Pain behind or in the back of the knee is relatively common. The pain behind your knee can be sharp and severe; or mild and dull.  In some of you, the pain in the back of the knee started after a sports injury. For others, the pain behind the knee began after bending down or even occurred at rest. 

Pain in the back of the knee can occur with or without swelling or a feeling of fullness.  Most causes of pain in the back of your knee are straightforward, and others might need urgent attention. In this post, we will review some of the most common causes of pain in this region of your knee.

What’s behind your knee? A brief anatomy lesson.  

The back of the knee is a complicated area.  There are several critical structures back there.  From a functional perspective, we have many muscles, such as the hamstring and calf muscles.  The hamstrings start at the pelvis, cross the back of the knee, and attach to your tibia or shin bone. The calf muscles start on the back of your thigh bone or femur, cross the knee and form the achilles tendon, which attaches to your heel. 

Behind our knee, we have critical structures such as the popliteal artery and the nerves to the leg. The nerves are the peroneal nerve and the tibial nerve.  The peroneal nerve is a troublemaker sometimes.  It doesn’t cause pain in the back of your knee but can cause pain elsewhere.  We discuss the peroneal nerve elsewhere on this page. 

Most people think their knee joint is in the front. But the back of our knee goes further back than we think.  The attachment of both the medial and lateral meniscus is in the back of the knee.  These meniscus attachment points are called roots.  Root tears can be a cause of severe knee pain which may start in the back of your knee. We cover root tears of the meniscus in this post.  

There is cartilage on the bones in the back of the knee.  Osteoarthritis can start back there, so the first sign of osteoarthritis could be pain in the back of your knee. 

Many of these structures in the back of the knee are capable of causing pain. Because of the complicated anatomy, a proper examination, Xrays, and perhaps an MRI will be useful in determining which structure could be the cause of your pain.  Once the cause of the pain is determined, the best possible treatment can be recommended. 

Below we are going to cover some of the more common causes of pain behind your knee. 

Common causes of pain in the back of the knee:

First, we will list the potential causes of pain behind your knee, then we follow through with a more detailed discussion of each potential cause of pain.  

• Swelling due to a Bakers cyst: A Bakers cyst is a common cause of swelling and pain behind your knee.
• Root tears of the meniscus
• Hamstring injury: usually occur higher in the thigh.
• Tears of the posterior horn of the medial meniscus 
• Deep vein thrombosis — or a blood clot in the back of your leg
• Overuse syndromes in runners and athletes.- usually causing a grinding or snapping in the back of the knee.
• Osteoarthritis: probably the most common cause of pain. Often due to swelling and inflammation.
• Nerve pain- the pain of sciatica can radiate to behind your knee

DVT: Deep vein thrombosis can cause pain in the back of your knee and calf

Deep vein thrombosis or DVT can cause pain in the back of your knee… but the pain is not often isolated to the back of the knee. There is usually calf pain, calf swelling and perhaps thigh pain too.    A DVT is not a common cause of pain and swelling, but I list it first because it can be a worrisome cause of pain. 

Usually, the pain from a DVT will also occur in the back of your calf or your inner thigh.  While not impossible, the pain can be isolated to just the back of your knee.  Most people with a DVT will also have swelling in their calf or leg.  In people who are obese, swelling of the leg is not uncommon so swelling alone does not mean you have a DVT.  

People who are at risk for a DVT include people who are obese, have cancer, chronic diseases, and those of you who recently traveled and sat still for hours/days while recovering from illness, injury, or surgery.  We do not know the exact incidence of people walking around with a DVT.  People who recently had surgery are at an increased risk for a DVT.  If your calf is tender and swollen and the back of your knee hurts, you need to see your doctor urgently or go to an emergency room. 

Meniscus tears and pain behind your knee

Root tears of the meniscus are prevalent. The “root” of a meniscus is where the meniscus attaches to the shin bone or tibia. Much like a tree roots into the ground, the meniscus has a firm, deep attachment to your bones as well. 

Sadly, over the years, these attachment points or roots can weaken.  A common story is that you bent down or knelt and felt a pop in the back of the knee.  Later that day or two days later, your knee is swollen, and the pain is very severe.  The root of the meniscus tore in this situation because it had degenerated from decades of activity. 

The pain from root tears often subsides over the next few weeks to months. By the time you see a doctor, and they order an MRI, the pain is often starting to improve.  This post below goes into far more detail about root tears as the cause of pain in the back of your knee.   

