Your knee is a complex structure consisting of three bones—the lower part of the thighbone, the upper part of the shinbone, and the kneecap. Then, there are strong ligaments and tendons that hold these bones together, as well as cartilage beneath the kneecap and between the bones to cushion and stabilize the knee. Damage or disease that affects any of these structures may lead to pain.
If you have knee pain, some common causes include:
There are different types of arthritis that affect the knee joint, the two most common ones being osteoarthritis and rheumatoid arthritis.
- Knee osteoarthritis develops as a result of “wear and tear” of the cartilage in the knee and is more common in people over the age of 50.1 As the cartilage deteriorates, pain develops, often gradually escalating from a sharp pain that worsens with knee movement to a constant dull, aching pain.
- Rheumatoid arthritis is an autoimmune disease whereby a person’s immune system attacks multiple joints in the body. In addition to pain, swelling, redness, and warmth over the kneecap may develop. Unlike osteoarthritis, knee pain from rheumatoid arthritis tends to improve with activity.
Knee Ligament Injuries
There are four ligaments in your knee—two collateral ligaments and two cruciate ligaments.
Collateral Ligament Injury
The collateral ligaments (medial collateral and lateral collateral) are found on the side of your knee and connect your thighbone (femur) to your lower leg bone. Injury to the medial collateral ligament (MCL) often results from a direct blow to the outside of the knee, which causes pain on the inside of the knee. A blow to the inside of the knee may cause a lateral collateral ligament (LCL) injury, which causes pain to the outside of the knee.
Cruciate Ligament Injury
The cruciate ligaments (anterior cruciate and posterior cruciate) cross each other inside the knee joint, with the anterior cruciate being in the front and the posterior cruciate being in the back. Anterior cruciate ligament injuries are the most common type of knee injury, often resulting from a direct blow or a sudden change in direction or speed when running.2 Usually, a “popping” noise is heard, along with sudden swelling, and a giving out of the knee.
Posterior cruciate ligament injuries are uncommon and are generally caused by some sort of high-energy force to the knee (for example, a bent knee colliding with the dashboard during a car accident). Besides pain at the back of the knee, knee swelling and stiffness are typical symptoms associated with this ligament injury.
Torn Knee Cartilage (Meniscus)
There are two “C” shaped, tough pieces of cartilage (called menisci) located between your thighbone and shinbone. Tearing of the meniscus is a common cause of knee pain and may occur in young people (often during sports) or older people, as the cartilage weakens with age making it more prone to tear.3 Besides pain, a person with a meniscus tear may initially hear a “pop” when the tear occurs. This is followed by a gradual development of knee stiffness and swelling, along with knee clicking, locking, or catching.
Patellar Tendonitis and Tear
Patellar tendonitis refers to inflammation of the patellar tendon—a large tendon that connects your kneecap to the top of our shinbone. Patellar tendonitis is most common in people who engage in sports or activities that require frequent running and jumping.4 Often times, people with this condition describes a constant dull pain that becomes sharp with activity.
Patellar tendonitis weakens the patellar tendon, making it more likely to tear. A patellar tendon tear causes severe pain, swelling over the knee, and a tearing or popping sensation. Depending on the degree of the tear, a person may notice an indentation at the bottom of the kneecap and experience walking difficulties due to the knee giving out.
Patellofemoral Pain Syndrome
Patellofemoral pain syndrome is most common in adolescents and young adults and is usually caused by vigorous activities that put stress on the knee, like running, squatting, or climbing stairs.5 This condition causes a dull, aching pain felt underneath the kneecap. Abnormal knee alignment may also cause or contribute to this condition. Besides pain, which worsens with activities that require frequent knee bending or sitting for long periods of time (for example, working at a desk), a person may note popping sounds in the knee when standing up from prolonged sitting or when climbing stairs. Knee swelling and locking are rarely seen with this syndrome.
In some people with patellofemoral pain syndrome, a condition called chondromalacia patella is present, which means that the cartilage behind the kneecap has softened and begun to wear away. It develops as a result of overuse (i.e. bending the knee too much) or from a knee injury. Symptoms include pain, either sharp or aching, located in front of, around, and/or behind the kneecap.
