. Conclusion. Risk factors for sagittal thoracic decompensation developing were sagittal imbalance at 8 weeks postoperatively (>= 5 cm), smaller lumbar lordosis compared with thoracic kyphosis (< 10 degrees) at 8 weeks postoperatively, preoperative sagittal imbalance (>= 5 cm), age at surgery (older than 55 years), and associated comorbidities. Sagittal thoracic decompensation adversely affected Scoliosis Research Society 24 outcomes scores.