The meniscus is a shock absorber.  When the root of the meniscus tears, the meniscus no longer works as a shock absorber.  Therefore, following a root tear, you may develop stress fractures or stress reactions.  That is why the pain worsens a few days after you felt the pop.

This post goes into detail about how root tears cause these stress fractures and how they can be treated. This is usually a situation where you have very severe pain and require crutches for support.    As I have talked about elsewhere, root tears will often cause a significant stress reaction or a stress fracture. When root tears lead to a stress reaction, the pain will often move from behind the knee to the inner side.

READ MORE ABOUT ROOT TEARS

READ MORE ABOUT STRESS REACTIONS DUE TO ROOT TEARS, AND HOW WE TREAT THEM.  

On some occasions, we need to consider surgery to repair these root tears… but this is not usually necessary.

Pain behind the knee in runners

Overuse syndromes are prevalent in runners. Most runners are going to experience an overuse injury during their running careers.  The most common cause of pain behind the knee in runners is due to a hamstring strain.  Hamstring strains that occur around the knee tend not to be as painful or as chronic as those that occur up higher in the buttock region. 

Runners should consider shortening their stride and increasing their cadence, as well as avoiding hills for a few weeks. In most cases, this approach should enable a painful hamstring to settle down.

A less common cause of pain in the back of the knee in a runner is bursitis that occurs where a few tendons cross over and therefore rub against each other.  The pain is usually associated with a grinding or snapping sensation as you squat down.  The grinding sensation is due to the hamstring tendons being irritated from rubbing against each other.  

Some believe the location of this friction might be due to one of your calf muscles rubbing along one of the hamstring muscles in the back of the knee.  This has also occurred in some patients after a hamstring ACL reconstruction.  Surgical treatment is rarely necessary for this situation.  

In runners, the pain in the back of the knee will usually subside with a change in their running style (shorter stride, higher cadence) and workout schedule.  Physical therapy may be useful, as well.

Bakers cyst and pain in the back of the knee

A Bakers cyst is a fluid-filled pocket in the back of the knee. Bakers cysts are a common cause of painful swelling.  If the cysts are small, they do not create much discomfort.  

A Bakers cyst can grow larger. If a cyst becomes large, it can put pressure on the muscles, blood vessels, and nerves behind the knee and can cause discomfort.  Most people with a Bakers Cyst will also have osteoarthritis.  

In most instances, treatments to diminish the swelling associated with arthritis will help reduce the pain and swelling from the cyst.  In the majority of cases, these cysts are not dangerous.  An ultrasound can usually tell if you have a simple cyst versus something more complex that warrants further evaluation with an MRI.  If the Bakers cysts are huge, then one treatment alternative is to have the fluid drained.  While that will result in relief of pain, the fluid might come back again.

Read more about a Bakers cyst.  

Osteoarthritis and pain in the back of the knee

Osteoarthritis is a widespread cause of pain behind your knee.  Some of you might also note that you have a loss of motion and can not fully bend the knee.  The pain from arthritis can be due to inflammation of the structures behind the knee.  That irritates the lining or inside of the knee joint and makes the joint stiff and painful.  

 If osteoarthritis is causing pain in the back of the knee you might note that the pain can refer up the back of the thigh, or down into the calf.  Many of you with arthritic knee pain will benefit from wearing a compression sleeve or brace.   You will also find that gentle stretching, an ice pack, or a warm compress can help calm arthritic pain.  

If the pain does not improve over a few days, consider seeing your doctor to look into why the back of your knee hurts.

Hamstring Injuries

Hamstring injuries are a prevalent injury in sports.  Hamstring injuries usually occur higher and in the back of the thigh up near the pelvis.  We discuss hamstring injuries and some of the difficulties in managing them here and here.  It is possible to injure the hamstring near the back of your knee too.  

Usually, the pain from a distal hamstring injury is about 4-6 inches above your knee.  The pain from a lower hamstring injury will be most severe immediately after the injury and start to improve within a few weeks.  It is important to begin stretching the hamstrings as soon as you tolerate it to prevent stiffness.

Nerve Pain 

Nerve pain can be present in the back of the knee.  Nerve pain generally radiates to the back of the knee from higher up the leg or buttock area.  The nerves are rarely a cause of pain that is isolated to the back of the knee and doesn’t radiate anywhere else.  

Pain in the back of the knee is common but can be non-specific.  There are many reasons why the back of your knee might be bothering you. I hope you find this short guide useful in determining the possible causes of your pain.