Pain on the inside of the knee typically points to a problem with one of several structures packed into that area: the medial collateral ligament (MCL), the medial meniscus, a fluid-filled cushion called a bursa, or the cartilage lining the joint itself. Which one depends on exactly where the pain is, how it started, and what makes it worse. The inner knee is the most common site of knee osteoarthritis and a frequent location for sports injuries, so this type of pain is extremely common across age groups.
MCL Sprains and Tears
The MCL is a band of tissue that runs along the inner edge of your knee, connecting your thighbone to your shinbone. Its job is to keep the knee from bending inward. MCL injuries usually happen during a sudden hit or twist, especially in contact sports, skiing, or any activity where the knee gets forced sideways.
MCL tears are graded by severity. A grade 1 tear means less than 10% of the ligament fibers are damaged. Your knee still feels stable, and you’ll notice tenderness and mild pain along the inner side. A grade 2 tear is a partial tear, usually of the outer portion of the ligament. Pain and tenderness are more intense, and your knee may feel loose when someone moves it by hand. A grade 3 tear is a complete rupture of both layers of the MCL. The knee feels very unstable, and the pain is severe.
A hallmark of MCL injuries is that the pain is located right along the inner joint line or slightly above or below it, and it often spikes when you try to push off, pivot, or change direction. A healthcare provider can usually diagnose an MCL tear with a physical exam by bending the knee to about 30 degrees and applying sideways pressure. This test, called the valgus stress test, has a sensitivity of 86% to 96% for detecting MCL tears.
Medial Meniscus Tears
The medial meniscus is a C-shaped piece of cartilage that sits between your thighbone and shinbone on the inner side, acting as a shock absorber. It tears more often than the lateral meniscus on the outer side, partly because it’s less mobile and absorbs more force during everyday movements.
What sets a meniscus tear apart from other causes of inner knee pain is the mechanical symptoms. You may feel a popping sensation at the moment of injury, followed by swelling and stiffness that builds over the next day or two. The more distinctive signs come later: a catching or clicking sensation during movement, difficulty fully straightening the knee, and a feeling that the knee is locked in place. Some people describe the knee “giving way” without warning. Pain tends to worsen with twisting or rotating motions, like pivoting on your foot or squatting.
Meniscus tears can happen during a single traumatic event (a deep squat, a hard pivot) or develop gradually as the cartilage weakens with age. In younger people, tears are more often caused by sports injuries. In people over 40, the meniscus can tear during seemingly minor movements because it has become brittle over time.
Pes Anserine Bursitis
If your pain is located about 2 to 3 inches below the inner knee joint, the likely culprit is pes anserine bursitis. The pes anserine bursa is a small fluid-filled sac that cushions the spot where three tendons from your hamstring and inner thigh muscles attach to the shinbone. When this bursa becomes inflamed, usually from overuse or repetitive stress, it produces a localized aching or burning pain on the upper inner shin, just below the knee.
This condition is especially common in runners, cyclists, and swimmers who increase their training too quickly. It also frequently affects people carrying extra body weight, since the added load puts more stress on the tendons and bursa with every step. The pain typically worsens when climbing stairs, getting out of a car, or doing any activity that repeatedly bends and straightens the knee. Unlike a meniscus tear, pes anserine bursitis doesn’t cause locking, catching, or a feeling of instability.
Medial Compartment Osteoarthritis
Osteoarthritis is the most common long-term cause of inner knee pain, particularly in people over 45. The knee joint has three compartments, and the medial (inner) compartment wears down more often than the others. A large systematic review found that isolated medial compartment osteoarthritis accounts for about 27% of all knee osteoarthritis cases, while patterns involving the outer compartment are considerably less common at around 15%. In the UK, roughly one in five people over 45 develop knee osteoarthritis in their lifetime.
Osteoarthritis pain on the inner knee tends to be a deep, dull ache that builds gradually over months or years. It’s usually worse after prolonged activity, especially walking, standing, or climbing stairs, and improves with rest. Morning stiffness lasting less than 30 minutes is typical. Over time, you may notice the knee feels stiff more often, swells after activity, or makes a grinding sensation during movement. The pain doesn’t come and go in the same dramatic way as a meniscus tear or ligament sprain; instead, it follows a slow, steady progression.
Plica Syndrome
A plica is a fold of tissue left over from early development that lines the inside of the knee joint. Most people have one and never know it. But when the medial plica becomes irritated from repetitive bending, overuse, or a direct blow, it can thicken and cause pain along the inner knee.
Plica syndrome produces a clicking or popping sound when bending or straightening the knee, pain that worsens after squatting, climbing stairs, or sitting for long periods, and sometimes a catching sensation when standing up. Some people can actually feel the swollen plica as a cord-like ridge when pressing near the kneecap. The pain tends to be vague and hard to pinpoint, which is one reason plica syndrome often gets overlooked or mistaken for other conditions.
How to Tell These Conditions Apart
The location and behavior of the pain offer the strongest clues. Pain right along the inner joint line that worsened after a specific impact or twist suggests an MCL sprain or meniscus tear. If the knee locks, catches, or clicks, a meniscus tear is more likely. If the knee feels unstable or loose, an MCL tear is the stronger possibility. Pain that sits 2 to 3 inches below the joint line and gets worse with repetitive bending points toward pes anserine bursitis. A slow-building ache in someone over 45 that worsens with weight-bearing activity is the classic pattern for osteoarthritis.
Imaging isn’t always necessary. Physical exams are highly reliable for MCL tears, and the McMurray test (a specific rotation maneuver) has about 88% sensitivity for detecting medial meniscus tears. An MRI is usually reserved for cases where the diagnosis is unclear or symptoms don’t improve with initial treatment.
Signs That Need Prompt Attention
Inner knee pain that lasts more than a few days, affects your daily routine, or makes it hard to move warrants a visit to a healthcare provider. If you can’t bear weight on the knee at all, especially after a known injury, don’t force it. Rapid swelling within hours of an injury, a visible deformity, or the inability to move the knee are reasons to seek care the same day. If the pain followed a severe fall or car accident, go to an emergency room to rule out a fracture or more complex ligament damage.