Why Knees Hurt

9) CNRI / Science Source

What causes pain behind the knee?

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There are many possible causes of pain in the back of the knee. Some are common and less serious, while others require more immediate medical attention.

The knee is a complex joint, and it takes a lot of impact from even simple everyday activities. People can often reduce or prevent knee damage by avoiding impact and strain on the joint.

Treatment for pain in the back of the knee will vary greatly depending on the cause.

Fast facts on pain in the back of the knee

• There are many possible causes of this kind of pain.
• Receiving early treatment for knee pain often prevents the injury from getting worse.
• In some cases, the pain may be due to fatigue or not stretching before exercise.

It is important to work closely with a doctor to diagnose pain in the back of the knee, as some causes require long-term treatment to heal completely.

Some possible causes of pain in the back of the knee include the following.

Leg cramps

Cramps occur when muscles become too tight. This tightness may be because the muscle is doing too much work without being stretched. If it is stretched and still cramps, the muscle may simply be overused.

Overuse syndrome can affect different areas of the knee. With this condition, a person might also feel a cramp in the thigh or calf near the knee.

The sensation resembles a sudden, painful spasm of the muscle. The pain may last for seconds or minutes and can range from uncomfortable to severe.

Some other possible reasons for leg cramp include:

• dehydration
• infections, such as tetanus
• liver disease
• excess toxins in the blood
• nerve problems

Pregnant people may also experience leg cramps as a normal effect of pregnancy.

Some people who often experience leg cramps may find relief through regularly stretching their calves. Also, they can try shortening their stride to put less strain on the knee and surrounding muscles.

Baker’s cyst

A Baker’s cyst is a pocket of fluid that builds up in the back of the knee, leading to pain and swelling.

Baker’s cysts may not be noticeable at first, as small cysts do not typically cause pain. However, as the cyst grows, it may shift the surrounding muscles or put pressure on the tendons and nerves, causing pain.

Baker’s cysts may grow to about the size of a table tennis ball. People with Baker’s cysts often feel pressure in the back of the knee, which may cause a tingling sensation if the cyst is affecting a nerve.

In most cases, Baker’s cysts are not a cause for concern, but treatment can relieve the symptoms.

Osteoarthritis

Osteoarthritis is a condition that wears down the cartilage of the joints over time. This condition can easily cause pain in the back of the knee.

People with osteoarthritis in the knee may experience other symptoms, such as loss of motion or difficulty bending the knee. Inflammation in the joint may make it stiff and painful. A person may also feel this discomfort in other places around the knee.

Other forms of arthritis that could be causing the pain include autoimmune conditions such as lupus and rheumatoid arthritis.

Runner’s knee

Runner’s knee refers to the wearing down of the cartilage in the knee joint. When the cartilage is gone, the bones of the knee rub together. Typically, this causes a dull, aching pain behind the knee.

Some other symptoms of runner’s knee include:

• the knee giving out or buckling randomly
• weakness in the knee and leg
• restricted movement in the leg and knee
• a crackling or grinding feeling when the knee bends

Hamstring injury

A hamstring injury is a tear or strain in one or more of the muscles in the back of the thigh. These muscles include:

• the biceps femoris
• the semitendinosus
• the semimembranosus

A hamstring strain happens if the muscle pulls too far. It may tear completely from being pulled too much, and this can take months to heal fully.

Hamstring injuries may be more common in athletes who run fast and in bursts, such as those who play basketball, tennis, or football.

Meniscus tears

The meniscus is a piece of cartilage on either side of the knee. Twisting motions while squatting or bending the leg may tear this cartilage. Many people hear a pop when they tear their meniscus.

The pain from a meniscus tear may not show up at first but typically worsens over the next couple of days.

Meniscus tears often cause other symptoms, including:

• loss of knee motion
• weakness and fatigue in the knee and leg
• swelling around the knee
• the knee giving out or locking up when used

Surgery may be necessary if a meniscus tear is severe and does not heal on its own.

Anterior cruciate ligament injuries

The anterior cruciate ligament (ACL) is a band of tissue that runs through the front of the knee joint, connecting the bones and helping keep the knee joint stable.

