Knee pain affects most people at one time or another. The knees support the weight of the body and enable leg movement. The regular stress of years of activity and wear can produce pain that can range from dull to debilitating. Intensive sports and exercise subject a body to the potential for knee pain and injury. People who are inactive are also susceptible to knee pain from falls, sprains or degenerative conditions such as arthritis.
The parts of the knee coordinate into a system to work smoothly and keep the legs moving. The joint formed at the knee connects the thigh bone (femur) with the shin bone (tibia) and is covered by the kneecap (patella). Ligaments and tendons join these bones and their associated muscles to provide flexibility and motion for the legs.
Some kinds of knee pain are caused by sudden trauma. Other conditions are the result of specific kinds of overuse or inflammation. For many older people, the onset of osteoarthritis produces knee pain and degeneration.
Physicians consulted for knee pain will conduct a physical examination to identify the pain. Imaging techniques such as x-rays, CAT scans or MRI can show the bones and soft tissues of the knee and may indicate the source of knee pain. Arthroscopy uses a specialized fiber optic instrument to view the interior of the knee and may also be used to repair damage.
Milder knee pain may be relieved with over-the-counter pain medications such as nonsteroidal anti-inflammatory drugs (NSAIDS). Rest, application of ice and elevation of the knee may also alleviate pain. More serious pain may require stronger medication, physical therapy or surgery. Grafts may be used to replace torn ligaments. Total knee replacement, a type of arthroplasty, uses artificial parts to replace the ends of the femur and tibia and can alleviate pain caused by degeneration of the joint.
People can prevent some knee problems by maintaining a healthy weight to minimize the strain on their knees. Exercises that promote stronger leg muscles will also help the knee, as will adequate warm-up and stretching before any exercise or athletic activity. Shoes that fit well and properly support the feet will also help prevent knee problems.
About knee pain
Knee pain is one of the most common reasons for visits to orthopedic physicians. It can originate from:
Within the knee joint
Around the knee (e.g., tendons, ligaments, muscles)
Referred pain (e.g., from the spine)
Causes of knee pain within the joint include:
Regular wear and tear related to aging
Chronic conditions (e.g., arthritis)
Sudden injury (e.g., a fall or sports injury)
The extra weight of obesity also increases the stress on joints, including the knees.
The knee is the joint that enables the leg to bend and extend. It connects the thigh bone (femur) in the upper part of the leg with the shin bone of the lower leg (tibia). The kneecap (patella) is the small bone that fits on the grooved ends of the femur and forms the top of the knee. The fibula, the other bone in the lower leg, joins the tibia before it reaches the knee.
Ligaments and tendons connect the bones and muscles that make the knee move. Ligaments connect the bones. Four ligaments join the femur and tibia at the knee. Along the sides of the knee, the medial collateral ligament (MCL) on the inside of the leg and the lateral collateral ligament (LCL) on the outside of the leg provide stability. Two ligaments cross the knee diagonally to join the femur and tibia – the anterior cruciate ligament (ACL) on the front of the knee and the posterior cruciate ligament (PCL) on the back. The ACL limits rotation and forward motion of the tibia. The PCL limits backward movement of the tibia. An ACL tear is a common sports injury.
Tendons connect muscle to bones. The quadriceps tendon connects the quadriceps muscle of the thigh to the patella and covers the patella. The patellar tendon connects the patella to the tibia. Technically, this is a ligament because it connects two bones (patella and tibia), but it is usually referred to as a tendon.
Soft tissues and fluids cushion the bones around the knee to enable smooth movement. Tissue called cartilage covers the ends of the bones where they adjoin other parts of the leg. Two pads of cartilage called menisci (one is called a meniscus) separate the femur and tibia. Fluid-filled sacs called bursae also provide cushioning between bones and tendons or ligaments.
The coordination of these bones, ligaments, tendons and cartilage enable the knee to bend the leg and support the body’s weight. Many conditions and injuries can cause knee pain, including overuse, chronic wear and tear on the joint, disease and inflammation.
