Improved Porous Coating for Bony Ingrowth

Approved by the FDA in 2005, hydroxyapatite (HA), a naturally occurring, crystalline component of healthy bone is applied into the surface of Stryker press-fit, un-cemented knee implants as a thin plasma coating, improving bone integration into press-fit implants. Wright Medical has developed a bone-inductive porous coat utilizing titanium foam.

Figure 1.Wright Medical Advance tibial base plate with titanium foam as porous coat.
Figure 3.Wright Medical Advance femoral component (underside view). Broader design fits most males.
Figure 5.Side view of Wright Medical Advance femoral component.
Figure 2.Stryker Triathlon tibial base plate with Hydroxyapatite coated beads as porous coat.
Figure 4.Stryker Triathlon femoral component (underside view). Narrower design fits most females.
Figure 6.Side view of Stryker Triathlon femoral component (reveals basic similarities).

Gender-specific Design

What is a gender-specific implant?

Previously, knee implants were designed using combined male and female "average" dimensions even though men and women are usually different. More recently, gender-specific knee implants have been designed and sized for either males or females. Generally speaking, men require broader implants than women.

The advantages of gender-specific knee implants is that they can more accurately crown (cap) and reseal the specific male or female bone structure.

Figure 7.Left: Wright Medical Medial Pivot femoral component size 4. Right: Stryker femoral component size 5.
Figure 8.Comparison of patellas.

Why Gender-specific Implants?

When male/female differences are not considered, implant designs may not provide optimal bone coverage. Inadequate bone capping may result in atrophy or dissolution of uncovered bone (osteolysis). Overcapping (protrusion beyond normal bone struction) may irritate soft tissues around the knee during activity. Optimizing coverage improves 1. Hemostasis (control of bleeding), 2. Bone integration into implants, 3. Knee stability, and 4. Loading patterns. Figures 9 and 10 show examples of undercoverage and overcoverage, respectively.

Figure 9.Example of undercoverage of male femur.
Figure 10.Example of overcapping of female femur.

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