Spine Journal - 2026-07-18 - Journal Article
Global sagittal mismatch, not isolated L1 pelvic angle achievement, is associated with mechanical failure after adult spinal deformity surgery.
Kim TY, Lin JD, Lombardi JM, Menger R, Pham MH, Tan LA, Tuchman A, Zuckerman SL, Osorio JA, Comprehensive Spine Study Group
Topics
Key Takeaway
Global T4-L1PA mismatch (OR 1.10 per degree) independently predicts mechanical failure after ASD surgery, while achieving the ideal L1PA target does not.
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Summary
This study asked whether achieving the ideal L1PA (0.5×PI−19°) or restoring global sagittal harmony (T4-L1PA mismatch) better predicts mechanical failure after long-segment ASD fusion to the pelvis. In 108 patients with 30.6% mechanical failure rate, multivariable logistic regression showed ideal L1PA achievement was not independently associated with failure, while absolute T4-L1PA mismatch carried an OR of 1.10 per degree (95% CI 1.01–1.20, p=0.03). Higher BMI was also independently associated with failure (OR 1.06, p=0.04).
Key Limitation
The 30.6% failure rate in only 108 patients from a single registry epoch (2019–2023) limits generalizability and statistical power, and the study cannot determine whether T4-L1PA mismatch is modifiable intraoperatively or simply a marker of overall deformity severity.
Original Abstract
BACKGROUND CONTEXT
Mechanical failure remains a common complication following adult spinal deformity (ASD) surgery. Although postoperative alignment targets such as the ideal L1 pelvic angle (L1PA) have been proposed to reduce failure risk, the relative importance of achieving local alignment targets versus restoring global sagittal harmony remains unclear.
PURPOSE
To evaluate the associations between postoperative L1PA metrics, global T4-L1PA mismatch, and mechanical failure following ASD surgery.
STUDY DESIGN
Retrospective analysis of a prospective, multicenter ASD registry.
PATIENT SAMPLE
Adult patients undergoing long-segment fusion from the lower thoracic spine to L2 extending to the pelvis between 2019 and 2023 with minimum 2-year follow-up.
OUTCOME MEASURES
Mechanical failure, defined as proximal junctional kyphosis/failure, rod fracture, implant failure, or pseudarthrosis requiring revision.
METHODS
Ideal L1PA was defined as 0.5×pelvic incidence-19°, with achievement defined as absolute deviation ≤2° on first standing postoperative radiograph. Global alignment was assessed using signed and absolute T4-L1PA mismatch. Univariable comparisons and multivariable logistic regression models adjusted for age, sex, and body mass index (BMI) were performed using R.
RESULTS
A total of 108 patients were included, of whom 33 (30.6%) experienced mechanical failure. In multivariable analyses, neither signed nor absolute deviation from ideal L1PA was independently associated with failure. In contrast, greater absolute T4-L1PA mismatch was independently associated with mechanical failure (OR 1.10 per degree; 95% CI 1.01-1.19; p = 0.04), whereas signed mismatch was not. When both variables were included in the same model, T4-L1PA mismatch remained significant (OR 1.10; 95% CI 1.01-1.20; p = 0.03), while ideal L1PA achievement did not. Higher BMI was also independently associated with failure (OR 1.06; CI 1.00-1.13; p = 0.04).
CONCLUSIONS
While achieving ideal L1PA goal did not mitigate the risk of mechanical failure following adult spinal deformity surgery, greater global sagittal mismatch, as measured by absolute T4-L1PA deviation, was independently associated with increased failure risk. These findings suggest that restoration of global sagittal harmony, rather than isolated local alignment targets, is critical for mechanical durability after ASD surgery.