CONTACT: JENNIFER BROWN
Iowa City IA 52242
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Release: Nov. 15, 2001
UI researcher studies causes of post-traumatic arthritis
IOWA CITY, Iowa -- Intraarticular injury (injuries occurring within a joint)
with cartilage damage can lead to post-traumatic arthritis, a condition characterized
by pain and stiffness in the affected joint. Intraarticular injuries are often
the result of high-energy injuries such as traffic accidents or bad falls.
A recent study by researchers at the University of Iowa and Oregon State
University may shed some light on the causes of post-traumatic arthritis and
explain why this arthritic condition is more severe and develops faster in
ankles than in knees.
"Of the three major joints in the leg, the hip, the knee and the ankle,
the knee is the most tolerant of injury and the ankle is the least tolerant,"
said Todd O. McKinley, M.D., UI assistant professor of orthopaedic surgery
and lead author of the study. "Interestingly, although knees are very
forgiving of post-traumatic arthritis, they have a fairly substantial incidence
of idiopathic arthritis, or arthritis for no reason. However, ankles, which
almost never get wear-and-tear arthritis, have a substantial incidence of
post-traumatic arthritis. So the two joints behave very differently."
Using high-resolution digital images McKinley and his colleague, Brain K.
Bay, Ph.D., associate professor of mechanical engineering at Oregon State
University, measured bone strain in knee and ankle joints with cartilage defects.
The researchers found that cartilage defects in the ankle joint increased
strain on bone near the joint, but the opposite was true for the knee joint,
where cartilage defects actually led to a decrease in bone strain next to
"The increase in strain in the ankle was expected," McKinley said.
"The decrease in strain in the knee was completely unexpected but the
results consistently indicated that the strain on the bone was going away."
The causes of post-traumatic arthritis are not well understood. However,
it is likely that joint injuries cause changes to load-transmission through
weight-bearing bones and this may play a role in development of the arthritic
The researchers took slices through ankle and knee joints from cadavers
and made defects of various sizes in the cartilage of those joints. The cartilage
defects were similar to the kind that might occur after an intraarticular
injury. The researchers then measured the bone strain in these samples using
a technique called digital image correlation whereby a computer program compares
high-resolution digital images of the bone under loaded and unloaded conditions
and analyzes how much strain the trabecular bone experiences. Trabecular bone
is the inner lattice of bone that sits underneath the cartilage near joints.
The study clearly shows that knees and ankles respond quite differently
to cartilage injury in the way the joint transmits load from the joint surfaces
through the bone. This finding may help explain why the knee and ankle behave
differently when injured.
McKinley, who also is a consultant physician at the Veterans Affairs Medical
Center in Iowa City, suggests that several features of the knee joint might
explain the decrease in bone strain and the greater ability to tolerate intraarticular
"The knee is not a very close-fitting joint and much of the knee's
stability is provided by the ligaments. Also, the cartilage is very thick,"
McKinley said. "The knee is more tolerant of a defect in the cartilage
because there is enough remaining cartilage to pick up the slack."
In contrast, the ankle is a very constrained joint with a fairly precisely
mated surface between the tibia (shinbone) and the talus (anklebone). In addition,
the cartilage at the ankle joint is about one third as thick as in the knee.
"The ankle has a lot less reserve to accommodate loss of cartilage,"
The study appeared in the September issue of the Journal of Orthopaedic
Research and was funded by grants from the Orthopaedic Research and Education
Fund, Orthopaedic Trauma Association and the Giannini Medical Scholars Foundation.
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