Porous implant mimicking bone may provide better, longer-lasting hip replacements

An implant developed by a team from McGill University (Montreal, QC, Canada) that mimics the porosity of real bones to keep existing bone tissue healthy may be longer lasting and cause less pain and fewer side effects than existing implants used in hip replacement surgeries.

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Nov 15, 2016

Researchers from McGill University (Montreal, QC, Canada) have developed a 3D printed, strong but fully porous hip replacement implant that they believe will last longer and cause fewer complications such as peri-prosthetic fracture during or after revision surgery than those currently in use, thanks to its bone-mimicking structure, which encourages existing bone to stay healthy.

The hip replacement implant, known as a femoral stem implant, connects the living femur with the artificial hip joint. It was designed by Damiano Pasini, who teaches mechanical engineering at McGill University and commenced work on the concept over 6 years ago.

“What we’ve done throughout the femoral stem is to replicate the gradations of density found in a real femur by using hollowed-out tetrahedra,” he explains. “Despite the fact that there are spaces within the tetrahedra, these forms are incredibly strong and rigid so they’re a very efficient way of carrying a load. Just think of the lattice-work in the legs of the Tour Eiffel.”

Existing implants have no or only surface porosity, which means that they absorb a significant amount of the mechanical stress that that the living femur normally absorbs. The reduced weight-bearing stress on the femur means that less cell formation is stimulated, increased bone resorption occurs, and bone tissue degrades and becomes less dense. Implants become painful and ultimately need to be replaced, but the lack of normal, healthy bone tissue to hold the replacement implant in place makes the subsequent surgery difficult.

The team carried out in vitro experiments in composite femurs and found 75% bone loss secondary to stress shielding in their implant compared with a fully solid implant, and have already filed patents on it. Furthermore, they believe that the compatibility of the design with existing technologies for hip replacement surgeries means it should be quick for the US FDA to approve and easy for surgeons to adopt: being fully tested, adjusted, accepted and ready for the clinic in as early as 3–5 years’ time.

Sources: Arabnejad S, Johnston B, Tanzer M, Pasini D. Fully porous 3D printed titanium femoral stem to reduce stress-shielding following total hip arthroplasty. J. Orthop. Res. doi:10.1002/jor.23445 (2016) (Epub ahead of print); https://www.mcgill.ca/newsroom/channels/news/towards-better-hip-replacements-263893.

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Alexandra Thompson

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