Surgical volume, the frequency with which surgeons and surgery centers perform complex surgical procedures, is clearly understood as a key determinant of healthcare quality. The Agency for Healthcare Research and Quality (AHRQ) includes “how many times have you done this procedure” as one of the 10 questions patients should ask their doctor. Consumer Reports similarly recommends patients inquire about surgical volume when choosing a physician. While over 15 million Americans undergo elective surgery each year, at an estimated total cost of $147.2 billion, patients and their families are often unable to consider surgical volume when choosing a provider.

Providers with higher surgical volume are expected to have fewer medical errors and defects, better acute outcomes overall, and other post-acute benefits following the surgical procedure. However, existing studies have only been able to leverage relatively small samples of data for specific surgical procedures. There is little to no publicly available information about surgical volume readily accessible for patients, their families, and payers.

In this brief, we use a large, observational sample of national health insurance claims for patients undergoing hip and knee replacement surgeries performed in 2021. Hip and knee surgeries are the most common elective orthopedic surgical procedures where provider choice is possible for patients, meaning that volume information, if available, could be helpful. We find low provider surgical volume negatively impacts post-acute outcomes across inpatient and outpatient settings, even after we control for patient characteristics and other factors. We find that treatment by higher-volume surgeons is particularly important for more clinically complex patients.

Major Findings

We analyze two of the most common types of surgical episodes, total hip arthroplasty (THA), commonly known as hip replacements, and total knee arthroplasty (TKA), commonly known as knee replacements. For both hip and knee replacements, higher provider surgical volume is associated with better outcomes across multiple dimensions and multiple care settings, even after adjusting for differences in patient characteristics:

• Lower rates of post-acute inpatient readmission at both 7 and 60 days
• Lower rates of revision surgeries
• Lower rates of post-surgical stay orthopedic specialist visits, emergency department visits, and inpatient days
• Lower episode-level and orthopedic-specific standard dollar amounts

Variation in Surgical Volume

Using commercial claims data, we calculated historical surgical volume using finalized claims from 2017 to 2020 and assessed recent professional surgical episodes using finalized 2021 claims for hip and knee replacements (identified using HCPCS/ICD-10 PCS). Our analytic sample consisted of 66,367 hip replacements performed by 10,100 providers and 111,666 knee replacements performed by 13,432 providers completed in 2021. We estimate that this sample accounts for approximately 14% of all hip and knee replacements completed annually in the US.

Figure 1 illustrates wide variation in prior surgical volume (2017-2020) for hip and knee replacements performed in 2021. While roughly one-third of 2021 hip and knee replacement episodes were performed by providers with 100 or more prior surgeries, approximately 50% of hip and knee replacement episodes were performed by providers who had performed less than 50 surgeries from 2017-2020; 17% of hip replacements and 13% of knee replacements in 2021 were performed by surgeons with less than 10 prior surgeries documented in the commercial claims data.

The Impact of Surgical Volume on Outcomes and Cost

Figure 2 presents a wide range of post-surgical hip and knee replacement outcomes in 2021 stratified by each surgeon’s volume in the preceding four years. For both the hip and knee replacement samples, higher surgical volume for a provider is associated with better outcomes, specifically:

• Lower rates of post-acute inpatient readmission at 7 and 60 days, with rates for high-volume surgeons between 37-51% less than low-volume surgeons
• Lower rates of revision surgeries
• Lower rates of post-surgical stay orthopedic specialist visits, emergency department visits, and inpatient days
• Lower episode-level and orthopedic-specific Clarify standard amounts,* with total hip and knee episode costs approximately $2,800 and $1,500 lower, respectively, when performed by a high-volume versus a low-volume surgeon

Surgical Outcomes by Place of Service

When we stratify hip and knee replacements by place of service (inpatient (IP), outpatient (OP), and ambulatory surgical center (ASC) settings), volume-outcome relationships largely remain. As shown in Figure 3, for hip replacements, we observe that:

• Post-surgical ED utilization rates are approximately 21% lower for high-volume surgeons in an IP setting compared to low-volume surgeons, 35% lower in an OP setting, and 34% lower in an ASC setting
• Readmission rates are approximately 32% lower for high-volume surgeons in an IP setting compared to low-volume surgeons, 47% lower in an OP setting, and 74% lower in an ASC setting
• Revision surgery rates are approximately 7% lower for high-volume surgeons in an IP setting compared to low-volume surgeons, 40% lower in an OP setting, and 5% higher in an ASC setting

