Geographic Variation and Determinants of Spine Surgery Utilization in a Universal Health System: Evidence From Brazil

Study Design: Nationwide ecological study. Objective: To evaluate the association between socioeconomic development, surgical workforce availability, and spine surgery utilization in the Brazilian public health care system, and to assess whether the effect of surgeon density is modified by regional socioeconomic context. Summary of Background Data: Substantial geographic variation in spine surgery utilization has been described in high-income countries, often attributed to differences in health care delivery rather than clinical need. However, data from middle-income countries with universal health care systems remain limited, particularly regarding the interaction between socioeconomic factors and workforce distribution. Materials and Methods: All 27 Brazilian federative units were analyzed from 2014 to 2023. Spine surgery rates per 100,000 inhabitants were obtained from the National Public Healthcare Database (DATASUS). Independent variables included the Human Development Index (HDI), surgeon density, and service availability. Associations were assessed using multiple linear regression and generalized linear models (GLMs) with a gamma distribution and log link function. Results: A total of 176,033 spine surgeries were performed. The mean surgery rate was 7.32 per 100,000 inhabitants (SD: 5.29), with marked regional variation. Higher rates were observed in the South and Southeast regions. In the final GLM, HDI was strongly associated with higher surgery rates (B=14.493; P <0.001), and surgeon density was also positively associated (B=0.714; P =0.014). A significant interaction between HDI and surgeon density indicated that the effect of workforce availability was greater in lower-HDI regions and attenuated in higher-HDI areas. Conclusion: Spine surgery utilization in Brazil varies substantially across regions and is strongly influenced by socioeconomic development. Workforce expansion alone may not increase surgical rates in more developed regions, but may significantly reduce disparities in underserved areas. These findings highlight the importance of context-specific strategies to improve equitable access to spine surgery.