A Baker’s cyst is swelling in the back of the knee joint and is sometimes a sign of another underlying problem such as a meniscus tear.6 While not all Baker’s cysts cause pain, if they do, the “tightening” pain is felt in the back of the knee and is often associated with knee stiffness and a visible bulge that worsens with activity.
Your prepatellar bursa (a fluid-filled sac) is located right over the kneecap. Prepatellar bursitis—when the bursa becomes inflammed— is most commonly caused by people who frequently kneel, like gardeners or carpet layers.7 Less commonly, an infection, gout, rheumatoid arthritis, or a direct blow to the knee may cause bursitis. Besides a mildly aching knee pain that may only be felt with knee movement or when touching the affected area, rapid swelling over the kneecap typically occurs.
Iliotibial Band Syndrome
Iliotibial band syndrome refers to inflammation of the iliotibial band—a thick collection of fibers that runs along the outside of the thigh. Iliotibial band inflammation commonly happens as a result of overuse, especially in runners, and causes an aching, burning pain on the outside of the knee joint.8 Sometimes, the pain spreads up the thigh to the hip.
Here are some less common causes of knee pain:
Intrasubstance signal within the anterior horn of the meniscus small focus of subchondral marrow edema within the lateral tibial plateau. which can be seen as a long, narrow opening or line of breakage made by cracking or splitting, causing levels of cartilage fissure, most commonly know as degeneration, usually in older people but sports, lots of concrete walk or running, injuries, and such can also bring about Cartilage fissure allowing for degeneration in the knees causing swelling, and pain, which can’t be repaired.
A dislocating kneecap causes acute symptoms during the dislocation and occurs from a sharp blow to the knee, such as from a car accident or fall to the ground.9 Besides pain in front of the knee, a person may notice knee buckling, slipping off to one side, or catching during movement. Knee swelling, stiffness, and cracking sounds are also common.
Gout is an inflammatory condition that occurs in people with high levels of uric acid in their bloodstream.10 These high levels of uric acid form crystals within certain joints, like the big toe, fingers, knee, or hip. A gout attack often affects one joint at a time, causing a severe, burning pain, as well as swelling, warmth, and redness of the affected area.
Plica syndrome is an uncommon cause of knee pain and occurs when a plica—an embryonic remnant of the synovial capsule of the knee joint—becomes irritated.11 People with plica syndrome often report middle and front knee pain that worsens with knee activity, like squatting, running, or kneeling, or with prolonged sitting. A popping sensation is often felt when bending the knee.
Osgood-Schlatter disease is a condition seen in children between the ages of nine and fourteen.12 This disease classically occurs after a recent growth spurt when irritation of the growth plate at the front of the knee joint develops, triggering pain and sometimes swelling just below the kneecap. The pain improves with rest and worsens with knee movement.
Osteochondritis dissecans (OCD) is another condition seen in children and adolescents that occurs as a result of a lack of blood supply to a small segment of the knee bone.13 This causes the affected bone and the cartilage covering it to loosen and separate away from the underlying bone. Pain poorly localized to the knee that is felt with activity is the first symptom. As the condition progresses, on and off swelling and knee stiffness may occur. Keep in mind, besides the knee, OCD may affect the ankle or elbow (although, usually only one joint is affected).
Knee Joint Infection
An infected knee joint causes significant knee pain, along with swelling, warmth, stiffness, and often times, a fever. Most of the time, a bacterial infection in the bloodstream is the culprit behind an infected joint.14
A fracture of the kneecap may occur from a fall directly onto the knee, or from a direct blow to the knee,15 like hitting the knee on the dashboard from a car accident. Besides significant discomfort, especially when trying to straighten the knee, bruising and swelling over the kneecap usually occurs.
Very rarely, a bone tumor, such as an osteosarcoma, may be the source of one’s knee pain.16 Associated symptoms like fever or unintentional weight loss and pain that is particularly worse at night may also be present.
When to See a Doctor
If you are unsure of the cause of your symptoms, or if you do not know the specific treatment recommendations for your condition, you should seek medical attention. Treatment of knee pain must be directed at the specific cause of your problem.
