Research

Introduction: The major deformity for isthmic spondylolisthesis occurs at the lumbosacral junction involving translation and angulation in the sagittal plane. This may significantly impair sagittal balance of the trunk and spine. There have been few studies investigating the role of the pelvis in sagittal balance. The goal of this study was to evaluate any changes that may occur in pelvic parameters and sagittal balance following surgery.

Methods: The pre-operative and post-operative sagittal plane x-rays of 30 patients undergoing surgery for high-grade isthmic spondylolisthesis were evaluated. All patients had either a Grade 4 or Grade 5 spondylolisthesis. Parameters measured included thoracic kyphosis, lumbar lordosis, center sacral axes, difference between hip and center sacral axes (Hip-CSA), pelvic incidence, sacral slope, and grade of spondylolisthesis. Changes from pre-operative to post-operative were analyzed.

Results: Significant improvements following surgery were observed in the L5 incidence, sacral slope, lordosis and percent slip. On average the positional pelvic parameters (pelvic incidence, pelvic tilt) do not change after reduction, some individual patients had decreases of the pelvis tilt and others were increased. The spinal axis as measured by Hip-CSA did not change significantly.

Conclusions: Changes in sagittal plane parameters of the spine and pelvis are seen following reduction and fusion for high-grade spondylolisthesis, including L5 incidence, sacral slope, percent slip and lordosis angle. These parameters appear to be important in restoring normal sagittal plane balance and morphology of the spine. The pelvic positional parameters do not appear to be important.