DOI: 10.1097/brs.0000000000005818 ISSN: 0362-2436

T4-L1PA Mismatch Predicts Mechanical Revision After Multilevel Fusion to the Upper Lumbar and Lower Thoracic Spine

Steven M. Maurer, Simon Ortiz, Pedro Augusto Rocha Torres, Julia Wimmer, Tom Folkerts, Bruno Verna, Jennifer Shue, Markus Loibl, Tamás F. Fekete, Matthias Pumberger, Federico P. Girardi, Frank P. Cammisa, Andrew A. Sama, Alexander P. Hughes, Marco D. Burkhard
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Study Design.

Retrospective single-center cohort study.

Objective.

To investigate whether postoperative T4-L1PA mismatch (T4 pelvic angle minus L1 pelvic angle) predicts mechanical revision within 5 years after multilevel fusion to the upper lumbar and lower thoracic spine, versus other alignment parameters.

Summary of Background Data.

T4-L1PA mismatch is an established predictor of mechanical failure after upper thoracic fusion to the sacropelvis. Its value in lower thoracic spine and upper lumbar constructs remains unclear.

Methods.

We retrospectively analyzed 204 patients who underwent posterior spinal fusion of 3 to 10 instrumented levels (upper instrumented vertebra [UIV] T8-L3) with distal fixation to the sacrum or ilium (2006-2024). Alignment was assessed preoperatively, at the first postoperative timepoint, and at 1 year: T4-L1PA mismatch, PI-LL mismatch, sagittal vertical axis, L1PA deviation, lordosis distribution index, and distal lordosis. The primary outcome was mechanical revision within 5 years. Cox regression, ROC, Kaplan-Meier, and combined-risk analyses were performed.

Results.

Thirty-three patients (16.2%) underwent mechanical revision within 5 years. On first postoperative radiographs, T4-L1PA mismatch predicted revision (hazard ratio [HR] 1.10, P =0.012), as did PI-LL (HR 1.03, P =0.027). Adjusted for PI-LL, age, and levels fused, T4-L1PA remained significant (HR 1.09, P =0.028) while PI-LL did not ( P =0.070). At 1 year (n=148, 16 events), T4-L1PA had an HR of 1.17 ( P =0.001; PI-LL P =0.171). Other parameters were non-significant. Five-year cumulative revision incidence rose from 6% with neither parameter malaligned to 19% with one and 39% with both (log-rank P =0.003).

Conclusions.

Postoperative T4-L1PA mismatch was the most consistent alignment predictor of mechanical revision over 5 years in thoracolumbar and upper lumbar fusions (UIV T8-L3) to the sacropelvis and remained independently prognostic at 1 year, with most revisions attributable to proximal junctional failure. PI-LL contributed early risk but weakened over time. Combined assessment identified a high-risk subgroup.

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