Most types of knee pain that you may have heard often occurs in the front, medial, or lateral side on the knee, such as ACL tear, lateral meniscus tear, and MCL injury. Pain behind the knee (or posterior knee pain) is somewhat less common than the other types of knee pain, but that doesn’t mean it’s less important. Because of the complexity and small size of the posterior knee anatomy, any injury or disease that occur there may be overlooked or misdiagnosed.
Many factors contribute to pain in the back of the knee. Sometimes it can be two or more factors, which include Baker’s cyst, hamstring strain, PCL tear, or even vascular problems in the posterior thigh.
Because of there many different factors to pain behind the knee and each person is unique, you will have to consult with your physician, physical therapist, or another qualified healthcare professional to rule out more common and serious symptoms before zeroing in on potential causes.
Posterior knee anatomy
Three bones make up the knee, which are the femur, tibia, fibula, and patella (kneecap). Together with the hamstrings, popliteal muscle, and gastrocnemius, both systems move the knee primarily as a hinge joint, along with the nerves, knee ligaments, and knee menisci. However, when there is an injury or disease, one might modify their movement pattern in the knee, which can adduct, abduct, and rotate internally or externally, when they ambulate.
The lateral and medial menisci cushions the knee joint, acting as shock absorbers, especially when you land on your feet, jump, or run. They also help distribute the synovial fluid in the knee that lubricates the joint. The medial meniscus is smaller than the lateral meniscus and is located in the inner part of your knee between the medial condyles of the femur and tibia. Because it is attached to the edge of the joint capsule and the lateral meniscus does not, the medial meniscus is more prone to tearing than the lateral meniscus because of its rigidity.
There are two types of stabilizers that support the knee joint: active and passive. Active stabilizers are the posterior leg muscles that were mentioned earlier. They help control the movement of the knee joint, such as acceleration and deceleration when you run.
Passive stabilizers are the knee ligaments: anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL). The ACL and PCL prevents the tibia and femur from sliding across from each other, while the MCL and LCL prevent the knee from moving too far or too close to the body’s midline.
Posterolateral corner of the knee (PLC)
One important area to understand pain behind the knee is the posterolateral corner of the knee (PLC). It consists of the popliteus muscle, popliteofibular ligament (PFL), and several ligaments that attach the fibula to the lateral femur. It basically stabilizes and controls the movement in the posterior knee, which reduces the risk of getting a PCL tear or injury.
The popliteus muscle originates from the lateral femoral condyle and inserts into the back of the tibia along the soleus line. Two of its main jobs are to “unlock” the knee to allow flexion and to pull back the lateral meniscus during knee flexion to prevent it from being sandwiched between the femur and tibia. When the knee is fully extended, the popliteus slightly laterally rotates the knee. During knee flexion, it medially rotates the knee.
The big posterior movers of the knee joint include the hamstrings and the gastrocnemius muscles. Three muscles make up the hamstrings: biceps femoris, semimembranosus, and semitendinosus.
The biceps femoris is the tear-shape bulge that you see among bodybuilders and sprinters. Both the semitendinosus and semimembranosus originate from the posterior part of the ischial tuberosity of the pelvis, but the semitendinosus insert into the proximal end of the tibia while the semimembranosus insert into the medial condyle of the tibia.
All three hamstring muscles work together to flex and extend the knee and provide limited knee rotation, adduction, and abduction. They also help decelerate knee extension, such as when you jog or walk down a steep road or walking down a flight of stairs.
The popliteal fossa—sometimes called a “kneepit”, an echo to the armpit— is packed with several nerves, blood vessels, and lymph nodes, such as the tibial and the common fibular nerves, popliteal artery and vein, and a saphenous vein. There is also a bursa in the knee that help to decrease friction when the knee moves. This is also the site of Baker’s cyst, which is the swelling of the knee bursa and may cause pain behind the knee.
