Pain on the inside of your knee typically comes from one of a handful of structures packed into that part of the joint: the medial collateral ligament (MCL), the medial meniscus, a small fluid-filled sac called the pes anserine bursa, or the cartilage surfaces of the bones themselves. Pinpointing which structure is involved usually comes down to where exactly the pain sits, what triggered it, and what movements make it worse.
Key Structures on the Inner Knee
The inside of your knee is the “medial” side, the part closest to your other leg. Two structures do most of the stabilizing work there. The MCL is a thick band of tissue connecting your thighbone to your shinbone, preventing the knee from bending inward. Just beneath it sits the medial meniscus, a wedge of tough cartilage that cushions the space between those two bones and absorbs shock with every step.
A few inches below the joint line, three tendons from your thigh and hamstring muscles converge on the shinbone at a spot called the pes anserinus. A bursa (a small, fluid-filled cushion) sits between those tendons and the bone to reduce friction. Any of these structures can become a source of pain, and each one produces a slightly different pattern of symptoms.
MCL Sprains and Tears
The MCL is the most commonly injured ligament on the inner knee. A direct blow to the outside of the knee, a sudden twist, or a hard change of direction can stretch or tear it. You’ll typically feel a sharp pain right along the inner edge of the joint, and the area will be tender to the touch. In more severe injuries the knee may feel loose or unstable, as though it could buckle inward.
MCL injuries are graded by severity. A mild (grade 1) sprain means the ligament is stretched but intact, and it usually heals within one to three weeks. A moderate (grade 2) tear involves partial disruption of the fibers and generally takes four to six weeks. A severe (grade 3) tear, where the ligament is fully torn, requires six weeks or more of recovery and sometimes a hinged brace, though surgery is rarely needed for isolated MCL injuries.
Medial Meniscus Tears
Meniscus tears are the single most common cause of persistent inner knee pain, and they happen on the medial side far more often than the outer side. In one MRI study of 100 symptomatic knees, 50 had medial meniscus tears compared to only 16 with lateral tears. The medial meniscus is less mobile than its outer counterpart, which makes it more vulnerable to grinding and shearing forces.
The hallmark symptoms are recurrent pain right at the joint line and episodes of catching or locking, especially when you squat or twist the knee. You may notice mild swelling and a feeling that something is “stuck” inside the joint. Over time, the quadriceps muscle on the front of the thigh can visibly shrink on the affected side from disuse. Pivoting, rotating, and deep bending tend to be the worst triggers, so avoiding those movements is usually the first piece of advice during recovery.
Pes Anserine Bursitis
If the pain is lower than you’d expect, roughly two to three inches below the inner joint line on the upper shinbone, the pes anserine bursa is the likely culprit. This spot becomes inflamed from repetitive knee bending, tight hamstrings, or activities that load the inner knee over and over, like running, soccer, or tennis.
Pes anserine bursitis shows up most often in two groups: athletes who ramp up training too quickly or use poor stretching habits, and adults between 40 and 60 who have osteoarthritis, carry extra weight, or have diabetes. Women are affected more often than men. An existing MCL injury or knock-kneed alignment (where the knees angle inward) also raises the risk. The pain usually worsens when climbing stairs or getting up from a chair, and the area is often tender when pressed directly.
Osteoarthritis of the Inner Knee
The medial compartment bears the majority of your body weight during walking, which is why osteoarthritis tends to wear down the inner knee first. As the cartilage thins, the bones gradually lose their cushion and the joint space narrows. Over time, extra bits of bone (bone spurs) can form around the edges of the joint.
The pattern is distinctive. Stiffness is worst first thing in the morning or after sitting for a while, then loosens up with gentle movement. The pain tends to build gradually over months or years rather than appearing after a single event. Activities that load the joint, like walking long distances, standing for extended periods, or going up and down stairs, make it worse. Carrying extra body weight accelerates the process: research on young adults with obesity shows they place a significantly greater inward (adduction) force on the knee with every step, which concentrates pressure on the medial cartilage even before age-related wear sets in.
Medial Plica Syndrome
A plica is a fold of the tissue lining the inside of the knee joint. Most people have one on the medial side and never know it’s there, but a sudden spike in activity, like starting a new exercise program or dramatically increasing mileage, can irritate it. The pain comes on relatively quickly and sits just in front of the inner joint line, where you may be able to feel a small, tender, movable lump under your fingers.
What sets plica syndrome apart from a meniscus tear is the absence of swelling and mechanical symptoms. There’s no catching, locking, or feeling of instability. The rest of the knee exam is normal. It often resolves on its own once the aggravating activity is scaled back.
How to Tell These Conditions Apart
Location is the strongest initial clue. Pain right at the joint line that catches or locks points toward a meniscus tear. Pain along the inner edge of the knee that followed a blow or twist suggests the MCL. Pain a few inches below the joint on the shinbone points to pes anserine bursitis. A gradual, stiffness-heavy pain that loosens with movement and worsens with weight-bearing activity is most consistent with osteoarthritis.
Age and activity level also help narrow things down. A young athlete who took a hit during a game is far more likely dealing with an MCL sprain. A runner in their 40s or 50s with tight hamstrings and pain below the joint line fits the profile for bursitis. A sedentary adult over 55 with morning stiffness and bone spurs on X-ray almost certainly has medial compartment osteoarthritis.
Signs That Need Prompt Attention
Most inner knee pain improves with rest, ice, and a temporary reduction in activity. But certain symptoms warrant a prompt visit. If your knee gives out or feels unstable when you put weight on it, if there is significant swelling, if you can’t fully straighten or bend the knee, or if you see an obvious deformity, those are signs of a more serious injury that may need imaging or specialist evaluation. A fever paired with redness, swelling, and pain raises the possibility of infection and should be evaluated urgently.