Pain behind the knee (posterior pain)

Pain behind the knee is also called posterior knee pain and often occurs alongside swelling at the back of your knee, which may spread to the back of your leg (calf). Severe swelling can prevent you from bending your leg. 

Symptoms associated with posterior knee pain

There are many different causes for pain at the back of your knee, with symptoms varying accordingly. Depending on the cause, symptoms include:

• A popping noise on injury
• Locking of your knee
• Sudden pain or muscle tightening at the back of your knee
• Stiffness and difficulty bending or straightening your leg 
• Swelling, bruising, redness and/or warmth
• Weakness in your knee — you may find it difficult to support your weight or stand on your tiptoes

What causes pain behind the knee?

There are many different causes of posterior knee pain, including injury, inflammation or infection of the knee joint, overuse, wear and tear with age, osteoarthritis, rheumatoid arthritis, cysts or in very rare cases, cancer. 

Leg cramps

Leg cramps occur when your leg muscles tighten up. Symptoms include a sudden muscle spasm, with pain lasting from several seconds up to 10 minutes. After the spasm, your muscles may feel sore for several hours.

Leg cramps are most common during exercise and pregnancy. However, they can also be caused by:

• Dehydration
• Infections eg tetanus
• Liver disease
• Problems with the nerves in your legs
• Toxins in your blood eg lead or mercury

Jumper's knee

This is also known as patellar tendonitis and occurs when a tendon in your knee is injured, often while playing sport. The tendon develops tiny tears that cause swelling stiffness, weakness and difficulty bending and straightening your knee.

Biceps femoris tendonitis (hamstring injury)

Your hamstrings are three muscles that run along the back of your thigh and help you bend your knee. Hamstring injuries most often occur when playing sports, usually when the hamstring is overstretched (strained or pulled hamstring). However, the hamstrings can also be torn, which can take several months to heal.

Baker's cyst

A Baker’s cyst is a fluid-filled sac that sits behind your knee that can develop if you have arthritis or sustain a knee injury, which causes your knee joint to become swollen and inflamed. 

In addition to posterior knee pain, symptoms include swelling, stiffness and difficulty bending or straightening your leg. Symptoms often worsen on activity and if the cyst bursts, you will feel a sudden, sharp pain. 

Symptoms include sudden pain and swelling, bruising and weakness in your leg.

Gastrocnemius tendonitis (calf strain)

Your calf muscles include the gastrocnemius muscle and the soleus muscle in the back of your lower leg. They help you bend your knee and point your toes. If you take part in sports where you suddenly have to go from standing to running (eg during tennis or squash), the gastrocnemius muscle can tear or become strained.

Symptoms include bruising, pain and swelling in your calf, and difficulty standing on your tiptoes.

Meniscus tear

The meniscus cartilage sits in your knee joint and acts as a cushion to stabilise it. Each of your knees has two menisci, one on each side. If you play sports that involve squatting or twisting your knee, you may tear this cartilage. With age, this cartilage weakens and can more easily tear with any twisting motion during everyday activities. 

You may hear a popping noise when it tears but have no immediate pain. However, over the next few days, knee pain will develop, as well as stiffness, swelling, weakness and/or locking or giving way of your knee.

Anterior cruciate ligament injury

The anterior cruciate ligament (ACL) is a ligament that runs along the front of your knee and connects your thigh bone to your shinbone. It helps stabilise your knee so you can move it smoothly.

ACL injuries are common when playing sports where you suddenly slow down, stop or change direction when running (eg football). You can also damage your ACL if you land badly after a jump or your knee is hit by a blunt object. You may hear a popping noise on injury followed by immediate pain and swelling. You may find it difficult to bend your knee and/or walk.

Posterior cruciate ligament injury (knee sprain)

The posterior cruciate ligament (PCL) is a ligament that runs along the back of your knee and connects your thigh bone to your shinbone. It helps stabilise your knee so you can move it smoothly. It is less likely than the ACL to be damaged, however, it can become damaged if your knee is hit by a blunt object (eg during a car accident). Occasionally, the PCL can be damaged by twisting your knee or missing a step when walking. It can be strained if it is overstretched and if enough pressure is applied it can tear in two.

Alongside posterior knee pain, symptoms include swelling, stiffness and weakness of the knee, as well as difficulty walking.

Chondromalacia

Chondromalacia occurs when the cartilage in your knee wears down, so your bones rub against each other. Common causes include injuries, wear and tear with age, overuse and arthritis. Symptoms include a dull ache behind your kneecap (patella) that may worsen when climbing the stairs or after sitting for a long time, difficulty moving your knee along its full range, weakness or giving way of your knee, and a cracking or grinding feeling when bending or straightening your knee.

