Measurement of gravity line position 15-25 years after Harrington-spondylodesis in adolescent idiopathic scoliosis

Aim: A prospective analysis was performed to evaluate the relation between sagittal spinal morphology, gravity line position and morphological parameters of the pelvis and lumbar spine. Method: 25 patients with a mean follow-up of 23 (15-37) years after thoracic Harrington distraction spondylodesis were included. Standing lateral full spine radiographs were performed while patients were standing on a force plate. Pelvic angles according to Duval-Beaupere were measured. Results: Pelvic incidence varied from 30degrees to 76degrees (mean 52.1degrees +/- 12.5degrees). Mean sacral slope was 36.4degrees ( +/- 7.8degrees). The average thoracic kyphosis (23.6degrees +/- 14.3degrees) and lumbar lordosis (36.4degrees +/- 9.2degrees) were diminished. The gravity line position was on average 10.9 mm ( +/- 21.6mm) posterior to the center of the femoral heads. Conclusion: Our method quantifies the relationship between the gravity line position and pelvic parameters according to Duval-Beaupere. The homogenous study group of patients with AIS after Harrington spondylodesis is characterized by decreased lumbar and thoracic profile and posterior displacement of the gravity line position.