Other pain areas related to knee pain
Knee pain can occur in conjunction with pain from other joints. For example, many hip problems cause knee pain when weight or stress from one joint (the hip) is shifted to the next joint (the knee) by connecting muscles and bones. Other types of leg pain can also cause knee pain.
Ankle and foot pain may also be felt in the knees. Problems related to flat feet or overpronated feet (feet that roll inward) can cause gait disturbances and knee pain. In addition, pain in the right foot, for example, may cause a person to favor that foot and the resulting overcompensation may cause pain in the left knee.
The knees may also be the recipient of referred pain, which originates in one area of the body but is perceived in another area. Some knee pain may be referred from the spine, back and sacroiliac areas. Even a herniated disc sometimes can cause knee pain.
Potential causes of knee pain
Knee pain can be caused by injuries and trauma that affect the mechanics of the knee (e.g., torn ligaments). Other kinds of knee pain are the result of degeneration and wear and tear such as arthritis. Still others may result from inflammation. Some knee pain may be caused by a combination of these causes. For example, athletes frequently develop tendinitis, an inflammation sometimes caused by overuse.
Some of the most common causes of knee pain include:
Arthritis. Arthritis, a degenerative disease of the joints, causes knee pain in many of its forms, such as rheumatoid arthritis, juvenile arthritis, Reiter’s syndrome or ankylosing spondylitis, although it is most common with osteoarthritis. The pain, swelling and stiffness may affect both knees and cause cartilage to deteriorate.
Gout is a type of arthritis where uric acid that is normally excreted builds up in a joint. It usually affects the big toe, but can also occur in the knee. Knee symptoms can include redness, swelling and intense sudden onset of pain, often occurring at night. Pseudogout, caused by calcium deposits, may also cause inflammation and intermittent pain and swelling in knees.
Soft tissue injuries. These may affect the ligaments, tendons and muscles. The most common knee ligament injuries are to the anterior cruciate ligament (ACL) across the front of the knee and medial collateral ligament (MCL), which runs vertically along the inside of the knee. Ligaments can be torn or sprained, usually from a twist during sports or a fall. The person may feel a pop and be unable to bear weight on the knee. When the knee is hyperextended, it moves farther forward than it should and may cause an ACL tear. This is a common injury among gymnasts. Injury to the posterior cruciate ligament (PCL) is more common in severe trauma, such as the knee hitting a dashboard in a car accident.
Slight or complete tears of a meniscus are commonly referred to as torn cartilage in the knee. They may occur from twisting knee movements when the foot is fixed, as in tennis or basketball. Meniscus tears or osteoarthritis may also result in a Baker’s cyst, an accumulation of fluid that forms behind the knee.
Other traumatic injuries. Injuries can cause fractures of the knee bones and sprains or tears to the ligaments and tendons. The patella (kneecap) may be dislocated, causing visible, side-to-side movement of the knee. A person who experiences a dislocated patella once is more susceptible to a recurrence.
Loose body. Pieces of bone or cartilage may break off and float inside the knee. It can be painful if it interferes with another part of the knee, such as the kneecap. About half of loose bodies in the knee are caused by osteochondritis dissecans, a disorder in which parts of bone and cartilage lose their blood supply and break off.
Inflammation. Tendinitis is irritation or inflammation of a tendon. For athletes, tendinitis in the patellar tendon is common and is known as jumper’s knee. Bursitis is inflammation of one or more of the bursae (fluid-filled sacs around the knee) and can cause warmth, swelling, redness, stiffness while walking and pain while kneeling or using stairs. Many people with various forms of arthritis also develop Many people with various forms of arthritis also develop bursitis. Enthesitis is inflammation of entheses, the sites where tendons or ligaments attach to bone.
