Anterior lumbar interbody implant placement and sagittal alignment proportionality: an evaluation using the global alignment and proportion score
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Published on: November 8, 2024
Francesco Caiazzo1, Jorge H Nuñez2, Lucas Capo3
1Clinica Sagrada Familia, Instituto Quirúrgico Spanò, Barcelona, 08022, Spain. fcaiazzo@iqspano.com.
Purpose:
The Global Alignment and Proportion (GAP) score is a key tool for assessing sagittal alignment proportionality and predicting complications and quality of life in adult deformity surgery. However, its utility for degenerative conditions treated with anterior lumbar interbody implants remains unanalyzed. This study aimed to evaluate the impact of anterior lumbar surgery with interbody implant placement on spinopelvic alignment parameters and to explore the applicability of the GAP score and its components in degenerative spine surgeries.
Methods:
The study included 45 adults (mean age, 45.2 years) with lumbosacral degenerative disc conditions who underwent one- or two-level anterior lumbar surgery (L4-L5 and/or L5-S1) using interbody implants (cages or prostheses) and completed a minimum follow-up of 12 months. Pre- and postoperative standing sagittal full-spine X-rays were used to measure key spinopelvic parameters (pelvic incidence, pelvic tilt, sacral slope, L1-S1 lordosis, L4-S1 lordosis, global tilt). GAP score components (Relative Pelvic Version, Relative Lumbar Lordosis, Lordosis Distribution Index, Relative Spinopelvic Alignment) and pathological alignment percentages were calculated. Pre- and post-operative measurements were compared using paired t-tests/Wilcoxon and Chi-square tests.
Results:
Anterior lumbar surgery significantly improved all spinopelvic parameters. L4-S1 lordosis increased from 29.4° (SD 10.0) to 39.1° (SD 5.2) (p < 0.001, ES 1.2); L1-S1 lordosis and sacral slope also showed large effect sizes (> 0.7). The mean GAP score value significantly decreased from 3.2 (SD 3.2) to 1.4 (SD 2.1) (p < 0.001). In addition, pathological alignment percentages were significantly reduced (i.e., excessive pelvic retroversion 46.6% to 13.3%; L4-S1 hypolordosis 35.5% to 2.2%; all p < 0.03).
Conclusions:
Anterior lumbosacral interbody fusion significantly improves sagittal alignment proportionality adjusted for PI.
