Knee Problems
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The knees provide stable support for the body and allow the legs
to bend and straighten. Both flexibility and stability are needed for standing
and for motions like walking, running, crouching, jumping, and turning.
Several kinds of supporting and moving parts, including bones,
cartilage, muscles, ligaments, and tendons, help the knees do their job. Any
of these parts can be involved in pain or dysfunction.
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There are two general kinds of knee problems: mechanical and inflammatory.
Some knee problems result from injury, such as a direct blow or
sudden movements that strain the knee beyond its normal range of movement.
Other problems, such as osteoarthritis in the knee, result from wear and tear
on its parts.
Inflammation that occurs in certain rheumatic diseases, such as
rheumatoid arthritis and systemic lupus erythematosus, can damage the knee.
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The point at which two or more bones are connected is called a
joint. In all joints, the bones are kept from grinding against each other by
padding called cartilage. Bones are joined to bones by strong, elastic bands
of tissue called ligaments. Tendons are tough cords of tissue that connect
muscle to bone. Muscles work in opposing pairs to bend and straighten joints.
While muscles are not technically part of a joint, they're important because
strong muscles help support and protect joints.
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Like any joint, the knee is composed of bones and cartilage, ligaments,
tendons, and muscles (see the diagram).
The knee joint is the junction of three bones: the femur (thigh
bone or upper leg bone), the tibia (shin bone or larger bone of the lower leg),
and the patella (knee cap). The patella is 2 to 3 inches wide and 3 to 4 inches
long. It sits over the other bones at the front of the knee joint and slides
when the leg moves. It protects the knee and gives leverage to muscles.
The ends of the three bones in the knee joint are covered with
articular cartilage, a tough, elastic material that helps absorb shock and
allows the knee joint to move smoothly. Separating the bones of the knee are
pads of connective tissue. One pad is called a meniscus (muh-NISS-kus). The
plural is menisci (muh-NISS-sky). The menisci are divided into two crescent-shaped
discs positioned between the tibia and femur on the outer and inner sides of
each knee. The two menisci in each knee act as shock absorbers, cushioning
the lower part of the leg from the weight of the rest of the body as well as
enhancing stability.
There are two groups of muscles at the knee. The quadriceps muscle
comprises four muscles on the front of the thigh that work to straighten the
leg from a bent position. The hamstring muscles, which bend the leg at the
knee, run along the back of the thigh from the hip to just below the knee.
Keeping these muscles strong with exercises such as walking up stairs or riding
a stationary bicycle helps support and protect the knee.
The quadriceps tendon connects the quadriceps muscle to the patella
and provides the power to extend the leg. Four ligaments connect the femur
and tibia and give the joint strength and stability:
- The medial collateral ligament (MCL) provides stability to the inner (medial)
part of the knee.
- The lateral collateral ligament (LCL) provides stability to the outer (lateral)
part of the knee.
- The anterior cruciate ligament (ACL), in the center of the knee, limits
rotation and the forward movement of the tibia.
- The posterior cruciate ligament (PCL), also in the center of the knee,
limits backward movement of the tibia.
Other ligaments are part of the knee capsule, which is a protective,
fiber-like structure that wraps around the knee joint. Inside the capsule,
the joint is lined with a thin, soft tissue called synovium.
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Doctors use several methods to diagnose knee problems.
Medical history--The patient tells the doctor details about
symptoms and about any injury, condition, or general health problem that might
be causing the pain.
Physical examination--The doctor bends, straightens, rotates
(turns), or presses on the knee to feel for injury and discover the limits
of movement and the location of pain. The patient may be asked to stand, walk,
or squat to help the doctor assess the knee's function.
Diagnostic tests--The doctor uses one or more tests to determine
the nature of a knee problem.
- X ray (radiography)--An x-ray beam is passed through the knee to
produce a two-dimensional picture of the bones.
- Computerized axial tomography (CAT) scan--X rays lasting a fraction
of a second are passed through the knee at different angles, detected by
a scanner, and analyzed by a computer. This produces a series of clear cross-sectional
images ("slices") of the knee tissues on a computer screen. CAT scan images
show soft tissues such as ligaments or muscles more clearly than conventional
x rays. The computer can combine individual images to give a three-dimensional
view of the knee.
