Full-Body Analysis of Age-Adjusted Alignment in Adult Spinal Deformity Patients and Lower-Limb Compensation

Abstract

Study design: Single-center retrospective review.

Objective: The present study evaluates the effect of increasing spinal deformity deviation from age-adjusted alignment ideals on lower extremity compensation.

Summary of background data: Although current understanding of compensatory mechanisms in adult spinal deformity (ASD) is progressing due to full-body stereographic assessment, the effect of age-adjusted deformity targets on lower-limb compensation remains unexamined.

Methods: ASD patients 18 years or older with biplanar full-body stereographic x-rays were included. Patients were stratified into age cohorts: younger than 40 years, 40-65 years, 65 years or older. Age-specific alignment goals (IDEAL) for pelvic tilt (PT), spinopelvic mismatch (PI-LL), sagittal vertical axis (SVA), and T1 pelvic angle (TPA) were calculated for each patient using published formulas and compared to patients' real (ACTUAL) radiographic parameters. The difference between ACTUAL and IDEAL alignment (OFFSET) was calculated. Analysis of variance compared ACTUAL, IDEAL, and OFFSET between age groups, and OFFSET was correlated with lower-limb compensation (sacrofemoral angle, pelvic shift, knee angle, ankle angle).

Results: Seven hundred seventy-eight patients with (74.1% female) were included. ACTUAL and IDEAL alignments matched for PT (P = 0.37) in patients younger than 40 years, SVA (P = 0.12) in patients 40 to 65 years and PT, SVA, and TPA (P > 0.05) in patients 65 years or older. SVA and TPA OFFSETs decreased significantly with increasing age (P < 0.001). Hip extension correlated with all OFFSETs in patients younger than 40 years (positively with PT, PI-LL, TPA; negatively with SVA). Knee flexion correlated with PI-LL, SVA, and TPA, across all age groups with strongest correlations (0.525 < r < 0.605) in patients 40 to 65 years. Ankle dorsiflexion only correlated positively with PT and PI-LL offsets in older (older than 40 years) age groups. Posterior pelvic displacement correlated positively with all OFFSET groups, and was highest (0.526 < r <0.712) in patients ages 40 to 65 years.

Conclusion: Age-adjusted ideals for sagittal alignment provide targets for patients with ASD. Offsets from actual alignment (more severe sagittal deformity) revealed differential recruitment of lower-limb extension, which varied significantly with age.

Level of evidence: 3.