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 < or = 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 (> or = 45 degrees) before surgery (vs. < 45 degrees, P = 0.009), smaller lumbar lordosis compared with thoracic kyphosis (< 20 degrees) at 8 weeks postoperatively (vs. > or = 20 degrees, 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 degrees (higher lumbar lordosis) is advisable in most circumstances to achieve optimal sagittal balance.