1215 Not All Proximal Junctional Kyphosis is Created Equally: A Deep Dive into Different Mechanisms of PJK and Their Severity

INTRODUCTION: Several different mechanisms contribute to proximal junctional kyphosis/failure (PJK/F) in adult spinal deformity (ASD) surgery, each of varying severity. METHODS: A single-institution, retrospective cohort study was performed for patients undergoing ASD surgery from 2009-21. The primary outcome was the mechanism of PJK/F. Secondary outcomes included time to PJK/F, PJA, reoperation, and neurologic deficit. RESULTS: Among 238 patients undergoing ASD surgery, 113 (47.5%) developed PJK/F with the following overlapping mechanisms: screw pullout (N=8, 7.1%), UIV fracture (N=17, 15.0%), UIV+1 fracture (N=9, 8.0%), screw haloing (N=14, 31.0%), fracture dislocation (N=13, 11.5%), supradjacent disc degeneration with or without listhesis (N=35, 31.0%), and radiographic kyphosis only (N=17, 15.0%). Mean time to diagnose PJK/F was 23.1±20.6m as follows: screw pullout (time to diagnosis=23.9m, PJA=19.9º), UIV fracture (23.8m, 25.6º), UIV+1 fracture (21.8m, 28.0º), screw haloing (21.8m, 19.0º), fracture dislocation (18.7m, 37.9º), disc degeneration (23.5m, 25.6º), and radiographic kyphosis only (25.9m, 19.5º) (p=0.986, p<0.001). Reoperation occurred in 45 (39.8%) patients as follows: 6/8 (75.0%) screw pullout, 6/17 (35.2%) UIV fracture, 4/9 (44.4%) UIV+1 fracture, 9/14 (64.3%) screw haloing, 6/13 (46.1%) fracture dislocation, 9/35 (25.2%) disc degeneration, and 7/17 (41.1%) radiographic kyphosis only (p=0.068). Neurologic Deficits occurred in 15 (13.3%) patients. CONCLUSIONS: Supradjacent disc degeneration was the most common mechanism causing PJK. Fracture dislocation presented earliest and with the most kyphosis. Reoperation occurred most often with screw pullout, fracture dislocation, and UIV+1 fracture. The overall rate of neurologic deficit was low and occurred most often with screw haloing and UIV+1 fracture.