Some signs that you should be seen by a doctor include:
- Inability to walk comfortably on the affected side
- An injury that causes deformity around the joint
- Knee pain that occurs at night or while resting
- Knee pain that persists beyond a few days
- Locking (inability to bend) the knee
- Swelling of the joint or the calf area
- Signs of an infection, including fever, redness, warmth
- Any other unusual symptoms
Many knee conditions can be diagnosed based on a medical history and physical examination alone.
When discussing your knee pain with your doctor, try to be as detailed as possible. This is because clues like the precise location and timing of your knee pain, along with associated symptoms, can help your doctor nail down the diagnosis.
Where on the knee you feel the pain can offer some clues about what type of injury or condition is causing the discomfort. For instance, pain on the inside or medial side of the knee (the side closest to the other knee) can be caused by medial meniscus tears, MCL injuries, and arthritis, whereas pain on the outside of the knee, or lateral side, is commonly caused by lateral meniscus tears, LCL injuries, IT band tendonitis, and arthritis.
Likewise, pain in the back of the knee may be due to a Baker’s Cyst. Pain over the front of the knee is most commonly related to the kneecap and can be caused by several different problems, such as chondromalacia or prepatellar bursitis.
Just as the location of knee pain may indicate what’s causing the problem, the time of day the pain is experienced can also offer insight. Pain while walking down steps is very commonly associated with kneecap problems, such as chondromalacia or prepatellar pain syndrome. Knee pain after first waking in the morning that quickly resolves with gentle activity is typical o early arthritis.
Besides pain, your doctor will also ask you whether you have noticed any swelling, or experienced symptoms like fever or chills (a sign of a potential infection) or other whole-body symptoms (for example, joint aches elsewhere, fatigue, or unexplained weight loss), which could indicate a systemic disease like rheumatoid arthritis.
In addition to a comprehensive medical history, a thorough physical exam is important to arrive at the correct diagnosis.17 While examining your affected knee, your doctor will look closely for swelling of the knee, and move the knee around to access for stability, noises, and locking.
Swelling of the knee is common with several different knee problems. When there is an effusion (excess fluid build-up around the joint) immediately after a knee injury, a possible cause is a severe injury to an internal joint structure, like the anterior cruciate ligament or a fracture of the top of the shin bone.
When swelling develops gradually over hours to days after an injury, it is likely to be something less severe, like a tear of the meniscus or a ligament sprain. Swelling that occurs without a present known injury can be due to osteoarthritis, gout, inflammatory arthritis, or a joint infection.
Range of Motion
Mobility of the knee can be affected by a number of common conditions. If mobility is chronically limited, often the cause is arthritis. When the surface of the joint becomes irregular as a result of arthritis, the mobility of the joint may become limited. If the mobility is limited after an acute injury, there is likely swelling limiting the motion, or a torn structure that is limiting the mobility.
The stability of the knee is provided by the ligaments that connect the shin bone (tibia) to the thigh bone (femur). When the ligaments are stretched or torn, the knee may feel as though it is giving way beneath the patient. A sensation that the knee may give out from beneath you is a common symptom of ligament injury.
Popping and snapping within the knee is common, and often not a symptom of any particular problem. When the pops are painless, there is usually no problem, but painful pops and snaps should be evaluated by your doctor. A pop is often heard or felt during an injury when a ligament, such as the ACL, is torn. Grinding or crunching are common symptoms of cartilage problems. If the cartilage is damaged, as in chondromalacia, a crunching sensation is often felt by placing the hand over the kneecap and bending the knee. A similar grinding sensation may be felt with knee arthritis.
Locking is a symptom that occurs when a patient cannot bend or straighten their knee. The locking can either be due to something physically blocking the motion of the knee or by pain preventing normal knee motion. One way to determine if there is something physically blocking knee motion is to have a health care professional inject the knee with a numbing medication. After the medication has taken effect, you can attempt to bend the knee to determine if the pain was blocking the motion or if there is a structure, such as a torn meniscus, that is blocking normal motion.
While not all knee conditions require an imaging test for diagnosis (for example, bursitis, tendonitis, or osteoarthritis), some do, such as a knee fracture or ligament or meniscus injury. In most cases, your doctor will start off with an X-ray, and then proceed with either an ultrasound or an MRI to evaluate soft tissue injuries like collateral ligament damage or tendonitis.
