Immediate Postoperative Change in the Upper Instrumented Screw-Vertebra Angle is a Predictor for Proximal Junctional Kyphosis and Failure

STUDY DESIGN: Retrospective review. OBJECTIVES: To determine if change in position of upper instrumented vertebral (UIV) screw between intraoperative prone and immediate postoperative standing radiographs is a predictor for proximal junctional kyphosis or failure (PJK/PJF). SUMMARY OF BACKGROUND DATA: Cranially directed UIV screws on postoperative radiographs have been found to be associated with PJK. Change in the screw position between intraoperative and immediate postoperative radiographs has not been studied. MATERIALS AND METHODS: Patients with posterior fusion greater than or equal to three levels and UIV at or distal to T8, and minimum two-year follow-up were identified from a single-center database. Primary outcomes were radiographic PJK/PJF or revision for PJK/PJF. Demographic, surgical, and radiographic variables, including intraoperative screw-vertebra (S-V) angle, change in S-V angle, direction of UIV screw (cranial-neutral-caudal), and rod-vertebra (R-V) angle were collected. RESULTS: Totally, 143 cases from 110 patients were included with a mean age of 62.9 years and a follow-up of 3.5 years. Fifty-four (38%) cases developed PJK/PJF, of whom 30 required a revision. Mean S-V angle was -0.9°±5.5° intraoperative and -2.8°±5.5° postoperative. The group with PJK/PJF had a mean S-V angle change of -2.5°±2.4 while the rest had a change of -1.0°±1.6 ( P =0.010). When the change in S-V angle was <5°, 33% developed PJK, this increased to 80% when it was ≥5° ( P =0.001). Revision for PJK/PJF increased from 16% to 60% when S-V angle changed ≥5° ( P =0.001). Regression analysis showed S-V angle change as a significant risk factor for PJK/PJF ( P =0.047, OR=1.58) and for revision due to PJK/PJF ( P =0.009, OR=2.21). CONCLUSIONS: Change in the S-V angle from intraoperative prone to immediate postoperative standing radiograph is a strong predictor for PJK/PJF and for revision. For each degree of S-V angle change, odds of revision for PJK/PJF increases by x2.2. A change of 5° should alert the surgeon to the likely development of PJK/PJF requiring revision. LEVEL OF EVIDENCE: Level II.