Cervical sagittal alignment variations and proximal junctional kyphosis after posterior fusion of AIS

Purpose: To determine the changes in cervical sagittal alignment(CSA), measure the incidence of proximal junctional kyphosis(PJK) and identify the correlation between these two parameters following segmental posterior spinal instrumentation and fusion. Materials and methods: From May 2008 to September 2011, 35 patients after posterior instrumentation and fusion to the upper thoracic vertebra due to adolescent idiopathic scoliosis in our department were eligible for this study. Pre and post operative and the last follow-up anteroposterior and lateral radiographs of the entire spine were reviewed. The following radiographic parameters were measured: cervical sagittal alignment, proximal junctional measurement(PJM) of the cobb angle, thoracic kyphosis and lumbar lordosis. In this study, positive values were used to denote kyphosis, while the negative values were used to indicate lordosis. The correlations between cervical sagittal alignment and proximal junctional measurement were also identified. Results: Preoperatively, the average CSA was +2.84 (range,-30.2-+35.6), and 48.6% was kyphosis (17/35); after surgery, the average CSA was +1.78 , and 51.4% was kyphosis(18/35) ; at the last follow up, the average CSA was +1.86, and 54.3% was kyphosis(19/35). Preoperatively, the average PJM was +3.87°; while postoperatively, the average PJM was +8.01°, and the incidence rate of proximal junctional kyphosis was 17.1% (6/35); at the last follow up, the average PJM was +9.70°, and 28.6% was PJK (10/35). significant correlation between the CSA and PJK was found postoperatively(r=-0.302), and at the last follow up (r=-0.564). Conclusion: Cervical kyphosis is frequent in AIS, and the change after posterior spinal fusion surgery is limited. The incidence rate of proximal junctional kyphosis is high, meanwhile there is a significant correlation between cervical sagittal alignment and proximal junctional kyphosis