ACL strains often happen due to sudden stops or changes in direction. Similarly to meniscus tears, a strain in the ACL may cause a popping sound, followed by pain and swelling.

A torn ACL is a well-known, serious injury, often side-lining an athlete for a long time. Torn ACLs usually require reconstructive surgery.

Posterior cruciate ligament injuries

The posterior cruciate ligament (PCL) plays a similar role to the ACL, though it is less likely to become injured than the ACL.

PCL injuries may happen during traumatic events, such as falling directly onto the knee from a height or being in a vehicle accident. With enough force, the ligament may tear completely.

PCL injuries cause symptoms such as:

• knee pain
• stiffness in the knee if bending
• difficulty walking
• swelling in the knee

Completely resting the knee may help a PCL strain heal. However, a severe PCL injury may require surgery.

Deep vein thrombosis

A thrombosis is a blood clot, and a deep vein thrombosis (DVT) occurs when a clot happens in the veins deep within the leg.

Many people who have a DVT feel more pain when they stand up. However, some may feel pain in their leg and knee at most times.

Some other symptoms of DVT may include:

• skin that is red or warm to the touch
• swelling in the area
• fatigue in the affected leg
• prominently visible surface veins

Risk factors for DVT can include carrying excess weight, being older, and smoking. People who lead sedentary lives may also be likely to experience DVT.

DVT needs medication and care, as it can become more serious if the clot breaks loose into the bloodstream.

Why Knees Hurt

Your knees have lots of moving parts, and you use them a lot, so lots of things can go wrong. Too much of one kind of motion, especially if you don’t work up to it, can lead to “overuse” injuries. Simple wear and tear is a problem, especially as you age. Accidents can crack bones and tear tissue. With some conditions, your body attacks its own joints. Your doctor can help you sort out what’s going on with your knee when it doesn’t feel right.

Dislocations and Fractures

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If your knee hurts intensely after a bump, bang, or fall, you may have broken one of the bones that meet up there — the thigh, shin, and kneecap — or shifted one out of place. Go to the emergency room or see a doctor as soon as possible. Sometimes fractures happen more slowly, causing tiny cracks at the ends of the leg bones. This can happen when you’ve started using your knee more.

Torn Anterior Cruciate Ligament

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You hear a pop and can’t move after you suddenly change direction — often while playing soccer, football, or basketball. You may have torn your ACL, which connects the femur and the tibia and prevents the tibia from moving too far forward. Your knee will hurt and swell and feel unstable.

You can tear or strain any of the tissues that hold your knee together: Ligaments connect bones to each other; tendons connect muscle to bone. Irritated tendons from using them too much? That’s tendinitis.

Iliotibial Band Syndrome

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The “IT band,” a ligament that runs along the outside of your thigh, can rub against the bone and get irritated and swollen. You’re more likely to get this when you run or ride your bike for exercise. It might hurt more if you go downhill or sit for a while. You may feel better after you warm up, but if you don’t rest the injury and give it a chance to heal, it could get worse.

Osteoarthritis

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It’s tough to bend or stretch your leg. Your knee feels stiff and sore and may swell after you’ve been moving around. You’ve probably worn down the cartilage, the stuff that helps cushion the ends of your bones. Because that takes time, this kind of arthritis is more common in people 65 and older. If you’re younger, you may get it because you’ve used your knee a lot after an injury, like a ligament tear.

Inflammatory Arthritis

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Besides pain and swelling, you may also feel tired, sick, or feverish. When you have an autoimmune disease, your immune system, which is meant to fight off germs, may attack your knees. For example, rheumatoid arthritis tends to affect hands and other joints in pairs on both sides of the body. Lupus goes after joints, muscles, and organs all over. Psoriatic arthritis often causes thick, discolored patches of skin, along with joint pain.

Bursitis

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This makes your knee swollen, stiff, and warm or tender to the touch, usually because you’ve overworked it. The condition is also known as “housemaid’s knee” or “clergyman’s knee” because people with these jobs are kneeling so much. It happens when small, fluid-filled sacs called bursa that help cushion your knee joint get irritated and swollen. You may ache even when you’re resting.

