Inside knee pain, also called medial knee pain, most often comes from one of a handful of structures on the inner side of the joint: the medial collateral ligament (MCL), the medial meniscus, the joint cartilage itself, or the tendons and bursae that cross below the kneecap. The cause depends heavily on your age, activity level, and whether the pain started suddenly or crept in over time.
MCL Sprains and Tears
The MCL is a thick band of tissue running along the inner edge of your knee, connecting your thighbone to your shinbone. It’s the most commonly injured ligament on the medial side, and it usually gets hurt in one of three ways: a direct blow to the outer knee (like a football tackle), planting your foot and cutting sharply in another direction, or deep squatting and heavy lifting that forces the knee inward.
MCL injuries are graded on a three-point scale. A grade 1 sprain means fewer than 10% of the ligament fibers are torn. Your knee still feels stable, but you’ll notice tenderness along the inner edge. A grade 2 sprain is a partial tear, typically of the superficial layer. Pain and tenderness are more intense, and the knee feels loose when someone pushes on it. A grade 3 tear is a complete rupture of both the superficial and deep layers. The knee is noticeably unstable, and pain is severe.
Most MCL injuries heal without surgery because the ligament has a good blood supply. Grade 1 sprains often resolve in a few weeks with rest and bracing. Grade 2 and 3 tears take longer, sometimes several months of structured rehabilitation, but the majority still respond to conservative treatment.
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 is more commonly torn than its outer counterpart, partly because it’s less mobile and absorbs more force during twisting movements.
A torn medial meniscus often announces itself with a popping sensation at the moment of injury. Afterward, you may notice swelling, stiffness, and pain that gets worse when you twist or rotate the knee. The hallmark symptom is a mechanical problem: the knee locks in place, catches during movement, or feels like it might give way. Some people find they can’t fully straighten the leg. These mechanical symptoms help distinguish a meniscus tear from a ligament injury, which tends to produce instability rather than locking.
In younger people, meniscus tears typically happen during sports or a sudden awkward twist. In people over 40, the cartilage becomes more brittle and can tear during ordinary activities like getting up from a low chair or stepping off a curb.
Osteoarthritis of the Medial Compartment
When knee osteoarthritis develops, it hits the inner compartment more often than any other part of the joint. A large meta-analysis found that isolated medial compartment arthritis accounts for about 27% of knee OA cases, while patterns involving the lateral (outer) compartment sum to roughly 15%. The reason is biomechanical: during normal walking, the medial compartment bears a larger share of your body weight.
Osteoarthritis pain on the inner knee tends to build gradually over months or years. It’s usually worst after prolonged activity or at the end of the day, and it improves with rest early on. Over time, morning stiffness becomes more noticeable, the joint may swell intermittently, and you might hear or feel grinding when you bend the knee. Unlike a meniscus tear, the pain is generally a deep ache rather than a sharp catch, though the two conditions frequently overlap in the same knee.
Pes Anserine Bursitis
This is a common but often overlooked cause of inner knee pain that sits slightly below the joint itself. The pes anserine bursa is a small fluid-filled sac located about 2 to 3 inches below the kneecap on the inner side of the shinbone, where three tendons converge. When it becomes inflamed, the pain is very localized to that lower spot, which helps distinguish it from problems inside the joint.
Bursitis here is triggered by repetitive knee bending, particularly in sports like soccer and tennis that involve lots of lateral movement. It’s also common in runners and in people who are overweight or have tight hamstrings. The telltale pattern: pain worsens when climbing stairs, kneeling, or standing up from a chair. It often flares at night if you sleep with your knees pressed together.
Plica Syndrome
A plica is a fold of the thin tissue lining the inside of your knee joint. Most people have one on the medial side and never know it’s there. But repetitive bending, a direct bump, or sudden overuse can irritate it, causing it to thicken and catch against the thighbone. The result is a dull ache or snapping sensation on the inner knee, usually above the joint line. That location is the key differentiator: meniscus pain tends to sit right at the joint line, while plica pain is higher.
Hip Problems That Mimic Knee Pain
Sometimes the source of inner knee pain isn’t in the knee at all. The obturator nerve, which provides sensation to the hip joint, also sends branches toward the inner knee. This means hip problems can generate referred pain that feels like it’s coming from the knee itself.
Hip osteoarthritis is the most common culprit. Studies suggest that up to 45% of people with confirmed hip OA report knee pain as part of their symptoms, and some describe knee pain as their primary complaint. In people under 45, hip impingement and labral tears are more likely sources of referred medial knee pain. Even problems in the lower back, particularly irritation of the L3 nerve root, can produce symptoms on the inner side of the knee without any knee damage at all. If your knee looks and tests normal but the pain persists, the hip and spine are worth investigating.
How These Conditions Are Told Apart
A physical exam can narrow the diagnosis quickly. For a suspected meniscus tear, a clinician will bend your knee fully, rotate your lower leg outward, and slowly straighten it while feeling for a pop or click along the inner joint line. For an MCL injury, they’ll push the knee inward with the leg straight, checking whether the joint gaps open more than it should. Tenderness 2 to 3 inches below the joint line points toward pes anserine bursitis, while tenderness above the joint line suggests plica syndrome.
Imaging fills in what the physical exam can’t. X-rays show arthritis and bone alignment. MRI reveals soft tissue problems like meniscus tears, MCL damage, and inflamed bursae. In cases where referred hip pain is suspected, imaging the hip or lower spine may be necessary to find the real source.
When Inside Knee Pain Needs Urgent Attention
Most causes of inner knee pain are not emergencies, but a few situations call for immediate evaluation. If you can’t put weight on the knee at all, don’t force it. If the knee locks and won’t unlock, swells rapidly after an injury, or feels grossly unstable (like it could buckle in any direction), these are signs of significant structural damage. Any knee pain following severe trauma, such as a hard fall or car accident, warrants an emergency visit to rule out fractures. Pain that persists for more than a few days, interferes with daily activities, or keeps getting worse also deserves a professional assessment rather than a wait-and-see approach.