Pain Behind the Knee

Written By: Chloe Wilson, BSc(Hons) Physiotherapy
Reviewed by: KPE Medical Review Board

Pain behind the knee is a common problem. Not only can it affect your ability to walk and carry out your usual activities, back of knee pain can also really affect your sleep.

Also known as posterior knee pain, pain behind the knee may develop gradually over time, or suddenly with an injury. 

There may be a general ache, leg movements may be restricted by swelling or there may be a sharp pain at the back of the knee. 

1. Bakers Cyst

A Bakers Cyst is the most common cause of pain behind the knee. Also known as a popliteal cyst, it develops when excess swelling in the knee seeps out of the back of the joint and pools in the popliteal bursa. The bursa becomes inflamed and swollen and people often say it feels like they have a squashy orange behind their knee.

Anything which causes swelling in the knee can lead to a Bakers Cyst, but the most common culprit is knee arthritis. In fact, around half of all knee arthritis sufferers will develop a Bakers Cyst at some point. Other common causes include gout, knee cartilage tears or a strong blow to the back of the knee.

A Bakers cyst usually causes tightness and pain behind the knee that gets worse when walking, kneeling, or bending and straightening the knee. The swelling at the back of the knee may fluctuate with a Bakers Cyst. Treatment focuses initially on reducing the pain and swelling, and in severe cases, the fluid may need to be drained by your doctor, known as aspiration.

2. Ligament Sprain

Another common cause of pain behind the knee is a ligament sprain. This is when one or more of the four knee ligaments gets overstretched and tears.

Knee ligament tears are usually caused by sudden twisting movements or a large force through the knee. Quick pivoting when running in cleats/studs is a common cause as the foot is held rigid while the rest of the body turns, twisting the knee. 

Common symptoms of a ligament sprain include knee instability, swelling and bruising and the associated pain behind the knee can lead to knee stiffness and difficulty walking. 

3. Posterior Cartilage Tear

A tear in the cartilage at the back of the knee is another common cause of pain behind the knee.

The knee is lined with a thick extra layer of cartilage, known as the meniscus, to protect it from repetitive impact. Think of it like an inbuilt shock absorber. 

Cartilage damage may develop:

• Suddenly: usually from twisting the knee awkwardly or from a large force through the knee
• Gradually: wear and tear over time causes thinning and fraying of the cartilage

4. Calf Tear

Pain behind the knee that is lower down in the calf region may be due to damage and tearing of one of the calf muscles, known as a calf strain.

Calf strains typically happened during activity, such as quickly changing speed or direction when running. The calf muscles get over stretched and tearing in the muscles leads to swelling and pain behind the knee. 

This usually results in back of knee pain and swelling and the symptoms of a calf tear typically get worse when walking or running, especially on tip toes.

Find Out More: Calf Tears - Causes, Symptoms & Treatment

5. Knee Arthritis

Arthritis is another possible cause of pain behind the knee. With knee arthritis, there is gradual wear and tear of the knee bones and cartilage. This erosion leads to the formation of bone spurs, and damages the smooth joint surfaces, as well as reducing the space between the knee bones. 

As a result, the bones and cartilage rub against each other as the knee moves which is not only painful, but can actual restrict movement.

Common symptoms of knee arthritis include knee stiffness (particularly in the morning), clicking or grinding noises and restricted knee mobility. Symptoms often fluctuate and may get worse during cold, wet weather.

6. Hyperextended Knee

A hyperextended knee is an injury where the knee bends back too far, damaging the structures at the back of the knee, resulting in pain behind the knee.

Knee hyperextension is a common sporting injury e.g. from an awkward tackle or skiing accident that forces the knee backwards. There tends to be a sharp or aching pain behind the knee, swelling, bruising and instability. Symptoms typically get worse when standing, walking or going down stairs.

PRICE treatment (protect, rest, ice, elevate, compress) tends to be the first port of call for treatment, followed by strengthening and stability exercises. If there is significant instability in the knee, then a knee brace may be helpful, but if one of more of the knee ligaments have ruptured, then surgery may be necessary.

7. Deep Vein Thrombosis (DVT)

Another possible cause of pain behind the knee is  Deep Vein Thrombosis. A DVT is a blood clot found in one of the deep leg veins. If it breaks off it can lead to a heart attack or stroke. 

The symptoms to watch out for that indicate a possible DVT include pain behind the knee or in the calf region associated with swelling, redness and warmth in the area. Symptoms are usually only felt in one leg, not both. 

People are at higher risk of developing a DVT after prolonged inactivity e.g. long-haul plane journey or after surgery. Pregnancy, obesity, genetics and certain medical conditions also increase the risk.

Self-Test: Pull your toes up towards you (your foot doing the work, not your hands) - an increase in the pain behind the knee/calf indicates possible DVT

Safety Warning: A DVT is a potentially life-threatening condition. If you are showing symptoms of a DVT seek immediate medical attention, even if the self-test is negative.

8. Hamstring Injuries

Pain behind the knee or in the back of the thigh may be caused by a tear in one of the hamstring muscles.

Hamstring tears develop when one of the muscles is overstretched, beyond their elastic limit, causing some or all of the muscle fibres to tear. This typically happens during sporting activities with sudden, fast movements e.g. sprinting, lunging and jumping. 

Common symptoms of a hamstring tear include sharp pain behind the knee or in the thigh at the time of injury, depending on where the tear is, which is usually followed by a dull aching sensation. The pain tends to get worse when bending the knee or with sudden acceleration or deceleration. 

What Causes Tightness Behind The Knee? 
Tightness behind the knee is often caused by tightness in the hamstring or calf muscles. The hamstring muscles run down the back of the thigh attaching behind the knee, and one of the calf muscles, gastrocnemius, starting from the back of the knee, travels down to the heel.

Tightness in these muscles is a common problem, particularly in men, and makes the back of the knee feel very tight. Simple knee stretches are the best way to treat the tightness and relieve back of knee pain.

What Causes Pain Behind The Knee After Sitting? 
Pain behind the knee after sitting for prolonged periods is often caused by arthritis. When we sit still, the fluid that lubricates the knee joint dries out slightly so when we then stand up, there is less cushioning.

The wear and tear associated with arthritis mean you can end up with the knee bones rubbing together, causing knee pain. Once you are up and moving about, the joint produces more synovial fluid so, after a few minutes of moving around, the back of knee pain eases off.