Patient education: Knee pain (Beyond the Basics)

KNEE PAIN OVERVIEW — The knee is a "hinge" type joint that allows the leg to bend and straighten (flex and extend) (picture 1). Of all the joints in the body, the knee is at the greatest risk of injury, age-related wear and tear, inflammatory arthritis, and septic (infection-related) arthritis.

KNEE PAIN CAUSES — There are many conditions that can cause knee pain. These are typically grouped into acute injuries, occurring after a single traumatic event, and overuse injuries, where the pain comes on gradually without a discrete inciting incident. The most common types of overuse and traumatic knee injuries are discussed below.

Overuse injuries

Patellofemoral pain — This is the most common cause of overuse knee pain. It causes pain in the front of the knee or deep in the knee behind the kneecap which worsens with squatting, running, prolonged sitting, or when climbing or descending steps. The pain usually comes on over time, without one specific episode of injury. Patellofemoral pain almost never results in a swollen knee.  

Think of the kneecap as a train and the groove of the thigh bone (femur) as a track: anything that causes the train (kneecap) to run off the track (thigh bone) can result in patellofemoral pain. The most common causes of patellofemoral pain are weak muscles (quadriceps and gluteals), tight muscles (hamstrings, quadriceps, and hip flexors), abnormal limb alignment (flat or high arched feet, knock knees or rotated hips), and/or overuse trauma from increasing physical training too quickly. Effective treatments include muscle strengthening exercises, muscle stretches, and slow progressive training regimens. Occasionally braces, taping, or foot orthotics may be helpful and can be prescribed by your physician. (See "Patellofemoral pain".)

Bursitis — The knee is lubricated by joint fluid that is produced by the lining of the joint and by six lubricating "bursa" sacs. The bursa sacs can become irritated as a result of injury, excessive pressure, or overuse; inflammation of a bursa is called bursitis. As the use of musculoskeletal ultrasound has increased, many conditions that were previously called "bursitis" have been reclassified as tendon problems because there is no bursa fluid seen on ultrasound, but instead just abnormal tendon. Pes anserine bursitis is one example. Fluid is almost never seen in the pes anserine region, just abnormal tendons. Pre-patellar bursitis in an exception. This is a true bursitis with an irritated, swollen fluid sac.

Patellar tendinopathy (also called patellar tendonitis or "jumper's knee") — The patellar tendon runs from the quadriceps muscle onto the shinbone (tibia). Working together, the quadriceps and patellar tendons enable a person to straighten their knee. In patellar tendinopathy, the tendon begins to degenerate or weaken. This degeneration can occur anywhere between the kneecap and the tendon's attachment to the tibia. Patellar tendinopathy causes pain in the patellar tendon during running, jumping, stair-climbing, squatting, or any other movement requiring rapid, forceful knee straightening.

The most common causes of patellar tendinopathy are weak quadriceps, hamstring, and gluteal muscles and/or tightness in these same muscle groups. Overuse or increases in physical training that are "too much or too fast" can also cause patellar tendinopathy. Effective first-line treatments include strengthening and stretching exercises for quadriceps, hip flexors, and gluteal muscle groups. Second-line treatments including novel injections (eg, platelet-rich plasma) remain investigational. Straps or braces across the patellar tendon may provide pain relief but are not likely to assist tendon healing.

Osteoarthritis — Osteoarthritis is caused by degeneration (or wearing out) of the articular cartilage. Articular cartilage is the protective, shock absorbing tissue covering the bone surfaces within a joint, including the undersurface of the kneecap. Osteoarthritis is the most common form of arthritis and the most common cause of joint pain in people over age 50. Classically, osteoarthritis causes morning pain and mild stiffness that improves as the joint starts moving, but then returns with increasing activity.

The most effective treatments for osteoarthritis are lifestyle changes. We often speak of "the big three" of osteoarthritis: (1) activity modification; (2) weight loss/maintenance; (3) and therapeutic exercise. Activity modification means substituting jumping, running, and other high-impact activities for lower-impact (gliding) activities like walking, swimming, biking, and elliptical exercise machines. Weight loss reduces pain by decreasing the load placed on affected joints. Overweight individuals can achieve substantial improvements in osteoarthritis pain by losing just 10 percent of their body weight. Therapeutic exercise involves regular low-impact aerobic activity and resistance exercises to build strength in shock absorbing and supporting muscles.

Other activities, such as yoga and Tai Chi, can improve symptoms in patients with osteoarthritis. Adjunctive osteoarthritis treatments include medications, injections, braces, and surgery. (See "Patient education: Osteoarthritis symptoms and diagnosis (Beyond the Basics)".)

