Evaluation of the sagittal profile in patients with thoracic adolescent idiopathic scoliosis Lenke type 1 following posterior correction

The principle philosophy of posterior spinal instrumentation and fusion (PSIF) for the treatment of adolescent idiopathic scoliosis (AIS) has changed during recent decades. In the past the treatment of AIS mainly focused on correction of the major curve in the frontal plane while the sagittal profile and balancing were only of inferior interest in treatment planning. Various long-term outcome studies have demonstrated that many AIS patients developed a flatback syndrome (decrease of thoracic kyphosis and lumbar lordosis) associated with pain. It was concluded that treatment of AIS should consider the sagittal profile and balance; however, there are only few studies addressing additional procedures, which include the correction of the sagittal profile. The purpose of this study was to evaluate the effects of different posterior correction techniques on sagittal profile and balance. A total of 36 consecutive patients with thoracic AIS, who were treated with selective thoracic posterior correction were included in this retrospective study. The patients were further assigned to three different subgroups according to different surgical strategies: A: pedicle screws, B: long-head pedicle screws and C: additional Ponte osteotomy. Standardized radiographs in the standing position of the whole spine in two planes were evaluated before and at least 2 years after correction for all patients and a subgroup analysis was done to identify differences between the three groups. A significant correction of the major curve was achieved in all three groups (p < 0.001). There was a significant difference between the groups with groups B and C showing significantly higher levels of major curve correction in comparison to group A (p < 0.001). Concerning the sagittal profile, there was a significant difference in the development of thoracic kyphosis (TK) and lumbar lordosis (LL). While a significant reduction of TK and LL was found in groups A and B after surgery, a significant increase of TK and LL was noted in group C which was associated with a decrease of pelvic tilt and an increase of sacral slope. The 2-year follow-up showed the lowest ODI-% value only in group C which was positively correlated with reduction in pelvic tilt. The results of this study underline that the PSIF technique alone using pedicle screws leads to a satisfactory correction in the frontal plane but is associated with adverse effects on the sagittal profile (flat back syndrome), corroborating previous studies. It was further shown that significant improvements of sagittal parameters were achieved by adding techniques for the lengthening of the dorsal thoracic column. This approach can therefore be recommended for the treatment of AIS Lenke type 1.