Behind-the-knee pain could be due to muscle strain or arthritis—or something far more serious. Orthopedic experts say these are the most common causes.
8 Causes for Pain Behind the Knee (And How to Treat It)
Updated on Jan. 23, 2025
About one in four adults experience chronic knee pain, though its prevalence continues to rise—even among younger people, according to 2019 research published in BMC Musculoskeletal Disorders.
“It’s much more common to have pain in front of the knee [or] under the kneecap,” says Jonathan D. Packer, MD, a sports medicine physician and Associate Professor of Orthopaedics at the University of Maryland School of Medicine. But there are several reasons that pain behind the knee can occur.
Knee pain is so common because many structures are responsible for proper knee motion, and our knees are essential for nearly every activity we perform, says James B. Chen, MD, a fellowship-trained orthopedic surgeon with DISC Sports & Spine Center in California. Dr. Packer adds, “With the way our bodies are designed, there’s a lot of forces that go through the knees, ankles, and hips. Any kind of motion that we do with walking, and especially with running or jumping, puts a lot more stress—sometimes five times the amount of stress—on these joints.”
8 Common Causes for Pain Behind the Knee
While joint problems are common, experts say there are multiple reasons you might have pain behind your knee—some of which are more concerning than others, requiring immediate medical care.
1. Baker’s cyst (popliteal cyst)
“The most common benign cause [of behind-the-knee pain] we see is a Baker’s cyst,” Dr. Packer says. “That’s where some fluid that comes from the knee joints finds a little passageway or pinhole to escape.”
Dr. Chen explains that the knee joints naturally contain lubrication fluid called synovial fluid. If there’s inflammation (swelling) in the knee, this leads to increased amounts of fluid, which, as Dr. Packer described, needs to “escape.” This then forms a cyst in the back of the knee. “Patients will oftentimes feel like there’s a mass in the back of the knee that feels tight when they bend it all the way or straighten the knee all the way,” Dr. Packer says.
“There are many conditions that can cause swelling in the knee,” Dr. Chen says—including injuries, chronic conditions like arthritis, and even age. That’s why a Baker’s cyst is often a sign of an underlying knee problem, explains Miho Tanaka, MD, PhD, the director of the Women’s Sports Medicine Program at Massachusetts General Hospital in Boston. But the cyst is typically harmless and will go away on its own by treating the underlying source of the swelling, she says.
2. Meniscus tear
According to the American Academy of Orthopaedic Surgeons, meniscus tears are among the most common knee injuries and a cause of pain behind the knee. “The meniscus is a cushion or shock absorber,” Dr. Chen explains. “However, it is actually a fairly complex structure that has different shapes and tolerates different forces.”
Typically, a meniscus injury occurs from a sudden twisting motion or sudden heavy loading on the knee. “But it can also simply happen over time from repetitive use,” he says.
“If a tear occurs, the resulting pain can radiate to the back of the knee due to swelling, the joint’s limited mobility, or the way the tear disrupts the normal mechanics of the knee,” Dr. Chen explains. “In some cases, the meniscus can cause a piece of cartilage to move out of place, resulting in irritation in the back of the knee. And when a larger tear occurs, this is often accompanied by limited range of motion and a feeling of ‘locking’ or instability.”
3. Arthritis and gout
As we age, arthritis can be a more common and independent cause of discomfort in the back of the knee, Dr. Chen says. Osteoarthritis is the most common type of the chronic disease, which causes the cartilage in your knee to wear out and cause pain, says Dr. Packer. Gout—inflammatory arthritis—can cause behind-the-knee pain as well.
Psoriatic arthritis also contributes to knee pain, as do autoimmune diseases, such as lupus and rheumatoid arthritis, according to the National Psoriasis Foundation and Johns Hopkins Medicine.
5. Calf or hamstring strains and cramps
“One of the most common causes is a strain of one of the muscles behind the knee,” Dr. Chen says. “The hamstrings, calf muscles, and tendons cross the knee joint behind the knee, and strains of these muscles from overactivity or injury can result in pain.”
Movements that require pushing off or severe knee bending tend to cause this calf and hamstring pain, respectively, according to Dr. Tanaka.
Calf or hamstring strains and cramps can generally be managed with ice, rest, gentle stretching, and anti-inflammatories, she says. Still, a tear often requires physical therapy as well—and, in severe cases, surgery. “However, one should seek care if there is swelling or persistent pain associated with this to rule out blood clots.”
6. Blood clot
A blood clot or deep vein thrombosis (DVT) can cause pain behind the knee. “And that is a very concerning cause because the clot can go to the lungs and be very dangerous,” Dr. Packer says.
He explains that pain from a blood clot can occur in the back of the knee, but it often radiates down to the calf or up to the back of the thigh. “Generally, it’s not isolated to just the back of the knee.”
He says that if you’re getting pain that’s going into the calf, pain if you push on the back of the knee, or have pain that’s not getting better when you rest or lay down, it’s important that you seek immediate medical care to check for a blood clot.
7. Ligament injuries
Various ligament injuries could contribute to behind-the-knee pain, reports Stanford Medicine Health Care. This includes a partially or entirely torn ACL (anterior cruciate ligament) or MCL (medial collateral ligament).
ACL tears are common with athletes, as ligaments can tear or stretch while twisting with planted feet. MCL tears occur when something strikes the outside of the knee, forcing it to buckle.
Along with many other knee injuries, both require the RICE treatment approach: rest, ice, compression, and elevation to reduce pain and swelling.
8. Tendonitis
Tendonitis is the inflammation or swelling of the tendons that attach a muscle to the bone. It’s most often the result of injury or overuse, though tendonitis can occur with aging as our tendons weaken and lose elasticity.
