Pain on the inside (medial side) of the knee is one of the most common knee complaints, and it can stem from several different structures packed into that area: ligaments, cartilage, tendons, bursae, or even a nerve. The cause often depends on your age, activity level, and whether the pain started suddenly or crept in over time. Here’s what might be behind it.
MCL Sprains and Tears
The medial collateral ligament (MCL) runs along the inner edge of your knee, connecting your thighbone to your shinbone and preventing the knee from bending inward. It’s one of the most frequently injured knee ligaments, typically hurt by a direct blow to the outside of the knee or a sudden twisting motion. Sports like football, soccer, and skiing are common culprits.
MCL injuries are graded by severity. A grade 1 sprain means less than 10% of the ligament’s fibers are torn. Your knee still feels stable, but there’s tenderness and mild pain along the inner side. These usually heal within one to three weeks. A grade 2 sprain is a partial tear, mostly of the superficial layer of the MCL. The knee feels loose when someone moves it by hand, and the pain is more intense. Recovery takes four to six weeks. A grade 3 tear means the ligament is completely torn through both its superficial and deep layers. The knee feels very unstable, and pain is severe. Healing takes six weeks or longer, and in some cases surgery is needed, particularly if other structures are damaged at the same time.
The hallmark of an MCL injury is sharp pain right along the inner knee joint line, often with swelling that develops within hours. If you felt a pop at the time of injury and can’t bear weight, that warrants urgent medical attention.
Medial Meniscus Tears
Each knee has two C-shaped pads of cartilage (menisci) that act as shock absorbers between the thighbone and shinbone. The medial meniscus sits on the inner side, and it tears more often than its outer counterpart because it’s less mobile and absorbs more force during everyday movement.
A torn medial meniscus causes pain along the inner joint line, but its signature symptom is mechanical: your knee may lock, catch, or feel like it’s giving way. Some people describe a sensation of something being “stuck” inside the joint, especially when trying to fully straighten or bend the leg. Swelling often develops gradually over a day or two rather than immediately. Squatting, twisting, or getting up from a chair can make the pain worse.
In younger people, meniscus tears usually result from a sudden twist during sports. In people over 40, the meniscus can tear with surprisingly little force because the cartilage has become more brittle with age. A doctor can often suspect a meniscus tear through a physical exam, rotating the knee at different angles while feeling for a click or pain along the joint line.
Knee Osteoarthritis
Osteoarthritis is the most common long-term cause of inner knee pain, especially in adults over 50. The medial compartment of the knee bears more load than the outer side during walking, and knee osteoarthritis affects this inner compartment 5 to 10 times more often than the lateral compartment in Western populations.
As the cartilage wears down, the space between the bones narrows. On an X-ray, this space may be visibly reduced or even absent in spots. The practical effect is pain that worsens with activity and improves with rest, stiffness after sitting for a while, and a gradual loss of range of motion. Over time, as cartilage wears unevenly on the inner side, the leg can develop a bowlegged alignment, which in turn puts even more stress on the medial compartment and accelerates the process.
Morning stiffness that lasts less than 30 minutes, a grinding or crunching sensation when bending the knee, and pain that flares after long walks or stair climbing are all typical patterns. Unlike a ligament or meniscus injury, osteoarthritis pain builds over months or years rather than arriving suddenly.
Pes Anserine Bursitis
This one often gets overlooked. The pes anserine bursa is a small fluid-filled sac that sits about 2 to 3 inches below the inner knee joint, cushioning the spot where three tendons from the thigh attach to the shinbone. When that bursa becomes inflamed, it causes a distinctive aching pain that’s lower than most other causes of medial knee pain.
Pes anserine bursitis is especially common in women, people with diabetes, and people carrying extra weight. It can also flare up in runners or anyone who suddenly increases their activity. The pain is typically worst when climbing stairs, getting out of a car, or lying on your side with your knees together at night. Because the pain sits below the joint line rather than on it, it can help distinguish this condition from a meniscus tear or MCL injury.
Plica Syndrome
A plica is a fold of tissue left over from how the knee developed before birth. Most people have them and never notice, but sometimes the medial plica (on the inner side of the kneecap) becomes irritated from overuse, a direct hit, or repetitive bending. When that happens, the fold thickens and catches against the end of the thighbone.
The telltale sign is a clicking or popping sensation when bending and straightening the knee, along with pain and localized swelling. It’s easy to confuse with a meniscus tear because both cause clicking and inner knee pain. The key difference is location: plica syndrome pain tends to sit above the joint line, closer to the kneecap, while meniscus pain is right along the joint line itself.
Nerve-Related Pain
Not all inner knee pain comes from the knee joint itself. The saphenous nerve, which runs down the inner thigh and passes through a narrow tunnel of tissue near the knee, can become trapped or irritated. This condition is probably under-recognized as a cause of medial knee pain.
Saphenous nerve entrapment produces a burning or shooting pain along the inner knee and sometimes down the inner shin, often accompanied by numbness or tingling. The pain doesn’t typically worsen with weight-bearing the way a joint or ligament problem does, and there’s usually no swelling or mechanical catching. If you’ve been evaluated for the more common causes and nothing quite fits, nerve entrapment is worth considering.
How to Tell the Difference
The pattern of your pain offers the strongest clues. Pain that appeared suddenly after a twist or impact points toward a ligament or meniscus injury. Pain that crept in over months, worsens with activity, and comes with stiffness suggests osteoarthritis. Pain that sits a few inches below the joint, especially if you’re a runner or have diabetes, fits pes anserine bursitis. Clicking near the kneecap with no history of injury leans toward plica syndrome. Burning or tingling without swelling raises the possibility of nerve involvement.
Swelling matters too. Rapid swelling within an hour of injury suggests bleeding inside the joint, often from a significant ligament tear. Swelling that builds over a day or two is more typical of a meniscus tear. Chronic, mild puffiness points toward arthritis. And no swelling at all, combined with burning pain, suggests a nerve issue rather than a structural one.
A few situations call for urgent evaluation: a knee that looks visibly deformed or bent at an unusual angle, a popping sound at the moment of injury followed by an inability to bear weight, sudden significant swelling, or intense pain that doesn’t improve with rest and ice. These patterns can indicate a severe tear or fracture that needs prompt imaging.