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Back of Knee Swollen?

| | Baker's Cyst, Knee
back of knee swollen

Back of knee swollen? Swelling in the back of the knee is not something that is talked about too often. It can be uncomfortable or sometimes painful with the movement of the knee or, even with rest. It often stems from an orthopedic-related issue or, perhaps some other medical condition. Let’s dive in…

What’s Causes Swelling in the Back of Your Knee?

The back of the knee contains a variety of anatomical structures that can be affected and result in pain, swelling, numbness, tingling, etc. Muscles and tendons behind the knee that could be the source of pain or pathology could be one or more of the following:

  • Gastrocnemius
  • Soleus
  • Semimembranosus
  • Semitendinosus
  • Biceps femoris
  • Popliteus
  • The Tibial nerve along with the Popliteal artery and vein travel down the middle of the back of the knee.
  • The Posterior horns of the menisci

Injury or pathology to any one of these can result in posterior knee swelling or pain.


Common symptoms include:

  • Swelling either in a particular area or throughout the knee
  • Pain can be local to the knee or travel down the leg potentially into the ankle or foot
  • if the Tibial nerve is affected, a tingling sensation or even a feeling of numbness can travel down the leg
  • Changes in skin color including redness or bruising could develop.


Baker’s Cyst

A Popliteal, or Baker’s Cyst, is a collection of fluid from the knee joint that can become trapped in the back of the knee. It is usually a result of knee arthritis or an injury such as damage to knee cartilage, which typically causes increased production of fluid. It can cause the back of the knee to feel tight and may even be painful with movement of the knee, or at rest. Oftentimes, patients cannot fully bend the affected knee as the fluid gets in the way. If the amount of fluid is large enough, it can potentially cause a mass effect, irritating the nerves and other structures behind the knee.

Popliteal Aneurysm

A Popliteal Aneurysm results from a weakness in the wall of the Popliteal Artery, which travels down the back of the knee. This weakness causes dilation or enlargement of the artery. Popliteal Artery Aneurysms are typically asymptomatic, meaning you may have one and not even know it. A symptomatic aneurysm warrants evaluation by a surgeon for repair due to increased incidence of amputation of the lower limb. Asymptomatic aneurysms should be monitored with duplex ultrasound but those less than 2 cm in diameter are generally safe.

Gastrocnemius Tear

The Gastrocnemius is the large calf muscle that starts at the knee and travels down to the heel. A sudden knee extension movement or other quick motion can injure the tendon fibers that attach the muscle to bone. An injury in this location is less common than an Achilles tendon injury, which are the fibers that make up the distal insertion of the Gastrocnemius. A torn calf muscle or tendon can result in bruising in the back of the lower leg as well as swelling and pain behind the knee and below. Minor strains can usually be treated conservatively while healing of larger tears can be enhanced by injection of Platelet-Rich Plasma or Bone Marrow Concentrate.

Deep Vein Thrombosis (DVT)

A Deep Vein Thrombosis (DVT) is when a blood clot forms in the larger veins of the extremities. A DVT can cause pain and swelling in the lower leg, behind the knee, or in the thigh, but may not cause any symptoms at all. They can occur with prolonged immobility such as a plane flight, long car ride, or bed rest after a surgical procedure. Also leading to an increased risk of clotting are cancer, smoking, obesity, pregnancy, and oral contraceptive medications. If some or all of the clot travels to the lungs, this can be a serious, life-threatening condition known as a Pulmonary Embolism (PE).

Synovial Sarcoma

The name “Synovial Sarcoma” is quite a misnomer (1), as it is not related to synovial tissue at all. It is rare cancer that is typically found around soft tissues near the knee, hip, ankle, and shoulder. Synovial Sarcoma usually affects those aged 15-40 and is a slow-growing type of cancer. Symptoms include localized pain in the area of the tumor and if it gets large enough, it can compress the tibial nerve, popliteal artery, or vein and cause a host of other related symptoms. Once identified, surgical removal of cancer and surrounding area is the usual treatment.


What can you do to prevent pain and swelling in the back of the knee? First off, take care of your knees! And by that, I mean your entire body, because after all – “The ankle bone’s connected to the knee bone…” and so on. Having a solid nutrition plan, maintaining an ideal weight, and regular exercise are all important components of keeping knee pain and swelling at bay. If your shoes are starting to get old and parts of the sole are wearing away, throw them out and get new ones. Worn-out shoes can alter biomechanics and result in problems in the foot, ankle, knee, hip, lumbar spine, and beyond! Running stores are a good place to visit as they will often do a video analysis of you walking or running in order to recommend footwear that best fits you.

Supplementation with natural anti-inflammatories such as Turmeric, Fish Oil, Bromelain, and others can help regulate the inflammatory process that comes along with living an active lifestyle. The Regenexx Advanced Stem Cell Support formula was created specifically to support joint and stem cell health.


In summary, this is an overview of some of the common, as well as more rare, disorders that can result in pain in the back of your knee. The physicians at Centeno-Schultz Clinic in Broomfield and Denver, Colorado are experts in the evaluation and treatment of neuromusculoskeletal conditions. It is important to have a physician in your corner who can also recognize the presence of other disorders that are not musculoskeletal-related (such as some of the ones mentioned above) so you can be referred to the right specialist for you and your needs. If the condition is orthopedic-related, our cutting-edge knee treatments using your body’s own ability to heal can help get you back to doing the activities you love to do, without surgery and the use of chronic pain medications.


(1) Miettinen M, Virtanen I. Synovial sarcoma–a misnomer. Am J Pathol. 1984 Oct;117(1):18-25. PMID: 6207733; PMCID: PMC1900555.


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