- Bone scan (radionuclide scanning)--A very small amount of radioactive
material is injected into the patient's bloodstream and detected by a scanner.
This test detects blood flow to the bone and cell activity within the bone
and can show abnormalities in these processes that may aid diagnosis.
- Magnetic resonance imaging (MRI)--Energy from a powerful magnet
(rather than x rays) stimulates knee tissue to produce signals that are
detected by a scanner and analyzed by a computer. This creates a series
of cross-sectional images of a specific part of the knee. An MRI is particularly
useful for detecting soft tissue damage or disease. Like a CAT scan, a computer
is used to produce three-dimensional views of the knee during MRI.
- Arthroscopy--The doctor manipulates a small, lighted optic tube
(arthroscope) that has been inserted into the joint through a small incision
in the knee. Images of the inside of the knee joint are projected onto a
television screen. While the arthroscope is inside the knee joint, removal
of loose pieces of bone or cartilage or the repair of torn ligaments and
menisci is also possible.
- Biopsy--The doctor removes tissue to examine under a microscope.
Knee Injuries and Problems
Arthritis
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Arthritis of the knee is most often osteoarthritis. In this disease,
the cartilage in the joint gradually wears away. In rheumatoid arthritis, which
can also affect the knees, the joint becomes inflamed and cartilage may be
destroyed.* Arthritis not only affects joints; it can also affect supporting
structures such as muscles, tendons, and ligaments.
Osteoarthritis may be caused by excess stress on the joint from
deformity, repeated injury, or excess weight. It most often affects middle-aged
and older people. A young person who develops osteoarthritis may have an inherited
form of the disease or may have experienced continuous irritation from an unrepaired
torn meniscus or other injury. Rheumatoid arthritis often affects people at
an earlier age than osteoarthritis.
* The National Institute of Arthritis and Musculoskeletal
and Skin Diseases Information Clearinghouse has separate publications on
osteoarthritis, rheumatoid arthritis, and knee replacement. See the end of
this booklet for contact information.
Someone who has arthritis of the knee may experience pain, swelling,
and a decrease in knee motion. A common symptom is morning stiffness that lessens
as the person moves around. Sometimes the joint locks or clicks when the knee
is bent and straightened, but these signs may occur in other knee disorders
as well. The doctor may confirm the diagnosis by performing a physical examination
and examining x rays, which typically show a loss of joint space. Blood tests
may be helpful for diagnosing rheumatoid arthritis, but other tests may be
needed too. Analyzing fluid from the knee joint may be helpful in diagnosing
some kinds of arthritis. The doctor may use arthroscopy to directly see damage
to cartilage, tendons, and ligaments and to confirm a diagnosis, but arthroscopy
is usually done only if a repair procedure is to be performed.
Most often osteoarthritis of the knee is treated with pain-reducing
medicines, such as aspirin or acetaminophen (Tylenol*); nonsteroidal anti-inflammatory
drugs (NSAIDs), such as ibuprofen (Motrin, Nuprin, Advil); and exercises to
restore joint movement and strengthen the knee. Losing excess weight can also
help people with osteoarthritis.
Rheumatoid arthritis of the knee may require physical therapy and
more powerful medications. In people with arthritis of the knee, a seriously
damaged joint may need to be replaced with an artificial one. (A new procedure
designed to stimulate the growth of cartilage by using a patient's own cartilage
cells is being used experimentally to repair cartilage injuries at the end
of the femur at the knee. It is not, however, a treatment for arthritis.)
* Brand names included in this booklet are provided
as examples only, and their inclusion does not mean that these products are
endorsed by the National Institutes of Health or any other Government agency.
Also, if a particular brand name is not mentioned, this does not mean or
imply that the product is unsatisfactory.
Chondromalacia (KON-dro-mah-LAY-she-ah), also called chondromalaciapatellae,
refers to softening of the articular cartilage of the knee cap. This disorder
occurs most often in young adults and can be caused by injury, overuse, parts
out of alignment, or muscle weakness. Instead of gliding smoothly across the
lower end of the thigh bone, the knee cap rubs against it, thereby roughening
the cartilage underneath the knee cap. The damage may range from a slightly
abnormal surface of the cartilage to a surface that has been worn away to the
bone. Chondromalacia related to injury occurs when a blow to the knee cap tears
off either a small piece of cartilage or a large fragment containing a piece
of bone (osteochondral fracture).