Controlling for Patient Case Mix and Provider Characteristics

While the results presented above are compelling, they could be influenced by patient characteristics or other factors. To control for this, we performed adjusted, multivariate analyses for hip and knee episodes, respectively, and surgical volume controlling for place of service, provider teaching affiliation status, provider state, patient demographics, and comorbidity status. Specifically, we model the probability of a patient experiencing any of three negative clinical events (a post-discharge ED visit, inpatient readmission, or revision surgery) following a joint replacement procedure. Estimates are presented in terms of percentage changes in average rates relative to the low-volume reference group. Our findings of the relationship between surgical volumes and outcomes persist, even after controlling for these other factors.

Figure 4 demonstrates that the impact of surgical volume on outcomes is maintained, albeit at lower levels, even after controlling for patient and provider characteristics for both hip and knee replacements. Further, when we estimate this relationship separately for patients with comorbidities (defined as patients with chronic kidney disease, hypertension, metastatic cancer, obesity, or peripheral vascular disease), we find an even stronger relationship between surgical volume and outcomes. We find that while surgical volume has benefits for all patients, the benefit of experienced surgeons increases for operations on higher acuity patients.

These estimates imply that all else equal, patients undergoing joint replacement surgery with a high-volume versus low-volume surgeon experience a substantial decrease in risk of experiencing any of the three negative outcomes considered. In terms of percentage changes from the high-volume category to the low-volume reference group, combined rates of post-surgical ED visits, inpatient readmissions, and revisions surgeries are approximately 14% lower for hip replacements and 19% lower for knee replacements, holding patient case mix and provider characteristics fixed. Equally important are place of service considerations. We similarly observe from this analysis that, all else equal, combined rates of negative outcomes for patients treated in outpatient and ASC settings are 13-24% and 27-45% lower on average, respectively, compared to hip and knee replacements performed in IP settings.

Conclusion

Our findings imply clinical benefits for patients who undergo hip and knee replacement surgeries with high-volume surgeons, even after adjusting for patient and other characteristics. Thousands of negative clinical events (i.e., readmissions, emergency department visits, and revision surgeries) could be avoided each year by steering patients to high-volume providers. Our findings here, while not completely ruling out the selection of higher-risk patients into inpatient settings, are also consistent with multiple smaller studies documenting that joint replacement surgeries completed in OP and ASC settings are associated with better or comparable outcomes with IP surgeries, with higher patient satisfaction and at substantially a lower cost.

Payers and health systems have begun to concentrate volume of surgeries and other procedures at specific sites within their networks, often referring to these locations as “centers of excellence” (COEs). For orthopedic surgeries, COEs are often implemented in OP or ASC settings. COEs have higher relative volume, are actively educating care teams about best practices and current medical research, often obtain special accreditations from national organizations and consistently generate improved outcomes versus lower-volume sites of care. Despite this, our study shows many patients continue to see surgeons with lower surgical volumes. In our commercial claims sample, over half of all hip replacements and over 4 in 10 knee replacements were completed by providers with less than 50 observed prior surgeries.

In addition, the general public, to the extent that it is even aware of the impact of surgical volume on outcomes, has few resources to proactively identify high-volume surgeons. One national advocacy organization, Leapfrog Ratings, has requested hospitals and other surgery centers volunteer volumes by surgical category for public reporting, but response rates to their surveys have been poor, with only around 25% of all provider groups reporting, and the general public is mostly unaware of these types of public reporting. CMS also releases machine-readable data files highlighting annual volume rates for the Medicare population, but this data remains inaccessible to most patients and patient advocates due to its complexity.

Healthcare stakeholders can build on these nascent efforts by:

• Setting minimum surgical volume standards for in-network surgeons as well as identifying or creating surgical COEs to better match patients with the right surgeon.
• Educating surgeons on the importance of gaining sufficient experience and specialization during their medical training, keeping their surgical volume above minimum thresholds, and continuing medical education around the ethics of scope of practice.
• Educating consumers and patient advocacy organizations by releasing comprehensive, multi-payer information on surgical volumes that can be used to identify high-volume, high-quality surgeons for elective surgeries.