It is generally accepted that the outcomes of shoulder arthroplasty tend to be better in the hands of surgeons performing high volumes of these cases. In some ways this is similar to the observation that golfers who have hit more balls or anglers who have extensive experience in placing a dry fly in the "sweet spot" will have better outcomes.

However in surgery the volume effect is more multifaceted. High volume surgeons are more likely to have well trained support staff - clinic personnel, operating room nurses and technicians, physical therapists - along with well established pathways to optimize efficiency and safety. They are more likely to have optimal support from representatives of implant companies, to have access to special tools and instruments, to work in medical centers that receive volume discounts on arthroplasty components (resulting in better cost-effectiveness), to conduct clinical research on methods to optimize their outcomes, and to afford and benefit from modern marketing strategies. Finally, high volume surgeons have the ability to select the better candidates for shoulder arthroplasty as well as those patients with better reimbursing health care coverage.

However, as demonstrated by the authors of Distribution of High-Volume Shoulder Arthroplasty Surgeons in the United States: Data from the 2014 Medicare Provider Utilization and Payment Data Release, many patients do not have access to high-volume surgeons as can be seen in their figure reproduced below showing the number of high-volume TSA surgeons by U.S. metropolitan areas. The map identifies the number of high-volume surgeons per estimated number of Medicare beneficiaries and locations of ASES fellowship programs among major metropolitan areas.

Several interesting questions arise:

(1) Because it may be expensive and inconvenient for patients to travel to a high volume surgeon for both the surgery and followup, on what basis can they decide if it is worth it?

(2) All arthroplasty surgeons start out as "low-volume" surgeons; if most arthroplasty cases are directed to high volume surgeons, how does a young surgeon become "high-volume"?

(3) What is a useful definition of a "high volume" surgeon; does the relationship between surgeon volume and patient outcome look like this (more is always better)

or this (after a certain volume, the number of cases matters less)?

(4) Considering the patients living in a community with a young "low volume" surgeon for whom it is impractical to travel a considerable distance to a "high volume" surgeon, by what means can we lessen the effect of low volume on outcome so that neither the patient cared for by the "low volume" surgeon or the low volume surgeons themselves are disadvantaged?

(5) And perhaps most importantly, how much of the "volume effect" is due to solely to volume and how much is due to selection bias determining which patients are treated by low volume surgeons?

Some if these points were explored by the authors of The Effects of Social and Demographic Factors on High-Volume Hospital and Surgeon Care in Shoulder Arthroplasty who sought to evaluate (1) the relationship between hospital and surgeon volumes of shoulder arthroplasty and complication rates and (2) patient demographics/socioeconomic factors that may influence access to high-volume shoulder arthroplasty care. They studied patients older than 40 years who underwent shoulder arthroplasty between 2011 and 2015 that were identified in the New York Statewide Planning and Research Cooperative System database.

7785 patients were included. Based on total annual volume, surgeons were assigned to the lowest 20% of the volume, middle 60% of the volume, or highest 20% of the volume.

Low-volume surgeons accounted for 1,666 procedures, and high-volume surgeons accounted for 1,642 procedures. They compared the practices of low and high volume surgeons.

There were two major findings:

(1) Older, Hispanic/African American, socially deprived, non-privately insured patients were more likely to be treated by low volume facilities and surgeons.

(2) Low-volume facilities and surgeons had higher rates of readmission, urinary tract infection, renal failure, pneumonia, and cellulitis than high volume facilities. Low-volume surgeons had patients with longer hospital lengths of stay.

What is not clear is to what degree #2 is related to #1.

Comment: This study identifies a selection bias influencing which patients are treated by low and high volume facilities and surgeons. However, the study does not clarify whether the rate of adverse outcomes is due to the differences in characteristics of the patients treated in low or high volume contexts or whether the rate of adverse outcomes is solely a factor of volume.

In order to answer this important question it is necessary to perform a multivariate analysis of the factors potentially associated with adverse outcomes - these factors should not be confined to volume, but rather should also include age, sex, insurance, Charlson comorbidity score and social deprivation index.

Such an analysis may reveal that low and high volume surgeons had relatively more comparable outcomes for patients that were comparable. Stated simply, it doesn't seem reasonable to compare the outcomes achieved by low-volume surgeons for patients with important risk factors to the outcomes achieved by high-volume surgeons on patients without these risk factors.

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