Scientific Article   |    
Association Between Hospital and Surgeon Procedure Volume and Outcomes of Total Hip Replacement in the United States Medicare Population*
Jeffrey N. Katz, MD, MS; Elena Losina, PhD; Jane Barrett, MSc; Charlotte B. Phillips, RN, MPH; Nizar N. Mahomed, MD, ScD; Robert A. Lew, PhD; Edward Guadagnoli, PhD; William H. Harris, MD; Robert Poss, MD; John A. Baron, MD, MPH
J Bone Joint Surg Am, 2001 Nov 01;83(11):1622-1629
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Background: The mortality and complication rates of many surgical procedures are inversely related to hospital procedure volume. The objective of this study was to determine whether the volumes of primary and revision total hip replacements performed at hospitals and by surgeons are associated with rates of mortality and complications.

Methods: We analyzed claims data of Medicare recipients who underwent elective primary total hip replacement (58,521 procedures) or revision total hip replacement (12,956 procedures) between July 1995 and June 1996. We assessed the relationship between surgeon and hospital procedure volume and mortality, dislocation, deep infection, and pulmonary embolus in the first ninety days postoperatively. Analyses were adjusted for age, gender, arthritis diagnosis, comorbid conditions, and income. Analyses of hospital volume were adjusted for surgeon volume, and analyses of surgeon volume were adjusted for hospital volume.

Results: Twelve percent of all primary total hip replacements and 49% of all revisions were performed in centers in which ten or fewer of these procedures were carried out in the Medicare population annually. In addition, 52% of the primary total hip replacements and 77% of the revisions were performed by surgeons who carried out ten or fewer of these procedures annually. Patients treated with primary total hip replacement in hospitals in which more than 100 of the procedures were performed per year had a lower risk of death than those treated with primary replacement in hospitals in which ten or fewer procedures were performed per year (mortality rate, 0.7% compared with 1.3%; adjusted odds ratio, 0.58; 95% confidence interval, 0.38, 0.89). Patients treated with primary total hip replacement by surgeons who performed more than fifty of those procedures in Medicare beneficiaries per year had a lower risk of dislocation than those who were treated by surgeons who performed five or fewer of the procedures per year (dislocation rate, 1.5% compared with 4.2%; adjusted odds ratio, 0.49; 95% confidence interval, 0.34, 0.69). Patients who had revision total hip replacement done by surgeons who performed more than ten such procedures per year had a lower rate of mortality than patients who were treated by surgeons who performed three or fewer of the procedures per year (mortality rate, 1.5% compared with 3.1%; adjusted odds ratio, 0.65; 95% confidence interval, 0.44, 0.96).

Conclusions: Patients treated at hospitals and by surgeons with higher annual caseloads of primary and revision total hip replacement had lower rates of mortality and of selected complications. These analyses of Medicare claims are limited by a lack of key clinical information such as operative details and preoperative functional status.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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    Jeffrey N. Katz
    Posted on February 27, 2002
    Volumes and Outcomes of Orthopaedic Procedures: Scientific and Policy Considerations
    Division of Rheumatology, Immunology, and Allergy, Brigham and Women's Hospital, Boston

    February 19, 2002 - submitted to JBJS 02/19/02 Re: JBJS: Commentary by Frederick A. Matsen III, MD

    Jeffrey N. Katz, MD, MS Elena Losina, PhD John A. Baron, MD, MPH Nizar N. Mahomed, MD, ScD Robert Poss, MD William H. Harris, MD Robert A. Lew, PhD Charlotte B. Phillips, RN, MPH Anne H. Fossel Nancy Maher, MPH Jessica Tullar, BA

    Corresponding author: Jeffrey N. Katz, MD, MS Division of Rheumatology, Immunology and Allergy Brigham and Women's Hospital 75 Francis Street Boston, MA 02115 jnkatz@partners.org

    We are pleased to respond to Dr. Matsen's thoughtful commentary on our article "Association Between Hospital and Surgeon Procedure Volume and Outcomes of Total Hip Replacement in the United States Medicare Population" (1). Dr. Matsen comments on scientific aspects of the association between volume and outcomes, including causality and severity adjustment, and on the clinical and health-care policy implications of our findings. Our response addresses both of these considerations.

