Sagittal plane correction in idiopathic scoliosis.
STUDY DESIGN: Patients with idiopathic scoliosis who had undergone posterior fusion by means of posterior multisegmented hook instrumentation were studied retrospectively. OBJECTIVES: To present the changes in projected thoracic hypokyphosis and the behavior of lumbar lordosis within and below the fusion. SUMMARY OF BACKGROUND DATA: Scoliosis is a three-dimensional deformity of the spine. The idiopathic cases usually exhibit a flattening of the sagittal curves, which had further deteriorated when the Harrington technique was used. The consequences included the flat back, angular increase of the lumbar lordosis below the fusion, and low back pain. Previous studies showed no or only moderate correction of thoracic hypokyphosis when using Cotrel-Dubousset instrumentation or its modifications were used. Harrington rod systems resulted in decreased lumbar lordosis in the fusion area and increased lordosis below the fusion. No background data were found concerning the effects of multisegmented hook instrumentation on the lumbar spine within and below the fusion. METHODS: For this study, 306 patients with idiopathic scoliosis who had undergone posterior spinal fusion with multisegmented hook systems using the derotation maneuver were analyzed after a mean follow-up period of 5 years and 4 months. The coronal plane curvature, the sagittal plane projection of the thoracic kyphosis, and the lumbar lordosis within and below the fusion were evaluated. RESULTS: The average coronal plane correction was 67.1%. Analysis of the sagittal contours demonstrated that the preoperative thoracic hypokyphosis (less than 20 degrees between T4 and T12) increased by an average of 12 degrees, and that 55.1% of hypokyphotic backs were corrected to the normal range (20 degrees to 40 degrees ). In patients with frank lordosis (kyphosis less than 10 degrees ), the degree of correction was higher (average, 16 degrees ), but complete correction was achieved in only 38.5% of the cases. In patients with mild lordosis (kyphosis between 10 degrees and 20 degrees ), the average correction was 8 degrees, and 71.3% of the patients were in the normal range after surgery. The normal preoperative thoracic kyphosis was preserved in 81.3% of the cases. In the lumbar area, the Cotrel-Dubousset instrumentation was capable of correcting the preoperative hypolordosis (less than -20 degrees between L1 and L5) in 94.4% of the cases. The normal preoperative lordosis (-20 degrees to -60 degrees ) was preserved in 97.9% of the cases. The hyperlordosis was corrected in all cases. Analysis of the data in terms of lower fusion limit showed that the lower the caudal hook, the greater the increase in the segmental lordosis within the fusion, without any increase distal to the fusion. No segmental hyperlordosis was observed below the fusion. CONCLUSIONS: The Cotrel-Dubousset technique ensures considerable sagittal correction of the spine. In the course of scoliosis correction, it is possible to preserve the normal preoperative sagittal profile of the spine, to correct the slightly flattened thoracic kyphosis, to increase materially the kyphosis of the frankly hypokyphotic spine, to preserve or restore normal lumbar lordosis in a considerable percentage of the cases, to avoid angular segmental hyperlordosis at the level of the first disc below the fusion, and to avoid retrolisthesis of the last fused vertebra.