By John Gever, Senior Editor, MedPage Today
Published: February
18, 2013
Reviewed by Robert Jasmer,
MD; Associate Clinical Professor of Medicine, University of
California, San Francisco
Failure
rates for hip implants were 29% higher for women than men in a large U.S.
registry study after controlling for a variety of
factors including device type, researchers said.
With a total of 35,140 patients
undergoing primary total hip arthroplasty followed for a median of 3 years, the
crude all-cause rate of failure (defined as subsequent revision surgery) was
2.3% for women (95% CI 2.1% to 2.5%) compared with 1.9% for men (95% CI 1.6% to
2.1%), according to Maria C.S. Inacio, MS, of the Southern California
Permanente Research Group in San Diego, and colleagues.
After adjustments for age, body mass
index, diabetes status, degree of presurgical symptom severity, implant
fixation method, device category, and femoral head size, the authors calculated
a hazard ratio (HR) for revision of 1.29 for women versus men (95% CI 1.11 to
1.51), they reported online in JAMA Internal Medicine.
The risk appeared most prominent for
aseptic revision (HR 1.32, 95% CI 1.10 to 1.58) compared with septic failure
(HR 1.17, 95% CI 0.81 to 1.68), the researchers found.
Larger femoral head sizes appeared
especially problematic for women. For head sizes of 36 mm or more, the adjusted
HR for failure in women versus men was 1.49 (95% CI 1.14 to 1.95), whereas
differences in revision rates for smaller head sizes were not significant after
adjustment.
Much
of the increased risk for women also seemed concentrated in metal-on-metal
implants, with a doubling in risk for women versus men (adjusted HR 1.97, 95% CI 1.29 to 3.00).
But that was primarily because of
reduced risk of failure with metal-on-metal devices in men (adjusted HR 0.68
versus highly crosslinked polyethylene, 95% CI 0.45 to 1.02), whereas in women,
the adjusted failure rates for metal-on-metal versus crosslinked polyethylene
were similar, adjusted HR 1.07, 95% CI 0.72 to 1.60).
Clinical Implications?
In an accompanying commentary, Diana
Zuckerman, PhD, of the National
Research Center for Women and Families in Washington, D.C., suggested
that the study's clinical implications were relatively trivial.
She noted that most patients
considering hip replacement are already suffering pain and limited mobility and
have few other options.
"Knowing that their chances of
success are lower than men's is not helpful to women who are unable to perform
many activities of daily living," Zuckerman argued.
Instead, she said, what is needed is
"long-term comparative effectiveness research based on large sample sizes,
indicating which total hip arthroplasty devices are less likely to fail in
women and in men, with subgroup analyses based on age and other key
patient traits, as well as
key surgeon and hospital factors."
But Glenn Don Wera, MD, of UH Case
Medical Center in Cleveland, told MedPage Today that the study provided
valuable insights into the reasons for higher failure rates in women.
He noted that the higher rate of revision in women was already
known from Medicare data. In the current study, however, "they were
able to control for a number of clinical factors, including the kind of
prosthesis the patient had, the experience level of the surgeon, and the
different institutions and the different prostheses they were using."
That the increased risk in women was
still evident despite adjusting for those factors indicates that something
else, such as women's generally smaller stature, is responsible, Wera
suggested.
Revision Rate: Beyond Infection
Data for the current study came from the Kaiser Permanente system's
registry of total joint replacements from 2001 to 2010. Procedures were
performed at 46 hospitals in California, Hawaii, Oregon, Washington, and
Colorado by 319 different surgeons.
The registry is the largest of its type in the
U.S., the authors said and includes data on surgeons' and hospitals'
arthroplasty procedure volumes; the patients and the implants they received
(cemented, uncemented, or hybrid); and implant bearing surface, such as metal
on metal, metal or ceramic on highly crosslinked polyethylene, or ceramic on
ceramic. The researchers put the DePuy metal-on-metal hip resurfacing monoblock
device into its own category.
Only patients undergoing unilateral
procedures were included in the analysis.
About 58% of the 35,140 procedures
were performed in women (mean age 65.7 versus 63.8 for men). Just over 60% of
both sexes had scores of 1 or 2 on the American Society of Anesthesiologists
index, with nearly all of the remainder having scores of 3 or more.
The age difference between men and
women was statistically significant. In addition, women in the cohort tended to be slightly more likely to
be white or Asian and to have osteoarthritis, rheumatoid arthritis, or
dysplasia. They were less likely to be diabetic or obese and to have
osteonecrosis or post-traumatic arthritis.
Not surprisingly, women were much
less likely to have implant femoral head sizes of 36 mm or more (32.8% versus
55.4% for men, P<0.001). About twice as many men as women had
metal-on-metal bearings (19.4% versus 9.6%), whereas ceramic or metal on highly
crosslinked polyethylene were more popular for female patients (P<0.001).
The DePuy resurfacing implant was
used in 1.3% of women versus 2.6% of men (P<0.001).
Preferences for fixation types also
differed between men and women, with hybrid methods more common in the women
and cementless fixation more common in men.
Mean surgeon and hospital volumes did
not differ between sexes.
The authors noted that with no significant increase in risk
of septic failure for women, their results mean that "factors other than
infection" are responsible for the higher overall revision rate.
Limitations to the analysis include
its observational design, the relatively short follow-up period, lack of data
on some potential confounding factors, and the use of revision surgery as the
definition of implant failure. Also, the researchers used relatively broad
categories of implant type, conceding that design variations within these
categories could have influenced the results.
The
study was funded by the FDA.
Study authors and Zuckerman declared
no relationships with commercial entities. Several study authors were Kaiser
Permanente employees.
Primary source: JAMA Internal Medicine
Source
reference:
Inacio M, et al
"Sex and risk of hip implant failure: Assessing total hip arthroplasty
outcomes in the United States" JAMA Intern Med 2013; DOI:
10.1001/jamainternmed.2013.3271.
Additional source: JAMA Internal Medicine
Source
reference:
Zuckerman D
"Hip implant failure for men and women: What and when we need to
know" JAMA Intern Med 2013; DOI: 10.1001/jamainternmed.2013.19.
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