    Scientific Considerations

    Dr. Matsen raises the question of whether outcomes beget volume (people flock to certain restaurants because the restaurants are excellent) or volume begets outcomes (practice makes perfect). In the absence of a randomized trial (which would probably be infeasible), we cannot establish causality with certainty. Luft and colleagues (2) proposed a method for gaining insight into the causal direction of volume- outcomes associations using cross-sectional data. We have adapted their approach, as follows:

    We start by recognizing that hospitals with more beds and those with teaching programs perform a higher volume of hip replacements. Indeed, these two factors explained 26% of the variance in the algorithm of total hip replacement volume in our analyses. We then examined the association between hospital mortality and the residuals from this regression. (The residual is the difference between the total hip replacement volume of the hospital predicted by its number of beds and its teaching status, and the actual total hip replacement volume.) If outcomes drive volume, then the residuals should be associated with mortality-that is, a hospital with especially high mortality should have lower annual total hip replacement volume than predicted on the basis of its number of beds and its teaching status (because patients would avoid the hospital). Similarly, a hospital with especially low mortality should have higher total hip replacement volume than predicted because patients would flock to the hospital. In fact, the residuals explained virtually none (0.04%) of the variability in mortality. This finding lends no support to the hypothesis that outcomes of hip replacement drive volume, and it is more consistent with a practice -makes-perfect mechanism.

    Dr. Matsen also raises the question of selection bias-whether low- volume surgeons tend to operate on patients who are at greater risk for complications. Indeed, patients who are operated on in low-volume hospitals are more likely to be older, less educated, non-white, and poor (our unpublished data). However, our analyses adjust for demographic and clinical factors, including age, race, gender, arthritis diagnosis, comorbidity, and poverty status. Even after this adjustment, low-volume hospitals and surgeons have worse perioperative outcomes. Thus, imbalance between high and low-volume centers on these variables does not account for the differences in outcome. Of course, claims data are not ideal sources of information on comorbidity and cannot account for differences in technical complexity among cases. Thus, it remains possible that aspects of case severity that we could not measure (or could not measure well) with claims data may explain some of the differences in outcome.

    Dr. Matsen asks whether the enhanced support services in high-volume centers account for the superior results. In work that is not yet published, we examined whether hospital characteristics explain the association between volume and outcome. Our analyses indicate that hospital characteristics account for little of the effect of volume on outcome, leaving us to conclude, once again, that a "practice-makes- perfect" effect is the dominant mechanism. Dr. Matsen's comment also raises the question of which has greater influence on outcomes, the experience of the surgeon or aspects of the hospital? We examined the independent effects of surgeon volume and hospital volume in our analyses. As our paper shows, mortality following primary total hip replacement is driven largely by hospital and not by surgeon volume. On the other hand, dislocation and infection are influenced by both hospital and surgeon volume, with much stronger contribution from surgeon volume. The finding that some outcomes are driven more by surgeon volume and others, by hospital volume has important implications for patient choice of hospital and surgeon. For example, even within high-volume hospitals that perform twenty-six to fifty total hip replacements per year in the Medicare population, surgeons who perform five or fewer cases per year have three- fold higher dislocation rates than do surgeons who perform over fifty per year (1).

    Dr. Matsen also asks whether there are discrete threshold volume values above which outcomes become stable. In response to this comment, we have split our highest volume stratum into two substrata, 100 to 150 cases per year and greater than 150. The mortality rates were 0.57% for the highest-volume substratum (greater than 150 cases) and 0.74% for the next stratum (100 to 150). These two mortality rates are not significantly different, but the pattern shows no evidence of a threshold. An analysis of dislocation yielded similar results. These limited data suggest that higher volume is associated with better perioperative outcome at all points along the continuum of hospital and surgeon volume, with no evidence of a discrete threshold.

