Vertebral growth after posterior spinal fusion for idiopathic scoliosis in skeletally immature adolescents. The effect of growth on spinal deformity

Abstract

We studied 29 girls and one boy with adolescent idiopathic scoliosis who were at Risser grade 0 at the time of posterior spinal fusion and were followed until maturity (mean 7.8 years). We used serial radiographs to measure the ratio of disc to vertebral height in the fused segments and to detect differential anterior spinal growth and assess its effect on scoliosis, vertebral rotation, kyphosis, and rib-vertebral-angle difference (RVAD). From one year after surgery to the latest review, the percentage anterior disc height decreased by nearly one-half and the percentage posterior disc height by nearly one-third in the fused segments (p < 0.001). There was a 4° increase in mean Cobb angle (p < 0.001), 11 patients (37%) having an increase of between 6° and 10°. There was a significant increase in mean apical rotation by 2° (p = 0.005), and four patients (13%) had an increase of between 6° and 16°. There was little change in kyphosis. There was an increase in mean RVAD by 4° (p = 0.003), seven patients (23%) showing a reduction by 1° to 7°, and 11 (37%) increases of between 6° and 16°. Spinal growth occurs after posterior fusion in adolescents who are skeletally immature, as a result of continued anterior vertebral growth. There is some progression of scoliosis, vertebral rotation, and RVAD, but little change in kyphosis. The increase in deformity is not enough to warrant the use of combined anterior and posterior fusion. The findings arc relevant to the management of progressive curves, the timing and extent of surgery, and the prognosis for progression of deformity in this group of patients.