Copyright © 2009 by The Journal of Bone and Joint Surgery, Inc.
Commentary & Perspective
Commentary & Perspective by
Robert Bucholz, MD*,
University of Texas Southwestern Medical Center, Dallas, Texas
Posted November 2009
"The Epidemiology of Bearing Surface Usage in Total Hip Arthroplasty in the
United States," by Bozic et al., is an analysis of data from the Nationwide Inpatient
Sample database between October 1, 2005 and December 31, 2006. It was during
this period that this hospital survey-based administrative database first collected
International Classification of Diseases, Ninth Revision, Clinical Modification
(ICD-9-CM) procedure codes that had been modified to include total hip arthroplasty
bearing-surface codes. Thus, the database provided a unique opportunity for the
investigators to track usage of various bearing surfaces and to detect variations
in usages nationally by patient age, sex, census region, payer class, and hospital
type. Aggregate data demonstrated that, for all patients in the sample, 51% had
metal-on-polyethylene bearing surfaces, 35% had metal-on-metal surfaces, and
14% had ceramic-on-ceramic surfaces. The findings of a preference for metal-on-polyethylene
surfaces for elderly patients and a preference for metal-on-metal or ceramic-on-ceramic
bearings for more active middle-aged patients were expected. Surprisingly, however,
40% of the metal-on-metal and 21% of the ceramic-on-ceramic implants were utilized
in patients who were sixty-five years of age or older. Bearing usage also varied
widely by age, hospital type, and geographic region throughout the United States.
As implant designs and surgical techniques for total hip arthroplasty have
evolved over the last several decades, the primary mode of late failure continues
to be osteolysis and aseptic loosening. Metal-on-metal and ceramic-on-ceramic
bearing surfaces offer the promise, as yet unproven with long-term survivorship
studies, for lower revision rates with regard to these etiologies1,2.
However, each of these bearing surfaces is associated with its own unique mechanical
and biologic problems as well as cost considerations3. American hip
arthroplasty surgeons are divided into camps, often with strong preferences for
routine usage of metal-on-highly cross-linked ultrahigh molecular weight polyethylene
or metal-on-metal or ceramic-on-ceramic bearing surfaces. These practice patterns
are founded on the surgeon's assessment of the relative theoretical advantages
and disadvantages of each bearing surface, the limited evidence-based medical
literature on the subject, clinical experience and training, and a host of other
factors. This study does not contribute to the debate regarding which bearing
surface is better; it merely documents which practice patterns are currently
used nationally. It provides an interesting snapshot of current practice and
a benchmark for future studies that will undoubtedly track longitudinal data
on changing practice patterns.
There were a number of weaknesses in the study. Each administrative database
that is commonly used for this type of study has its own relative strengths and
weaknesses. The Nationwide Inpatient Sample estimates national trends from a
20% sample of all American hospitals. While this sample is probably representative
of the population of all American hospitals, the bearing surface data were listed
as an optional modifier code reported in conjunction with the primary procedure
code for hip arthroplasty. During the study period, only 40% of the hospitals
elected to use this supplemental code for bearing surface. It is reasonable to
speculate that the 60% of hospitals that failed to provide a modifier did not
bother since only a single bearing surface (e.g., metal-on-polyethylene) was
implanted by those surgeons. If this were true, the reported usages in this study
may be inaccurate. Clearly, a validation study to confirm the accuracy of the
claims data in this sample is needed.
A second potential weakness of this database was the mode of data collection.
Hospital coding personnel reviewed hospital operative notes and discharge summaries
to identify the correct bearing-surface modifier. It is unknown if any of these
individuals had adequate training to accurately identify the bearing surface
implanted in any given patient. Implant bar codes, if they were available, would
be a much more precise means of documenting implant usage. Again, an audit is
needed to determine the level of accuracy of the reported bearing-surface modifiers.
A final weakness of this epidemiological study is that the data-collection
process commenced prior to the widespread publicity on chronic squeaking problems
with ceramic-on-ceramic bearing surfaces3. While the prevalence, etiology,
and magnitude of this problem are currently under intense debate, this issue
will undoubtedly impact the relative rates of bearing-surface usage. Such longitudinal
data reflecting surgeons' reactions to new clinical problems with regard to bearing
surfaces would be revealing and, no doubt, will be forthcoming soon.
The importance and the weaknesses of this study emphasize once again the need
for a comprehensive national hip and knee arthroplasty registry. While the logistical,
financial, and legal obstacles to such a registry are formidable, it is imperative
that such a database be designed and developed. It is only through such detailed
and universal registry data that a comprehensive, accurate assessment of the
usage and relative merits of bearing surfaces can be accomplished. The efforts
of the American Academy of Orthopaedic Surgeons and the American Association
of Hip and Knee Surgeons to establish an operational registry in the near future
should be strongly supported by our profession.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate family received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.
References
1. Sharkey PF, Parvizi J. Alternative bearing surfaces in total hip arthroplasty. Instr Course Lect. 2006;55:177-84.
2. Bozic KJ, Morshed S, Silverstein MD, Rubash HE, Kahn JG. Use of cost-effectiveness analysis to evaluate new technologies in orthopaedics. The case of alternative bearing surfaces in total hip arthroplasty. J Bone Joint Surg Am. 2006;88:706-14.
3. Lieberman JR. Two alternative bearings for total hip arthroplasty: more data are needed. J Am Acad Orthop Surg. 2009;17:61-2.
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