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Misaligned legs, extra pounds worsen bad knees
Last Updated: 2004-12-08 9:37:34 -0400 (Reuters Health)
By Amy Norton
NEW YORK (Reuters Health) - Being overweight can speed the progression of
knee osteoarthritis, but the effect may be limited to people who are
moderately "bowlegged" or "knock-kneed," a new study suggests.
Among more than 200 adults with knee osteoarthritis who were followed for 30
months, higher body mass index, or BMI, was associated with a greater risk
of worsening arthritis.
However, further analysis showed this was true only of patients who were
either moderately bowlegged -- meaning their legs curved outward in the area
of the knee -- or moderately knock-kneed -- meaning their knees curved
inward toward each other.
In contrast, high BMI did not speed arthritis progression in patients whose
legs had a "neutral" alignment or those with a severe degree of
misalignment.
Weight loss has been seen as one way overweight people might stall the
deterioration in their arthritis-affected knees. The new findings suggest
that any benefit of weight loss may be limited to patients with moderate
malalignment in the legs, the study's lead author, Dr. David T. Felson of
Boston University, told Reuters Health.
Felson and his colleagues report the findings in the journal Arthritis &
Rheumatism.
Being overweight is already considered a risk factor for developing knee
osteoarthritis, in which the cartilage of the joint breaks down, leading to
pain, stiffness and immobility. But the effect of body weight on the
condition's progression has been less clear, according to Felson.
To see whether limb alignment affects the relationship between BMI and
arthritis progression, Felson and his colleagues followed 227 older men and
women with knee arthritis for 30 months, using X-rays to estimate cartilage
loss in the joint over time.
Overall, the researchers found, arthritis worsened in 23 percent of the
affected knees, with the risk climbing in tandem with BMI -- but only in
those with a moderate degree of limb misalignment.
As for why BMI did not affect arthritis progression in people with neutral
alignment, Felson said it is likely due to the fact that in these
individuals, the heavy "joint loading" caused by excess pounds is fairly
evenly distributed across the knee.
At the other end of the spectrum, severe misalignment in the legs may be
enough in itself to worsen knee arthritis, so that no other risk factor --
including a high BMI -- much of an effect, according to the researchers.
Indeed, they found that limb alignment alone was a strong predictor of
arthritis progression -- with nearly half of the severely misaligned limbs
showing progression, versus 22 percent and 9 percent of moderately
misaligned and neutrally aligned limbs, respectively.
SOURCE: Arthritis & Rheumatism, December 2004.
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