Global alignment and proportion (GAP) scores in an asymptomatic, nonoperative cohort: a divergence of age-adjusted and pelvic incidence-based alignment targets

Purpose: To investigate GAP scores in an asymptomatic cohort of adults, including older adults with age-expected changes in spinal alignment. Methods: One hundred and twenty asymptomatic volunteers underwent full-body radiographic scans. Demographics and sagittal radiographic parameters (pelvic incidence, sacral slope, L1-S1 lordosis, L4-S1 lordosis, and global tilt) were measured and GAP scores calculated (www.gapcalculator.com). Mann–Whitney U test compared groups. Results: Eighty-five individuals (65 female, average age 48 ± 16 years, BMI 27 ± 6 kg/cm²) were analyzed. The median GAP score was that of a proportioned spine (0, range 0–10). 20% were moderately disproportioned and 6% were severely disproportioned. The mean relative pelvic version, relative lumbar lordosis (RLL), lumbar distribution index (LDI), and relative spinopelvic alignment were all considered aligned, although the mean RLL and LDI scores were both greater than 1. When categorized by age (< 60 years, ≥ 60 years), the median GAP score of the younger group was 0 (normal), while the median GAP score of the older cohort was 1 (normal) and different from the younger group (p < 0.001). Conclusion: Most patients in this asymptomatic, nonoperative cohort were normally proportioned. However, a large percentage of asymptomatic volunteers were moderately or severely disproportioned. Older patients had higher scores, indicating some disproportion. There was also a small number of severely sagittally misaligned and poorly proportioned, yet asymptomatic, volunteers. Further refinement of individualized targets is needed to determine the effect on mechanical complications and quality of life given the divergent recommendations of age-adjusted targets and GAP targets.