Osgood-Schlatter disease. This inflammation of the patellar tendon is caused by repetitive stress on the top of the tibia (shin bone). It is common among teenagers whose bones are still growing, especially young athletes who run and jump. Its main symptom is pain below the knee joint.
Iliotibial band syndrome. The ligament that runs from the outside of the pelvic bone down to the tibia can tighten and rub against the femur, causing knee pain. It produces sharp knee pain or pain along the thigh. The syndrome is most common among runners, particularly those with unequal leg lengths or those with weakened hip abductors who experience some sideways leg motion.
Chondromalacia. This is a softening of the cartilage under the kneecap, causing the kneecap to rub against the femur. Trauma may cause chondromalacia when a blow to the kneecap tears off cartilage or bone.
Patellofemoral syndrome. This pain in and around the kneecap may occur in one or both knees. Its cause may be related to abnormal movement of the patella when the knee bends. This condition is often called runner’s knee because it is common in runners. It is also sometimes called moviegoer’s knee because prolonged sitting with the knee bent can set off the pain.
Patellar tendinopathy (jumper’s knee). Sports that involve jumping or quickly changing direction are a leading cause of damage to the patellar tendon connecting the kneecap and shinbone.
Plica syndrome. When the fetal development of knee tissue is incomplete, it leaves several compartments of tissue (plicae) instead of one large cavity. For people who have this interrupted tissue development, injury and overuse can irritate the excess tissue in the knee.
Referred nerve pain. A pinched nerve in the back – for example, sciatica resulting from a herniated disc, spinal stenosis or degenerative disc disease - can cause pain radiating down the leg to the knee and beyond.
Complex regional pain syndrome. A chronic pain condition in a leg (or arm) that usually occurs after significant trauma to the limb.
Gait disturbances. Unstable gait can cause pressure on muscles and the knee joint, causing pain.
Bone tumors. In rare cases, some tumors (masses of abnormal tissue) in the bones of the leg may cause knee pain, but more commonly pain occurs closer to the site of the tumor.
Other causes of knee pain include infections. For example, Lyme disease, which is caused by bacteria transmitted by tick bites, frequently causes knee pain.
Fibromyalgia, a condition characterized by fatigue and muscle pain, may cause knee pain, especially in children. Many other conditions ranging from chronic fatigue syndrome to lupus to sickle cell anemia can cause widespread pain and may affect the knees.
Common tests for knee pain
Several tests are commonly used to determine or rule out the causes of knee pain. A physician will take a medical history to learn about any injuries or conditions that may be related to the knee pain. A physical examination will include movement of the knee to determine how much it can bend, straighten and rotate. The patient may be asked to walk or squat to further assess knee function.
The physician may conduct a pain assessment and may order tests such as:
X-ray. Uses low-dose radiation to create images of bones.
CAT scan (computed axial tomography). Uses multiple x-ray images combined to provide a three-dimensional image of the knee. CAT scans can show soft tissue, such as ligaments and muscles.
MRI (magnetic resonance imaging). Uses powerful magnets to create cross-sectional images of tissues. MRIs are useful in diagnosing soft tissue damage or disease.
Arthroscopy. Specialized tube with optic fibers (arthroscope) is inserted in an incision in the knee. It can provide images of the interior of the joint. Special instruments may also be inserted to remove loose bone or cartilage fragments or repair injuries.
Bone scan. A small amount of radioactive material is injected into the bloodstream and is detected with a scanner. This type of radionuclide imaging may detect abnormalities in blood flow or other cell activity.
Blood tests. May be used to identify or rule out the possibility of infection and certain kind of arthritis.
Biopsy. A small amount of tissue can be removed from the knee and examined for abnormalities.
Relief options for knee pain
For many kinds of knee pain, common sense ideas provide the best relief. Knee pain can often be alleviated by following the RICE principles:
Rest the knee.
Ice the joint.
Compress the knee with an elastic brace.
Elevate the knee.
