Superior Extension of Upper Instrumented Vertebrae in Distraction-based Surgery: A Surrogate for Clinically Significant Proximal Junctional Kyphosis

Background Proximal junctional kyphosis (PJK) is a reported complication of distraction-based growth-friendly surgery for early-onset scoliosis (EOS). A potential consequence of PJK is revision surgery with superior extension of the upper instrument vertebrae (UIV). The purpose of this study was to determine the risk of radiographic and clinically significant PJK during growth-friendly surgery. Methods This is a retrospective review of children treated with distraction-based growth-friendly surgeries from two EOS registries with minimum two-year follow-up. PJK is defined as clinically significant in this study if surgery with superior extension of the UIV was performed. Results Of 419 total patients, there was a 20% risk of developing clinically significant PJK (24% rib vs. 15% spine-based anchors, p = .03). These patients had a mean preoperative age of 5.6 years (5.2-year rib vs. 6.0-year spine, p < .001), scoliosis of 73° (69° rib vs. 77° spine, p < .001), and kyphosis of 51° (47° rib vs. 56° spine, p < .01). Regression analysis demonstrated that these differences in age, scoliosis, and kyphosis between anchor type did not account for a significant proportion of the measured variance. Conclusions There was a 20% risk of developing clinically significant PJK, with a slightly higher risk for patients treated with rib-based proximal anchors (24%) than for those patients treated with spine-based proximal anchors (15%). Level of Evidence Level III.