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New joint replacement material developed
at MGH put to first clinical use
New form of polyethylene will allow
stronger, more versatile joint replacement
BOSTON - July 23, 2007 - Massachusetts General Hospital (MGH)
surgeons have performed the first total hip replacement using a
joint socket lined with a novel material invented at the MGH. An
advance over first-generation highly crosslinked polyethylene, which
was also developed at MGH and significantly reduced a serious complication
of early hip implants, the new material may be applied in replacements
for a wider variety of joints in a more diverse group of patients.
"We think this material could be used for any joint in the
body and in any implant design, even those demanding higher flexion
and more mobility," says Orhun Muratoglu, PhD, co-director
of the Harris
Orthopædics Biomechanics and Biomaterials Laboratory (OBBL)
at MGH, who developed the new material in collaboration with scientists
at the Cambridge Polymer Group.
Total replacements for hips and other joints were developed in the
late 1960s, but it soon became apparent that hip implants could
start loosening about 5 years after surgery and would eventually
fail completely. A team led by William Harris, MD, DSc, now director
emeritus of the MGH OBBL, investigated this complication and found
that long-term friction of the implant's head against the polyethylene-lined
joint socket would break off small particles of polyethylene. The
body's immune system reacted against these foreign particles, eventually
destroying adjacent bone tissue and causing the implant to loosen
- a condition called periprosthetic osteolysis.
Harris and his colleagues, working with polymer chemists from MIT,
found that high doses of radiation would "crosslink" the
polyethylene, bonding molecules together to produce a much more
durable material. The procedure also generates free radicals that
could lead to oxidization and degradation of the implant, but the
research team found that melting the material would eliminate free
radicals. The first-generation
highly crosslinked polyethylene was approved by the FDA for
use in implants in 1999 and has been licensed to Zimmer, Inc.
However, the MGH researchers knew that the first-generation material
had limitations in strength that made it unsuitable for some types
of joint replacement implants. Subsequently, Muratoglu found that
oxidation could be blocked by diffusing the antioxidant vitamin
E throughout the polyethylene material. Both mechanical testing
and animal studies have shown that the new material resists wear
as well as the first generation and is much stronger. Vitamin-E-stabilized,
highly crosslinked polyethylene has also received FDA approval for
use in joint implants and has been licensed to both Zimmer and to
Biomet, Inc., which made the implant used in the first surgical
procedure on July 16.
"This material will allow us to offer our patients very long-term,
high-performance joint replacements," says Andrew A. Freiberg,
MD, chief of the Arthoplasty
Service in the MGH Department of Orthopædics, who performed
the first implant with the new material. "It should be suitable
for higher-stress applications in younger patients, those who are
more active and those who are heavier."
MGH orthopædic surgeons are running an international study
in 7 countries to study the new material, with a focus on measuring
long-term performance of the Vitamin-E stabilized bearing surfaces.
Patients can be enrolled as part of this study if they meet the
entrance requirements and are able to follow up at MGH or another
participating hospital for at least five years. Those interested
in the program should call Janet Dorrwachter at (617) 726-2939.
Massachusetts General Hospital, established in 1811, is the original
and largest teaching hospital of Harvard Medical School. The MGH
conducts the largest hospital-based research program in the United
States, with an annual research budget of more than $500 million
and major research centers in AIDS, cardiovascular research, cancer,
computational and integrative biology, cutaneous biology, human
genetics, medical imaging, neurodegenerative disorders, regenerative
medicine, systems biology, transplantation biology and photomedicine.
MGH and Brigham and Women's Hospital are founding members of Partners
HealthCare HealthCare System, a Boston-based integrated health care
delivery system.
Media Contact: Sue
McGreevey, MGH Public Affairs
Physician Referral Service: 1-800-388-4644
Information about Clinical Trials
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