    Dr. Matsen asks whether these observations must be confirmed for each individual surgical procedure (e.g., total shoulder arthroplasty) or whether the volume-outcome associations seen with one procedure can be generalized to others. A recent review of the literature on volume-outcome associations found significant inverse associations in 77% of reports (3). Thus, the association is not universal. We hesitate to generalize from our hip replacement findings to other orthopedic procedures until more research on some of these procedures has been performed.

    Policy Implications

    The decision of whether to have surgery in a high or a low-volume center is complex, especially if the patient lives a great distance from a high-volume center. The advantages of care in a high-volume center are clear. For example, mortality within ninety days of elective primary total hip replacement in high-volume centers is just 58% of that in the lowest- volume centers (1). While this relative risk is impressive, the absolute risk difference in ninety-day mortality is modest (1.3% in hospitals that perform ten or fewer cases per year versus 0.7% in hospitals that perform greater than 100). If we assume these mortality rates, then for every 167 patients whose care is transferred from a low-volume hospital that performs fewer than ten total hip replacements per year in the Medicare population to a hospital that performs more than 100, one life would be saved (1/0.006 = 167). On a national scale, if the approximately 6700 patients who had primary total hip replacement in centers with annual volumes of less than ten per year in 1995 were instead referred to centers with volumes in excess of 100 per year, forty lives would be saved. If these patients were referred to centers with fifty-one to one hundred cases per year (mortality = 0.9%), twenty-seven lives would be saved.

    While potential advantages of shifting patients from low to high- volume centers are easy to calculate, the disadvantages of referral to a high-volume center are more subtle. Many patients prefer to receive care in low-volume settings. The reasons that patients select low-volume centers are not well studied but likely include the hospital affiliation of the surgeon whom they are referred to, the recommendation of their primary-care physicians, recommendations of family and friends, convenience of the location for patients and their families and friends, and other factors. Some patients might simply refuse to have the procedure if it could only be performed in the distant high-volume center rather than the local low-volume hospital. This would have important effects on quality-adjusted life expectancy. A patient with a ten-year life expectancy who spends the remainder of his or her life with end-stage hip arthritis would live two to five quality-adjusted life-years less than a patient who has a successful total hip replacement (4-6). We have not modeled the trade-offs formally, but it is clear from these examples that mandatory referral to a high-volume center saves some lives at the expense of an unknown but potentially large number of quality-adjusted life-years. Our data also suggest that patients who elect not to travel to the high- volume center may be older, poorer, and less educated. Thus, mandatory referral to high-volume centers could exacerbate existing disparities in utilization of total hip replacement among whites, blacks, and Hispanics, as well as between poor and non-poor (7).

    In response to another of Dr. Matsen's questions, we are unaware of whether low-volume surgeons are at legal risk, but it would seem prudent from this standpoint to fully disclose surgeon and hospital volume. Our data do not provide answers to several other provocative questions that Dr. Matsen raises, including how to align financial incentives with referral to high-volume centers and how to manage the tension between educating surgeons in the techniques of arthroplasty and the resultant increase in low- volume surgeons. We invite continued dialogue, research, and policy analysis to address these important concerns.

    These complex issues are especially critical because payers are paying attention to volume. The Centers for Medicare and Medicaid Services (CMS), which manage the Medicare program, have initiated a pilot program that designates centers of excellence for total hip and knee replacement surgery. Similar programs in cardiac surgery were successful in reducing costs with no compromise in outcomes. Volume is one of many indicators of quality used in the CMS project. Payers in the private sector have also committed to using high-volume providers. The Leapfrog Group, a consortium of major businesses dedicated to improving health-care quality and efficiency, has identified referral to high-volume providers as a strategic goal for improving employees' health (8). We believe that programs to restrict care to high-volume centers should await formal, comprehensive policy analysis and that the choice of hospital and surgeon should be left with the patient. We agree with Dr. Matsen that the medical community has an obligation to fully inform patients of these volume- outcome relationships and of the volume of surgeries performed by specific surgeons and hospitals. As with many other complex medical and surgical decisions, we believe that patient preferences should drive the choice of surgeon and hospital and that our job as researchers and clinicians is to inform patients fully and help them to make choices that are congruent with their preferences (9).


