University of Iowa Health Care researchers working with San Diego-based
biotechnology company Kinetikos Medical, Inc. (KMI) have developed a new
total wrist prosthesis for patients with severe wrist arthritis. The Universal
2 total wrist system, developed by Brian D. Adams, MD, professor of orthopaedic
surgery, and Nicole M. Grosland, PhD, assistant professor of orthopaedic
surgery and biomedical engineering, was designed at the University of Iowa
Orthopaedic Biomechanics Laboratory.
Although attempts at total wrist replacement have historically been
fraught with complications, early indications are that the Universal 2’s
unique design, which closely mimics the normal wrist anatomy, will overcome
past obstacles. The prosthesis, which uses the same materials and some
of the same mechanical concepts as in total hip and total knee replacement,
is engineered for both performance and longevity.
"The best patient for the Universal 2 prosthesis is an individual
with severe wrist arthritis who is not routinely involved in activities
that place high demands on the hand and wrist," said Adams, who performs
between 15 and 20 wrist replacements per year. Since the Universal 2 device
was cleared to market by the FDA earlier this year, approximately 30 of
the new prostheses have been implanted. "The long-term prognosis
for these patients is excellent for both function and durability,"
Adams said.
Each phase of development of the Universal 2 included both laboratory
testing and computer modeling. This work was completed in the UI Orthopaedic
Biomechanics Lab, which has been actively involved in research of the
hand and wrist and the development of implants since the 1960s. The research
team consists of faculty and professional engineers who work collaboratively
with faculty orthopaedic surgeons.
"The computer model allowed information to be gathered that is
not readily available through experimental testing alone," Grosland
said. "For example, the model depicted how the components move relative
to each other, how loads transfer through the prosthesis and into the
surrounding bone, and how the materials may deform under high stress."
Laboratory experiments were used to test motion at the articulating
surfaces, to determine the strength of the connections between the plastic
and metal parts, and to assess the durability of the metal stems that
fix into the bone.
Adams and his colleagues evaluated other wrist replacement devices in
developing their new design. "Our first goal was to improve the shapes
of the articulating surfaces. By changing these shapes, stresses on bone
and the prosthesis, as well as the risk of dislocation, were greatly reduced,"
he said.
Additional enhancements in the Universal 2 include the option to implant
the prosthesis without cement when indicated by the physician, preservation
of more bone, an offset position of the prosthesis within the bone to
increase wrist motion and power, and precise instrumentation for accurate
insertion of the prosthesis. |
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