Spine - 2026-05-15 - Journal Article
Mechanical Failures as Predicted by Achieving Local Versus Global T4-L1 Hip Axis Goals : A Single-center Experience.
Joseph K, Bui TT, Yahanda AT, Gupta VP, Vogl S, Yakdan S, Galla JT, Ruiz-Cardozo MA, Barot K, Chakladar S, Poulin ND, Challagundla A, Ng J, Krishnan A, Brehm SN, Benedict B, Clohisy JC, Pallotta N, Gupta MC, Neuman BJ, Hills J, Kelly MP, Hafez D, Greenberg JK, Ray WZ, Molina CA
Topics
Key Takeaway
Hip Axis Error (HAE) predicts mechanical failure after ASD surgery with OR=1.20 per degree (P<0.001), outperforming L1PA Error as a predictor regardless of fusion length.
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Summary
This study evaluated whether T4-L1 Hip Axis Error (HAE) and L1PA Error (L1PAE) predict mechanical failure in 271 ASD patients fused from L2 or above to the pelvis between 2016 and 2024. HAE was a significant independent predictor of mechanical failure (OR=1.20 per degree, P<0.001) while L1PAE was not, with positive HAE (anterior T4 tilt) conferring the highest risk; higher BMI and short constructs independently predicted greater HAE magnitude. HAE remained predictive in both short and long fusion constructs, and its predictive value persisted even in patients who achieved L1PA targets.
Key Limitation
Follow-up duration for mechanical failure ascertainment is not reported, making it impossible to determine whether failures were captured at a consistent or sufficient time point across patients.
Original Abstract
STUDY DESIGN
Retrospective cohort study.
OBJECTIVE
To evaluate the predictive value of T4-L1 Hip Axis Error (HAE) and L1PA Error (L1PAE) on mechanical failure following adult spinal deformity (ASD) surgery, and to assess how error directionality and fusion length influence outcomes.
SUMMARY OF BACKGROUND DATA
The T4-L1 Hip Axis is a novel framework for defining normative sagittal alignment by aligning thoracic and lumbar curvatures relative to the pelvis. Prior studies suggest that deviation from this axis may contribute to mechanical complications following ASD surgery. However, the impact of directionality, construct length, and specific risk factors remains underexplored.
METHODS
A retrospective review was conducted of 271 ASD patients who underwent fusion from L2 or above to the pelvis between 2016 and 2024. T4PA and L1PA were measured from six-week postoperative standing radiographs. Alignment errors (HAE, L1PAE) were calculated based on the target threshold derived from prior normative studies. Multivariate logistic regression identified predictors of mechanical failures. Subgroup analyses were stratified by fusion length and error direction.
RESULTS
HAE was a significant predictor of mechanical failure (OR=1.20 per degree, P <0.001), whereas L1PAE was not. HAE remained predictive regardless of whether patients achieved L1PA targets. In short fusions, both the signed and absolute value of HAE were associated with mechanical failure. Positive HAE (anterior T4 alignment) conferred the highest risk. Higher BMI and short constructs were independent predictors of increased HAE.
CONCLUSIONS
HAE is a robust, direction-sensitive predictor of mechanical failure in ASD surgery. Its predictive power surpasses L1PAE and remains significant in both long and short segment fusions. HAE should be routinely measured and minimized intraoperatively to reduce postoperative mechanical complications.