The most frequent symptom is a dull pain around or under the knee
cap that worsens when walking down stairs or hills. A person may also feel
pain when climbing stairs or when the knee bears weight as it straightens.
The disorder is common in runners and is also seen in skiers, cyclists, and
soccer players. A patient's description of symptoms and a followup x ray usually
help the doctor make a diagnosis. Although arthroscopy can confirm the diagnosis,
it's not performed unless the condition requires extensive treatment.
Many doctors recommend that patients with chondromalacia perform
low-impact exercises that strengthen muscles, particularly the inner part of
the quadriceps, without injuring joints. Swimming, riding a stationary bicycle,
and using a cross-country ski machine are acceptable as long as the knee doesn't
bend more than 90 degrees. Electrical stimulation may also be used to strengthen
the muscles. If these treatments don't improve the condition, the doctor may
perform arthroscopic surgery to smooth the surface of the cartilage and "wash
out" the cartilage fragments that cause the joint to catch during bending and
straightening. In more severe cases, surgery may be necessary to correct the
angle of the knee cap and relieve friction with the cartilage or to reposition
parts that are out of alignment.
The meniscus is easily injured by the force of rotating the knee
while bearing weight. A partial or total tear may occur when a person quickly
twists or rotates the upper leg while the foot stays still (for example, when
dribbling a basketball around an opponent or turning to hit a tennis ball).
If the tear is tiny, the meniscus stays connected to the front and back of
the knee; if the tear is large, the meniscus may be left hanging by a thread
of cartilage. The seriousness of a tear depends on its location and extent.
Generally, when people injure a meniscus, they feel some pain,
particularly when the knee is straightened. If the pain is mild, the person
may continue moving. Severe pain may occur if a fragment of the meniscus catches
between the femur and the tibia. Swelling may occur soon after injury if blood
vessels are disrupted, or swelling may occur several hours later if the joint
fills with fluid produced by the joint lining (synovium) as a result of inflammation.
If the synovium is injured, it may become inflamed and produce fluid to protect
itself. This makes the knee swell. Sometimes, an injury that occurred in the
past but was not treated becomes painful months or years later, particularly
if the knee is injured a second time. After any injury, the knee may click,
lock, or feel weak. Although symptoms of meniscal injury may disappear on their
own, they frequently persist or return and require treatment.
In addition to listening to the patient's description of the onset
of pain and swelling, the doctor may perform a physical examination and take
x rays of the knee. The examination may include a test in which the doctor
bends the leg, then rotates the leg outward and inward while extending it.
Pain or an audible click suggests a meniscal tear. An MRI may be recommended
to confirm the diagnosis. Occasionally, the doctor may use arthroscopy to help
diagnose and treat a meniscal tear.
If the tear is minor and the pain and other symptoms go away, the
doctor may recommend a muscle-strengthening program. Exercises for meniscal
problems are best started with guidance from a doctor and physical therapist
or exercise therapist. The therapist will make sure that the patient does the
exercises properly and without risking new or repeat injury. The following
exercises after injury to the meniscus are designed to build up the quadriceps
and hamstring muscles and increase flexibility and strength.
- Warming up the joint by riding a stationary bicycle, then straightening
and raising the leg (but not straightening it too much).
- Extending the leg while sitting (a weight may be worn on the ankle for
this exercise).
- Raising the leg while lying on the stomach.
- Exercising in a pool (walking as fast as possible in chest-deep water,
performing small flutter kicks while holding onto the side of the pool,
and raising each leg to 90 degrees in chest-deep water while pressing the
back against the side of the pool).
If the tear is more extensive, the doctor may perform arthroscopic
or open surgery to see the extent of injury and to repair the tear. The doctor
can sew the meniscus back in place if the patient is relatively young, if the
injury is in an area with a good blood supply, and if the ligaments are intact.
Most young athletes are able to return to active sports after meniscus repair.
If the patient is elderly or the tear is in an area with a poor
blood supply, the doctor may cut off a small portion of the meniscus to even
the surface. In some cases, the doctor removes the entire meniscus. However,
osteoarthritis is more likely to develop in the knee if the meniscus is removed.
