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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.


ACL Tears

The Anterior Cruciate Ligament (ACL) is one of four major ligaments in the knee. It is an important stabilizer of the knee and prevents the shin bone (tibia) from sliding in front of the thigh bone (femur). The ACL is susceptible to injury. It is most likely to be injured during activity or by impact. A torn ACL is a common injury for athletes at all levels, but it is most common for people who are active or who experience impact injuries to the knee. ACL injuries can happen to anyone of any age, condition, or ability, and it can be injured in many ways. Examples include abruptly changing direction, slowing down while running, landing incorrectly, or getting struck by someone or some object.

Read More About ACL Tears

Baker’s Cyst

A Baker’s cyst can cause knee pain. A Baker cyst is swelling caused by fluid from the knee joint protruding to the back of the knee. They are NOT a true cyst since it has communication with the synovial sac. They typically arise from degenerative changes or injury to the articular cartilage (arthritis) or meniscus. At the Centeno-Schultz Clinic, we believe that baker’s Cysts are simply a barometer of the health of the knee joint. In a healthy knee, there are absent whereas with injury and degenerative changes they are common. They arise between the tendons of the medial head…

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EDS in Children

Ehlers-Danlos Syndrome (EDS) refers to a group of disorders that affect the body’s connective tissue including skin, tendons, and ligaments. It is a hereditary disorder which means you are born with it. EDS has many different signs and symptoms which can vary significantly from patient to patient. It most commonly affects the skin, joints, and blood vessels. The estimated prevalence for all EDS varies between 1/10,000 and 1/25,000. The three most common types of EDS are: Hypermobile, Classic, and Vascular. We have used these skills and knowledge to treat the loose ligaments commonly found in EDS in children. Treatment options include bone marrow concentrate (BMC) and PRP.

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Ehlers-Danlos Syndrome (EDS)

Disorders that affect and weaken the connective tissues such as tendons and ligaments. It is a hereditary disorder which means you are born with it.  EDS has many different signs and symptoms which can vary significantly depending upon the type of EDS and its severity.   It most commonly affects the skin, joints, and blood vessels.  Joints are typically hypermobile with excessive joint range of motion because of a defect in collagen formation. In most cases Ehlers-Danlos syndrome is inherited. That is to say that you are born with it. The two main ways EDS is inherited are: autosomal dominant inheritance and autosomal recessive inheritance…

Read More About Ehlers-Danlos Syndrome (EDS)

Hamstrings Tendinopathy

Your hamstrings are the thick muscles in the back of your thigh that are responsible for the movement of your hip, thigh, and knee. The hamstrings are made of three distinct muscles: Semitendinosus, Semimembranosus, and Biceps Femoris. What is Hamstrings Tendinopathy? Tendons are thick pieces of connective tissue that connect muscle to bone. They function to transfer the force generated by muscle contraction into movement. Hamstring tendinopathy, also known as a “calf strain,” is an injury to the affected tendon. It usually occurs when you bend your knee or extend your leg, putting too much force on the hamstring tendon….

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Knee Arthritis

In the human body, a joint is simply where 2 ends of bone come together. At the ends of these bones, there is a thick substance called “Hyaline Cartilage” that lines the ends. Hyaline cartilage is extremely slippery which allows the two ends of the bone to slide on top of each other. Then there is a capsule that connects the two ends filled with “synovial fluid” that acts as a further lubricant to make it more slippery! Arthritis in the knee is defined by loss of the hyaline cartilage plus other changes that happen to the bone such as additional bone being laid down (bone spurs/osteophytes). The cartilage layer is worn down to the point of exposing the underlying bone they cover…

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Meniscus Tears

The meniscus is a c-shaped piece of cartilage in the knee that functions as an important shock absorber. It is sandwiched between the thigh and shin bone. There are two menisci per knee. One on the inside portion of the knee (medial) one on the outside aspect (lateral). The knee meniscus is susceptible to injury. The most common injury is a tear in the meniscus. Not all meniscus tears however cause pain. When symptomatic a meniscus tear can cause pain, swelling, and restriction in range of motion. Tears in the knee meniscus can arise from trauma or degeneration. There are many different types of meniscus tears based upon locations….

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PCL Sprain

The Posterior Cruciate Ligament is one of the paired ligaments in the middle of the knee. It is made up of 2 separate bundles: The two bundles of the PCL, and the ALB (anterior lateral bundle), and the PMB (posterior medial bundle), function synergistically to provide stability. The PCL functions as one of the main stabilizers of the knee joint and serves primarily to resist excessive posterior translation of the tibia relative to the femur. The PCL also acts as a secondary stabilizer of the knee preventing excessive rotation specifically between 90° and 120° of knee flexion. A PCL sprain happens when force is applied beyond…

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PCL Tear

The Posterior Cruciate Ligament (PCL) is a paired ligament in the middle of the knee. It is made up of two separate bundles: ALB (anterior lateral bundle) and PMB (posterior medial bundle). These bundles work synergistically to provide stability. The PCL plays an important stabilizing role in the knee joint by resisting excessive posterior translation of the tibia relative to the femur. Between 90 and 120 degrees of knee flexion, it serves as secondary support for preventing excessive rotation. PCL tears happen when force is applied beyond what the PCL tensile strength is capable of resisting. The tensile strength of the PCL is well documented…

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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 the 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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