Posterior knee nerves
A few major nerves in the back of the knee can influence posterior knee pain. These nerves stem from the sciatic nerve, a major contributor to sciatica. The tibial nerve innervates ankle and toe muscles. A layer of popliteal fascia covers the nerve, which separates it from the medial cutaneous sural nerve and the small saphenous vein.
The common peroneal nerve innervates the extensor muscles of the ankle and toes, while the saphenous nerve is a sensory nerve that innervates the skin at the front of the kneecap and the inner side of the thigh and foot.
Along with inflammation, infection, and central sensitization (a condition where pain becomes chronic, occurs primarily in the brain and spinal cord), damage to these nerves or peripheral sensitization may also be primary contributors to behind-the-knee pain.
Causes and symptoms of pain behind the knee
Causes of posterior knee pain come in a garden variety, similar to other types of knee pain and shoulder pain. Sometimes more than one of these factors can cause the pain. A brief review of the scientific behind the causes and symptoms of these pain behind the knee.
Osteoarthritis is a common type of knee condition that affects about 250 million people worldwide and about 27 million in the U.S. Those who are more likely to get it are the elderly, females, the obese, and people of African descent. It is primarily caused by the wear and tear of the articulation of the knee joint, which results in the gradual loss of the knee menisci (cartilage) and increase of inflammation in the area.
While knee osteoarthritis can increase the risk of getting knee pain, a 2018 systematic review of 63 studies found that some people with this condition have no pain. Researchers from this study pooled data from nearly 5,400 knees among more than 4,700 adults, they found that about 4% to 14% of the patients who were less than 40 years old showed signs of osteoarthritis. Among those who are 40 and higher, about 19% to 43% are asymptomatic.
This seems to reflect on a 2015 study that found that asymptomatic patients with disc herniation and other spine pathologies are more prevalent among older adults than younger adults. Brinjikji et al. concluded that degenerative changes of the spine and disc are part of a normal aging process rather than a “disease” that needs to be “fixed.”
A Baker’s cyst, or a popliteal cyst or bursa, is a fluid-filled sac that may likely be caused by a meniscus tear, osteoarthritis, injury, or another disorder in the knee joint. Symptoms may be a sharp pain in the back of the knee or calf muscle and swelling of the popliteal cyst.
The cyst may rupture if there is a fast accumulation of fluid in it, and the fluid may leak out into surrounding tissue, causing further inflammation. Symptoms in this case may be a sensation of “water running down the calf” and swelling and sharp pain in the calf muscles.
A common injury among running and sprinting sports like soccer, rugby, and some track and field events, a hamstring strain often occurs at the long head of the biceps femoris during the end phase of the leg swing during a sprint.
Research finds that hamstring strains are more common toward the hip rather than toward the knee. However, the pain may radiate down or may be felt at the back of the knee.
Hamstring strains are classified into I (mild), II (moderate), or III (severe), which is based on the degree of pain, loss of range of motion, and loss of strength. They can be a mild tear in the muscle or tendon or a complete tear.
Interestingly, tears or other types of lesions do not necessarily cause pain or dysfunction. In a 2016 study of 506 hamstrings from 253 patients with no hamstring or knee pain, 15% of them had a partial tear on both hamstrings and 2% had complete tears on both sides. These tears seem to be more common among older adults than younger adults.
The posterior cruciate ligament (PCL) is one of the four ligaments that attach the femur to the tibia and assist in knee movement. It connects the tibia at the space between the medial and lateral condyles and the lateral of the medial condyle of the femur.
It is the largest and strongest ligament among the four knee ligaments, which makes it less prone to tearing and other types of injury. Still, it can still tear, and isolated PCL tear is much less common than other ligament tears, with a prevalence of 2 cases per 100,000 people in the U.S.
However, they cited that pain from PCL tears are seldom isolated causes, and other risk factors that increase the likelihood of getting a tear, such as knee arthritis and the need for a knee arthroplasty.
