Risk Factors of Proximal Junctional Kyphosis in Adolescent Idiopathic Scoliosis—The Pelvis and Other Considerations

Study Design Prospective multicenter database study. Objectives To assess the incidence of proximal junctional kyphosis (PJK) in operative adolescent idiopathic scoliosis (AIS) using contemporary surgical techniques and to identify risk factors for PJK. Summary of Background Data The incidence of PJK has been reported as high as 46% in AIS. Factors associated with PJK have been incompletely explored. Methods Prospectively enrolled 851 AIS patients (2000–2011, 78.5% female, average 14.4 years) were evaluated 2 years postoperatively. Radiographic and sagittal spinopelvic parameters and rod contour angle (RCA), a new measure that reflects the proximal contouring of the rod, were independently evaluated for association with PJK based on Lenke type. Multivariate logistic regression with backward elimination was performed to identify risk factors for PJK. Results Overall PJK incidence was 7.05% and varies based on Lenke type (Lenke 1, 6.35%; Lenke 2 and 4, 4.39%; Lenke 3 and 6, 11.64%; and Lenke 5, 8.49%; p =.06). Among patients with Lenke 1 curves, risk factors for PJK were loss of kyphosis after surgery, and stopping caudal to the upper end vertebra (UEV). The risk of developing PJK increases by 7.1% with each lost degree of kyphosis compared with preoperation that occurs after the instrumentation is placed. For Lenke 2 and 4 curves, loss of kyphosis and more lordotic (negative) RCA were risk factors for PJK. For Lenke 3 and 6 curves, larger preoperative T5–T12 kyphosis was the only significant risk factor for PJK. Upper instrumented vertebra (UIV) at or cephalad to the UEV was associated with increased risk of PJK in Lenke 5 curves, which was contrary to the finding for Lenke 1 curves. No significant correlation was found between sagittal pelvic parameters and developing PJK. Conclusion The incidence of PJK in patients after surgery for AIS is 7.05% and varies based on Lenke type. Loss of kyphosis, larger preoperative kyphosis, UIV caudal to the proximal UEV (Lenke 1), UIV at or cephalad to the UEV (Lenke 5), and decreased RCA were the major risk factors for PJK in AIS. Level of Evidence Level II.