Runner’s Knee

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You’ll feel this in the front of your knee, around the kneecap. Your knee may hurt after you sit with it bent for a while or when you try to kneel. It may pop or crack when you climb stairs. Typically, patellofemoral pain syndrome comes from overuse, misalignment between your hip and ankle, a weak thigh muscle, or the breakdown of cartilage behind your kneecap — or a combination of these. It’s common in women and young athletes.

Torn Meniscus

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A sudden twist or pivot — especially with your full weight on your knee — can tear a meniscus, the rubbery cartilage that acts as a cushion between the bones of your thigh and shin. You have one on each side of your ACL. They may be more susceptible to tears because of arthritis or age. The pain can be hard to pinpoint and describe. Your knee may get stiff, swollen, and hard to move and extend.

Baker’s Cyst (Popliteal Cyst)

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This fluid-filled sac at the back of your knee may bulge out or get so tight that it’s hard to fully bend or stretch your leg. It may be caused by another problem, like arthritis or a tear in your meniscus. The cyst itself usually doesn’t hurt unless it bursts, which can make the back of your knee and calf swell and bruise.

Gout and Pseudogout

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Both have similar symptoms: The pain and swelling are often intense and hit you fast. Your knee may be stiff, red, and hot. It happens when crystals gather in the joint. Gout is from a buildup of uric acid and often affects the big toe. Pseudogout is caused by calcium pyrophosphate.

Infection

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Another illness or a direct injury to the joint can cause septic arthritis. The pain will come on quickly, and you’ll also be sick, cranky, and running a fever. Your doctor may use a needle to take some fluid from your knee to figure out which bacteria is causing it so they know how to treat it. Though it doesn’t happen as much, viruses and parasites can infect your joints, too.

Referred Pain

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Problems somewhere else — in your back, hip, or foot, for example — can make your knee sore. Nerves can move pain from one area to another, or your brain may get confused about the source of pain signals. The feeling is real, but there may be nothing wrong with your knee itself.

What You Can Do

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Take over-the-counter NSAID drugs like ibuprofen and naproxen to ease pain and swelling. RICE — rest, ice, compression, and elevation — can often help, too: Get off your feet. Raise your leg so it’s higher than your heart. Put a cold pack in a thin cloth or towel on your knee for 10-20 minutes at a time, several times a day. Wrap an elastic bandage around your knee when you’re up and about, snug but not tight.

When to See Your Doctor

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Don’t wait if your knee pain is sudden and intense. Pick up the phone if it won’t go away or gets worse.

To make a diagnosis, your doctor might take X-rays or other images of your knee. Blood or knee fluid samples can help confirm or rule out certain conditions. Treatment may include medication, special exercises, braces, or in some cases surgery. Losing weight could help lessen pressure and strain on your knees.

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Mayo Clinic: “Knee pain,” “Torn meniscus,” “Baker’s cyst,” “Gout,” “Pseudogout,” “Septic arthritis.”

UpToDate: “Approach to the adult with knee pain likely of musculoskeletal origin,” “Approach to the adult with unspecified knee pain,” “Iliotibial band syndrome.”

OrthoInfo: “Common Knee Injuries,” “Patellofemoral Pain Syndrome,” “What Are NSAIDs?” “Sprains, Strains and Other Soft-Tissue Injuries.”

Arthritis Foundation: “What is Osteoarthritis?” “Benefits of Weight Loss.”

National Institute of Arthritis and Musculoskeletal and Skin Diseases: “Arthritis,” “Rheumatoid Arthritis,” “Gout” “Handout on Health: Rheumatoid Arthritis.”

CDC: “National Institute for Occupational Safety and Health: Preventing Knee Injuries and Disorders in Carpet Layers.”

Annals of The Royal College of Surgeons of England: “Hip osteoarthritis: where is the pain?”

BMJ Case Reports: “Hip arthritis presenting as knee pain.”

Medical News Today: “Knees ache? it could be your hips’ fault.”