Sagittal Thoracic Decompensation (STD) Following Adult Lumbar Spinal Instrumentation and Fusion to L5 or S1: Causes, Incidence, and Risk Factors Analysis

Summary: The overall incidence of sagittal thoracic decompensation (STD) after long adult lumbar deformity spinal instrumentation and fusions to L5 or S1 (out of 95 patients with 2-15.8 years follow-up) was 24% due to severe suprajacent disc degeneration, compression fracture, and global progression of the thoracic kyphosis. Age at operation >55 years and preoperative sagittal imbalance significantly increased the risks of a subsequent STD and SRS-24 outcomes scores were significantly affected by STD.

Purpose: To analyze the causes, incidence of and risk factors for sagittal thoracic decompensation (STD) in adult lumbar deformity spinal instrumentation and fusion to L5 or S1.

Methods: A clinical and radiographic assessment of 95 adult lumbar spinal deformity patients (average age, 55.8 years) who underwent long lumbar (fusion from the lower thoracic spine to L5-S1) spinal instrumentation and fusion between 1985 and 2002 with a minimum 2-year follow up (average, 4.5 years) were analyzed. We define STD as a progressive kyphotic deformity of the thoracic spine after a lumbar fusion which subsequently resulted in a C7 plumb relative to the posterior aspect of the L5-S1 disc at 8cm or greater.

Results: The overall incidence of STD after long adult lumbar spinal deformity fusions to L5 or S1 was 24% (23/ 95 cases): 10 severe suprajacent disc degenerations, 5 compression fractures, and 8 global progressions of the thoracic kyphosis. Factors which were statistically significant were age at surgery >55 years (20/23 patients, p=0.003) and preoperative sagittal imbalance (C7 plumb to S1>5cm; 16/23 patients, p=0.004) to overall thoracic decompensation. Proximal stop at L1 or L2 demonstrated a higher incidence for severe proximal disc degeneration (p<0 .001). Patients with subsequent STD had significantly lower total SRS-24 outcome scores than those without (75/120 vs 89/120, p="0.004)."

Conclusion: The overall incidence of STD after long adult lumbar spinal deformity instrumentation and fusions to L5 or S1 was 24%. Age at operation >55 years and preoperative sagittal imbalance with a C7 plumb to S1>5cm significantly increased the risks of STD. Proximal stop at L1 or L2 demonstrated a higher proximal junctional angle increase and more severe junctional disc degeneration. SRS-24 outcomes scores were adversely affected by STD.