Medical researchers are investigating a procedure called an allograft, in which
the surgeon replaces the meniscus with one from a cadaver. A grafted meniscus
is fragile and will shrink and tear easily. Researchers have also attempted
to replace a meniscus with an artificial one, but this procedure is even less
successful than an allograft.
Recovery after surgical repair takes several weeks, and postoperative
activity is slightly more restricted than when the meniscus is removed. Nevertheless,
putting weight on the joint actually fosters recovery. Regardless of the form
of surgery, rehabilitation usually includes walking, bending the legs, and
doing exercises that stretch and build up leg muscles. The best results of
treatment for meniscal injury are obtained in people who do not show articular
cartilage changes and who have an intact ACL.
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Injury to the cruciate ligaments is sometimes referred to as a "sprain."*
The ACL is most often stretched or torn (or both) by a sudden twisting motion
(for example, when the feet are planted one way and the knees are turned another).
The PCL is most often injured by a direct impact, such as in an
automobile accident or football tackle.
* The National Institute of Arthritis and Musculoskeletal
and Skin Diseases Information Clearinghouse has a separate publication on
sprains and strains. See the end of this booklet for contact information.
Injury to a cruciate ligament may not cause pain. Rather, the person
may hear a popping sound, and the leg may buckle when he or she tries to stand
on it. The doctor may perform several tests to see whether the parts of the
knee stay in proper position when pressure is applied in different directions.
A thorough examination is essential. An MRI is very accurate in detecting a
complete tear, but arthroscopy may be the only reliable means of detecting
a partial one.
For an incomplete tear, the doctor may recommend that the patient
begin an exercise program to strengthen surrounding muscles. The doctor may
also prescribe a brace to protect the knee during activity. For a completely
torn ACL in an active athlete and motivated person, the doctor is likely to
recommend surgery. The surgeon may reattach the torn ends of the ligament or
reconstruct the torn ligament by using a piece (graft) of healthy ligament
from the patient (autograft) or from a cadaver (allograft). Although synthetic
ligaments have been tried in experiments, the results have not been as good
as with human tissue. One of the most important elements in a patient's successful
recovery after cruciate ligament surgery is a 4- to 6-month exercise and rehabilitation
program that may involve using special exercise equipment at a rehabilitation
or sports center. Successful surgery and rehabilitation will allow the patient
to return to a normal lifestyle.
The MCL is more easily injured than the LCL. The cause is most
often a blow to the outer side of the knee that stretches and tears the ligament
on the inner side of the knee. Such blows frequently occur in contact sports
like football or hockey.
When injury to the MCL occurs, a person may feel a pop and the
knee may buckle sideways. Pain and swelling are common. A thorough examination
is needed to determine the kind and extent of the injury. To diagnose a collateral
ligament injury, the doctor exerts pressure on the side of the knee to determine
the degree of pain and the looseness of the joint. An MRI is helpful in diagnosing
injuries to these ligaments.
Most sprains of the collateral ligaments will heal if the patient
follows a prescribed exercise program. In addition to exercise, the doctor
may recommend ice packs to reduce pain and swelling and a small sleeve-type
brace to protect and stabilize the knee. A sprain may take 2 to 4 weeks to
heal. A severely sprained or torn collateral ligament may be accompanied by
a torn ACL, which usually requires surgical repair.
Knee tendon injuries range from tendinitis (inflammation of a tendon)
to a ruptured (torn) tendon. If a person overuses a tendon during certain activities
such as dancing, cycling, or running, the tendon stretches like a worn-out
rubber band and becomes inflamed. Also, trying to break a fall may cause the
quadriceps muscles to contract and tear the quadriceps tendon above the patella
or the patellar tendon below the patella. This type of injury is most likely
to happen in older people whose tendons tend to be weaker. Tendinitis of the
patellar tendon is sometimes called jumper's knee because in sports that require
jumping, such as basketball, the muscle contraction and force of hitting the
ground after a jump strain the tendon. After repeated stress, the tendon may
become inflamed or tear.
