What’s Causing This Pain in the Back of My Knee?

Medically reviewed by William Morrison, MD on September 18, 2017Written by Stephanie Watson on September 18, 2017

Is this cause for concern?

The knee is your body’s biggest joint and one of its most injury-prone areas. It’s made up of bones that can fracture or move out of joint, as well as cartilage, ligaments, and tendons that can strain or tear.

Some knee injuries eventually heal on their own with rest and care. Others require surgery or other medical interventions. Sometimes pain is a sign of a chronic condition like arthritis that damages the knee gradually over time.

Here are some of the conditions that can cause pain in the back of your knee, and what to expect if you have one of them.

1. Leg cramps

A cramp is a tightening of a muscle. Muscles in the calves are most likely to cramp, but other leg muscles can cramp up, too — including muscles in the back of the thigh near the knee.

You’re more likely to have leg cramps when you exercise or during pregnancy. Other possible causes include:

  • nerve problems in your legs
  • dehydration
  • infections, such as tetanus
  • toxins, like lead or mercury in the blood
  • liver disease

When you have a cramp, you’ll suddenly feel your muscle contract, or spasm. The pain lasts anywhere from a few seconds to 10 minutes. After the cramp passes, the muscle may be sore for a few hours. Here’s how to put a stop to the pain and prevent future leg cramps.

2. Jumper’s knee

Jumper’s knee is an injury to the tendon — the cord that connects your kneecap (patella) to your shinbone. It’s also called patellar tendonitis. It can happen when you jump or change direction, such as when playing volleyball or basketball.

These movements can cause tiny tears in the tendon. Eventually, the tendon swells up and weakens.

Jumper’s knee causes pain below the kneecap. The pain gets worse over time. Other symptoms include:

  • weakness
  • stiffness
  • trouble bending and straightening your knee

3. Biceps femoris tendonitis (hamstring injury)

The hamstring consists of a trio of muscles that run down the back of your thigh:

  • semitendinosus muscle
  • semimembranosus muscle
  • biceps femoris muscle

These muscles allow you to bend your knee.

Injuring one of these muscles is called a pulled hamstring or a hamstring strain. A hamstring strain happens when the muscle is stretched too far. The muscle can completely tear, which can take months to heal.

When you injure your hamstring muscle, you’ll feel a sudden pain. Injuries to the biceps femoris — called biceps femoris tendinopathy — cause pain in the back of the knee.

Other symptoms include:

  • swelling
  • bruising
  • weakness in the back of your leg

This type of injury is common in athletes who run fast in sports like soccer, basketball, tennis, or track. Stretching the muscles out before play can help prevent this injury from occurring.

4. Baker’s cyst

A Baker’s cyst is a fluid-filled sac that forms behind the knee. The fluid inside the cyst is synovial fluid. Normally, this fluid acts as a lubricant for your knee joint. But if you have arthritis or a knee injury, your knee may produce too much synovial fluid. The extra fluid can build up and form a cyst.

Symptoms include:

  • pain in and behind your knee
  • swelling behind your knee
  • stiffness and trouble flexing your knee

These symptoms can get worse when you’re active. If the cyst bursts, you’ll feel a sharp pain in your knee.

Baker’s cysts sometimes go away on their own. To treat a large or painful cyst, you may need steroid injections, physical therapy, or to have the cyst drained. It’s important to determine if an underlying problem is causing the cyst, such as arthritis. If so, taking care of this problem first may result in the Baker’s cyst clearing up.

5. Gastrocnemius tendonitis (calf strain)

The gastrocnemius muscle and the soleus muscle make up your calf, which is the back of your lower leg. These muscles help you bend your knee and point your toes.

Any sport that requires you to quickly go from a standing position to a run — like tennis or squash — can strain or tear the gastrocnemius muscle. You’ll know that you’ve strained this muscle by the sudden pain it causes in the back of your leg.

Other symptoms include:

  • pain and swelling in the calf
  • bruising in the calf
  • trouble standing on tiptoe

The pain should subside depending on the size of the tear. Resting, elevating the leg, and icing the injured area will help it heal faster.

6. Meniscus tear

The meniscus is a wedge-shaped piece of cartilage that cushions and stabilizes your knee joint. Each of your knees has two menisci — one on either side of the knee.

Athletes sometimes tear the meniscus when they squat and twist the knee. As you get older, your meniscus weakens and degenerates and is more likely to tear with any twisting motion.

When you tear a meniscus, you might hear a “popping” sound. At first the injury might not hurt. But after you walk on it for a few days, the knee can become more painful.

Other symptoms of a meniscus tear are:

  • stiffness in the knee
  • swelling
  • weakness
  • locking or giving way of the knee

Rest, ice, and elevation of the affected knee can help alleviate the symptoms and allow it to heal faster. If the tear doesn’t improve on its own, you might need surgery to repair it.

