Regional disparities in shoulder surgery related to distribution of specialists: national database analysis

Background: Rotator cuff tears are the most common shoulder disorders requiring surgical management. In Japan, reverse total shoulder arthroplasty was introduced in 2014, initially restricted to certified surgeons. While this system ensured that only trained specialists could perform reverse total shoulder arthroplasty, it may have limited access to surgery. This study aimed to analyze regional disparities in shoulder surgeries and their correlation with shoulder specialists using the national database. Methods: A retrospective epidemiological study was conducted using the Japanese national claims database and Japanese Shoulder Society (JSS) membership records (2014-2022). Rotator cuff repair (RCR), shoulder arthroplasty volumes, and incidence in each prefecture were calculated per population. Gini coefficients assessed regional disparities, and a generalized linear mixed model evaluated the correlation between JSS membership and surgical volumes. Results: RCR showed stable regional disparities (Gini coefficient remained around 0.3) over 9 years, whereas shoulder arthroplasties exhibited extreme inequality in 2014 (Gini coefficient: 0.6), improving to moderate levels (Gini coefficient: 0.3) by 2022. JSS membership distribution was moderately equitable (Gini coefficient: 0.2). Prefectures with higher JSS membership demonstrated significantly higher surgical volumes (RCR: coefficient = 0.009, P < .001; shoulder arthroplasty: coefficient = 0.012, P < .001). Discussion: RCR exhibited moderate regional disparities, whereas shoulder arthroplasty disparities were initially extreme but stabilized as volumes increased. This trend reflects the growing accessibility of shoulder arthroplasty due to the dissemination of certified surgeons. The correlation between shoulder specialists and surgical volumes for both procedures underscores the specialization required for these surgeries.