People with tendinitis often have tenderness at the point where
the patellar tendon meets the bone. In addition, they may feel pain during
running, hurried walking, or jumping. A complete rupture of the quadriceps
or patellar tendon is not only painful, but also makes it difficult for a person
to bend, extend, or lift the leg against gravity. If there is not much swelling,
the doctor will be able to feel a defect in the tendon near the tear during
a physical examination. An x ray will show that the patella is lower than normal
in a quadriceps tendon tear and higher than normal in a patellar tendon tear.
The doctor may use an MRI to confirm a partial or total tear.
Initially, the doctor may ask a patient with tendinitis to rest,
elevate, and apply ice to the knee and to take medicines such as aspirin or
ibuprofen to relieve pain and decrease inflammation and swelling. If the quadriceps
or patellar tendon is completely ruptured, a surgeon will reattach the ends.
After surgery, the patient will wear a cast for 3 to 6 weeks and use crutches.
For a partial tear, the doctor might apply a cast without performing surgery.
Rehabilitating a partial or complete tear of a tendon requires
an exercise program that is similar to but less vigorous than that prescribed
for ligament injuries. The goals of exercise are to restore the ability to
bend and straighten the knee and to strengthen the leg to prevent repeat injury.
A rehabilitation program may last 6 months, although the patient can return
to many activities before then.
Osgood-Schlatter disease is caused by repetitive stress or tension
on part of the growth area of the upper tibia (the apophysis). It is characterized
by inflammation of the patellar tendon and surrounding soft tissues at the
point where the tendon attaches to the tibia. The disease may also be associated
with an injury in which the tendon is stretched so much that it tears away
from the tibia and takes a fragment of bone with it. The disease most commonly
affects active young people, particularly boys between the ages of 10 and 15,
who play games or sports that include frequent running and jumping.
People with this disease experience pain just below the knee joint
that usually worsens with activity and is relieved by rest. A bony bump that
is particularly painful when pressed may appear on the upper edge of the tibia
(below the knee cap). Usually, the motion of the knee is not affected. Pain
may last a few months and may recur until the child's growth is completed.
Osgood-Schlatter disease is most often diagnosed by the symptoms.
An x ray may be normal, or show an injury, or, more typically, show that the
growth area is in fragments.
Usually, the disease resolves without treatment. Applying ice to
the knee when pain begins helps relieve inflammation and is sometimes used
along with stretching and strengthening exercises. The doctor may advise the
patient to limit participation in vigorous sports. Children who wish to continue
moderate or less stressful sports activities may need to wear knee pads for
protection and apply ice to the knee after activity. If there is a great deal
of pain, sports activities may be limited until discomfort becomes tolerable.
This is an overuse condition in which inflammation results when
a band of a tendon rubs over the outer bone (lateral condyle) of the knee.
Although iliotibial band syndrome may be caused by direct injury to the knee,
it is most often caused by the stress of long-term overuse, such as sometimes
occurs in sports training.
A person with this syndrome feels an ache or burning sensation
at the side of the knee during activity. Pain may be localized at the side
of the knee or radiate up the side of the thigh. A person may also feel a snap
when the knee is bent and then straightened. Swelling is usually absent and
knee motion is normal. The diagnosis of this disorder is typically based on
the symptoms, such as pain at the outer bone, and exclusion of other conditions
with similar symptoms.
Usually, iliotibial band syndrome disappears if the person reduces
activity and performs stretching exercises followed by muscle-strengthening
exercises. In rare cases when the syndrome doesn't disappear, surgery may be
necessary to split the tendon so it isn't stretched too tightly over the bone.
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Osteochondritis dissecans results from a loss of the blood supply
to an area of bone underneath a joint surface and usually involves the knee.
The affected bone and its covering of cartilage gradually loosen and cause
pain. This problem usually arises spontaneously in an active adolescent or
young adult. It may be due to a slight blockage of a small artery or to an
unrecognized injury or tiny fracture that damages the overlying cartilage.
A person with this condition may eventually develop osteoarthritis.
Lack of a blood supply can cause bone to break down (avascular
necrosis).* The involvement of several joints or the appearance of osteochondritis
dissecans in several family members may indicate that the disorder is inherited.
* The National Institute of Arthritis and Musculoskeletal
and Skin Diseases Information Clearinghouse has a separate publication on
avascular necrosis. See the end of this booklet for contact information.
