Subspecialization of Surgical Specialties in the US.

Importance: Subspecialists-physicians with narrower clinical focus-play an increasing role in US health care, particularly in surgery, where most trainees now pursue fellowship training. Yet little is known about the degree of subspecialization among practicing surgeons and the evolving role of surgical generalists. Objective: To quantify trends in surgical subspecialization and examine the geographic distribution of subspecialists and the procedural scope of surgical generalists. Design, Setting, and Participants: A retrospective cohort study using 100% Medicare Part B data from 2000, 2010, and 2021, including all fee-for-service beneficiaries treated by physicians in general surgery, neurosurgery, ophthalmology, orthopedic surgery, and otolaryngology was caried out. A novel classification method combining k-means clustering, large language models, and expert validation to distinguish subspecialists from surgical generalists based on procedural claims was used. The analysis was undertaken in 2023 and 2024. Main Outcomes and Measures: The number of distinct subspecialties, the share of subspecialists in each surgical specialty, their geographic distribution across hospital referral regions (HRRs), and the association between subspecialist supply and procedural diversity among generalists. Results: Overall, more than 70 000 surgeons were included. The share of subspecialists increased from 38% in 2000 to 58% in 2021, reflecting the growth of recognized subspecialties (from 24 to 33) and expansion of existing ones. Subspecialization rates varied by specialty, rising from 9% to 28% in otolaryngology and from 66% to 77% in neurosurgery. While subspecialist supply per 100 000 fee-for-service beneficiaries remained stable, the mean number of surgical generalists per 100 000 declined from 105 to 50. A 10% increase in subspecialist supply in an HRR was associated with a 0.94% decrease (95% CI, -0.15% to -0.41%) in the number of unique procedures performed by generalist surgeons. Conclusions and Relevance: This cohort study found that subspecialization has considerably reshaped the surgical workforce, concentrating care among subspecialists while narrowing the procedural scope of generalist surgeons. These shifts raise concerns about access to generalist care, particularly in regions with declining generalist supply, and suggest the need for policies that consider both specialization and geographic equity in surgical workforce planning.