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 When women had less strength in muscles known as the knee extensors,
or quadriceps, which help straighten the leg for standing, climbing
and kicking, they were 47 percent more likely to develop knee
arthritis than women who had stronger knee extensors, the study
found.
Weakness in the knee flexor muscles on the back of the legs, also
known as hamstrings, was associated with 41 percent greater odds of
knee osteoarthritis in women.
Thigh muscle strength didn't appear to influence the risk of knee
osteoarthritis for men, researchers report in Arthritis Care and
Research.
"While our recent study has highlighted the important role of strong
thigh muscles in reducing the risk of knee osteoarthritis
development, particularly in women, it is not possible to guarantee
that having strong thigh muscles will protect women from developing
knee osteoarthritis because there are many other factors that play
into the disease," said lead study author Dr. Adam Culvenor, a
researcher at Paracelsus Medical University in Salzburg, Austria.
"Nevertheless, our results suggest that optimizing quadriceps and
hamstring strength may help to lower the risk of developing knee
osteoarthritis," Culvenor added by email.
For the study, Culvenor and colleagues examined data from MRIs of
thigh muscles and muscle strength tests for 186 adults with knee
osteoarthritis and another 186 without the condition.
Because obesity is independently associated with an increased risk
of knee osteoarthritis, researchers also examined data on
participants' weight relative to their height, a measure known as
body mass index (BMI).
At the start of the study, participants were 61 years old on
average.
Even after adjusting for BMI, women with weaker knee extensor
muscles were 33 percent more likely to have knee osteoarthritis, and
women with weaker flexor muscles were 28 percent more likely to
develop knee arthritis.
With men, even after researchers accounted for BMI, they still
didn't find a statistically meaningful association between thigh
muscle strength and knee arthritis.
While the role of thigh muscle weakness as a risk factor for knee
osteoarthritis is not fully understood, the quadriceps can help
prevent the development and progression of this knee condition by
acting as shock absorbers and stabilizers for the knee, Culvenor
said.
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Without strong quadriceps muscles, more stress is placed on the
cartilage within the knee, and this has been suggested to induce a
degenerative process, wearing down of the cartilage and ultimately
osteoarthritis, Culvenor added.
The different results between men and women could be explained by
the muscles’ response to greater body mass, Culvenor said. In men, a
greater body mass was associated with increased muscle strength,
whereas muscles didn’t respond and get stronger in women with a
greater body mass.
"This is likely because muscles in men with greater body mass have
more contractile tissue and strength, whereas in women with greater
body mass more non-contractile adipose tissue is deposited within
the muscle and hence cannot produce as much force," Culvenor said.
Limitations of the study include the lack of an exact measurement of
voluntary muscle activation to determine thigh muscle strength or a
precise assessment of intramuscular fat, the authors note. Both of
these details might help explain differences between men and women
in the study.
Still, the results make sense because muscle strength, body
structure and usage of the joint affects the odds that knee
osteoarthritis will develop as well as its severity, said Dinesh
Bhatia, a researcher at North Eastern Hill University in Meghalaya,
India, who wasn't involved in the study.
"If the muscles are weaker people try to overcompensate using their
normal muscles for a certain period of time, after which it can no
longer handle the stress/ strain and gives in," Bhatia said by
email. "Hence, therapists advise muscle strengthening and other
techniques to reduce overburdening of the joint and avoid or reduce
knee osteoarthritis pain."
SOURCE: http://bit.ly/2lbKrpd Arthritis Care and Research, online
February 8, 2017.
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