Discomfort or pain behind the knee can be perplexing. It’s not nearly as common as pain around the kneecap or on the sides of the knee—but that doesn’t mean you should ignore it, says sports medicine orthopedic surgeon Jourdan M. Cancienne, MD.
What causes pain behind the knee?
Injuries often are the cause of pain behind the knee, but it sometimes can happen as you get older, especially if you have a degenerative condition such as arthritis. Usually, the pain from arthritis is more on the sides and front of the knee, but it can create pain anywhere. Here are some of the other culprits…
Baker cyst (popliteal cyst)
This is the most common cause of behind-the-knee pain. Named after William Morrant Baker, the 19th-century surgeon who first described it, a Baker cyst is a fluid-filled cyst that forms in the space behind the knee joint, known as the popliteal fossa. This cyst typically is a consequence of inflammation in the knee, which can be due to an arthritic condition such as osteoarthritis or rheumatoid arthritis, or possibly a tear in a meniscus, one of the C-shaped pieces of cartilage that cushion the knee.
Inflammation causes extra fluid in the area, and that typically leads to swelling. In the case of a Baker cyst, the fluid takes the path of least resistance and flows toward the back of the knee, causing a noticeable bulge over time. Note: Sometimes the fluid is resorbed into the surrounding tissue, and a Baker cyst resolves on its own.
A Baker cyst can cause pain or a feeling of tightness or stiffness, making it hard to flex the leg because the cyst gets in the way of the knee’s ability to bend. You can manage mild symptoms with an oral anti-inflammatory, pain relievers and rest. This strategy can take up to six weeks to work, but it’s also important to treat the source of the inflammation that led to the cyst, be it arthritis or a meniscus tear.
You also may benefit from a cortisone injection into the knee to reduce inflammation (and, in turn, fluid) followed by physical therapy. It is also possible to aspirate, or remove, the fluid from the cyst, which can provide relief, but unless you’re addressing the source of the fluid, it is likely to come back.
Though rarely needed, minimally invasive arthroscopic surgery is an option for a very stubborn cyst. The surgeon removes that one-way valve so that the fluid can pass freely throughout the knee.
Note: Baker cysts develop over time. One might be discovered before it becomes bothersome if you happen to have an imaging test for an unrelated problem. If the cyst isn’t causing you any problems, there’s nothing you need to do about it.
Tendinitis
Tendons are strong ropelike bands of tissue that connect muscle to bone. Specific tendons, including hamstring tendons, travel behind the knee and down the leg, attaching to the top of the tibia, the bone between the knee and the ankle. Tendinitis, or inflammation of one or more of these tendons, can create pain behind the knee. The most common cause of tendinitis is overuse—repeating the same motion over and over, often when playing sports. You may feel discomfort primarily when you do the movement that caused the condition, though you can feel pain behind the knee simply when walking.
Your doctor can identify tendinitis during a physical exam if he/she can reproduce your pain by compressing or manipulating your tendons. For mild cases, anti-inflammatory medication and hamstring stretches can help. If the pain doesn’t improve, your doctor might recommend a formal physical therapy program with hands-on work on the hamstrings and specific exercises based on your individual needs.
Meniscus tear
Sometimes the problem is not in the back of the knee but pain that is radiating to that area. A common cause is a meniscus tear, even without the presence of a Baker’s cyst. Treatment depends on the size, location and extent of the tear. In many cases, a cortisone injection and physical therapy will ease the pain. The response to a cortisone injection can be unpredictable, with some patients receiving months of relief and others experiencing only a few weeks of relief. If the response to the injection is lasting, these can be repeated as needed but only up to three to four times a year at most.
If it’s the more serious meniscus root tear, surgery typically is necessary. This tear happens where the cartilage attaches to the bone and must be repaired to prevent long-term dysfunction. A root tear doesn’t occur from twisting or pivoting movements—it can happen during an everyday activity like stepping off a sidewalk curb. Having knee arthritis also can increase your risk.
Posterior cruciate ligament (PCL) injury
Most people are familiar with anterior cruciate ligament (ACL) injuries, but injuries also can happen to the ligament behind the knee, though they’re less common. PCL injuries typically occur from significant trauma, such as a serious accident, so symptoms generally are not limited to pain behind the knee and you’d likely experience instability with the leg.
When to See an Orthopedist
If you experience persistent pain behind your knee for the first time, get it checked out. Some causes can be diagnosed with a physical exam, but you likely will need an X-ray (this will also identify any arthritis in the area) and possibly an MRI so that your doctor can see the tendons and menisci and assess the knee’s structural integrity.
This is not a “no pain, no gain” situation where you should continue to do what you’re doing, thinking that it’s going to get better on its own. Knee instability is not something you can work through.