While it may seem obvious that knee pain originates from the knee, this is not always the case. Sometimes a problem in the lower back, sacroiliac joint, or hip refers pain to the knee. Your doctor will suspect a referred source based on your physical exam, as pain from a non-knee location will not cause knee tenderness when pressing on it. There will also be no knee swelling present and your knee will have a normal range of motion.
Some common treatments for knee pain are listed here (although, not exhaustive) and not all of these treatments are appropriate for every condition.
Many therapies for knee pain are simple, straightforward, and can be done at home.
The first treatment for most common conditions that cause knee pain is to rest the joint, allowing the immediate inflammation to subside. Sometimes, this is the only step needed to relieve knee pain.
Besides rest, applying a cold gel pack, bag of ice, or a bag of frozen vegetables on the knee is perhaps the most commonly used treatment for knee pain. When icing your knee, be sure to not directly apply the ice to your skin and ice for only 15 to 20-minute sessions (multiple times per day).
Depending on the diagnosis, your doctor may recommend knee support to ease your pain. For example, in the case of patellar tendonitis, your doctor may advise supportive taping and patellar tendon straps. For prepatellar syndrome, a lightly wrapped elastic bandage over the knee (with a hole where the kneecap is) may be recommended.
Physical therapy is an extremely important aspect of treatment for almost all orthopedic conditions. Physical therapists use different techniques to increase strength, regain mobility, and help return patients to their pre-injury level of activity.
The American Academy of Orthopedic Surgeons (AAOS) emphasizes the importance of engaging in an exercise conditioning program (under the guidance of your doctor and physical therapist) after a knee injury or surgery. One knee conditioning program the AAOS suggests focuses on stretching and strengthening the muscles that support the knee, including the quadriceps, hamstrings, inner and outer thigh muscles, and buttocks.
Medication is often utilized not only to alleviate pain but also to help treat the underlying knee problem.
Nonsteroidal anti-inflammatory medications, commonly referred to as NSAIDs, are some of the most commonly prescribed medications, especially for patients with knee pain caused by problems such as arthritis, bursitis, and tendonitis.
Besides NSAIDs, other pain medications your doctor may recommend (especially for a diagnosis of osteoarthritis) include:
- Tylenol (acetaminophen)
- Cymbalta (duloxetine)
- Topical capsaicin
If your pain is persisting despite conservative therapies like rest, ice, and taking an NSAID, your doctor may inject cortisone—a powerful medication that treats inflammation—into your knee. Examples of knee conditions that may warrant a cortisone injection include bursitis (the fluid in the bursa will be drained first before the cortisone is injected), a Baker’s cyst (the primary treatment), and knee osteoarthritis. Hyaluronic acid injections may also be used to ease the pain of knee osteoarthritis.
Depending on your diagnosis, other medications, like a disease-modifying anti-rheumatic drug (DMARD) to treat rheumatoid arthritis, antibiotics to treat an infected knee joint, or an oral steroid to treat a gout flare, may be warranted.
Complementary and Alternative Therapies
A number of mind-body therapies, such as acupuncture and tai chi, may be used to treat knee pain, especially knee osteoarthritis.
While once popular, the dietary supplements glucosamine and chondroitin have fallen out of favor for treating knee osteoarthritis. This is due to their lack of benefit based on scientific studies; although, some people may obtain mild relief. Like any medication, vitamin, or supplement, be sure to talk with your doctor first before taking it to be certain it is safe for you.
Surgery is generally reserved for specific diagnoses, such as:
- Advanced cases of knee osteoarthritis
- Chronic knee dislocation
- Anterior and posterior cruciate ligament injuries
- Certain knee fractures
- Certain infected knee joints that require surgical drainage
There are several things you can do to prevent knee injuries and/or prevent the progression of chronic knee conditions, like osteoarthritis:
- Lose weight if overweight or obese
- Engage in low-impact aerobic exercises that place less stress on your knee, like swimming or cycling
- Wear knee pads if your work on your knees or participate in contact sports like basketball or wrestling
- Strengthen and stretch your quadriceps and hamstrings
- Apply ice and elevate your knees after exercising