Almost Half of Older Americans Will Suffer Painful
Knee Osteoarthritis if They Live to 85
Obese have a significantly higher lifetime risk,
64.5% compared to 34.9% for normal weight, 44.1% for overweight
Read more below
about why your knee hurts.
Sept. 2, 2008 – A new study has determined that
almost half of all U.S. adults will develop painful osteoarthritis of
the knee by age 85, but this problem mushrooms to almost two-thirds of
older people who are obese.
The study, based at the University of North
Carolina at Chapel Hill, finds that a person’s lifetime risk rose as
their body mass index or BMI increased, with the greatest risk found in
those whose weight was normal at age 18 but were overweight or obese at
45 or older.
“These results show how important weight management
is for people throughout their lives,” said Dr. Joanne Jordan, principal
investigator of the Johnston County Osteoarthritis Project and senior
study author.
“Simply put, people who keep their weight within
the normal range are much less likely to develop symptomatic knee
osteoarthritis as they get older and thus much less likely to face the
need for major surgical procedures, such as knee replacement surgery.”
The study also sends an important message to
physicians, said Jordan, director of the Thurston Arthritis Research
Center and professor of medicine and orthopaedics in the School of
Medicine at the University. “They need to include the risk of knee
osteoarthritis in the discussion when counseling patients about weight
management and they need to factor that risk into their treatment
plans.”
Why Your Knee Hurts
The location of knee pain can help identify the problem.
Pain on the
front of the knee can be due to bursitis, arthritis, or softening of the
patella cartilage as in chondromalacia patella.
Pain on the sides of the
knee is commonly related to injuries to the collateral ligaments,
arthritis, or tears to the meniscuses.
Pain in the back of the knee can
be caused by arthritis or cysts, known as Baker’s cysts. Baker’s cysts
are an accumulation of joint fluid (synovial fluid) that forms behind
the knee.
Overall knee pain can be due to bursitis, arthritis, tears in
the ligaments, osteoarthritis of the joint, or infection.
Instability, or giving way, is also another common knee problem.
Instability is usually associated with damage or problems with the
meniscuses, collateral ligaments, or patella tracking.
The results were published in the Sept. 15, 2008
issue of Arthritis Care & Research. Lead author of the report is Louise
Murphy, Ph.D. of the Centers for Disease Control and Prevention in
Atlanta. Murphy led the data analysis and the CDC is the primary funder
of the Johnston County Osteoarthritis Project.
In the study, researchers collected and analyzed
data over a 13-year period from 3,068 men and women 45 years old and
older who live in Johnston County, N.C.
At two separate points during the study, each
participant was interviewed at home and given a clinical exam that
included taking X-ray images of their knees and measuring their BMI.
They were interviewed a second time two weeks after
the clinical exam.
In addition, researchers calculated the subjects’
BMI at age 18 based on their self report of height and weight at that
age.
After all data were collected, researchers
estimated the lifetime risk of symptomatic osteoarthritis in at least
one knee using logistic regression models of statistical analysis.
They found that the lifetime risk of symptomatic
knee osteoarthritis was 44.7 percent.
There were no significant differences in risk
related to a participant’s sex, race or education level.
However, obese participants had a significantly
higher lifetime risk, 64.5 percent compared to 34.9 percent for normal
weight and 44.1 percent for overweight participants.
Those with a history knee injury also had a higher
risk than those without, 56.8 percent compared to 42.3 percent.
Normal in teens, obese in later years increases
risk
A separate analysis of BMI across the span of
participants’ lives found that those who had a normal weight at age 18
and at their baseline and follow up visits had the lowest risk (29.2
percent) while those who reported a normal weight at 18 but were
overweight or obese at the two later time points had the highest risk
(59.9) percent.
Your knees may hurt but you live longer if you
run!
Disability and survival curves continued to diverge
after the 21-year follow-up as participants approached their ninth
decade of life
Aug. 11, 2008
Although the participants in this study all live in
the same relatively rural county in the South, the lifetime risk of knee
arthritis is likely high in the rest of the U.S. as well, the
researchers wrote. They concluded that the study “underscores the need
for public health weight loss and management interventions” that would
help decrease the risk.
Editor's Notes:
Besides Jordan, UNC authors of the study include
Todd A. Schwartz, Dr.P.H., Gary Koch, Ph.D. and William D. Kalsbeek,
Ph.D., all from the UNC School of Public Health; and Jordan B. Renner,
M.D., from the School of Medicine.
In addition to Murphy, study authors not at UNC
include Charles G. Helmick, M.D., of the CDC; Gail Tudor, Ph.D. of
Huston College in Bangor, Maine; Anca Dragomir, Ph.D., who earned her
Ph.D. at UNC but now works at the National Institutes of Health; and
Gheorghe Luta, Ph.D., who also earned his Ph.D. at UNC and is now at
Georgetown University Medical Center.
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