knee is a relatively simple joint, however it
performs a complicated task. The knee needs to
function properly to provide flexible mobility
while bearing considerable weight. While walking
down the street, our knees bear three to five
times our body weight. When climbing stairs,
that force can multiply to seven times our body
weight. The compact structures, bone and
cartilage, of the knee bear the weight and the
joint is supported by muscles and ligaments.
Most people have had a minor knee problem at one
time or another. Most of the time our body
movements do not cause problems. Knee symptoms
develop from everyday wear and tear, overuse, or
injury. Knee problems and injuries occur most
frequently during sports or recreational
activities, work-related tasks, or home
The knee is the largest joint in the body. The
upper and lower bones of the knee are separated
by two discs (menisci). The upper leg bone
(femur) and the lower leg bones (tibia and
fibula) are connected by ligaments, tendons, and
muscles. The knee joint is really two joints:
the patello-femoral joint, where the large bone
of the upper leg connects with the knee cap; and
the tibio-femoral joint, where the upper leg
bone hinges with the large bone of the lower
leg. These bones are held in place by passive
restraints called ligaments. The joint is
further supported by muscle tissue. When
conditioned and strengthened, these muscles
apply forces that help stabilize the joint. The
menisci are pads of cartilage that help to
stabilize the bones and provide shock
The surface of the bones inside the knee joint
is covered by articular cartilage. The articular
cartilage absorbs shock and provides a smooth,
gliding surface for joint movement. Although a
knee problem is often caused by an injury to one
or more of these structures, it may have another
cause. Some people are more likely to develop
knee problems than others. Many jobs, sports and
recreation activities, getting older, or having
a disease such as osteoporosis or arthritis
increase the chances of having a knee problem.
Sudden (acute) injuries
Injuries are the most common cause of knee
problems. Sudden (acute) injuries may be caused
by a direct blow to the knee or from abnormal
twisting, bending the knee, or falling on the
knee. Pain, bruising, or swelling may be severe
and develop within minutes of the injury. Nerves
or blood vessels may be pinched or damaged
during the injury. The knee or lower leg may
feel numb, weak, or cold; tingle; or look pale
or blue. Acute injuries include:
Sprains, strains, or other injuries to the
ligaments and tendons that connect and support
A tear in the rubbery cushions of the knee
Ligament tears. The medial collateral ligament
(MCL) is the most commonly injured ligament of
Breaks (fracture) of the kneecap, lower
portion of the femur, or upper part of the tibia
or fibula. Knee fractures are most commonly
caused by abnormal force, such as a falling on
the knee, a severe twisting motion, severe force
that bends the knee, or when the knee forcefully
hits an object.
Kneecap dislocation. This type of dislocation
occurs more frequently in 13- to 18-year-old
girls. Pieces of bone or tissue (loose bodies)
from a fracture or dislocation may get caught in
the joint and interfere with movement.
Overuse injuries occur with repetitive
activities or repeated or prolonged pressure on
the knee. Activities such as stair climbing,
bicycle riding, jogging, or jumping stress
joints and other tissues and can lead to
irritation and inflammation. Overuse injuries
Inflammation of the small sacs of fluid that
cushion and lubricate the knee (bursitis).
Inflammation of the tendons (tendinitis) or
small tears in the tendons (tendinosis).
Thickening or folding of the knee ligaments (Plica
Pain in the front of the knee from overuse,
injury, excess weight, or problems in the
kneecap (patellofemoral pain syndrome).
Irritation and inflammation of the band of
fibrous tissue that runs down the outside of the
thigh (iliotibial band syndrome).
Conditions that may cause knee problems
Problems not directly related to an injury or
overuse may occur in or around the knee.
Osteoarthritis (degenerative joint disease)
may cause knee pain that is worse in the morning
and improves during the day. It often develops
at the site of a previous injury. Other types of
arthritis, such as rheumatoid arthritis, gout,
and lupus, also can cause knee pain, swelling,
Osgood-Schlatter disease causes pain,
swelling, and tenderness in the front of the
knee below the kneecap. It is especially common
in boys ages 11 to 15.
A popliteal (or Baker's) cyst causes swelling
in the back of the knee.
Infection in the skin (cellulitis), joint
(infectious arthritis), bone (osteomyelitis), or
bursa (septic bursitis) can cause pain and
decreased knee movement.
A problem elsewhere in the body, such as a
pinched nerve or a problem in the hip, can
sometimes cause knee pain.
Osteochondritis dissecans causes pain and
decreased movement when a piece of bone or
cartilage or both inside the knee joint loses
blood supply and dies.
Treatment of Knee Pain
Treatment for a knee problem or injury may
include first aid measures, rest, bracing,
physical therapy, medicine, and in some cases
surgery. Treatment depends on the location,
type, and severity of the injury as well as your
age, health condition, and activity level (such
as work, sports, or hobbies). Unfortunately,
there is no quick cure for a knee injury.
Physical therapy plays a key role in treating
and rehabilitating the knee.
An evaluation of the trunk and lower extremity
to identify the predisposing factors that are
causing knee pain. The evaluation will look at
muscle strength, flexibility, coordination,
joint mobility and stabilziation, and balance. A
treatment plan is then developed to suit a
person's individual condition. The treatment
program will focus on achieving normal motion
and increasing lower extremity muscular
performance and strength. A second component of
the treatment plan involves activities leading
to a gradual return of normal activities.
Your knees tolerance for stressful activities
will decrease with age and loss of conditioning.
So, stresses that would not have caused injury
last year could hurt your knee today. A decrease
in your level of activity over a period of time
will also contribute to the vulnerability of
your knees. An exercise program designed by your
physical therapist, and applying some good
common sense, can be your best protection from
Don't carry objects that are too heavy. Use a
step stool. Do not stand on chairs or other
Wear knee guards during sports or recreational
activities, such as roller-skating or soccer.
Stretch before and after physical exercise,
sports, or recreational activities to warm up
Use the correct techniques or positions during
activities so that you do not strain your
Use equipment appropriate to your size,
strength, and ability. Avoid repeated movements
that can cause injury. In daily routines or
hobbies, look at activities in which you make
repeated knee movements.
Consider taking lessons to learn the proper
technique for sports. Have a trainer or person
who is familiar with sports equipment check your
equipment to see if it is well suited for your
level of ability, body size, and body strength.
If you feel that certain activities at your
workplace are causing pain or soreness from
overuse, call your human resources department
for information on other ways of doing your job
or to talk about using different equipment.
Keep your knees and the muscles that support
them strong and flexible.
Avoid activities that stress your knees, such
as deep knee bends or downhill running.
Wear shoes with good arch supports.
Do not wear high-heeled shoes.
Replace running shoes every 300 to 500 miles
(480 to 800 kilometers).