Cervical sagittal plane decompensation after surgery for adolescent idiopathic scoliosis: an effect imparted by postoperative thoracic hypokyphosis

Object. Several studies have characterized the relationship among postoperative thoracic, lumbar, and pelvic alignment in the sagittal plane. However, little is known of the relationship between postoperative thoracic kyphosis and sagittal cervical alignment in patients with adolescent idiopathic scoliosis (AIS) treated with all pedicle screw constructs. The authors examined this relationship and associated factors. Methods. A prospective database of pediatric patients with AIS undergoing spinal fusion between 2003 and 2005 was reviewed for those who received predominantly pedicle screw constructs for Lenke Type 1 or Type 2 curves. Parameters analyzed on pre- and postoperative radiographs were the fusion levels; cervical, thoracic, and lumbar sagittal balance; and C-2 and C-7 plumb lines. Results. Preoperatively, 6 (Group A) of the 22 patients included in the study had frank cervical kyphosis (mean angle 13.0 degrees) with mean associated thoracic kyphosis of 27.2 degrees (range 16 degrees-37 degrees). Postoperatively, cervical kyphosis 13.0 degrees) remained in the patients in Group A along with mean thoracic kyphosis of 17.7 degrees (range 4 degrees-26 degrees, p < 0.05). Preoperatively, the remaining 16 of 22 patients had neutral to lordotic cervical alignment (mean -13.8 degrees) with thoracic kyphosis (mean 45 degrees, range 30 degrees-76 degrees). Postoperatively, 8 (Group B) of these 16 patients demonstrated cervical sagittal decompensation (> 5 degrees kyphosis), with 6 showing frank cervical kyphosis (10.5 degrees, p < 0.05). In Group B, the mean postoperative thoracic kyphosis was 25.6 degrees (range 7 degrees-49 degrees, p < 0.05). The other 8 patients (Group C) had mean postoperative thoracic kyphosis of 44.1 degrees (range 32 degrees-65 degrees), and there was no cervical decompensation (p < 0.05). Conclusions. The sagittal profile of the thoracic spine is related to that of the cervical spine. The surgical treatment of Lenke Type 1 and 2 curves by using all pedicle screw constructs has a significant hypokyphotic effect on thoracic sagittal plane alignment (19 [86%] of 22 patients). If postoperative thoracic kyphosis is excessively decreased (mean 25.6 degrees, p < 0.05), the cervical spine may decompensate into significant kyphosis. (DOI: 10.3171/2011.6.SPINE1012)