Engineering Hip Implants That Last
Due to the advent of artificial hips, individuals with irreparable damage to the joint have been able to resume active, pain free lives for the last 50 years. However, some hip replacements do not function as well as intended. In particular, metal-on-metal implants demand accurate positioning during surgery and those which are not positioned optimally are susceptible to early failure, especially in small female patients.
Some physicians are even calling for a ban on the use of artificial joints composed of cobalt-chromium alloys in which the joint’s metal ball rubs against its metal socket whenever the user is walking. Poorly designed or positioned implants can lead to high rates of wear and this releases cobalt-chromium ions into the blood and lymph systems, potentially damaging organs and causing inflammation. Metal ions are also suspected carcinogens.
Researchers at the Fraunhofer Institute in Germany are working on a project called “ENDURE” (Enhanced Durability Resurfacing Endoprosthesis). The results of this project have yielded a new kind of hip implant that, unlike, the conventional counterpart implants on the market today, provide a metal-free solution and bone-like flexibility. This is due to a metal-free, high tech material. The hip socket is composed of a carbon fiber-reinforced, polymer composite. For the femoral head, ceramic was employed.
The ENDURE implants follow the key bone-preserving principle of hip resurfacing: they are thin-walled shells which replace the bearing surface of the joint articulation alone, rather than using large metal stems for support (requiring removal of significant volume of bone). Engineers have also redesigned the way the prosthesis is mechanically attached to the bone. Using a press-fit, the round ball and socket are tapped into the prepared femoral head and into the natural concave surface of the pelvis.
To ensure the best possible positioning of the artificial hip, researchers have developed a size-scalable tool that attaches the implant to standard surgical instruments, enabling implantation, re-alignment, and removal. In many instances, there is challenge involved in attaching instruments to the thin-walled cup implant, while using enough strength for implant repositioning. The instrument also uses a smart pin combination allowing for strong, quick attachment and detachment by the surgeon.
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