Sometimes the acronym PRICE is used, when “protect the knee” is considered the first principle.
For mild arthritis and some other forms of knee pain, the physician may recommend analgesics or nonsteroidal anti-inflammatory drugs (NSAIDs). An NSAID gel applied to the knee can avert the stomach upset that oral NSAIDs may cause.
Corticosteroid injections may help alleviate some knee pain, but in some cases, repeated injections can damage the joint. For certain sprains and tears, immobilizing the knee can help the tear heal.
Other relief options may include:
Physical therapy. This usually concentrates on strengthening the surrounding muscles to support the knee better. Leg raises and extensions may be used. Activities that limit impact on the knee, such as walking, swimming and water aerobics, may also be part of a physical therapy regimen.
Modalities. Numerous physical agents can be used in treating knee pain. Some can be used by the patient at home, and others are applied by a physical therapist or other healthcare professional. Modalities include:
Thermotherapy (heat), such as ultrasound therapy
Cryotherapy (cold)
Hydrotherapy (water)
Electrical therapy, such as TENS
Acupuncture. The insertion of needles at certain points on the body to promote healing. A recent study by the National Institutes of Health indicated that acupuncture can provide relief from knee pain for osteoarthritis patients.
Arthroscopy. This optical fiber instrument can be used for identification and treatment of knee pain. For treatment, special instruments are inserted through small incisions with the arthroscope to remove loose bodies, repair torn cartilage or ligaments or shave off small pieces of bone. A local, regional or general anesthetic may be used for arthroscopy.
Open surgery. Complicated knee injuries or deterioration may require an open surgical procedure. Sometimes ligaments, usually the anterior cruciate ligament (ACL), are replaced with another ligament or tendon from the leg or from a donor. To avoid the need for replacing ruptured ligaments and to improve function, researchers are studying methods of repairing ACL tears through means such as arthroscopically stitching the torn ends together and introducing a collagen gel scaffold at the site to promote healing.
In other cases, joint replacement surgery (arthroplasty) is used when the knee has degenerated, usually from osteoarthritis. The U.S. Food and Drug Administration (FDA) has recently approved an artificial knee designed to fit women, who receive the majority of knee implants.
Prevention methods for knee pain
Many general practices to promote good health can help prevent knee injury and pain. Maintaining a healthy weight reduces stress on the knees and lessens wear and tear on the joints. Avoiding obesity reduces the risk of needing a knee replacement later in life.
Proper warm-up and stretching before exercise or athletic activity can protect the knees. Exercises that strengthen muscles around the knee can help prevent knee injury. Also, exercises to increase the mobility of the knee are helpful.
Any changes to exercise programs or sports activities should be undertaken gradually, without sudden increases in activity. Exercise programs should also allow recovery time, with at least one day of rest between days of repetitive muscle exercise.
Good foot health will also help protect the knees. Properly fitting shoes support the feet and ankles and maintain the body’s alignment. Some knee problems caused by flat or overpronated feet (feet that turn inward) can be avoided by using commercially available shoe inserts or special inserts called orthotics.
In recent years, some people with osteoarthritis have used supplements of glucosamine and chondroitin to alleviate pain and potentially slow deterioration of cartilage. The use of such supplements is not regulated, and their efficacy has not been proven. A clinical study sponsored by the National Institutes of Health found these supplements may help relieve moderate to severe knee osteoarthritis, but in many cases they provided no more relief than a placebo (sugar pill).
Questions for your doctor regarding knee pain
Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about knee pain:
What is causing my knee pain?
What tests might I need, and what do they involve?
Do I need to repeat x-rays from time to time?
Will rest make my knee pain go away?
Will exercise lessen my knee pain?
What kind of exercises should I perform or avoid?
Do the sports I play contribute to knee pain?
Has inactivity or excess weight been a cause?
Are there medications to help my knee pain?
Do these medications pose any risks?
Could surgery be needed to alleviate my knee pain? If so, what kind?
