Reciprocal sagittal alignment changes after posterior fusion in the setting of adolescent idiopathic scoliosis

Abstract

Surgical adolescent idiopathic scoliosis (AIS) management can be associated with loss of thoracic kyphosis and a secondary loss of lumbar lordosis leading to iatrogenic flatback. Such conditions are associated with poorer clinical outcomes during adulthood. The aim of this study was to evaluate sagittal plane reciprocal changes after posterior spinal fusion in the setting of AIS. Thirty consecutive adolescents (mean age 14.6years) with AIS Lenke 1, 2 or 3 were included in this retrospective study with 2year follow-up. Full-spine standing coronal and lateral radiographs were obtained preoperatively, at 3 and 24months postoperatively. Coronal Cobb angle, thoracic kyphosis (TK) and lumbar lordosis (LL) were measured. Surgical procedure was similar in all the cases, with use of pedicular screws between T11 and the lowest instrumented vertebra (≥L2), sublaminar hooks applied in compression at the upper thoracic level and sub-laminar bands and clamps in the concavity of the deformity. Statistical analysis was done using t test and Pearson correlation coefficient. Between preoperative and last follow-up evaluations a significant reduction of Cobb angle was observed (53.6° vs. 17.2°, p<0.001). A significant improvement of the instrumented thoracic kyphosis, TK (19.7° vs. 26.2°, p<0.005) was noted, without difference between 3 and 24months postoperatively. An improvement in lumbar lordosis, LL (43.9° vs. 47.3°, p=0.009) was also noted but occurred after the third postoperative month. A significant correlation was found between TK correction and improvement of LL (R=0.382, p=0.037), without correlation between these reciprocal changes and the amount of coronal correction. Results from this study reveal that sagittal reciprocal changes occur after posterior fusion when TK is restored. These changes are visible after 3months postoperatively, corresponding to a progressive adaptation of patient posture to the surgically induced alignment. These changes are not correlated with coronal plane correction of the deformity. In the setting of AIS, TK restoration is a critical goal and permits favorable postural adaptation. Further studies will include pelvic parameters and clinical scores in order to evaluate the impact of the noted reciprocal changes.