Commentary & Perspective on
"Association Between Hospital and Surgeon Procedure Volume and Outcomes of Total Hip Replacement in the United States Medicare Population"
By Jeffrey N. Katz, MD, MS, et al.

Commentary & Perspective by Marc F. Swiontkowski, MD*,
Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, MN

Numerous studies have assessed the relationship between surgeon and hospital service volume and patient outcomes. To list just a few, coronary stent placement, organ transplantation, carotid endarterectomy, and cancer surgery have been studied in well-designed analyses^1-4. We also have cursory information from one state's hospital discharge database that there is, in fact, a significant relationship between surgeon volume and the risk of complications following total hip arthroplasty⁵. These studies confirm the principle that practice makes perfect: the more you and your hospital do, the better your patient's results.

In this issue of The Journal, Katz and colleagues present an analysis of Medicare claims data on total hip replacement procedures performed during a one-year period (July 1995 through June 1996). This data source is widely used to track clinical problems in the elderly. More than 97% of those over the age of sixty-five in the United States are covered by Medicare. The data set is comprehensive and of relatively high quality in terms of accuracy. By necessity, Medicare patients covered by health maintenance organizations were excluded, but during the year of the study these constituted only a small sector of the United States population over the age of sixty-five, and a particularly healthy segment at that. More than 55,000 patients (94%) of the patients undergoing primary total hip arthroplasty had a diagnosis of osteoarthritis. Nearly 13,000 or 93% of the patients who had revision arthroplasty had their procedures performed electively, i.e., for reasons other than acute fracture of the bone around the implant. The outcomes of interest were death, dislocation, deep infection, and pulmonary embolus. Importantly, these authors studied the effects of medical comorbidity on these outcomes.

What are the salient findings? 12% of the primary hip replacements and 49% of the revisions were carried out in institutions in which ten or fewer of these procedures were performed in the Medicare population during the year studied. 52% of the primary hip replacements and 77% of the revisions were carried out by surgeons who performed ten or fewer of these procedures that year in the Medicare population. Hospitals in which more than 100 hip replacements were performed had a significant decrease in the mortality rates of their patients undergoing those procedures. Primary hip replacements carried out by surgeons who did fifty or more of these procedures had lower rates of dislocation than those done by surgeons who performed five or fewer. Patients undergoing revision arthroplasty by surgeons who performed more than ten that year had significantly lower mortality rates than those whose surgeons performed three or fewer.

What we don't know from this study is the incidence of nonfatal complications that did not require hospital readmission. We also don't know the quality of the result—the ability of these patients to ambulate and perform routine activities of daily living, outcomes which patients and surgeons alike highly value.

There are dangers in overinterpreting these results. In regard to the association of volume vs. outcome, one surgeon's results may not be comparable to another's. Innate skills and judgment, fellowship training, patient selection, and preoperative planning are highly variable among individual surgeons; therefore, it is incumbent upon each surgeon to follow his or her own patients both in terms of the outcomes studied here—mortality, dislocation, deep infection, and pulmonary embolus—and functional outcomes. This study provides some parameters for assessing outcomes on the basis of the individual surgeon. To facilitate a more careful analysis of this component, organizations such as the Hip Society and the Knee Society can play an important role in organizing outcome studies done at the regional and state levels. It is dangerous to make the assumption that a given surgeon who performs fewer than ten primary hip replacements per year is not as qualified as his/her higher-volume colleagues. This study does indicate, however, that volume is one factor which seemingly does play a role in some outcomes of both primary and revision hip arthroplasty.

In addition to mortality rates, a national hip registry can provide important information on functional outcomes. A national hip registry also can help to better elucidate the relationship between hospital and surgeon procedure volume and the outcomes of total hip arthroplasty. However, great caution must be exercised because registries must be comprehensive, and the follow-up must be as complete as possible, in order for them to be effective. The possibility of selection bias and a high rate of subjects lost to follow-up will make conclusions so limited as to be useless. Perhaps resources that would be dedicated to such registries would be better allocated to prospective, multicenter outcomes projects that can be administered at the regional and state levels and can take advantage of the established organizational structure and analytical resources of local medical schools. Either way, this association of surgeon and hospital procedure volume as it relates to outcomes in patients undergoing total joint arthroplasty is of major concern to orthopaedists and deserves the investment of our attention and appropriate resources.

*The author did not receive grants or outside funding in support of his research or preparation of this manuscript. He did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated.

References

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2. Edwards EB, Roberts JP, McBride MA, Schulak JA, Hunsicker LG. The effect of the volume of procedures at transplantation centers on mortality after liver transplantation. New Engl J Med. 1999;341:2049-53.
3. Cebul RD, Snow RJ, Pine R, Hertzer NR, Norris DG. Indications, outcomes, and provider volumes for carotid endarterectomy. JAMA. 1998;279:1282-7.
4. Begg CB, Cramer LD, Hoskins WJ, Brennan MF. Impact of hospital volume on operative mortality for major cancer surgery. JAMA. 1998;280:1747-51.
5. 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.