Effect of cage geometry on sagittal alignment after posterior lumbar interbody fusion for degenerative disc disease.

PURPOSE To compare the sagittal alignment of the lumbar spine after one-segment posterior lumbar interbody fusion (PLIF) using the horizontal cylinder (HC) or open box (OB) type cage. METHODS 66 patients underwent instrumented one-segment PLIF with bone grafting for lower lumbar degenerative disease. HC-type cages were used in 33 men and 13 women aged 20 to 73 (mean, 47) years between September 2001 and July 2004. OB-type cages with a 3-degree lordotic angle were used in 9 men and 11 women aged 25 to 70 (mean, 53) years between July 2004 and September 2006. Pre- and post-operative lumbar lordosis and intervertebral body angles in the fused and upper adjacent levels in the 2 groups were compared. RESULTS There was no significant difference between the 2 groups with regard to changes in the lumbar lordosis and intervertebral body angle in the fused and upper adjacent levels. In both groups, the upper adjacent intervertebral body angle increased significantly by about 2 degrees. CONCLUSION Lumbar alignment was similar after the use of the HC- or OB-type cages. This may be due to the surgical procedure and insufficient cage lordotic angle.