Common causes of a PCL tear is trauma to the knee or tibia when the foot is plantar flexed, a car accident, or non-contact injuries from sports that require quick changes of direction like rugby, American football, and skiing.
Research finds that meniscus tears—medial and lateral—are often asymptomatic and do not affect normal knee function much. According to a 2014 review, four studies on the prevalence of meniscus tears show that “healthy knees and osteoarthritic knees with a meniscal tear are not more painful than those without a tear.”
A 2020 study on 230 sedentary adults in the U.K. found that nearly all the subjects had at least one knee “abnormality,” where about 30% of them had a meniscus tear.
Thus, it is unlikely that meniscus tears would be a major culprit in the pain behind the knee, but clinicians should not completely rule out this option.
Like a hamstring strain, a calf strain (or gastrocnemius strain) is a muscle tear in the gastrocnemius muscle that often occurs when the knee is fully extended and the foot is dorsiflexed during strenuous activities. It is more common to get a strain in the medial side of the calf muscle than the lateral.
In a 2017 systematic review of ten studies of more than 5,300 athletes in various sports (e.g. basketball, rugby, soccer), increasing age and previous calf injury are the highest predictors of whether someone would get a calf strain or not.
Deep vein thrombosis
Deep vein thrombosis (DVT) is a blood clot that forms in the veins deep in the posterior thigh or the lower leg. Risk factors of getting DVT are trauma to the vein, high venous pressure, reduced blood flow, and increased blood viscosity.
About 1 out of 1,000 adults in the U.S. have this condition, and there is a 5.5% chance that death can happen within a month of diagnosis of DVT, according to a 2017 retrospective study.
If DVT occurs in the leg, symptoms may include pain behind the knee, swelling of the tissues near the blood clot, reddish and warm skin, and tenderness to touch.
This list is not exhaustive of all the possible causes. A qualified healthcare professional can rule out certain causes and potentially pinpoint the root of your posterior knee pain.
Do exercises help with pain behind the knee?
There are many types of treatments for different types of pain in the back of the knee, but there is no cookie-cutter way to address all of them.
For some types of posterior knee pain, like strains, exercise may be the primary treatment for symptoms as the patients heal and gradually return to the performance level prior to the injury.
A team of researchers from the University of São Paulo identified three primary phases of exercise treatment. In the initial phase, the purpose of therapeutic is to “restore normal neuromuscular control and prevent the formation of tissue fibrosis.” These exercises would consist of low-intensity, strengthening exercises when the hamstrings and the knee joint are isolated.
In the intermediate phase, exercises get more intense and focus on eccentric strength. Current evidence shows some effectiveness of eccentric strength training for both healthy people and recovering patients.
In the final phase, higher intensity eccentric strength exercises combined with plyometrics and sports specific drills should be the primary focus.
For knee osteoarthritis, a 2015 Cochrane Review found that knee pain was “significantly reduced” when compared with other types of non-exercise intervention among 44 randomized controlled trials. Thirteen trials found that exercise in general improved the quality of life among most of the other subjects compared to those who did not exercise. However, the benefits appears to be short-term.
Examples of eccentric strength training—where the focus is on the control of the lengthening of the hamstring muscles against a resistance—would be assisted Nordic hamstring curls, prone or seated hamstring curls, and quadruped single leg extensions.
Nordic hamstring curls
Leg Curls with a Dumbbell
Hamstring curls with sliders
Prevention is still the best “medicine” to minimize the risk of getting most types of knee pain. Given the existing body of evidence on exercise and the nature of pain, sometimes the pain behind the knee can be more complex than the “one cause” hypothesis that we usually hear from some clinicians (e.g. “Oh, it’s your posture! That’s why your knee hurts.”). Since that there may be multiple causes of knee pain and each person has a unique health history, lifestyle, and beliefs about pain, consider different options for explanations and treatments for your specific pain.