Distinct Mechanisms of Proximal Junctional Kyphosis and Their Clinical Implications.

Abstract

Retrospective cohort study. In patients undergoing adult spinal deformity (ASD) surgery, we sought to: (1) describe mechanisms of Proximal junctional kyphosis/failure (PJK/F), and (2) compare time-to-diagnosis, proximal junctional angle (PJA), reoperation, and neurologic deficit between PJK/F mechanisms. PJK/F includes several different failure mechanisms. ASD patients (2009-21) with ≥5-level fusion, sagittal/coronal deformity, and 2-year follow-up were included. Primary outcome was mechanism of PJK/F, defined as a PJA≥10° and ≥10° change from preoperative. PJK/F mechanisms were: screw pullout, UIV fracture, UIV+1 fracture, screw lucency, fracture dislocation, supradjacent disc-degeneration with/without listhesis, and radiographic kyphosis only. Descriptive and bivariate statistics were performed. Among 238 patients, 113(47.5%) developed PJK/F: screw pullout (7.1%), UIV fracture (15.0%), UIV+1 fracture (8.0%), screw lucency (12.4%), fracture dislocation (11.5%), supradjacent disc-degeneration with/without listhesis (31.0%), and radiographic kyphosis only (15.0%). One mechanism was seen in 91(80.5%) patients, and 2+ mechanisms in 22(19.5%). Median time-to-PJK/F diagnosis was 5.3 (IQR: 1.4-17.7) months: screw pullout (8.3m, PJA=19.9°), UIV fracture (3.8m, 25.6°), UIV+1 fracture (11.8m, 28.0°), screw lucency (12.8m, 19.0°), fracture dislocation (1.6m, 27.9°), disc-degeneration (4.5m, 25.6°), and radiographic kyphosis only (6.1m, 19.5°) (P=0.986, P<0.001). Reoperation occurred in 45(39.8%) patients: 6/8(75.0%) screw pullout, 6/17(35.2%) UIV fracture, 4/9(44.4%) UIV+1 fracture, 9/14(64.3%) screw lucency, 6/13(46.1%) fracture dislocation, 9/35(25.2%) disc-degeneration, and 5/17(29.4%) radiographic kyphosis only (P=0.068). Neurologic Deficits occurred in 15(13.3%) patients: UIV fracture 3(17.6%), UIV+1 fracture 2(22.2%), screw lucency 5(35.7%), fracture dislocation 2(15.4%), disc-degeneration 2(5.7%), kyphosis only 1(5.9%) (P=0.093). Supradjacent disc-degeneration was the most common PJK mechanism. Fracture dislocation presented earliest and with greatest kyphosis. Reoperation was most frequent with screw pullout, lucency, and UIV+1 fracture, while neurologic deficits were most common with lucency and UIV+1 fracture. These results demonstrate that PJK/F occurs in many different forms and ideally should be analyzed independently to further improve our treatment of this vexing complication.