THE SAGITTAL PELVIC TILT INDEX AS A CRITERION IN THE EVALUATION OF SPONDYLOLISTHESIS - PRELIMINARY-OBSERVATIONS

Study Design. Radiographic analysis of a pediatric population with spo ndylolisthesis was performed to examine sagittal plane pelvic rotation and degree of slip over time. Objectives. To determine whether the de gree of standing sagittal offset of L5 with respect to the acetabulum correlated with slip progression and symptoms. Summary of Background D ata, The natural history of isthmic spondylolisthesis remains unclear. Attempts to predict slip progression in the clinical setting, and thu s the possible need for eventual surgical intervention, remain impreci se. Predicting slip progression based on sagittal alignment of the L5 vertebra with respect to the acetabulum has been proposed by some inve stigators. Methods. Fifty-two children and adolescents were followed c linically and radiographically for an average of 5.6 years. Serial lat eral standing radiographs that included the hips and lumbar spine were measured to compute a sagittal pelvic tilt index. The latter value is a ratio of relative distances from the center of S2 to the projection of L5 and the center of the femoral heads on the horizontal. Results. Of the 52 patients studied, 38 have remained asymptomatic without sig nificant slip progression or change in sagittal pelvic tilt index rati o. Of the original group, 13 patients had significant symptoms and rev ealed a decrease in the sagittal pelvic tilt index over time. Eight of the 13 stabilized at the end of adolescence, whereas 5 had continued decrease in the sagittal pelvic tilt index ratio. These five required operative treatment for pain and progressive slip. Conclusions. The sa gittal pelvic tilt index gives the examiner an objective measure of th e stability of the lumbosacral junction by quantifying the relationshi p between S2, the center of the hip, and L5. A decreasing sagittal pel vic tilt index ratio in this preliminary series correlated with slip p rogression and risk of conservative treatment failure, whereas those p atients with a stable sagittal pelvic tilt index did not progress and remained clinically asymptomatic.