Pain on the inside of your knee, known as the medial side, usually comes from one of a handful of common causes: a ligament sprain, a meniscus tear, bursitis, or arthritis. Which one depends on how the pain started, where exactly it sits, and what makes it worse. The inner knee is a layered structure with ligaments, tendons, cartilage, and fluid-filled cushions all packed into a small space, so pinpointing the source matters.
MCL Sprain or Tear
The medial collateral ligament (MCL) runs along the inside of your knee, connecting your thighbone to your shinbone. It’s the most common ligament injured in the knee, and it typically happens when a force pushes the knee inward: a side-impact collision in a sport like football or soccer, a sudden change of direction while skiing, or even slipping on ice with your lower leg splaying outward.
An MCL injury often announces itself with a pop on the inside of the leg, followed by tenderness, stiffness, and sometimes swelling. Pain can range from mild to severe depending on the grade of the tear:
- Grade 1: Minor tenderness and pain at the injury site. You can usually return to normal activity within a few days to a week and a half.
- Grade 2: Noticeable looseness in the knee, significant pain and tenderness on the inner side, and sometimes swelling. Recovery takes two to four weeks.
- Grade 3: Considerable pain, some swelling, and the knee feels unstable. Healing takes four to eight weeks, longer if the ACL is also damaged.
Most MCL sprains heal without surgery. The key early steps are rest, icing, compression, and keeping weight off the knee until the pain settles. A brace that limits side-to-side motion can help during recovery.
Medial Meniscus Tear
Each knee has two C-shaped pads of cartilage that act as shock absorbers between the thighbone and shinbone. The one on the inner side is the medial meniscus, and it tears more often than the outer one because it’s less mobile and absorbs more load during twisting movements.
A torn meniscus often produces a popping sensation at the moment of injury. In the days that follow, you may notice swelling, a catching or clicking feeling when you bend the knee, and episodes where the knee locks in place and won’t straighten. The pain tends to sit right along the joint line, the crease where the two bones meet on the inner side. This is a useful detail: pain directly at that joint line points more toward a meniscus problem than other inner-knee conditions.
Small tears sometimes calm down with rest and targeted strengthening. Larger tears, especially ones that cause locking, may need a procedure to trim or repair the damaged cartilage.
Pes Anserine Bursitis
If your pain is lower than you’d expect, about two to three inches below the joint line on the inner side of your shinbone, it may be pes anserine bursitis. Three tendons from your thigh muscles attach to the shin at a spot called the pes anserinus, and a small fluid-filled sac (bursa) sits between those tendons and the bone to reduce friction. When that sac becomes inflamed, it produces a localized, aching pain that’s often worse when climbing stairs or getting out of a chair.
Common triggers include repetitive knee bending in sports like soccer or tennis, tight hamstrings, knock-kneed alignment, and ramping up training too quickly without proper stretching. An existing MCL injury can also shift stress to this area and set off bursitis as a secondary problem. Treatment centers on reducing the inflammation with rest and ice, then addressing the underlying cause, whether that’s hamstring tightness, training errors, or alignment issues.
Medial Compartment Osteoarthritis
In adults over 50, the most common explanation for persistent inner-knee pain is osteoarthritis that has settled into the medial compartment. The inner side of the knee bears more load than the outer side during walking, so the cartilage there wears down faster over time. Previous injuries, excess body weight, and jobs or sports that put repetitive stress on the knees all accelerate the process.
The pain typically builds gradually over months or years rather than appearing overnight. You might notice stiffness first thing in the morning that loosens up after a few minutes of movement, aching after prolonged sitting, and a grinding sensation when bending or straightening the leg. Swelling can come and go, often flaring after a more active day. X-rays usually confirm the diagnosis by showing narrowed joint space on the inner side of the knee. In some cases, an MRI or CT scan is ordered to get a closer look at the cartilage and surrounding tissue.
Plica Syndrome
The knee joint is lined with a thin membrane, and some people have a fold of that membrane on the inner side called a medial plica. It’s a normal anatomical variation, but when the plica gets irritated from overuse or a direct blow, it can thicken, catch on the end of the thighbone, and produce a dull, aching pain on the inner knee. The key difference from a meniscus tear is the location: plica pain tends to sit above the joint line, while meniscus pain is right at the joint line. It’s frequently misdiagnosed as a meniscus problem because the symptoms overlap, so the exact spot where you feel the most tenderness is an important clue.
How to Narrow Down the Cause
A few questions can help you sort through the possibilities before you see a provider. Did the pain start suddenly during an activity, or creep in over weeks? A sudden onset with a pop suggests a ligament or meniscus injury. Gradual onset with morning stiffness leans toward arthritis. Pain specifically two to three inches below the joint that worsens with stairs points to bursitis.
Pay attention to what makes it worse. Pain when you push your knee inward, or when someone bumps the outside of your leg, implicates the MCL. Catching or locking when you twist suggests a meniscus tear. Aching that builds with activity and fades with rest is more typical of arthritis or bursitis.
Strengthening the Inner Knee
Regardless of the specific cause, strengthening the muscles that support the inner knee helps reduce pain and prevent recurrence. The inner thigh muscles (adductors) and the quadriceps, particularly the portion that sits just above and to the inside of the kneecap, are the primary stabilizers of the medial knee.
A simple starting exercise is a side-lying hip adduction: lie on the side of the affected leg, keep the leg straight, and slowly lift it toward the ceiling against gravity. Once that becomes easy, add a light ankle weight, starting around five pounds and working up to ten. Straight-leg raises lying on your back target the quadriceps without putting pressure through the joint. Gentle hamstring stretches address tightness that contributes to both bursitis and general medial knee stress. The goal is to build support around the joint gradually, not to push through sharp pain.
Signs That Need Prompt Attention
Most inner-knee pain responds to a period of rest and targeted strengthening, but some patterns warrant faster evaluation. Significant swelling that develops within hours of an injury, inability to bear weight, a knee that locks and won’t unlock, or a visible deformity all call for urgent care. A knee that is red, hot to the touch, and accompanied by a fever could signal an infection and needs same-day evaluation. Pain that limits your ability to fully bend or straighten the leg, or that persists beyond two to three weeks without improvement, is worth getting checked even if it doesn’t feel like an emergency.