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Common Hip Condition May Not Always Cause Osteoarthritis in Some Racial Groups
June 28, 2007
Osteoarthritis is the most common joint disorder worldwide, yet the
cause of osteoarthritis of the hip is still unknown. One condition that
may play a role is femoro-acetabular impingement (FAI), in which the
femoral head of the thighbone causes damage by rubbing abnormally on
the hip socket (acetabulum). FAI caused by an abnormality in the hip
socket can lead to osteoarthritis, but it is not known if FAI that is
not caused by a defect can also lead to the condition.
Recognizing that the Asian lifestyle requires a larger range of
hip motion than the Western lifestyle, a new study examined FAI in
Japanese patients with normal hips. The study will be published online
in the Journal of Orthopaedic Research, the official journal of the
Orthopaedic Research Society.
Led by Mitsuyoshi Yamamura of Kyowakai Hospital in Osaka,
Japan, researchers conducted a study on five healthy female volunteers
between the ages of 18 and 26. They defined impingement using an
open-configuration MRI, which allows imaging of the hip joint
throughout the entire range of motion, by imaging subjects in the
W-sitting position (in which the legs are bent behind the person) in
two variations with the legs flexed to different degrees. Images were
then obtained for 5 sitting positions, including sitting straight,
bowing while sitting straight, sitting cross-legged, W-sitting, and
squatting. Most of these positions are used in eating, socializing and
in religious or traditional ceremonies and squatting is the position
usually used for defecation in Asia and the Middle East.
The results showed that impingement occurred in all subjects in
the W-sitting position and was also seen in 2 subjects in the squatting
position. The largest hip internal rotation angle was seen in the
W-sitting position. "No subjects complained of hip pain while
maintaining any of the positions, even though the MR imaging process
took from 10 to 14 minutes," the authors note.
Populations in the Middle East and Asia
have a low incidence of osteoarthritis in those with normal hips even
though they regularly adopt positions that induce FAI, which suggests
that FAI might not cause degenerative change in the hips. The
researchers speculate that this may be related to soft tissue laxity
around the hip, citing reports that joint laxity or range of motion
differ by race. In addition, they note that impingement did not appear
to be associated with pathology both in the present study and another
study involving the shoulder area. Another reason FAI may not cause hip
damage is that the positions in the study were static, as opposed to
repetitive trauma, which the study did not evaluate.
The authors acknowledge that since the study was so
small, the findings cannot necessarily be generalized to all Asian
populations. Also, it is not known whether the subject in the study
will develop osteoarthritis in the future. However, they note it is
remarkable that FAI was seen in all 5 subjects. "This suggests that,
depending on race, femoro-acetabular impingement might not always be a
cause of osteoarthritis of the hip," they conclude. "Further work in
this area, including healthy males and patients with abnormalities,
will confirm this conclusion."
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