Study finds no difference between gender-specific and standard femoral implants

No one denies that men and women are built differently. Anatomic and musculoskeletal differences are easily identifiable. But when it comes to total knee arthroplasty (TKA), a “gender-specific” design has no better or worse outcomes than a conventional design, according to the results of a Korean study presented at the 2010 AAOS Annual Meeting.

The study involved 30 female patients (average age 69.5 years) with a diagnosis of bilateral knee osteoarthritis. During bilateral TKA, a conventional implant was used in one knee and a gender-specific design was used in the opposite knee. Assignment of implant was both random and blinded to the surgeon and the patient. All surgeries were performed between May 2007 and April 2008; patients were followed for a minimum of 1 year.

Clinical evaluation involved range of motion (ROM), Hospital for Special Surgery (HSS) score, Knee Society (KS) score, and Western Ontario and McMaster Osteoarthritis Index (WOMAC). Radiographic evaluations included implant position, posterior offset, and patellar position (patellar tilt and congruence angle). In addition, patients were asked which knee they preferred.

“Clinically, there was no significant difference in terms of ROM, HSS, KS, and WOMAC scores between the two groups preoperatively,” reported the authors. Nor did they find any clinically significant differences at the most recent follow-up after the surgery.

For example, knees with the conventional implant had an average range of motion of 134.4 degrees, average HSS score of 93, average KS score of 140.0, and average WOMAC score of 31.8. Knees with the gender-specific implant had an average range of motion of 131.1 degrees, average HSS score of 92.5, average KS score of 138.3, and average WOMAC score of 32.9.

“On knees using the gender-specific implant,” they reported, “larger femoral implants could be used without mediolateral overstuffing. The knees with a gender-specific implant also showed a larger posterior femoral offset (mean: 4.1 mm larger).”

Two independent investigators performed all radiologic measures and found that the mean preoperative and postoperative alignment was similar in both groups. Additionally, no significant difference was found for the mechanical axis alignment.

Finally, the researchers found no overwhelming patient preference for the gender-specific implant. When asked which knee they preferred, 15 patients said both knees were the same, 9 preferred the gender-specific knee, and 7 preferred the knee with the conventional implant.

As a result, the authors conclude, “Gender-specific implants would only appear to be a surgical option for adaptation of individual anatomic variances.”

The authors of “Total Knee Arthroplasty using Gender-Specific or Unisex Prostheses in Bilateral Simultaneous Cases” are Eun Kyoo Song, MD; Jong Keun Seon, MD; Sang Jin Park, MD; Dam Seon Lee, MD; and Mun Su Jeong, MD. Dr. Song reports ties to Aesculap/B.Braun; his coauthors report no conflicts.

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