What is pain behind the knee?

Some of the most common causes of pain behind the knee (posterior knee pain) include, Baker's cyst, arthritis, infection, injury, tumor, or deep vein thrombosis.
Some of the most common causes of pain behind the knee (posterior knee pain) include, Baker's cyst, arthritis, infection, injury, tumor, or deep vein thrombosis.

Since the knee is the largest and most complex joint in the body, it makes sense that it might hurt sometimes. Although knee pain is a common complaint, it is less common behind the knee.

Pain in the back of the knee is called posterior knee pain, and it can have a variety of causes. Occasionally, posterior knee pain is "referred" from the front of the knee or the spine.

Symptoms of pain behind the knee

Since several conditions can cause pain behind the knee, the symptoms can vary. The most common symptoms include:

Varying types of pain

The pain can be sharp, dull, or burning. It may come on suddenly or gradually. It may be constant, or it may occur when you put weight on the leg or when you bend the knee. This information can help a doctor diagnose your knee problem.

Swelling or stiffness

The knee may look swollen or misshapen. You may be unable to bend the knee, or your knee may pop, lock up, or collapse when you put weight on it. These symptoms usually indicate that you have sustained an injury, but there are other possibilities as well.

Redness or warmth

Under certain circumstances, the back of your knee could feel hot to the touch, or redness could be visible. You might also have a fever. These symptoms would point to a different cause than if you only have pain.

Causes of pain behind the knee

Pain behind the knee can be simple or difficult to diagnose, depending upon the cause. Here are some of the most common causes of posterior knee pain:

Baker's cyst

A lump-like swelling behind the knee is characteristic of Baker's cyst, making it fairly easy to diagnose. This type of cyst is also called a popliteal cyst because it is located in the popliteal fossa, a small hollow at the back of the knee.

It forms when synovial fluid gathers at the back of the knee. Injury or stress from arthritis can trigger the accumulation of fluid.

Different forms of arthritis

Arthritis is the generic name given to diseases that affect the joint. Arthritis can cause pain anywhere in the knee joint, including the back.

Knee pain is most often associated with osteoarthritis, the type that is related to aging or overuse. Knee pain can also occur with rheumatoid arthritis, but it will occur in both knees at once.

Gout is a type of arthritis that first attacks the big toe, but later attacks may strike the knees. Septic or infectious arthritis is caused by an infection that lodges in a joint, usually a knee.

Infection

Besides infection in the knee joint (infectious arthritis), posterior knee pain could result from several other infections, including:

These infections have different causes and symptoms, although pain, redness, heat, and swelling are typical of most infections.

Injury

Damage to a muscle, tendon, ligament, or other connective tissue could cause posterior knee pain. Such injuries can be acute or caused by overuse. Hamstring injuries, meniscus tears, and injuries to the posterior cruciate ligament (PCL) are three injuries that may cause pain in the back of the knee.

Tumor

It is rare that knee pain is caused by a tumor, but both malignant and benign tumors can occur near the knee. Three types of cancer that could cause posterior knee pain are:

  • Liposarcoma, cancer that grows in fat tissue and can occur behind the knee
  • Osteosarcoma, cancer that can appear in the long bones of the leg
  • Synovial sarcoma, a misnamed cancer occurring in large joints that doesn't actually occur in synovial fluid

Deep vein thrombosis

Deep vein thrombosis (DVT) is caused by a blood clot deep in a vein. In most cases, the clot is in the pelvis, thigh, or calf, but it can cause pain anywhere in the leg, including the back of the knee.

DVT can be a life-threatening condition. If part of the blood clot breaks loose and travels to the lungs, it can block blood flow. If the clot stays in place, it can damage the valves in the veins, causing pain, swelling, ulcers, and serious symptoms.

QUESTION

Medically speaking, the term "myalgia" refers to what type of pain? See Answer

When to see the doctor for pain behind the knee

Most posterior knee pain calls for a visit to the doctor. If you have signs of an infection or DVT, you should go immediately. You should also go immediately for severe pain.

If your symptoms are less urgent, your doctor is still the best one to guide your recovery. In the meantime, you can temporarily manage your pain with over-the-counter medications like ibuprofen. For knee injuries, you may use the RICE protocol: rest, ice, compress, and elevate.

Diagnosis of pain behind the knee

A physical exam is of primary importance in diagnosing posterior knee pain from injury or arthritis. The doctor will manipulate the legs to check rotation, flexion, and stability and to see which movements cause pain.

The doctor may also use imaging procedures such as ultrasound, X-ray, CT, arthrography, and MRI. Sometimes, the doctor will draw fluid from the knee for laboratory examination.

The doctor will use physical examination, lab studies, and imaging if they suspect an infection, tumor, or DVT. A doctor can usually diagnose a Baker's cyst by sight, but they may confirm the diagnosis with an imaging procedure.

Treatment for pain behind the knee

Treatment for posterior knee pain depends on the diagnosis. Damage from injury, wear and tear, or arthritis may be treated with rest, medications, physical therapy, injections, or surgery.

Some Baker's cysts go away on their own, and some require treatment, possibly including draining the cyst.

Other causes of pain behind the knee, such as infection, tumors, or DVT, will require highly individualized treatment following diagnosis.

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Medically Reviewed on 12/10/2020
References
American Cancer Society: "What Is a Soft Tissue Sarcoma?"

Arthritis Foundation: "When Knee Pain May Mean Arthritis."

Bupa: "Pain behind the knee (posterior knee pain)."

CDC: "Cellulitis: All You Need to Know."

CDC: "Venous thromboembolism."

Current Reviews in Musculoskeletal Medicine: "Posterior knee pain."

Johns Hopkins: "Liposarcoma."

Johns Hopkins: "Osteosarcoma."

Mount Sinai: "Baker cyst."

NYU Langone Health: "Types of Bone and Joint Infections."

Stanford Health Care: "Septic Bursitis."

University Health News Daily: "Pain Behind Knee: Injury vs. Disease-Related Causes."