Additional growth of the spine and changes in spinal alignment after posterior spinal fusion in adolescent idiopathic scoliosis

OBJECTIVE: Previous studies have evaluated growth in spinal height immediately following surgical posterior correction of idiopathic scoliosis, yet have not reported on further spinal growth following surgery. The aims of this study were to investigate the characteristics of spinal growth after scoliosis surgery and determine whether they affect spinal alignment. METHODS: The study included 91 patients (mean age 13.93 years) who underwent spinal fusion using pedicle screws for the treatment of adolescent idiopathic scoliosis (AIS). The study population included 70 female and 21 male patients. The height of the spine (HOS), length of the spine (LOS), and spinal alignment parameters were measured on anteroposterior and lateral radiographs. A stepwise multiple linear regression analysis was used to examine the variables that affected HOS gain from growth. The patients were divided into two groups, the growth group and the nongrowth group, according to whether the HOS gain from growth exceeded 1 cm, to analyze the effect of spinal growth on its alignment. RESULTS: The mean (± SD) HOS gain from growth was 0.88 ± 0.66 (range -0.46 to 3.21) cm, with 40.66% of patients exhibiting growth ≥ 1 cm. This increase was significantly related to young age, male sex, and a small Risser stage (sex: b = -0.532, p < 0.001, male = 1, female = 2; Risser stage: b = -0.185, p < 0.001; age: b = -0.125, p = 0.011; adjusted R2 = 0.442). The variation in LOS was similar to that of HOS. Thoracic kyphosis and upper instrumented vertebra-lowest instrumented vertebra Cobb angle were reduced in both groups, with a greater reduction observed in the growth group. Patients with an increase in HOS < 1 cm showed a larger lumbar lordosis and a greater tendency for the sagittal vertical axis (SVA) to shift backward and the pelvic tilt to decrease (anteverted pelvis) than in the growth group. CONCLUSIONS: The spine still has growth potential after corrective fusion surgery for AIS, and 40.66% of the patients in this study continued to vertically grow by 1 cm or more. Unfortunately, the height changes cannot be accurately predicted by currently measured parameters. Changes in the sagittal alignment of the spine may affect the vertical growth increment.