Pain behind the knee (posterior pain)

Expert reviewer, Mr Damian McClelland, Trauma and Orthopaedic Consultant, and Clinical Director for Musculoskeletal Services at Bupa
Next review due March 2022

Pain behind the knee is also called posterior knee pain. ‘Posterior’ just means behind.

As well as pain, you may have swelling just at the back of the knee or that extends into the calf. The swelling may be large enough to stop you bending your leg properly.

A diagram by Bupa of where back knee pain is located

Causes of pain behind the knee

There is no single cause, but there are a number of reasons why you may have pain behind the knee. It may be linked to:

  • increasing age and presence of osteoarthritis
  • rheumatoid arthritis in adults or children
  • knee injury (ligament injury or torn cartilage)
  • a cyst
  • inflammation or infection in the joint
  • a benign or cancerous growth (this is very rare)

Conditions associated with pain behind the knee

Two common conditions that cause pain behind the knee are:

A cyst is a collection of fluid inside a thin layer. A popliteal cyst is a cyst in the shallow depression at the back of the knee. It’s often linked to other conditions affecting the knee, including osteoarthritis, rheumatoid arthritis, cartilage injuries and inflammation of the knee joint. Many types of injury can cause a collection of fluid. Often it will be a heavy blow to the front of the knee, from falling forwards or playing a contact sport. The natural mechanism of the knee pushes this excess fluid backwards and it collects in the depression at the back of the knee, over time, causing a cyst to form.

A posterior cruciate ligament injury is caused by overstretching or tearing of this ligament, which runs across the knee from the thigh to the shin bone. It often results from a heavy blow to the front of a bent knee, sometimes from falling forwards or during a contact sport, such as rugby. Other typical injuries can occur when the knee hits the dashboard during a car accident or when the leg is over-straightened and the knee is bent backwards. Doctors call this hyperextension.

Osteoarthritis of the knee is a common cause of knee pain. The smooth, shiny cartilage that lines the knee joint becomes worn and rough. This causes pain and increasing damage to the knee over time. It mostly affects people over 50. The older you are, the more likely you are to get it.

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Symptoms of pain behind the knee

Symptoms you may have with pain behind the knee will vary, depending on the cause. You may have swelling or pain with particular movements.

A popliteal cyst causes swelling at the back of the knee, which can be quite noticeable. A very large swelling may stop you from fully straightening your leg.

The swelling may come and go, getting bigger or shrinking over time. If the cyst bursts, you may have swelling and pain in your calf.

If you have a swollen, tender calf, it’s very important to see a doctor as the swelling can also be caused by a clot in your leg (deep vein thrombosis), which needs to be treated urgently.

If your cyst bursts, you may hear a pop and feel warmth spread down your calf. You may develop redness or bruising anywhere from the back of your knee down to your ankle and the top of your foot.

With a posterior cruciate ligament (PCL) injury, it’s more common to have other knee injuries as well. But if you have only injured your PCL, you may just feel vague discomfort or instability in your knee. You may feel pain behind your knee, but some people have pain at the front of the knee as well. You may also have pain when kneeling. A chronic or long-term PCL injury can cause pain when slowing down from running, walking downhill or going down stairs.

Osteoarthritis usually causes pain when you’re bearing weight, which is relieved by rest. Stiffness and loss of movement is often worst first thing in the morning or after sitting for a while and eases once you start moving around.

Diagnosis of pain behind the knee

Your doctor will examine your knee and take a history, asking about:

  • the type of pain you have, when it started and whether it comes and goes
  • how active you are
  • any activity, accident or injury that could have caused it

If you have signs of a popliteal cyst, your doctor may suggest an ultrasound scan. If they suspect a posterior cruciate ligament injury, they may suggest an X-ray or a magnetic resonance imaging (MRI) scan.

Managing pain behind the knee

You can help yourself by keeping weight off your leg as far as possible, using an ice pack and taking painkillers, such as ibuprofen. If you can’t put weight on your leg, you may need crutches.

Popliteal cysts often get better on their own and you may not need any further treatment. But it’s a good idea to see a doctor if you have pain behind the knee. It may be something more urgent (such as a blood clot in the leg). With posterior cruciate ligament injury, you can develop complications later if you are not treated. You should see a doctor if:

  • you cannot put weight on the affected leg
  • you have severe pain, even when not bearing weight
  • your knee buckles, clicks, or locks
  • your knee is deformed or misshapen
  • your knee is hot, red or very swollen or you have a fever
  • you have pain, swelling, numbness, tingling, or a bluish discoloration in your calf
  • you’re still in pain after three days

Treatment of pain behind the knee

The treatment that you have for pain behind your knee will depend on what condition is causing the pain.

For information on treatments, please see the relevant knee condition page.

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  • Reviewed by Alice Windsor, Specialist Health Editor, Bupa UK Health Content Team, March 2019
    Expert reviewer, Mr Damian McClelland, Trauma and Orthopaedic Consultant, and Clinical Director for Musculoskeletal Services at Bupa
    Next review due March 2022