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AAOS Now

Published 4/1/2009
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Jennie McKee

Is a gender-specific design necessary?

Findings do not support need for female-specific implant designs

“Specific anatomic differences are thought to account for gender-specific outcomes after total knee arthroplasty (TKA); however, using prospectively collected data, our study found that females had higher early improvement in function and pain scores after unisex TKA than males,” said Thoralf R. Liebs, MD, the lead author of a paper that was presented at the 2009 AAOS Annual Meeting.

Dr. Liebs noted that because the findings suggest that women benefit from TKA to a higher degree than men, regardless of the type of implant, the need for female-specific implant designs is not substantiated.

Study composition
Researchers collected data on patients diagnosed with osteoarthritis who were scheduled to undergo unilateral hip or knee replacement surgery at five participating centers in Germany between January 1, 2003, and April 30, 2006. Patients enrolled in the trial were asked to complete a questionnaire on comorbidities at time of admission to the hospital. For the purpose of this analysis, only patients receiving TKA or unicondylar knee arthroplasty (UKA) were included (141 males and 353 females).

All patients completed daily physiotherapy, which consisted of exercises to improve range of motion, muscle tension, venous return, balance, coordination, and gait. They also were taught how to handle activities of daily living, including transfers, walking, and negotiation of stairs and uneven surfaces.

“Patients used continuous passive motion machines on a daily basis after suction drains were removed,” said Dr. Liebs. “They also received analgesics according to a standard scheme.”

Follow-up results
Researchers recorded patient-reported physical function preoperatively and at 3, 6, 12, and 24 months postoperatively, using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Investigators also obtained WOMAC scores for leg-specific stiffness and pain, as well as ratings from the mental and physical component summaries of the 36-item Short Form General Health Survey (SF-36).

To determine WOMAC scores, responses were recorded on a visual analog scale with terminal descriptors. Scores for each category were standardized on a score of 0 to 100; higher scores indicated less pain, stiffness, or dysfunction.

At the time of surgery, females were significantly older than males (mean age 70.8 years v 67.8 years, P < 0.001). In addition, mean WOMAC scores indicated that females had less physical function (54.8 v 47.3, P = 0.002), more pain (54.0 v 47.9, P = 0.007), and more stiffness (54.1 v 46.1, P = 0.007) compared to males.

Investigators did not find any statistically significant differences between the sexes regarding body mass index (BMI) or the number of comorbidities and additional limitations. Females, however, had significantly lower mean scores on the mental component summary of the SF-36 (48.0 [± 12.1] v 51.7 [± 11.9], P = 0.004), and the Knee Society Function Scale (51.9 [± 13.3] v 57.4 [± 12.6], P < 0.001).

At 3-, 6-, 12-, and 24-month follow-up, researchers found no statistically significant differences between sexes for all raw outcomes studied. At the 3-month follow-up, mean WOMAC function and pain improvement scores were higher for female patients than for male patients (function: 28.1 v 22.5, P = 0.014; pain: 31.6 v 24.9, P = 0.011). The difference continued at the 6-month follow-up (function: 32.2 v 27.1, P = 0.034; pain: 36.2 v 30.8, P = 0.029) (Fig. 1).

Drawing conclusions
The rationale for gender-specific TKA design, noted Dr. Liebs, is based on specific anatomic differences and the assumption that outcomes for women are inferior following TKA using a unisex implant.

“And yet,” he said, “this analysis clearly showed that, as measured by the WOMAC scale, women have lower functional levels before undergoing knee arthroplasty and greater improvement in health-related quality of life when compared to men after undergoing the procedure.”

Dr. Liebs pointed out that the failure of the study to identify statistically significant differences in the raw outcomes between the sexes after knee arthroplasty raises the question of whether the WOMAC as an outcome measure is just not sensitive enough to capture the differences in postoperative outcomes.

“It remains to be demonstrated whether gender-specific TKA designs reveal improved raw outcome scores when compared among females,” added Dr. Liebs.

Dr. Liebs’ co-authors include Wolfgang Herzberg, MD; Wolfgang Rüther, MD, PhD; Martin Russlies, MD; Jörg Haasters, MD, PhD; and Joachim Hassenpflug, MD, PhD. The authors report the following disclosures: Dr. Liebs—Bayer Health Care and DePuy, a Johnson & Johnson Company; Drs. Haasters, Herzberg, and Russlies—none; Dr. Rüther—Zimmer; Dr. Hassenpflug—DePuy, a Johnson & Johnson Company.

Jennie McKee is a staff writer for AAOSNow. She can be reached at mckee@aaos.org