Importance: Although the association between annual surgeon total thyroidectomy volume and clinical outcomes is well established, published methods typically group surgeons into volume categories. The volume-outcomes association is likely continuous, but little is known about the point at which the annual surgeon procedure volumes begin to be associated with a decrease in complication rates.
Objective: To model the volume-outcomes association as a continuous function and identify the point at which increasing surgeon volume begins yielding better outcomes.
Design, setting, and participants: A retrospective cohort study was conducted in 2018 to 2019 on 10 546 patients from 2 Kaiser Permanente regions (Northern and Southern California), who underwent total thyroidectomy from January 1, 2008, through December 31, 2015, and were followed up through December 31, 2017. The association between annual surgeon procedure volume and outcomes was modeled with analyses that accounted for an association of unknown form and surgeon-specific effects, after adjusting for sociodemographics, prior-year utilization, and multiple comorbidities. Data were analyzed from October 2018 to April 2019.
Exposure: Total thyroidectomy.
Main outcomes and measures: Presence or absence of transient and permanent hypoparathyroidism and vocal cord paralysis (VCP) in relation to surgeon volume of total thyroidectomies.
Results: Of 10 546 patients in this study, 8500 (81.0%) were male and 4877 (46.2%) aged 45 to 64 years. Surgeons with annual volumes of 1 to 9 total thyroidectomies operated on 2912 patients (27.7%), those with an annual volume of 10 to 19 operated on 3404 (32.6%), and those with an annual volume of 20 or more operated on the remaining 4232 (40.6%). During 2008-2015, a mean of 53.5 (range, 46-198) thyroidectomies were performed each year by surgeons with an annual volume of 40 or more procedures. A generalized additive model showed that the occurrence rates of VCP and hypoparathyroidism began to decrease at annual surgeon procedure volumes of 18.2 (95% CI, 15.0-21.5) and 18.1 (95% CI, 13.8-21.3) procedures per year, respectively. The model revealed a subsequent increase in complication rates for transient VCP. With the use of a refined model, statistically significant decreases were noted in the occurrence rates of complications as annual surgeon volumes increased. Among all 10 546 patients who underwent total thyroidectomy, 632 (6.0%) experienced transient hypoparathyroidism and 170 (1.6%) experienced permanent hypoparathyroidism, whereas 440 (4.2%) experienced transient VCP and 182 (1.7%) experienced permanent VCP. Absolute decreases in complication rates when all surgeons had modeled minimum annual procedure volumes greater than 40 were low, ranging from 0.6% for permanent VCP and hypoparathyroidism to 1.5% for transient hypoparathyroidism.
Conclusions and relevance: In this study, occurrence rates of transient and permanent hypoparathyroidism and VCP appeared to decrease as the annual surgeon procedure volume increased, but the absolute decrease may be modest if the affected health system already has low complication rates. Shifting patients to higher-volume surgeons to realize these reductions may be of variable attractiveness in systems with low baseline complication rates.