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If Your Knees Ache It Could Be Your Hips Fault
June 12, 2007
Howard shuffles slowly into his physician's office, complaining of
persistent pain in his right foot. An examination reveals that his foot
is fine, but that he has a pinched nerve in his neck and that's what is
making his foot hurt.
Meanwhile, a few blocks down the street, Mary Ann limps into her
doctor's examining room, almost in tears over the relentless ache in
her left knee. It turns out that both of her knees are in perfect
shape. The doctor, however, informs her that the pain in her knee might
be a sign of a hip disorder, and subsequent examination confirms this
to be the case.
What both patients are experiencing is a phenomenon known as
"referred pain," which Daniel Mazanec, M.D., a rheumatologist and
director of the Spine Center at Cleveland Clinic, describes simply as
"pain in an area of the body that is distant from the source of the
pain," according to the Cleveland Clinic's Arthritis Advisor. A classic
example of referred pain, he notes, is the distress experienced in the
left arm by a person in the midst of a heart attack. And for some
people with acute appendicitis, the first warning sign will not be in
the abdomen but in the right shoulder.
Referred pain is not to be confused with radiated pain. "If you have a
herniated disk," Dr. Mazanec explains, "you'll have pain in your back
and you're also likely to have it in your leg, because that's where the
nerve that's irritated happens to travel and the pain can be expected
to radiate along that pathway. Referred pain, on the other hand,
travels along unexpected pathways."
Shared 'wiring' system
In describing the complex neurologic processes that are associated with
referred pain, Dr. Mazanec says, "Think of innervation the nervous
system that serves a muscle or an organ as an interconnected wiring
network that travels throughout the body. A liver abscess can result in
shoulder pain, for example, because the liver is situated below the
diaphragm, and the 'wires' (nerves) from the diaphragm enter the spinal
cord at the same point as the wires (nerves) from the shoulder. They
share the same neurologic pathways to the brain, and sometimes the
electrical signals become intermingled."
This intermingling of pathways is not an abnormality, he notes. Rather,
it results from the normal emergence of the nervous system in the
embryonic stage, when the development of all of the body's "wiring"
proceeds in close proximity. "Over time," says Dr. Mazanec, "the
pathways serve different parts of the body, but they continue to share
the innervation they shared in the embryo, when they were
geographically in the same location."
Patients with arthritis can also experience referred pain. "It almost
always occurs in the joints," says Dr. Mazanec, "and it is most
frequently observed in people with hip osteoarthritis. It's not unusual
for patients with this condition to experience pain in the groin. But
there may also be discomfort or pain in the front of the thigh that
runs all the way down to the knee."
Knee pain that accompanies hip osteoarthritis may intensify over time,
Dr. Mazanec explains, and worsening discomfort will result from
movement of the hip rather than from overuse of the knee, since the
hip-to-knee referral of pain does not go both ways.
Another example of referred pain would be evident in a patient with
cervical (neck) arthritis. "In this case," says Dr. Mazanec, "you can
experience what we call nerve entrapment, and the pain caused by the
pinched nerve can radiate down the arm. But if you have an arthritic
problem in the joints of the neck and there is no nerve entrapment,
that pain can be perceived in the upper back."
If a patient complains of persistent knee pain, it is by no means
assumed that the hip is responsible for the problem, since knee
osteoarthritis is common. "We would examine the knee," says Dr.
Mazanec, "but we would also look at the hip. If we conclude that the
knee joint is normal, we would assess the patient's mobility. We might
then suspect that hip osteoarthritis is the source of the knee pain.
"We wouldn't immediately conclude that it's a case of referred pain
from the hip," says Dr. Mazanec. "We would confirm our diagnosis with
an X-ray." In some cases, he adds, the examination may yield
"confusing" results, in which case the patient might be given a
hip-joint injection of a novocaine-like drug. "If this eliminates the
knee pain," says Dr. Mazanec, "it would confirm that the problem is in
If knee pain is found to have its source in an
arthritic hip, therapy would center primarily on treatment of the hip,
ranging from the use of nonsteroidal anti-inflammatory drugs, to
physical therapy, to hip replacement.
Dr. Mazanec points out that referred pain is not an
imaginary phenomenon. It is real and may signal the presence of a
serious underlying condition affecting a remote part of the body. "If
you experience any kind of pain," he advises, "don't wait a month to
see if it goes away. If it persists, see your doctor."
What You Can Do
Keep track of your pain's characteristics and
communicate this information to your physician. If the site of your
pain appears normal, have an X-ray of other body components that may be
causing the pain.
Talk to your doctor about treatment options drug therapy, physical therapy, or replacement.
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