    1. Katz JN, Losina E, Barrett J, Phillips CB, Mahomed NN, Lew RA, Guadagnoli E, Harris WH, Poss R, Baron JA. Association between hospital and surgeon procedure volume and outcomes of total hip replacement in the United States Medicare population. J Bone Joint Surg Am. 2001;83:1622-9.

    2. Luft HS, Hunt SS, Maerki SC. The volume-outcome relationship: practice-makes-perfect or selective-referral patterns? Health Serv Res. 1987;22:157-82. 3. Maria Hewitt for the Committee on Quality of Health Care in America and the National Cancer Policy Board. Interpreting the volume-outcome relationship in the context of health care quality: workshop summary (2000). books.nap.edu/books/NI000322/html/index.html. Accessed 19 Feb 2002.

    4. Chang RW, Pellisier JM, Hazen GB. A cost-effectiveness analysis of total hip arthroplasty for osteoarthritis of the hip. JAMA. 1996;275:858-65.

    5. Laupacis A, Bourne R, Rorabeck C, Feeny D, Wong C, Tugwell P, Leslie K, Bullas R. The effect of elective total hip replacement on health-related quality of life. J Bone Joint Surg Am. 1993;75:1619-26.

    6. Katz JN, Phillips CB, Fossel AH, Liang MH. Stability and responsiveness of utility measures. Med Care. 1994;32:183-8.

    7. Escalante A, Barrett J, del Rincon I, Cornell JE, Phillips CB, Katz JN. Disparity in total hip replacement between Hispanic and non- Hispanic Medicare beneficiaries. Unpublished data.

    8. The Leapfrog Group. www.leapfroggroup.org/index.html. Accessed 13 Feb 2002.

    9. Katz JN. Patient preferences and health disparities. JAMA. 2001;286:1506-9.

    Frederick A. Matsen, III, MD
    Posted on February 05, 2002
    The Relationship of Surgical Volume to Quality of Care: Challenges and Opportunities
    University of Washington

    "Association Between Hospital and Surgeon Procedure Volume and Outcomes of Total Hip Replacement in the United States Medicare Population" (2001;83:1622-9), by Katz et al., provides the basis for discussing one of the most important issues facing health care today-the results of specialization. Their data support the concept that specialists provide better outcomes. Specifically, in the Medicare population, patients treated with primary total hip replacement by surgeons who performed more than fifty of these procedures per year had a markedly reduced complication rate in comparison with those patients whose surgeons performed ten or fewer of these procedures per year.

    In a paper presented at the annual meetings of the AAOS and the American Shoulder and Elbow Surgeons in 2001, we reported the results of a study that made use of the 1998 database of the Center for Medical Consumers (http://www.medicalconsumers.org/#Main_Index) to determine the volume distribution among surgeons and hospitals in New York State of total/partial shoulder replacements, total/partial hip replacements, and total knee replacements1. We learned that 14,644 hip replacements, 12,328 knee replacements, and 902 shoulder replacements were performed by 1175, 820, and 389 surgeons, respectively. Approximately forty per cent of surgeons who performed hip and knee replacements in New York State performed ten or more replacements in that year. In contrast, only ten ( <_3 of="of" all="all" surgeons="surgeons" who="who" performed="performed" shoulder="shoulder" replacements="replacements" did="did" ten="ten" or="or" more="more" such="such" procedures="procedures" in="in" _1998="_1998" and="and" than="than" three-quarters="three-quarters" these="these" only="only" one="one" two.="two." seventy-eight="seventy-eight" percent="percent" the="the" were="were" by="by" fewer="fewer" per="per" year="year" whereas="whereas" _31="_31" hip="hip" knee="knee" arthroplasties="arthroplasties" low-volume="low-volume" surgeons.="surgeons." forty="forty" patients="patients" had="had" arthroplasty="arthroplasty" operated="operated" upon="upon" two="two" year.="year." table="table" p="p" />

      Hip Knee Shoulder
    Surgeons performing >10/yr 39.0 41.5 2.6
    Surgeons performing 1-2/yr 30.7 25.5 78.2
    Patients having arthroplasty by surgeon performing >50/yr 19.5 29.8 0
    Patients having arthroplasty by surgeon performing >10/yr 83.0 85.0 22.0
    Patients having arthroplasty by surgeon performing 1-2/yr 2.9 2.2 44.2
    *All values are given as percentages.