“If you’re doing a new activity—or, let’s say you’re a runner or a cyclist and you’ve increased a lot of mileage—oftentimes, tendonitis will be in a very focal spot, a very specific area, and will also correspond to the activity,” Dr. Packer says.
Patellar tendonitis—also known as jumper’s knee—is one type that tends to cause pain behind the knee. This is caused by stress on the knee’s patellar tendon, which can result from overuse, a sudden increase in activity, repetitive jumping, muscle imbalances, poor flexibility, and even foot shape (if you have high arches or flat feet, for instance).
Other possible causes of behind-the-knee pain
There are other physical issues that can indirectly trigger pain behind the knee. This is because the knee is a complex joint, explains Dr. Chen, and it’s common that there are multiple things going on at the same time. For instance, an injury may cause referred pain in the back of the knee—even if the main issue is elsewhere in the body.
Iliotibial band syndrome
As one example, iliotibial band (IT band) syndrome typically causes pain on the outside of the knee, Dr. Chen says. This syndrome can cause bursitis—irritating inflammation of a fluid-filled sac called the bursa.
Although the typical locations affected are the front of the knee or the inner lower part of the knee, it’s possible that the inflammation leads to pain behind the knee as well.
Runner’s knee
“Runner’s knee is patellofemoral syndrome, typically associated with overuse and pain under the kneecap,” Dr. Chen says. But swelling from runner’s knee can result in pain both in the front of the knee from pressure on the patella (the kneecap) and pain behind the knee from the inflammation.
Infection
“It’s definitely possible that an infection can cause pain behind the knee, and that would be associated with swelling and redness around that area,” Dr. Packer says. “I wouldn’t say it’s very common—particularly just in the back of the knee. But that’s something that has to be considered, especially if it’s gradually getting worse and if you have other symptoms, like a fever.”
An infection in the knee could be caused by a cut that gets infected, an infection that spreads through the bloodstream, or a post-surgical infection.
Pinched nerve
Sometimes a pinched nerve behind the knee—such as the sciatic nerve, which runs from the lower back to your feet—can cause pain in the back of the knee and the calf, Dr. Packer says. “But that [pain] tends to go all the way up and down the leg. So, in general, that wouldn’t be isolated to just the knee.”
How pain behind the knee is diagnosed
“A clinical exam can typically be enough to diagnose the cause of pain behind the knee,” Dr. Chen says.
Pamela Mehta, MD, a board-certified orthopedic surgeon and founder of Resilience Orthopedics in San Jose, CA, explains that your doctor will ask you questions about:
- How long you’ve had pain
- If there was something that happened to cause it, such as a sports injury
- What makes it better or worse
“Alongside this, they will also examine your knee to look for signs of which part of your knee is affected,” Dr. Mehta says.
Dr. Packer adds that he first gains an overview of the pain a patient is experiencing. “I always ask: Does it go anywhere? Does it go down to the foot or ankle or up to the hip? If that’s the case, it’s very unlikely the pain is from the actual knee joints.”
Based on these initial steps, your doctor can narrow down the potential causes and order follow-up tests to confirm or rule out diagnoses. “For example, if it seems likely from your history and exam that there is likely to be a tendon or ligament injury, your doctor will order an MRI scan,” Dr. Mehta says. “X-rays are also very common as a first-line investigation, as are ultrasound and CT scans.”
She says that if your doctor can’t determine the cause of your knee pain, they might opt for an arthroscopy. During this surgical procedure, a small camera is inserted into your knee joint to directly visualize any problems.
Treatment for pain behind the knee
“As with most musculoskeletal injuries, the first-line recommendation is to attempt a brief trial of rest, ice, compression, and elevation (RICE),” Dr. Chen says. “If pain persists or worsens after a short trial, it would be advisable to get an evaluation by a professional, as treatment for the underlying cause may vary.”
He says that, depending on the cause, clinical treatment options can include:
- Physical therapy or guided exercises
- Medications such as non-steroidal anti-inflammatory medications (NSAIDs)
- Aspiration or removal of fluid with an injection to reduce symptoms
“Occasionally, surgical intervention is needed if the underlying diagnosis is arthritis or a meniscus tear,” he says. “However, for the vast majority of cases, this only becomes advisable if nonoperative modalities do not resolve symptoms.”
When to see your doctor
“Pain behind the knee is very common and something we all are likely to experience,” Dr. Chen says. But if your pain does not improve with rest and at-home care—or your condition worsens—you should seek medical attention.
He says that other signs that you should see a doctor for behind-the-knee pain include:
- Notable instability
- Inability to bear weight on the knee
- A visible deformity
- A traumatic event with an audible pop and a large amount of swelling
It’s also important to see a doctor right away if you’re experiencing signs of a blood clot. These symptoms can include:
- Pain behind the knee
- Pain that radiates up or down your leg
- Swelling
- Cramping or soreness
- Skin changes
About the experts
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Sources
- BMC Musculoskeletal Disorders: “Knee problems are common in young adults and associated with physical activity and not obesity: the findings of a cross-sectional survey in a university cohort”
- American Academy of Orthopaedic Surgeons: “Meniscus Tears”
- Arthritis Foundation: "What Is Osteoarthritis?"
- National Psoriasis Foundation: "About Psoriatic Arthritis"
- Johns Hopkins: What Are Common Symptoms of Autoimmune Disease?
- Sports Health: "Baker’s Cyst: Diagnostic and Surgical Considerations"
- Stanford University Health Care: Causes of Knee Ligament Injuries
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