Acute injuries

Muscle strain — The quadriceps muscles (front of the thigh) and the hamstring muscles (back of the thigh), which straighten and bend the knee respectively, are susceptible to strain ("pulled muscles"). Such strains occur most often in sports requiring rapid acceleration and deceleration (basketball, softball, American football, soccer), and less common in routine fitness activities (jogging, swimming, rowing).  

Rest, ice, and compression are good first-line treatment for most muscle strain injuries. Over-the-counter acetaminophen or ibuprofen can decrease pain but should generally not be used for longer than a week without the advice of a physician. Inability to walk or to actively bend or straighten the knee, swelling of the knee joint, or pain that lasts longer than two weeks without improvement should be evaluated by a clinician.

Meniscus tear — The meniscus is a specialized "shock absorber" cartilage located in the knee joint between the thigh (femur) and shin (tibia) bones. There are two menisci in the knee, one on the inside (medial meniscus) and one of the outside (lateral meniscus).  

Two types of meniscal tears can occur. Traumatic tears occur when a sudden, twisting force tears an otherwise healthy meniscus. Traumatic meniscal tears are most common in young athletes. Degenerative meniscal tears occur when routine forces (jogging, sports participation, yard work) cause tears in menisci that have become soft and weak due to age, arthritis, or other factors. Patients with degenerative tears often report feeling fine until after the exacerbating activity, when swelling and pain begin. Degenerative meniscal tears are most common in patients over age 40. Traumatic meniscus tears in younger athletes often require arthroscopic surgery to repair or remove portions of the torn meniscus. Degenerative meniscus tears in athletes over 40 are typically best treated without surgery.

Knee ligament sprain or tear — The knee joint is held together by four ligaments: the inner and outer hinge ligaments (medial and lateral collateral ligaments) and the crossing (cruciate) ligaments, which sit in the middle of the joint (the anterior and posterior cruciate ligaments) (figure 1). Injuries to the collateral and posterior cruciate ligaments typically occur when an object or another player strikes the knee. Anterior Cruciate Ligament (ACL) injuries occur most often without direct contact to the affected knee during seemingly innocuous movements like cutting, pivoting, or landing from a jump. Common symptoms associated with knee ligament injuries include joint swelling, pain, and a sensation that the knee "gives way" during certain movements.

Injuries to the collateral ligaments usually heal with rest, bracing, and rehabilitation. Even grade 3 or "complete" injuries rarely require surgery. Injuries to the anterior cruciate ligament (ACL) typically require surgery in individuals who wish to return to demanding activities that require cutting, pivoting, or jumping. (See "Patient education: Anterior cruciate ligament injury (Beyond the Basics)".)

INITIAL TREATMENT — Physical therapy is essential to the treatment and prevention of many of the conditions that affect the knee joint and its surrounding supporting structures. Physical therapy for knee pain often includes ice, stretching, and muscle strengthening exercises.

Activity limitations — To speed recovery and protect against future knee damage, activities that cause pain should be avoided temporarily.

If the knee is swollen or sore, the following positions and activities should be avoided until knee pain and swelling resolve:

●Squatting

●Kneeling

●Twisting and pivoting

●Jogging

●Aerobics, dancing

●Playing sports

●Swimming using the frog or whip kick

The following types of exercise equipment should be avoided if the knee is swollen or sore, unless specifically prescribed by a physical therapist or physician:

●Stair stepper

●Rowing machine

●Squats

●Leg extensions

The preferred exercise equipment for the knee should provide smooth motion of the knee, strengthening of the front and back thigh muscles (quadriceps and hamstring muscles), minimal jarring and impact to the joint, and the least amount of bending necessary. These activities are acceptable alternatives to those listed above:

●Fast walking

●Water aerobics

●Swimming using the crawl stroke

●Cross country ski or elliptical-type machines

●Soft platform treadmill

Ice and elevation — Ice is useful for the control of pain and swelling. It can be applied to the knee for 15 to 20 minutes as often as every two to four hours, particularly after physical activity. A bag of ice, frozen vegetables, or a frozen towel work well. The swollen knee should be elevated above the level of the heart while icing.

Pain relief — If needed, a non-prescription pain medication such as acetaminophen (Tylenol), ibuprofen (eg, Advil, Motrin) or naproxen (eg, Aleve) can be taken (see "Patient education: Nonsteroidal antiinflammatory drugs (NSAIDs) (Beyond the Basics)"). No more than 3000 mg of acetaminophen is recommended per day. Anyone with liver disease or heavy alcohol use should speak with his or her healthcare provider before taking acetaminophen. Individuals with a history of heart attack, stomach/intestinal bleeding, or kidney disease should speak with their health care provider before taking ibuprofen, naproxen, or other nonsteroidal antiinflammatory drugs (NSAIDs). Individuals taking more than one medicine to lower blood pressure should also be cautious about taking NSAIDs.

