Are there gender-specific differences in knee anatomy? If so, do these differences result in higher failure rates for women who have total knee arthroplasty (TKA)? Would a gender-specific knee implant improve the success rates among women who have TKA?

These are the questions that technology overview on gender-specific knee replacements prepared by the AAOS Technology Assessment Project Team hoped to answer. The result of their efforts was presented to the AAOS Board of Directors at its December 2007 meeting.

In its final form, the technology overview did not make recommendations for or against the use of gender-specific knee replacements. Instead, it encouraged readers to consider the information presented and reach their own conclusions. The overview, therefore, can serve as an education tool for physicians.

A systematic review methodology was used, based on studies published as of November, 2006 on gender-specific knee replacements.

Gender-specific anatomic differences
According to the overview, the following differences in bony anatomy have been documented between male and female knees:

• Men have larger femurs than women (anterior-posterior height, transepicondylar width, height of the lateral and medial condyles).
• Women have a narrower medial-lateral width for the same anterior-posterior dimension of the distal femur.
• The trochlear groove is externally rotated relative to the epicondylar axis in women and internally rotated relative to the same axis in men.
• Women have a larger Q angle, a larger ratio between the length of the patellar tendon and the greatest diagonal length of the patella on a lateral knee radiograph (patella alta), and a more negative congruence angle (indicating that the lowest portion of the patella is more medial relative to a line bisecting the sulcus angle) than men.
• Men and women of the same height have similar Q angles and taller people have slightly lower Q angles.

The overview also reported some variances in patellofemoral joint biomechanics between sexes, particularly in the size of the patellofemoral contact area and the degree of patellofemoral contact pressures.

Two key questions
The project team framed two key questions, developed article inclusion/exclusion criteria, and then conducted systematic literature searches. Only articles that met the a priori criteria were included; each article was assigned a level of evidence.

The first key question was whether women had higher failure rates than men after traditional knee replacement surgery. The 24 articles that met the team’s criteria did “not consistently show differences between men and women in most of the outcomes of tricompartmental total knee replacement surgery…regardless of whether a study examined revision rates, reoperation rates, range of motion, and scores on several outcomes instruments…in both studies that attempted to adjust for potential risk, and in non-risk adjusted studies.”

The second question asked whether the use of gender-specific knee replacement increased the rates of successful knee replacement surgery in women. The team could not identify any clinical studies that directly addressed this question.

Not an official position
The AAOS technology overview on gender-specific knee replacement is not intended to convey any official AAOS position on gender-specific knee implants. Instead, the information is provided as a service to help members identify and evaluate the available published literature on this topic so that they can provide the best possible care to their patients.

Mary Ann Porucznik is managing editor of AAOS Now. She can be reached at porucznik@aaos.org