7. Anterior cruciate ligament injury

The anterior cruciate ligament (ACL) is a band of tissue that runs through the front of your knee joint. It connects your thighbone to your shinbone and helps stabilize and provide movement to your knee.

Most ACL injuries happen when you slow down, stop, or change direction suddenly while running. You can also strain or tear this ligament if you land a jump wrong, or you get hit in a contact sport like football.

You might feel a “pop” when the injury happens. Afterward, your knee will hurt and swell up. You might have trouble fully moving your knee and feel pain when you walk.

Rest and physical therapy can help an ACL strain heal. If the ligament is torn, you’ll often need surgery to fix it. Here’s what to expect during ACL reconstruction.

8. Posterior cruciate ligament injury

The posterior cruciate ligament (PCL) is the ACL’s partner. It’s another band of tissue that connects your thighbone to your shinbone and supports your knee. However, the PCL isn’t as likely to get injured as the ACL.

You can injure the PCL if you take a hard blow to the front of your knee, such as in a car accident. Sometimes injuries occur from twisting the knee or missing a step while walking.

Stretching the ligament too far causes a strain. With enough pressure, the ligament can tear into two parts.

Along with pain, a PCL injury causes:

  • swelling of the knee
  • stiffness
  • trouble walking
  • weakness of the knee

Rest, ice, and elevation can help a PCL injury heal faster. You might need surgery if you’ve injured more than one ligament in your knee, have symptoms of instability, or you also have cartilage damage.

9. Chondromalacia

Chondromalacia happens when the cartilage inside a joint breaks down. Cartilage is the rubbery material that cushions bones so they don’t scrape against one another when you move.

Injury to the knee, or a gradual wearing down from age, arthritis, or overuse, can cause chondromalacia. The most common site of cartilage breakdown is underneath the kneecap (patella). When the cartilage is gone, the knee bones scrape against each other and cause pain.

The main symptom is a dull ache behind your kneecap. The pain may get worse when you climb stairs or after you’ve been sitting for a while.

Other symptoms include:

  • trouble moving your knee past a certain point
  • weakness or buckling of the knee
  • a cracking or grinding feeling when you bend and straighten your knee

Ice, over-the-counter pain relievers, and physical therapy can help with the pain. Once the cartilage is damaged, chondromalacia won’t go away. Only surgery can fix the damaged cartilage.

10. Arthritis

Arthritis is a degenerative disease in which the cartilage that cushions and supports the knee joint gradually wears away. There are a few types of arthritis that can affect the knees:

  • Osteoarthritis is the most common type. It’s a gradual breakdown of cartilage that occurs as you age.
  • Rheumatoid arthritis is an autoimmune disease in which the immune system mistakenly attacks the joints.
  • Lupus is another autoimmune disease that causes inflammation in the knees and other joints.
  • Psoriatic arthritis causes joint pain and scaly patches on the skin.

You can manage arthritis pain with exercise, injections, and pain medicines. Rheumatoid arthritis and other inflammatory forms of the condition are treated with disease-modifying drugs that dampen the immune system response and bring down inflammation in the body. Find out how else you can manage arthritis pain.

11. Deep vein thrombosis

Deep vein thrombosis (DVT) is a blood clot that forms in a deep vein inside the leg. You’ll feel pain in the leg, especially when you stand up. Here’s how to tell if you have a blood clot.

Other symptoms include:

  • swelling of the leg
  • warmth in the area
  • red skin

It’s important to get DVT treated as quickly as possible. A clot can break free and travel to the lungs. When a clot gets lodged in an artery of the lungs it’s called pulmonary embolism (PE). PE can be life-threatening.

DVT is treated with blood thinners. These medicines prevent the clot from getting bigger and stop new clots from forming. Your body will eventually break up the clot.

If you have a big clot that’s dangerous, your doctor will give you drugs called thrombolytics to break it up more quickly.

Tips for quick relief

You should

  • Rest the knee until it heals.
  • Hold ice on it for 20 minutes at a time, several times a day.
  • Wear a compression bandage to support the knee, but make sure it’s not too tight.
  • Elevate the injured knee on a pillow or several pillows.
  • Use crutches or a cane to take weight off the knee.
  • Take over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) for pain relief, such as aspirin (Bufferin), ibuprofen (Advil), and naproxen (Naprosyn).

When to see your doctor

You may be able to treat pain from a minor injury or arthritis at home. But call your doctor if you experience the following:

  • The affected leg is red.
  • The leg is very swollen.
  • You’re in a lot of pain.
  • You’re running a fever.
  • You’ve had a history of blood clots.

They can determine the root cause of your knee pain and help you find relief.

You should also seek immediate medical attention if you’re experiencing:

  • severe pain
  • sudden swelling or warmth in the leg
  • trouble breathing
  • a leg that can’t hold your weight
  • changes in the appearance of your knee joint
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