Zimmer Biomet® Gender Solutions

NexGen®
High-Flex Implants

Because Women and Men are Different

It’s all about shape.

Women and men are different. That’s not news to the medical establishment. What is news is that Zimmer Biomet is first in the orthopaedic industry to address this fact… with the introduction of the Zimmer-Biomet® Gender Solutions™ NexGen® High-Flex Implants.

What makes them revolutionary is the way in which they compensate for the most important differences between women’s and men’s knees. It isn’t strictly a matter of size; it’s a matter of shape.

Why a woman’s knee?

A growing body of research has led to breakthroughs in distinctive female and male diagnoses and treatments — for conditions ranging from heart disease to rheumatoid arthritis. The need to account for gender-specific solutions in orthopaedics is apparent.

  • Orthopaedic surgeons have reported anatomical differences in women’s and men’s knees for years 1,2,3,4,5,6,7,8
  • Orthopaedic surgeons often have to consider intraoperative adjustments during knee surgery to accommodate women’s anatomical differences. 4
  • Women account for nearly twothirds of knee arthroplasties performed annually in the U.S. 9,10
  • Women are three times more likely than men to forego knee arthroplasty.11

Two distinct populations:
women and men

Pioneering research conducted by Zimmer Biomet has mapped the anatomical differences between female and male knees,12,13 laying the foundation for the design and development of Gender Solutions High-Flex Femoral Implants.

  • Three-dimensional CT data was collected and analysed for more than 800 femurs and patellas.
  • Significant differences were identified between female and male knee anatomy.
  • Plotting M/L and A/P dimensions of the distal femur reveals two distinct populations: female and male.

Implant designs that distinguish between female and male anatomical differences allow for improved implant fit and fewer intraoperative adjustments.


Gender Solutions High-Flex Femoral Implants address the distinctive differences typically found in the female anatomy.

Anterior flange width

The femoral anterior resection of the female bone is narrower than the male femoral anterior resection.

It’s all about shape

Modified Anterior Flange
Anterior flange thickness

Research has shown that the female knee has a less-pronounced anterior condyle than males.2,13 This less-pronounced anterior condyle results in less bone being resected from the female knee:

• 0.8mm less on the lateral condyle (p < 0.02).13
• 1.3mm less on the medial condyle (p < 0.01).13
Gender Solutions High-Flex Femoral Implants address the distinctive anterior condyle differences by:
• Reducing the anterior flange thickness of the implant.
• Recessing the patellar sulcus.
• Retaining the clinically successful NexGen patellar articulation.
• Avoiding overstuffing that may limit postoperative range of motion14,15 that can occur when placing a traditional implant on a resected female knee.

“Twenty-five years ago TKA femoral components were symmetrical. As we recognized the need to improve patellar tracking, industry responded by offering left and right components. Providing an implant that better accommodates the patellar tracking typical of the female patient is just one of the design innovations that the Gender Solutions NexGen High-Flex Femoral Components offers.”

Aaron G. Rosenberg M.D., Professor of Orthopaedic Surgery

Increased Trochlear Groove Angle

Patellar maltracking remains a concern —particularly with females —following total knee arthroplasty.5 Research documents that women have a statistically significant higher Q-angle than men.6,7,8 Gender Solutions High-Flex Femoral Implants replicate the distinct Q-angle difference by increasing the trochlear groove angle of the implant three degrees.

Modified ML/AP Aspect Ratio


CT data documents distinctive shape differences in female and male distal femurs.12,13
Female femurs are:
• More trapezoidal-shaped.
• Narrower in the M/L dimension when compared to a male femur of the same A/P dimension.

Female and male Aspect Ratio


When a traditional implant is placed onto a resected female knee:

• The implant may overhang the bone at the distal, anterior, and posterior M/L interfaces, which may lead to soft-tissue irritation and affect soft-tissue balancing.1,3,4

• The surgeon may be faced with intraoperative adjustments to compensate for the overhang. Gender Solutions High-Flex Femoral Implants have been narrowed mediolaterally.

This allows surgeons to address the female population with unprecedented accuracy.

Femoral mapping — applying the science

To address the issue of overhang in female knee arthroplasty, Zimmer has devised a unique patent pending method for predetermining the contour of a resected bone and the fit of an implant on the bone, and applied this novel method in its development of the Gender Solutions High-Flex Femoral Implant.

01

The three-dimensional inner box shape of the traditional implant is determined.

02

This shape is then extracted…

03

…and unfolded into a twodimensional profile.

04

The resection planes of the female bone are rendered in a two-dimensional profile and overlayed on the implant profile.


05

Arrows indicate the areas where traditional implants overhang the female bone.

06

Additional female data sets are then added to increase the statistical accuracy.

07

A two-dimensional female profile is created…

08

…that replicates the shape of the female bone.

“Historically we have shaped the patients to fit the implants. Now we have implants shaped to fit the patients.”

Robert E. Booth, Jr., M.D.

References:


1. Hitt K, Shurman IIJ, Greene K, et al. Anthropometric measurements of the human knee: correlation to the sizing of current knee arthroplasty systems. J Bone Joint Surg. 2003;85:155-122.
2. Poilvache PL, Insall JN, Scuderi GR, Font-Rodriguez DE. Rotational landmarks and sizing of the distal femur in total knee arthroplasty, Clin Orthop. 1996;331:35-46.
3. Vaidya SV, Ranawat CS, Aroojis A, Laud NS. Anthropometric measurements to design total knee prostheses for the Indian population. J Arthroplasty. 2000;15(1):79-85.
4. Chin KR, Dalury DF, Zurakowski D, Scott RD. Intraoperative measurements of male and female distal femurs during primary total knee arthroplasty. J Knee Surg. 2002;15(4):213-214.
5. Csintalan RP, Schulz MM, Woo J, McMahon PJ, Lee TQ, Gender Differences in Patellofemoral Joint Biomechanics, Clin Orthop. September, 2002; 402:260-269.
6. Aglietti P, Insall JN, Cerulli G. Patellar pain and incongruence. I: Measurements of incongruence. Clin Orthop. 1983;176:217-224.
7. Hsu RWW, Himeno S, Coventry MB, Chao EYS. Normal axial alignment of the lower extremity and load bearing distribution at the knee, Clin Orthop. 1990;255:215-227.
8. Woodland LH, Francis RS. Parameters and comparisons of the quadriceps angle of college-aged men and women in the supine and standing positions. American Journal of Sports Medicine. 1992;20:208-211.

 

9. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics. 2003 National Hospital Discharge Survey, Advance Data No. 359. July 8, 2005; Table 8:14.
10. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics. 2003 National Hospital Discharge Survey, Advance Data No. 359. July 8, 2005; Table 10:16.
11. Hawker G, Wright J, Coyte P, et al., Differences between men and women in the rate of use of hip and knee arthroplasty, The New England Journal of Medicine. 342:1016-1022, 2000.
12. Mahfouz M, Booth R Jr, Argenson, J, Merkl, BC, Abdel Fatah EE, Kuhn MJ. Analysis of variation of adult femora using sex specific statistical atlases. Presented at: Computer Methods in Biomechanics and Biomedical Engineering Conference; 2006.
13. Data on file at Zimmer Biomet
14. Scott NW. Pearls on avoidance and treatment of intraoperative and postoperative complications – exposure of the stiff knee. Presented at: American Association of Hip and Knee Surgeons, Knee Society Specialty Day; March 25, 2006.
15. Bengs BC, Scott RD. The effect of patellar thickness on intraoperative knee flexion and patellar tracking in total knee arthroplasty. J Arthroplasty. 2006;21(5):650-655.