If normal healing doesn't occur, cartilage separates from the diseased
bone and a fragment breaks loose into the knee joint, causing weakness, sharp
pain, and locking of the joint. An x ray, MRI, or arthroscopy can determine
the condition of the cartilage and can be used to diagnose osteochondritis
dissecans.
If cartilage fragments have not broken loose, a surgeon may fix
them in place with pins or screws that are sunk into the cartilage to stimulate
a new blood supply.
If fragments are loose, the surgeon may scrape down the cavity
to reach fresh bone and add a bone graft and fix the fragments in position.
Fragments that cannot be mended are removed, and the cavity is drilled or scraped
to stimulate new cartilage growth. Research is being done to assess the use
of cartilage cell and other tissue transplants to treat this disorder.
Plica (PLI-kah) syndrome occurs when plicae (bands of synovial
tissue) are irritated by overuse or injury. Synovial plicae are the remains
of tissue pouches found in the early stages of fetal development.
As the fetus develops, these pouches normally combine to form one
large synovial cavity. If this process is incomplete, plicae remain as four
folds or bands of synovial tissue within the knee. Injury, chronic overuse,
or inflammatory conditions are associated with this syndrome.
People with this syndrome are likely to experience pain and swelling,
a clicking sensation, and locking and weakness of the knee. Because the symptoms
are similar to those of some other knee problems, plica syndrome is often misdiagnosed.
Diagnosis usually depends on excluding other conditions that cause similar
symptoms.
The goal of treatment is to reduce inflammation of the synovium
and thickening of the plicae. The doctor usually prescribes medicine such as
ibuprofen to reduce inflammation. The patient is also advised to reduce activity,
apply ice and an elastic bandage to the knee, and do strengthening exercises.
A cortisone injection into the plica folds helps about half of those treated.
If treatment fails to relieve symptoms within 3 months, the doctor may recommend
arthroscopic or open surgery to remove the plicae.
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Extensive injuries and diseases of the knees are usually treated
by an orthopaedic surgeon, a doctor who has been trained in the nonsurgical
and surgical treatment of bones, joints, and soft tissues such as ligaments,
tendons, and muscles. Patients seeking nonsurgical treatment of arthritis of
the knee may also consult a rheumatologist (a doctor specializing in the diagnosis
and treatment of arthritis and related disorders).
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Some knee problems, such as those resulting from an accident, can't
be foreseen or prevented. However, a person can prevent many knee problems
by following these suggestions:
- Before exercising or participating in sports, warm up by walking or riding
a stationary bicycle, then do stretches. Stretching the muscles in the front
of the thigh (quadriceps) and back of the thigh (hamstrings) reduces tension
on the tendons and relieves pressure on the knee during activity.
- Strengthen the leg muscles by doing specific exercises (for example, by
walking up stairs or hills, or by riding a stationary bicycle). A supervised
workout with weights is another way to strengthen the leg muscles that support
the knee.
- Avoid sudden changes in the intensity of exercise. Increase the force
or duration of activity gradually.
- Wear shoes that both fit properly and are in good condition to help maintain
balance and leg alignment when walking or running. Knee problems can be
caused by flat feet or overpronated feet (feet that roll inward). People
can often reduce some of these problems by wearing special shoe inserts
(orthotics). Maintain a healthy weight to reduce stress on the knee. Obesity
increases the risk of degenerative (wearing) conditions such as osteoarthritis
of the knee.
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Three types of exercise are best for people with arthritis:
- Range-of-motion exercises help maintain normal joint movement and
relieve stiffness. This type of exercise helps maintain or increase flexibility.
- Strengthening exercises help keep or increase muscle strength.
Strong muscles help support and protect joints affected by arthritis.
- Aerobic or endurance exercises improve function of the heart and
circulation and help control weight. Weight control can be important to
people who have arthritis because extra weight puts pressure on many joints.
Some studies show that aerobic exercise can reduce inflammation in some
joints.
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National
Institute of Arthritis and Musculoskeletal and Skin Diseases Information
Clearinghouse
American Academy of Orthopaedic
Surgeons
American College
of Rheumatology
American Physical Therapy
Association
Arthritis Foundation
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Ankylosing Spondylitis
