An analysis of sagittal spinal alignment following long adult lumbar instrumentation and fusion to l5 or S1: Can we predict ideal lumbar lordosis?

STUDY DESIGN. A retrospective study. OBJECTIVE. To determine factors controlling sagittal spinal balance after long adult lumbar instrumentation and fusion from the thoracolumbar spine to L5 or S1. SUMMARY OF BACKGROUND DATA. To our knowledge, no study on postoperative sagittal balance following long adult spinal instrumentation and fusion to L5 or S1 has been published. METHODS. A clinical and radiographic assessment of 80 patients with adult lumbar deformity (average age 53.4 years) who underwent long (average 7.6 vertebrae, 5-11 vertebrae) segmental posterior spinal instrumentation and fusion from the thoracolumbar spine to the L5-S1 (average 4.5 years, 2-15.8-year follow-up) was performed. We defined the optimal sagittal balance (n = 42) group, the distance from C7 plumb to superior posterior endplate of S1 ≤3.0 cm, and the suboptimal sagittal balance (n = 38) group, the distance from C7 plumb to superior posterior endplate of S1 >3.0 cm at ultimate follow-up. RESULTS. The optimal sagittal balance group (C7 plumb, average -0.6 ± 2.5 cm) had the larger average angle differences between lumbar lordosis and thoracic kyphosis (P < 0.0001), preoperative smaller pelvic incidence (P = 0.007), smaller average thoracolumbar junctional angle (T10-L2) increase (P < 0.0001), and bigger lumbar lordosis angle increase (P = 0.014) at ultimate follow-up. Patients with optimal sagittal balance at ultimate follow-up had significantly higher total Scoliosis Research Society 24 outcome scores than those with suboptimal sagittal balance (P = 0.015). Risk factors that were statistically significant for the suboptimal sagittal balance group included pelvic incidence compared with lumbar lordosis (<45°) before surgery (vs.- <45°, P = 0.009), smaller lumbar lordosis compared with thoracic kyphosis (<20°) at 8 weeks postoperatively (vs.- ≥ 20°, P = 0.013), and older than 55 years of age at surgery (vs.- 55 years or younger, P = 0.024). CONCLUSION. A sagittal Cobb angle difference between lumbar lordosis and thoracic kyphosis of >20°(higher lumbar lordosis) is advisable in most circumstances to achieve optimal sagittal balance.