Stretching exercises — Depending upon the injury or condition causing pain, patients can begin stretching exercises as soon as the day following an injury. Stretch gently and gradually, holding consistent pressure at the end of the stretch. Avoid "bouncing" or rapid "ballistic" stretches as these can damage already injured tissue. Stretches should be held for 20 to 30 seconds and should be performed on both injured and uninjured legs. Each muscle should be stretched three to five times per session and stretching sessions may be performed one to four times each day.

Hamstring stretch — Sit on the floor or bed with the affected leg extended straight out in front of you. The opposite leg may be bent or may hang off the bed. Keeping the affected leg straight, lean forward and reach for the ankle. Hold for 30 seconds but do not bounce. Sit up straight. Repeat as above.

Quadriceps stretch — Stand behind a chair, holding the top of the chair with one hand. Bend the knee and grab the foot with the hand on the same side of the body. Stand up straight. Gently pull the foot towards the body. Hold for 30 seconds, holding constant pressure on the foot (do not pull-release-pull). Release the foot. Repeat 10 to 15 times.

Runner's stretch — Face a wall and stand 18 to 24 inches away. Place hands at head height and lean into the wall, keeping legs and back straight. You can rest your head on your hands, against the wall. You should feel a stretch in the muscles in the back of the calf. Hold for 30 seconds. Repeat 10 to 15 times.

Strengthening exercises — Rehabilitation of the knee almost always includes strengthening exercises. Patients gradually progress from exercises performed with a straight knee (eg, straight leg raises) to exercises that require some degree of knee bending (eg, squats). Initial exercises often include the following:

Straight leg raises — Sit on the edge of a chair or lie down on the back. Bend the opposite leg (picture 2). Keep the affected leg perfectly straight and raise it 3 to 4 inches off the ground. Hold for 5 seconds. Repeat 10 to 15 times (one set). Perform a total of three sets.

As your condition improves, perform straight leg raises with weights at the ankle; begin with a 2 pound weight and gradually increase to a 5 to 10 pound weight (pennies or fishing weights in an old sock, two cans in a purse, or Velcro ankle weights).

Hip abduction — Lie on your side on the bed or floor. The affected leg should be on top and should be held straight. The bottom leg should be bent. Hold the top leg straight and raise it 3 to 4 inches towards the ceiling. Hold for 5 seconds then slowly release. Repeat 10 to 15 times (one set). Perform a total of three sets.

Hip adduction — Lie on your side on the bed or floor. The affected leg should be on bottom and should be held straight. The top leg should be bent with the foot placed in front of the bottom leg. Lift the bottom leg 3 to 4 inches. Hold for 5 seconds then slowly release. Repeat 10 to 15 times (one set). Perform a total of three sets.

Quarter squats — Stand 18 to 24 inches from a wall. Lean back against the wall. Bend both knees slightly (the buttocks should not be lower than the knees), keeping the back straight (picture 3). Hold for five seconds then slowly stand up straight. Rest as needed. Repeat 10 to 15 times (one set). Perform a total of three sets. To increase the difficulty, bend the knees more deeply, hold for a longer time, and increase the speed.

Alternately, use an exercise ball to perform squats. Stand up straight, holding the ball between your back and the wall. Slowly bend the knees and lower the back (roll the ball down the wall). Hold for a count of five. Stand up. Repeat 10 to 15 times.

WHERE TO GET MORE INFORMATION — Your healthcare provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient education: How to use crutches (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

Patient education: Osteoarthritis symptoms and diagnosis (Beyond the Basics)
Patient education: Anterior cruciate ligament injury (Beyond the Basics)
Patient education: Nonsteroidal antiinflammatory drugs (NSAIDs) (Beyond the Basics)

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

Anterior cruciate ligament injury
Clinical manifestations of rheumatoid arthritis
Approach to the adult with unspecified knee pain
Knee bursitis
Medial (tibial) collateral ligament injury of the knee
Meniscal injury of the knee
Running injuries of the lower extremities: Risk factors and prevention
Patella fractures
Patellofemoral pain
Clinical manifestations and diagnosis of osteoarthritis

The following organizations also provide reliable health information.

●National Library of Medicine

     (https://medlineplus.gov/healthtopics.html)

●Human Performance Resource Center Online

     (www.hprc-online.org)

●American Academy of Orthopaedic Surgeons

     (http://orthoinfo.aaos.org/)

●National Institute of Arthritis and Musculoskeletal and Skin Disease

     (www.niams.nih.gov)

●American College of Rheumatology

     (www.rheumatology.org)

●Arthritis Foundation

     (www.arthritis.org)

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