292. Global Alignment and Proportion (GAP) score with modified age factor: GAP-A score

Abstract

BACKGROUND CONTEXT The Global Alignment and Proportion (GAP) score is a PI-based method of analyzing the sagittal plane, developed to predict the risk of mechanical complications following spinal correction surgery. Our study examined the age factor of 60 as a parameter for GAP score calculation in a healthy US population. Modifying the age factor with score substractions at the cut-offs of age 65 and 70 creates the Global Alignment and Proportion with Modified Age Factor (GAP-A) Score, which better compensates for the sagittal imbalance that occurs naturally with increasing age and affects the healthy elderly population. The GAP score was developed to predict mechanical complications following spinal correction surgery. It is a pelvic-incidence based method of analyzing the sagittal plane. The GAP parameters include relative pelvic version, relative lumbar lordosis, lordosis distribution index, relative spinopelvic alignment (RSA), and an age factor of 60. An age >= 60 years old receives a score of 1, while age PURPOSE The aim of the study was to adjust the age factor in calculation of GAP scores among healthy United States adult volunteers with no prior spinal pathology, in order to compensate for the natural age-related sagittal imbalance among the elderly population. STUDY DESIGN/SETTING Retrospective review of prospectively collected data PATIENT SAMPLE A total of 87 healthy volunteers were included in the study. Mean age was 54.9±15.1 (20-84) years. Exclusion criteria included any major spinal pathology or surgery, terminal illness, morbid obesity or any significant comorbid condition. OUTCOME MEASURES GAP scores with the age factor removed and GAP-A scores. METHODS Preliminary GAP scores with the age factor removed were assessed in 87 healthy volunteers that met inclusion criteria. The preliminary GAP scores were grouped based on age groups in increments of 5 or 10 years, and these scores were analyzed to search for discrepancies from the baseline trend. Original GAP scores were calculated for the same 87 healthy volunteers. GAP-A scores were calculated with the same parameters as the original GAP scores, with the exception of the age factor. In GAP-A scores, in addition to the age factor of adding 1 point if age>60, the number of points were subtracted from each age group in the same amount that showed discrepancies in the Preliminary GAP score trend. The percentages of Proportioned, Moderately Disproportioned, and Severely Disproportioned volunteers were then compared between GAP scores and GAP-A scores. RESULTS Preliminary GAP scores show a 2- and 4-point discrepancy after age 65 and age 70 respectively. After adjustment those two age groups by subtraction of 2 and 4 points from original GAP scores, the percentages of Proportioned and Moderately Disproportioned increased in GAP-A scoring systems. Conversely, Severely Disproportioned groups decreased in GAP-A scoring system. Proportioned volunteers changed from 47.1% to 52.9%, Moderately Disproportioned volunteers changed from 39.1% to 37.9%, and Severely Disproportioned volunteers changed from 13.8% to 9.2% CONCLUSIONS Our study examined the age factor parameter in calculation of GAP scores in a healthy U.S. population. We found proportioned percentage from Original GAP scores increases by subtractions at age cut-offs of 65 and 70, which was the discrepancies found from Preliminary GAP scores. We called this system the Global Alignment and Proportion with Modified Age Factor (GAP-A) scoring system. This system can be proposed as a better alternative in compensating for the natural sagittal imbalance affecting the healthy elderly population. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.