Comparison of Proximal Junctional Failure and Functional Outcomes Across Varying Definitions of Proximal Junctional Kyphosis

BACKGROUND: Proximal junctional kyphosis (PJK) is a well-recognized complication following surgery for adult spinal deformity (ASD); however, definitions for PJK and its clinical implications can significantly vary by study. This study compares multiple definitions of PJK and describes incidence and clinical significance by definition. METHODS: From 2014 to 2019, patients with ASD who underwent spinal fusion were identified. Nine definitions of PJK were created based on previously established definitions using the following upper instrumented vertebra D2 (UIVD2) sagittal Cobb measurements: A= >= 10 postoperative AND preoperative, B = >= 10 postoperative, C = >= 10 preoperative, D = >= 15 postoperative AND preoperative, E = >= 15 postoperative, F = >= 15 preoperative, G = >= 20 postoperative AND preoperative, H = >= 20 postoperative, I = >20 preoperative. Incidence of PJK was calculated by definition. Area under the curve (AUC) was calculated based on a receiver operating characteristic to assess ability to predict proximal junctional failure (PJF). Univariate analysis was performed to assess association with postoperative Oswestry Disability Index (ODI) scores. - RESULTS: Across 82 patients, the incidence of PJK and AUC by definition was as follows: A= 47%, 0.47; B= 72%, 0.65; C = 49%, 0.45; D = 27%, 0.46; E = 57%, 0.62; F= 27%, 0.46; G= 10%, 0.55; H= 40%, 0.71; I= 10%, 0.55. No definition was associated with postoperative ODI CONCLUSIONS: The incidence of PJK significantly decreased with stricter definitions. Definitions utilizing only postoperative UIVD2 values had higher incidences but were more likely to capture patients who developed PJF. No definition was associated with postoperative ODI scores. UIVD2 >= 20 was best in distinguishing patients who developed PJF.