U.S. Department of Health and Human Services

Public Health Service

National Institutes of Health

National Institute of Arthritis and 

Musculoskeletal and Skin Diseases

NIH Publication No. 01–4912

May 2001
This booklet is not copyrighted. Readers are encouraged

to duplicate and distribute as many copies as needed.

Additional copies of this booklet are available from

National Institute of Arthritis and Musculoskeletal

and Skin Diseases 

NIAMS/National Institutes of Health

1 AMS Circle

Bethesda, MD 20892–3675

You can also find this booklet on the NIAMS Web site at

www.niams.nih.gov/hi/topics/kneeproblems/kneeqa.htm.
Acknowledgments

The NIAMS gratefully acknowledges the assistance of Barbara Mittleman, M.D.,

and James Panagis, M.D., M.P.H., NIAMS, NIH; John H. Klippel, M.D., Arthritis

Foundation, Atlanta, Georgia; Frank A. Pettrone, M.D., Arlington/Vienna, Virginia;

and W. Norman Scott, M.D., Beth Israel Medical Center, New York, New York, in

the preparation and review of this booklet.
Information Box

Lateral View of the Knee . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
28

■ American Academy of Orthopaedic Surgeons

P.O. Box 2058

Des Plaines, IL 60017

Phone: 800–824–BONE (2663) (free of charge)

www.aaos.org

The academy provides education and practice management services for orthopaedic surgeons and allied health

professionals. It also serves as an advocate for improved

patient care and informs the public about the science

of orthopaedics. The orthopaedist’s scope of practice

includes disorders of the body’s bones, joints, ligaments,

muscles, and tendons. For a single copy of an AAOS

brochure, send a self-addressed stamped envelope to

the address above or visit the AAOS Web site.

■ American College of Rheumatology

1800 Century Place, Suite 250

Atlanta, GA 30329

Phone: 404–633–3777

Fax: 404–633–1870

www.rheumatology.org

This national professional organization can provide

referrals to rheumatologists and allied health professionals, such as physical therapists. One-page fact sheets are

available on various forms of arthritis. Lists of specialists

by geographic area and fact sheets are also available on

this Web site.
2

What Causes Knee Problems?

There are two general kinds of knee problems: mechanical

and inflammatory.

Mechanical Knee Problems

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. 

Inflammatory Knee Problems

Inflammation that occurs in certain rheumatic diseases, such

as rheumatoid arthritis and systemic lupus erythematosus,

can damage the knee.

Joint Basics

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.
26

What Types of Exercise Are Most Suitable for

Someone With Knee Arthritis?

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.
4

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.

Muscles

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.
24 

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.

What Kinds of Doctors Treat Knee Problems?

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).
6 

How Are Knee Problems Diagnosed?

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. 
22

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.

Symptoms and Diagnosis

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.

Treatment

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

* 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.
8 

Knee Injuries and Problems

Arthritis

What Is Arthritis of the Knee? 

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.

Signs and Diagnosis

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

* 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.
20 

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.

Treatment

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.

What Causes Iliotibial Band Syndrome?

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.
10 

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.)

Cartilage Injuries and Disorders

What Is Chondromalacia?

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).

Symptoms and Diagnosis

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
18 

after a jump strain the tendon. After repeated stress, the 

tendon may become inflamed or tear.

Symptoms and Diagnosis

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.

Treatment

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.
12 

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.

Symptoms 

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.

Diagnosis

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.
16 

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.

What Is the Most Common Cause of Medial and Lateral

Collateral Ligament Injuries?

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.

Symptoms and Diagnosis

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
14 

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. 
14 

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. 
16 

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.

What Is the Most Common Cause of Medial and Lateral

Collateral Ligament Injuries?

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.

Symptoms and Diagnosis

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
12 

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.

Symptoms 

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.

Diagnosis

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.
18 

after a jump strain the tendon. After repeated stress, the 

tendon may become inflamed or tear.

Symptoms and Diagnosis

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.

Treatment

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.
10 

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.)

Cartilage Injuries and Disorders

What Is Chondromalacia?

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).

Symptoms and Diagnosis

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
20 

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.

Treatment

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.

What Causes Iliotibial Band Syndrome?

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.
8 

Knee Injuries and Problems

Arthritis

What Is Arthritis of the Knee? 

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.

Signs and Diagnosis

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

* 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.
22

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.

Symptoms and Diagnosis

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.

Treatment

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

* 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.
6 

How Are Knee Problems Diagnosed?

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. 
24 

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.

What Kinds of Doctors Treat Knee Problems?

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).
4

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.

Muscles

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.
26

What Types of Exercise Are Most Suitable for

Someone With Knee Arthritis?

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.
2

What Causes Knee Problems?

There are two general kinds of knee problems: mechanical

and inflammatory.

Mechanical Knee Problems

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. 

Inflammatory Knee Problems

Inflammation that occurs in certain rheumatic diseases, such

as rheumatoid arthritis and systemic lupus erythematosus,

can damage the knee.

Joint Basics

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.
28

■ American Academy of Orthopaedic Surgeons

P.O. Box 2058

Des Plaines, IL 60017

Phone: 800–824–BONE (2663) (free of charge)

www.aaos.org

The academy provides education and practice management services for orthopaedic surgeons and allied health

professionals. It also serves as an advocate for improved

patient care and informs the public about the science

of orthopaedics. The orthopaedist’s scope of practice

includes disorders of the body’s bones, joints, ligaments,

muscles, and tendons. For a single copy of an AAOS

brochure, send a self-addressed stamped envelope to

the address above or visit the AAOS Web site.

■ American College of Rheumatology

1800 Century Place, Suite 250

Atlanta, GA 30329

Phone: 404–633–3777

Fax: 404–633–1870

www.rheumatology.org

This national professional organization can provide

referrals to rheumatologists and allied health professionals, such as physical therapists. One-page fact sheets are

available on various forms of arthritis. Lists of specialists

by geographic area and fact sheets are also available on

this Web site.
Information Box

Lateral View of the Knee . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Acknowledgments

The NIAMS gratefully acknowledges the assistance of Barbara Mittleman, M.D.,

and James Panagis, M.D., M.P.H., NIAMS, NIH; John H. Klippel, M.D., Arthritis

Foundation, Atlanta, Georgia; Frank A. Pettrone, M.D., Arlington/Vienna, Virginia;

and W. Norman Scott, M.D., Beth Israel Medical Center, New York, New York, in

the preparation and review of this booklet.
This booklet is not copyrighted. Readers are encouraged

to duplicate and distribute as many copies as needed.

Additional copies of this booklet are available from

National Institute of Arthritis and Musculoskeletal

and Skin Diseases 

NIAMS/National Institutes of Health

1 AMS Circle

Bethesda, MD 20892–3675

You can also find this booklet on the NIAMS Web site at

www.niams.nih.gov/hi/topics/kneeproblems/kneeqa.htm.
U.S. Department of Health and Human Services

Public Health Service

National Institutes of Health

National Institute of Arthritis and 

Musculoskeletal and Skin Diseases

NIH Publication No. 01–4912

May 2001