Proximal junctional kyphosis in adult spinal deformity: a novel predictive index.

PURPOSE: Proximal junctional kyphosis (PJK) is a devastating complication for adult spinal deformity (ASD) after correction surgery. However, there is no consensus on the risk factors of PJK, and whether it can be predicted remains unknown. The aim of this study is to detect the primary risk factors for PJK in ASD, and introduce a novel index for prediction of PJK.

METHODS: Medical records of 62 ASD patients receiving correction surgery from January 2010 to January 2015 were analyzed. Spino-pelvic parameters were evaluated on lateral films before surgery, at 2 weeks' and at follow-up. Primary factors for PJK were evaluated. PJK index was proposed and verified.

RESULTS: Cervical lordosis at follow-up, postoperative C2-C7 SVA, C2-C7 SVA at follow-up, postoperative T1 slope, T1 slope at follow-up, preoperative TLK, LL at follow-up, preoperative PT, postoperative PT, PT at follow-up, preoperative SS, postoperative SS, SS at follow-up, preoperative PT/SS, postoperative PT/SS and PT/SS at follow-up were significantly different between ASD with and without PJK. Adjusted logistic regression analysis showed that preoperative TLK, LL at follow-up, preoperative PT/SS and PT/SS at follow-up were primary factors for PJK. PJK index was defined as 0.160*LL at follow-up-0.121*preoperative TLK-4.625*preoperative PT/SS-3.315*PT/SS at follow-up. On the basis of ROC curve, if PJK index was smaller and larger than - 2, the occurrence rate of PJK and non-PJK was 82 and 95%, respectively.

CONCLUSIONS: Preoperative TLK, LL at follow-up, preoperative PT/SS and PT/SS at follow-up were primary factors for PJK. PJK index could be used to predict occurrence of PJK effectively. These slides can be retrieved under Electronic Supplementary Material.