    These results, coupled with those of Katz et al., suggest that many patients are undergoing arthroplasty done by surgeons who do not perform this procedure frequently, that the complication rate is higher for these low-volume surgeons, and that the skew in the distribution of experienced surgeons is more dramatic for shoulder arthroplasty than it is for hip or knee replacement.

    Patients routinely ask, "Who is the best person to do my procedure?" The answers often given are: "Someone on the provider list of your health plan", "Someone near your home," or "Someone suggested by your primary care physician." Rarely given are the answers "Someone who does a critical number of these procedures" or "Someone who can document his or her personal efficacy in treating the condition in question." Where should the standard of excellence fit into the formula for surgeon selection, and by what means can information about surgeon experience be provided to patients considering surgery?

    There are now over twenty articles documenting the correlation between procedure volume and results of total joint replacement in the peer-reviewed literature. Katz et al. provided another. What is missing is a discussion of the underlying causes of this correlation. The authors may wish to comment on the following. · Is the busiest surgeon busiest because she or he does the best job, i.e., is volume a marker of quality (as in the case of restaurants, where the best ones tend to have the longest lines out front)? · Does the busiest surgeon do the best job because he or she has done more; does 'practice make perfect'? · There is evidence that low-volume surgeons tend to operate on patients who have a greater risk of complications2. Does a surgeon's experience improve patient selection (as in buying art or watermelons)? · Does high volume beget better support services for a procedure; are the better nurses and therapists assigned to frequently performed procedures (like the benefits assigned to frequent fliers)? · Is there a limit to the volume effect, or does quality continue to improve with increasing volume?

    What is also missing is a discussion of the implications of the data. The authors may also wish to consider the following questions:

    · If volume data are important, for what procedures should surgeon volume data be collected, how, and by whom? · If quality and volume are associated, shouldn't the volume data be made accessible to patients so that they can consider this information along with that regarding proximity and payer in making the decision of where to have surgery? Is the surgeon or center obligated to disclose volume as a part of informed consent? With a few exceptions, such surgeon-specific data are difficult for patients to acquire. · For patients electing to have surgery performed by 'low-volume surgeons,' how can they be protected from the potential risks of this choice? · Are low-volume surgeons at enhanced legal risk? If so, how might they be protected? · In that low-volume surgeons have a financial disincentive to refer their patients to high volume surgeons, how can this conflict of interest be best handled? · Are the AAOS and implant companies encouraging surgeons to perform arthroplasties by holding "sawbones" 'learning centers,' even though the surgeons who attend may perform only one or two of these procedures per year? · Is the volume effect transferable, i.e., if one is a high-volume surgeon in terms of performing hip arthroplasties, does this experience apply to knee, hip, ankle, and shoulder arthroplasties as well? · Recognizing that every surgeon begins his or her career as a "low-volume surgeon," how can our educational process accommodate the inevitability of the learning curve in a way that does not jeopardize patient care? · What do the effects of surgeon procedure volume suggest to payers, such as Medicare, with respect to regionalization of major surgical procedures? · If low volumes of total hip replacement (i.e., Answers to these questions have huge implications for surgical education, practice distribution, and health-care financing. The Journal and the orthopaedic community are challenged to consider these implications, remembering that our first duty is to the patients we serve. What is in their best interest?

    Sincerely, Frederick A. Matsen III, MD

    1. Hasan SS, Leith JM, Smith KL, Matsen FA III. The distribution of shoulder replacements among surgeons is significantly different than that of hip or knee replacements. Presented at: The Annual Meeting of the American Academy of Orthopaedic Surgeons; 2001 Feb 28- Mar 4; Orlando, Florida. [Poster no. PE261].

    2. Kreder HJ, Deyo RA, Koepsell T, Swiontkowski MF, Kreuter W. Relationship between the volume of total hip replacements performed by providers and the rates of postoperative complications in the State of Washington. J Bone Joint Surg Am. 1997;79:485-94.

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