Arthritis

Arthritis causes inflammation of your joints due to the cartilage in your knee wearing away. There are several different types of arthritis that can affect your knee and cause posterior knee pain: 

• Osteoarthritis — the most common type of arthritis caused by wear and tear of the cartilage in your joints over time
• Psoriatic arthritis — arthritis that causes joint pain and scaly skin
• Rheumatoid arthritis — an autoimmune disease where your own immune system mistakenly attacks your joints

Lupus, an autoimmune condition related to arthritis, can also cause knee pain due to inflammation of your joints.

Deep vein thrombosis (DVT)

DVT is a blood clot that develops in a deep vein in your leg. This causes leg pain, especially when you stand up. If this occurs in a vein behind your knee (popliteal vein thrombosis) you can experience posterior knee pain. Other symptoms of a DVT include redness, swelling and warmth of your leg.

Hyperextension

Hyperextension refers to bending your knee too far backwards, which often occurs when playing sports. In addition to posterior knee pain, symptoms include weakness in your knee and unsteadiness.

Diagnosis of pain behind the knee

If you have pain behind your knee, it is important to see your doctor to rule out anything serious such as a DVT. 

For posterior knee pain caused by a minor injury or arthritis, you can treat this at home with rest and pain relief. However, you should see a doctor if

• You are in pain
• You have a fever
• You have a history of blood clots
• Your affected leg is red or swollen

Your doctor will perform a physical examination of your knee and ask you questions about your symptoms and your medical history. This includes: 

• How active you are
• When your pain started and what you were doing at the time
• Whether you can think of any injury or activity that may be causing your symptoms
• Whether your pain comes and goes

If you have symptoms of a Baker’s cyst your doctor may recommend an ultrasound scan. 

If you have symptoms of a posterior cruciate ligament injury, they may recommend an X-ray or MRI scan.

You should seek urgent medical attention if you:

• Are in severe pain
• Can’t bear any weight on your affected leg
• Have difficulty breathing
• Have sudden swelling or warmth in your leg
• Notice that your knee is misshapen

How do you relieve pain in the back of your knee?

• Apply ice packs for 20 minutes three to four times a day
• Elevate your affected leg using pillows to the same height or slightly higher than the level of your knee
• Rest your leg and try to keep any weight off it — you can use crutches or canes to help keep weight off your affected knee
• Take over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) eg for aspirin, ibuprofen or naproxen
• Wear elastic compression bandages — make sure they are not on too tight as this can further damage your knee and leg

Treatment of pain behind the knee

Rest, applying ice packs, taking painkillers and physiotherapy can all be used to treat posterior knee pain. Depending on the severity and underlying cause of your knee pain, your doctor may also prescribe medication and/or recommend surgery. 

Treatment for Baker’s cysts

Baker’s cysts can go away on their own or with treatment of the underlying condition causing your cyst (eg arthritis). However, if you have a large or painful cyst, your doctor may recommend steroid injections, physiotherapy or drainage of the cyst.  

Treatment for gastrocnemius tendonitis

Your knee pain should subside with rest, elevation of your leg and applying ice packs. How long this takes will depend on the size of the tear.

Treatment for meniscus tear

Rest, elevation of your leg and applying ice packs may be enough to treat your tear. However, if your tear doesn’t improve on its own, your doctor may recommend surgery.

Treatment for ACL injury

Rest and physiotherapy can treat an ACL injury. However, if your ACL is torn, you may need surgery.

Treatment for PCL injury

Your knee pain should subside with rest, elevation of your leg and applying ice packs. However, your doctor may recommend surgery if you have injured more than one ligament, are unsteady on your feet or have also damaged cartilage in your knee.

Treatment for chondromalacia

Applying ice packs, taking over-the-counter painkillers and physiotherapy can treat chondromalacia. However, if the cartilage in your knee is damaged, you will need surgery.

Treatment for arthritis

Arthritis can’t be cured but it can be managed with exercise, painkillers and medications, including injections.

Rheumatoid arthritis can be treated with disease-modifying drugs that suppress your immune system and reduce inflammation.

Treatment for DVT

DVT is treated with blood thinners, which prevent the clot growing and new clots forming. Eventually, your body will break down the DVT.

Complications from rear knee pain

There are different complications from rear knee pain, depending on the underlying cause. 

A DVT should always be treated urgently as it can travel to your lungs and cause a pulmonary embolism, which is life-threatening. 

To avoid complications from rear knee pain, you should see a doctor if:

• You have a fever
• You have a bluish discoloration, pain, swelling, numbness or tingling in your affected leg
• You have severe pain even when your leg is not bearing weight
• Your pain lasts longer than three days or gets worse
• Your affected leg can’t bear weight

You should also see a doctor if your knee:

• Clicks, locks or gives way
• Is misshapen
• Is warm, red or swollen