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Questions and Answers About Knee
Problems
Knee problems commonly occur in young people and adults.
This booklet contains general information about several knee
problems. It includes descriptions and a diagram of the different
parts of the knee. Individual sections of the booklet describe
the symptoms, diagnosis, and treatment of specific types of
knee injuries and conditions. Information on how to prevent
these problems is also provided.
What Do the Knees Do? How Do They Work?
The knee is the joint where the bones of the upper leg meet the bones of the lower leg, allowing hinge-like movement while providing stability and strength to support the weight of the body. Flexibility, strength, 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. Each of these structures is subject to disease and injury. When a knee problem affects your ability to do things, it can have a big impact on your life. Knee problems can interfere with many things, from participation in sports to simply getting up from a chair and walking.
What Causes Knee Problems?
Knee problems can be the result of disease or injury.
Disease
A number of diseases can affect the knee. The most common
is arthritis. Although arthritis technically means “joint
inflammation,” the term is used loosely to describe
many different diseases that can affect the joints. We’ll
describe some of the most common forms of arthritis and their
effects on the knees a bit later in the booklet.
Injury
Knee injuries can occur as the result of a direct blow or
sudden movements that strain the knee beyond its normal range
of motion. Sometimes knees are injured slowly over time.
Problems with the hips or feet, for example, can cause you
to walk awkwardly, which throws off the alignment of the
knees and leads to damage. Knee problems can also be the
result of a lifetime of normal wear and tear. Much like the
treads on a tire, the joint simply wears out over time. We’ll
discuss some of the most common knee injuries later in this
booklet, but first we’ll take a look at the structure
of the knee joint.
What Are the Parts of the Knee?
Like any joint, the knee is composed of bones and cartilage,
ligaments, tendons, and muscles.
Bones and Cartilage
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.
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.
Tendons and Ligaments
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.
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.
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.
To read about all the different knee injuries and disorders,
please see the rest of this article from the National Institute
of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Information Clearinghouse at: http://www.niams.nih.gov/hi/topics/kneeprobs/kneeqa.htm
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