Additional Information about:
The Use of Carbon-Fiber-Reinforced (CFR) PEEK Material in Orthopedic Implants: A Systematic Review

Hip implant for long-term use – Clinical Studies to Start

Thanks to artificial hips, people with irreparable damage to the
joint have been able to lead active, pain-free lives for the
past 50 years. Still, some hip replacements do not function
completely as intended, and metal-on-metal implants in
particular, demand accurate positioning in surgery and implants
positioned non optimally are often susceptible to premature
failure notably in small female patients. Physicians are even
calling for a prohibition on the use of artificial joints made
of cobalt-chromium alloys in which the joint’s metal ball rubs
against its metal socket whenever the wearer walks. Poorly
designed or positioned metal on metal implants can lead to
higher wear rates and this releases elevated cobalt-chromium ion
levels that spread out through the blood and lymph, potentially
damaging organs and triggering inflammation. Metal ions are also
suspected carcinogens. Because these hip replacements are so
robust, however, to date they have often been implanted in
young, active patients.

A metal-free composite

Researchers at the Fraunhofer Institute for Manufacturing
Engineering and Automation IPA in Stuttgart, partnering in an
international team on an EC-funded project entitled “ENDURE”
(Enhanced Durability Resurfacing Endoprosthesis), have now
developed a new kind of hip implant that, unlike the
conventional counterpart implants on the market today, provide a
metal-free solution and bone-like elasticity. This is the result
of a metal-free, high-tech composite: The hip socket is made of
carbon fibre-reinforced PEEK – a high-strength, wear resistant,
biocompatible polymer composite. For the femoral head, ceramic
was used. In addition to this, a hydroxylapatite coating at the
interface to the bone helps ensure that the bone tissue will
fuse thoroughly with the surface structure of the implant. “The
cobalt-chromium implants in use to date are very rigid, and the
load transfer to the bone is non-optimal leading to potential
adverse bone adaptation. Thanks to the new combination of
materials, the transmission of force through the PEEK hip socket
to the pelvic bone is modeled on natural conditions. And there
are no metal ions released,” notes IPA engineer Jasmin Hipp. The
researcher and her team were able to confirm the good wear
resistance in initial tests of the new hip replacement using a
robot that simulated various series of movements such as walking
or climbing and descending stairs. The experiments used a
prototype of the implant.

The ceramic femoral head fits perfectly into the PEEK hip socket. Tiny pins protect bone tissue

The ENDURE implants follow the bone-preserving principle of
hip resurfacing: they are thin-walled shells which replace the
bearing surface of the joint articulation alone, instead of
employing large metal stems for support, which require a
substantial volume of bone to be removed. Researchers have also
redesigned the way the prosthesis is mechanically attached to
the bone. Without cement, and using a press-fit and an integral
scaffold-type structure on the surfaces of the implant that
contact the bone, the hemispherical ball and socket are tapped
onto the prepared femoral head and into the acetabulum – the
natural, concave surface of the pelvis – and anchored in place.

To ensure the best possible positioning of the artificial
hip, the researchers at IPA have developed a size-scalable tool
that attaches the implant to standard surgical instruments,
enabling implantation, re-alignment and removal. The tool can be
discarded after a single use – like a disposable surgical glove.
The challenge is to attach instruments to the very thin-walled
cup implant, with sufficient strength for implant repositioning.
The instrument features a smart collet pin combination allowing
strong, quick, single-position attachment and detachment by the
surgeon. The scientists have already submitted a patent
application for the tool. A team of physicians at the University
of Newcastle have demonstrated in operations performed on
cadavers, the new hip can be set in place and, if necessary,
removed without any difficulties. Meanwhile, the preclinical
studies have been completed, and final development work is being
planned to allow clinical studies to commence. Partners in the
EU-funded project are Aurora Medical, Medicoat, Hunt
Developments, Ala Ortho, CeramTec, Invibio, Biomatech and the
Universities of Gothenburg and Southampton.