Copyright © 2009 by The Journal of Bone and Joint Surgery, Inc.
Commentary & Perspective
Commentary & Perspective by
J. David Blaha, MD, and Kristi Overgaard, BS*,
University of Michigan, Ann Arbor, Michigan
Posted October 2009
The article by Fehring et al., titled "Differences Between the Sexes in the
Anatomy of the Anterior Condyle of the Knee," presents the results of a well-done
study to determine whether there is a clinically significant difference in the
size and shape of the knee on the basis of sex. These investigators measured
magnetic resonance images and determined no significant difference in the ratio
of anterior condyle to epicondyle geometry (i.e., the aspect ratio). The result
is straightforward, easily understood, and statistically significant. The comparisons
to previous studies that have demonstrated similar results lend credence to the
conclusion that there is no significant sex-based difference in the anatomy of
the anterior femoral condyle.
The controversy that has led to this and other similar investigations has
been sparked by research that has found differences not only in the size but
also in the shape of the female knee as compared with the male knee. This has
led to the introduction of "gender-specific" implants that are purported to provide
a better fit to the female knee and thus give better clinical results. Booth1 has
called gender-specific implant designs "the next level of sophistication." Data presented by him2 and others3 appear to support the idea that there is a significant difference in the shape of the female knee and thus suggest that there is reason to consider a "gender-specific" total
knee prosthesis. Merchant et al.4 evaluated these data and concluded
differently—that of the three purported differences (i.e., increased Q angle,
less prominent anterior medial and anterior lateral condyles, and reduced medial-lateral
to anterior-posterior aspect ratio) "the first two proposed differences do not
exist, and the third is so small that it likely has no clinical effect." The
results of our studies (Blaha et al.5) and the study of Bellemans
et al.6 from this year's annual meetings, question the existence of
significant differences between male and female knees on the basis of sex alone.
We reanalyzed previously reported data generated from the measurement of cadaver
femora and concluded that there was no significant difference between men and
women in the aspect ratio except for one comparison that suggested that the female
knee had a relatively larger ratio on the lateral side—opposite to what has been
found in other studies that were supportive of sex-based differences. Bellemans
et al.6 evaluated 1000 knees with computed tomography and concluded
that women have smaller knees, men have larger knees, and, in the region of overlap,
the "morphotype" (i.e., endomorph, mesomorph, or ectomorph) played a significant
role in determining the shape of the distal part of the femur. However, Ngai
and Wimmer7 reported a difference in the kinematics of the stance
phase of gait in women who were undergoing total knee arthroplasty, a finding
that might support the need for a different prosthesis for women. Clinically,
there is no evidence that women have a worse outcome than men do after traditional
total knee arthroplasty4,8. This important aspect of the debate calls
into question the need for special implants for the female population.
Based on genetic differences, women are, in general, smaller in size than
men. The fact that women generally have smaller bones than men do is a "sex-based" difference,
but men of smaller build fall into the "female range"
and women of larger stature fall into the "male range." In fact, one knee prosthesis
that is marketed as specific for women is reported to be appropriate for 10%
of men who undergo total knee arthroplasty1.
If science were all that is driving this argument, then one would expect the
controversy to fade to the background until compelling evidence surfaced that
such a difference exists and is important to patient care. The controversy might
have faded were it not for the appreciable marketing effort to encourage the
use of "gender-specific" implants. In broadcast, print, and electronic media,
direct-to-consumer marketing has led to increased awareness of the prostheses "made
for women." Some orthopaedic surgeons, as a result of this marketing effort,
have felt compelled to acquiesce to patients'
demands. Those who do not agree with the concept have spent considerable time
talking to patients to explain why they believe that such implants are unnecessary.
Direct-to-consumer marketing can serve a laudatory function by informing patients
of treatments about which they otherwise might not have known. However, this
advertising may lead to confusion for patients, who may be wrongly led to believe
that minor differences represent major advances9. The American Academy
of Orthopaedic Surgeons addressed this possibility in its position statement
on pharmaceutical and device company direct-to-consumer advertising, saying that "information should be scientifically substantiated, accurately presented, and free of false
or misleading claims."9 There is no mechanism, however, to ensure
that implants are marketed according to these guidelines10.
Current controversy about the cost of medical care has heightened the awareness
of "cost-effective" treatments. "Gender-specific"
implants are sold at a premium price on the basis of better fit and thus better
function. Surgeons are held to the standard of evidence-based decisions for patients.
When patients are presented with marketing messages that are not evidence based,
surgeons are placed in the difficult circumstance of not providing a treatment
that a patient requests because of the lack of good evidence for the effectiveness
of that treatment. Therefore, we strongly advocate "evidence-based marketing." In
both direct-to-consumer marketing and in advertising in medical journals, industry
should limit itself to evidence-based conclusions when extolling the features
and benefits of a product.
*The authors did not receive any outside funding or grants in support of their research for or preparation of this work. The authors, or a member of their immediate families, received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (Wright Medical Technology).
References
1. Booth RE Jr. Sex and the total knee: gender-sensitive designs. Orthopedics. 2006;29:836-8.
2. Booth RE Jr. The gender-specific (female) knee. Orthopedics. 2006;29:768-9.
3. Conley S, Rosenberg A, Crowninshield R. The female knee: anatomic variations. J Am Acad Orthop Surg. 2007;15 Suppl 1:S31-6.
4. Merchant AC, Arendt EA, Dye SF, Fredericson M, Grelsamer RP, Leadbetter WB, Post WR, Teitge RA. The female knee: anatomic variations and the female-specific total knee design. Clin Orthop Relat Res. 2008;466:3059-65. Erratum in: Clin Orthop Relat Res. 2009;467:585-6.
5. Blaha JD, Mancinelli C, Overgaard K. Failure of Sex to Predict the Size and Shape of the Knee. Presented as a scientific exhibit at the Annual Meeting of the American Academy of Orthopaedic Surgeons, 2009 Feb 25-28, Las Vegas, NV. Scientific Exhibit No. SE27.
6. Bellemans J, Carpentier K, Vandenneucker H, Vanlauwe J, Victor J. Both morphotype and gender influence the shape of the knee in patients undergoing TKA. Clin Orthop Relat Res. 2009 Aug 8. [Epub ahead of print.]
7. Ngai V, Wimmer M. Are TKR knee kinematics influenced by gait kinetics? Trans Orthop Res Soc. 2009;34:Paper no. 0192.
8. American Academy of Orthopaedic Surgeons. Gender-specific knee replacements: a technology overview. J Am Acad Orthop Surg. 2008;16(2):63-7.
9. American Academy of Orthopaedic Surgeons. Pharmaceutical and device company direct to consumer advertising. Position statement 1162. October 2004. Available at: http://www.aaos.org/about/papers/position/1162.asp. Accessed 2009 Feb 1.
10. Bozic KJ, Smith AR, Hariri S, Adeoye S, Gourville J, Maloney WJ, Parsley B, Rubash HE. The impact of direct-to-consumer advertising in orthopaedics. Clin Orthop Relat Res. 2007;458:202-19.
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