Making a Better Joint Replacement
About 750,000 knee and hip replacements are performed each year in the United States, 10 percent of which will need to be done again at some point over the life of the artificial joint. These replacements typically last only 15 years before the implants wear down or become loose and have to be replaced. Younger people with advanced osteoarthritis may have to wait for the pain relief that comes with a joint replacement because they don’t want a repeat surgery down the road.
What Problem Was Studied?
Many artificial joints are made of titanium. The surface of this metal is either roughed up or coated with ceramic so the implant will bond to the bone receiving the implant. These current methods work to an extent, but can fail before the user is done with the joint.
In research funded in part by the Arthritis Foundation, scientists at Georgia Institute of Technology in Atlanta sought to find a way to improve the lifetime of titanium joints by promoting a better connection with bone.
What Was Done in the Study?
Principal investigator, and recipient of an Arthritis Foundation grant, Andrés García, PhD, described their solution, “We designed a coating that specifically communicates with cells and we’re telling the cells to grow bone around the implant.” The coating the team created contains an engineered protein that mimics fibronectin, which then binds to molecules in the body called integrins. This fibronectin–integrin complex sends signals to the body causing bone to form around the implant.
To test whether their new coating will work inside a living being, the research team coated tiny titanium cylinders with their engineered-protein polymer. Holes were then drilled into rats’ leg bones and the cylinders were pressed into place. Other cylinders that had no coating and ones that had a different coating were also tested. Bone growth around the titanium was analyzed after four weeks.
What Were the Study Results?
Analysis of the bone–implant interface revealed extensive bone growth and a 70 percent enhancement in the amount of contact between the implant and bone with the specially coated implants compared with the other two implants tested.
The scientists also checked the strength of the implant bond by measuring the amount of force required to pull the cylinders out of the bone. The study showed “significantly higher mechanical fixation” of the implants coated with the engineered protein over the other implants.
What Does This Mean to People With Arthritis?
García concludes, “This study demonstrates that bioactive coatings can enhance healing responses and functional integration of biomedical implants.” The research team’s next step toward seeing this coating put to use in hip and knee replacements is optimizing the coating and testing it in models that imitate fully loaded joints.
Petrie TA, Raynor JE, Reyes CD, et al. The effect of integrin-specific bioactive coatings on tissue healing and implant osseointegration. Biomaterials 2008;29:2849-57.
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