Roussouly morphotypes, GAP score, and lumbar distribution index in an asymptomatic Turkish adult population: age- and...

This study aimed to establish normative values for Roussouly morphotypes, Global Alignment and Proportion (GAP) scores, and Lumbar Distribution Index (LDI) in a large Turkish adult cohort, and to analyze their relationships with age, sex, and spinopelvic morphology.

A retrospective radiographic analysis was conducted on 512 asymptomatic adults (mean age: 32.6 ± 13.8 years; 39.5% male, 60.5% female) who were selected from individuals presenting to an orthopedic outpatient clinic with postural abnormalities or suspected spinal deformity and who underwent standardized standing scoliosis radiographs between 2015 and 2025. Spinopelvic parameters, Roussouly classification, GAP scores, and LDI were assessed by two independent spine surgeons. Interobserver reliability was tested using intraclass correlation coefficients (ICC) and weighted kappa statistics. Statistical comparisons were performed by sex, age, and morphotype.

Type 3 was the most prevalent Roussouly morphotype (53.5%), followed by Type 2 (17.4%), Type 1 (15.2%), and Type 4 (13.9%). Females were more frequently represented in Types 3 and 4 (p = 0.031). Type 4 prevalence increased with age, particularly after 70 years. Mean GAP score was low (1.6 ± 1.9) and did not differ by sex, though it increased slightly with advancing age (r = 0.195, p < 0.001). Mean LDI was 66.2 ± 13.9, significantly higher in females (p = 0.043). Across morphotypes, PI increased progressively from Type 1 to Type 4 (p < 0.001), LDI was highest in Type 1 and lowest in Type 4 (p < 0.001), and GAP scores were lowest in Type 3 and highest in Type 1 (p < 0.001). Interobserver reliability was excellent for all measures (ICC > 0.90, weighted κ = 0.95).

This study provides normative data on Roussouly morphotypes, GAP scores, and LDI in a Turkish adult cohort. Type 3 predominates, with significant age- and sex-related variations, including higher LDI values in females and an increasing prevalence of Type 4 with age. These findings highlight the influence of demographic and ethnic factors on sagittal morphology and support the use of population-specific reference values. However, as the cohort was derived from individuals undergoing radiographic evaluation in a clinical setting, the results should be interpreted with caution and may not fully represent the general population.