Abstract
Background We sought to determine which aspect of the upper instrumented vertebrae (UIV)—tilt angle or screw angle—was more strongly associated with: (1) proximal junctional kyphosis/failure (PJK/F), (2) other mechanical complications and reoperations, and (3) patient-reported outcome measures (PROMs).
Methods A single-institution, retrospective cohort study was undertaken for patients undergoing adult spinal deformity (ASD) surgery from 2011 to 2017. Only patients with UIV at T7 or below were included. The primary exposure variables were UIV tilt angle (the angle of the UIV inferior endplate and the horizontal) and UIV screw angle (the angle of the UIV screws and superior endplate). Multivariable logistic regression included age, body mass index, osteopenia/osteoporosis, postoperative sagittal vertical axis, postoperative pelvic-incidence lumbar lordosis mismatch, UIV tilt angle, and UIV screw angle.
Results One hundred and seventeen patients underwent adult spinal deformity surgery with a minimum of 2-year follow-up. A total of 41 patients (35.0%) had PJK and 26 (22.2%) had PJF. (1) UIV tilt angle: 96 (82.1%) had lordotic UIV tilt angles, 6 (5.1%) were neutral, and 15 (12.8%) were kyphotic. (2) UIV screw angle: 38 (32.5%) had cranially directed screws, 4 (3.4%) were neutral, and 75 (64.1%) were caudally directed. Both lordotic-angled UIV endplate (OR = 1.06, 95% CI = 1.01–1.12, and P = 0.020) and cranially directed screws (OR = 1.19, 95% CI = 1.07–1.33, and P < 0.001) were associated with higher odds of PJK, with a more pronounced effect of UIV screw angle compared with UIV tilt angle (Wald test, 9.40 vs 4.42). Similar results were found for PJF. Neither parameter was associated with other mechanical complications, reoperations, or patient-reported outcome measures.
Conclusions UIV screw angle was more strongly associated with development of PJK/F compared with tilt angle. Overall, these modifiable parameters are directly under the surgeon’s control and can mitigate the development of PJK/F.
Clinical Relevance Surgeons may consider selecting a UIV with a neutral or kyphotically directed UIV tilt angle when performing ASD surgery with a UIV in the lower thoracic or lumbar region, as well as use UIV screw angles that are caudally directed, for the purprose of decreasing the risk of developing PJK/F.
Level of Evidence 3.
- Adult spinal deformity
- vertebral tilt angle
- upper instrumented vertebra
- screw angle
- proximal junctional kyphosis
- mechanical complications
- patient-reported outcomes
Footnotes
Funding The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests The authors report no conflicts of interest in this work.
Disclosures Dr. Zuckerman reports being an unaffiliated neurotrauma consultant for the National Football League and consultant for Medtronic. Dr. Stephens is a consultant for Nuvasive and Carbofix and receives institutional research support from Nuvasive and Stryker Spine. Dr. Abtahi received an institutional research support from Stryker Spine. No other perceived conflict of interest by any of the listed authors.
Ethics Approval Statement This study was approved by the IRB committee at Vanderbilt University Medical Center (IRB#211290). We certify that the study was performed in accordance with the ethical standards as laid down in the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards.
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