Does Quantity Equal Quality? The Volume-Outcome Relationship in TKA in the Age of the Bundle
A recent study examined the effect of surgical volume on 90-day complication rates, 90-day mortality rates, and 2-year revision rates among total knee arthroplasty patients operated on in New York state – valuable information to have in the era of bundled payments.
Mitchell C. Weiser, MD, MEng, and William J. Long, MD, FRCSC
Wilson S, Marx RG, Pan TJ, Lyman S. Meaningful thresholds for the volume-outcome relationship in total knee arthroplasty. J Bone Joint Surg Am, 2016 Oct 19;98(20):1683-1690
Prevailing wisdom suggests that “high-volume” total knee arthroplasty (TKA) surgeons and surgical centers achieve superior clinical outcomes for their patients with fewer complications.However, the definition of “high volume” is variable in previous literature, and has been defined as low as more than 6 cases per year to more than 70 cases per year.This study by Wilson et al sought to better-define the volume-outcome relationship in TKA surgery by trying to answer the following questions:
- What surgeon-volume thresholds are most predictive of 90-day complication and 2-year revision rates?
- What hospital-volume thresholds are most predictive of 90-day complication and 90-day mortality rates?
Using the New York State Department of Health’s Statewide Planning and Research Cooperative System (SPARCS) Database, they examined surgeon and surgical center outcomes for 289,976 patients who underwent TKA between 1997 and 2011.Surgeon-specific endpoints included:
- 2-year revisions defined by ICD-9 codes
- 90-day complications identified by ICD-9 codes
Hospital-specific endpoints included:
- 90-day complications
- 90-day all-cause in-hospital mortality
Data were analyzed by applying stratum-specific likelihood ratio (SSLR) analysis to receiver operator characteristic (ROC) curves. SSLR is an iterative statistical process that identifies meaningful thresholds in data sets.
Using this method, Wilson et al were able to define critical thresholds for case volume for surgeons and surgical centers. Surgeon-specific endpoint results included:
- Volume thresholds for 2-year revision risk
- Low-volume surgeons: 0-12 TKA/year, revision risk 3.3%; Cox-proportional hazard analysis hazard ratio compared with high–volume surgeons: 1.56 (95% CI, 1.44-1.69)
- Medium-volume surgeons: 13-59 TKA/year, revision risk 2.6%; Cox-proportional hazard analysis hazard ratio compared with high-volume surgeons: 1.26 (95% CI, 1.19-1.34)
- High-volume surgeon: >60 TKA/year, revision risk 2.0%
Volume thresholds for 90-day complications risk:
- Low-volume surgeons: 0-11 TKA/year, complication rate 9.8%; odds ratio compared with very high-volume surgeons: 1.85 (95% CI, 1.75-1.97)
- Medium-volume surgeons: 12-64 TKA/year, complication rate 7.9%; odds ratio compared with very high-volume surgeons: 1.49 (95% CI, 1.41-1.56)
- High-volume surgeons: 65-145 TKA/year, complication rate 6.9%; odds ratio compared with very high-volume surgeons: 1.27 (95% CI, 1.20-1.34)
- Very high-volume surgeons: >146 TKA/year, complication rate 5.7%
Hospital-specific endpoint results included:
- Volume thresholds for 90-day complication risk
- Low-volume centers: 0-89 TKA/year, complication rate 9.2%; odds ratio compared with high-volume centers: 1.37 (95% CI, 1.32-1.42)
- Medium-volume centers: 90-235 TKA/year, complication rate 7.6%; odds ratio compared with high-volume centers: 1.13 (95% CI, 1.10-1.17)
- High-volume centers: >236 TKA/year, complication rate 6.8%
Volume thresholds for 90-day all-cause in-hospital mortality
- Low-volume centers: 0-644 TKA/year, mortality rate 0.31%; odds ratio compared with high-volume centers: 2.21 (95% CI, 1.45-3.41)
- High-volume centers: >645 TKA/year, mortality rate 0.11%
The effect of surgeon volume on 90-day complication rates in low-, medium-, and high-volume centers was also examined (Table 1). Table 1. Surgeon Volume, Hospital Volume, and 90-Day Complication Rates
Knee osteoarthritis affects more than 50% of adults over the age of 65, and this is predicted to help push the demand for primary TKA to more than 3 million cases per year by 2030.
In addition, the Centers for Medicare and Medicaid Services (CMS) has tied surgeon and hospital compensation for total joint arthroplasty (TJA) to outcomes measures under various provisions of the Medicare Access and CHIP Reauthorization Act (MACRA). Within the next several years, CMS will begin to compare surgeons and hospitals by metropolitan region and tie compensation to outcomes relative to one’s peers.
Not surprisingly, the highest-volume surgeons at the highest-volume centers had the lowest rates of revisions, complications, and mortality. This reaffirms the belief that higher surgical volume begets better outcomes.
The study by Wilson et al used a large patient database to provide insight into the volume thresholds that are clinically meaningful. However, given the nature of the database and its geographic limitation to the state of New York, it may be difficult to extrapolate the results to other surgeons and centers around the country.
Further study is needed to see if these volume thresholds are clinically applicable to surgeons and hospitals on a larger scale. Nonetheless, the results of the study are important to take into consideration in the age of bundled payment for TJA.
Based on the results of this study, low- and medium-volume surgeons and centers should carefully assess their practices to decide if TKA remains a valuable service for them to offer. Those that continue to provide TKA surgery should consider evaluating and adopting the best practices of higher-volume surgeons and centers to improve patient outcomes and promote value.
This will become critical once surgeon and hospital compensation becomes tied to performance relative to their peers.
Mitchell C. Weiser, MD, MEng, is an Adult Reconstruction Fellow with the ISK Institute and NYU Langone Medical Center-Hospital for Joint Diseases, New York, New York. William J. Long, MD, FRCSC, is an Attending Orthopaedic Surgeon with the ISK Institute and Clinical Associate Professor of Orthopaedic Surgery, Division of Adult Reconstruction, Department of Orthopaedic Surgery, at NYU Langone Medical Center-Hospital for Joint Diseases, New York, New York.