Inner knee pain that appears during activities like walking often points to an issue on the medial side of the joint. The knee is a complex structure of bone, cartilage, ligaments, and fluid-filled sacs that work together to bear weight and create movement. Pain while bearing weight, such as when taking a step, suggests a problem with one of these load-bearing or stabilizing components.
Structural Damage to the Joint
One source of sudden inner knee pain is an injury to the Medial Collateral Ligament (MCL). This tissue runs along the inside of the knee, connecting the thigh bone (femur) to the shin bone (tibia). The MCL prevents the lower leg from bending too far inward, maintaining joint stability during walking and weight shifts. An injury often results from a direct blow to the outside of the knee or a severe twisting motion when the foot is planted.
A sprain or tear of the MCL causes immediate pain and tenderness, aggravated when the knee is stressed by lateral forces, such as planting the foot during a stride. The severity of the tear, graded from I to III, determines the level of instability and the ability to bear weight. Even a mild Grade I sprain creates noticeable discomfort because the ligament is stretched or partially torn. In more severe Grade II or III tears, the knee may feel unstable, making a normal walking gait difficult.
Another mechanical source of pain is a tear in the medial meniscus, the cartilage pad that acts as a shock absorber between the femur and the tibia. Tears can occur traumatically from a sudden rotation or twist while the foot is planted, or they can result from gradual degeneration. When damaged, a piece of the cartilage can interfere with the smooth movement of the joint, causing pain that is often deeper than a ligament injury. This internal interference can be felt as a clicking, catching, or locking sensation noticeable with every step.
Inflammation of Tendons and Sacs
Pain originating slightly below the inner joint line often signals an inflammatory condition affecting the soft tissues. This area is the location of the pes anserinus, or “goose’s foot,” which is the combined attachment point for the tendons of the sartorius, gracilis, and semitendinosus muscles. These tendons insert onto the upper inner surface of the shinbone (tibia) and help flex the knee and rotate the leg inward. Repetitive motion, such as running or cycling, can create friction and strain at this attachment site.
The pain is often due to pes anserine bursitis, which is the inflammation of the small, fluid-filled bursa situated between the tendons and the bone. When the bursa becomes irritated and inflamed, it swells, causing localized tenderness and a dull ache distinct from deep joint pain. This discomfort is worse with activities that engage the hamstrings, such as climbing stairs, standing up from a seated position, or increasing walking intensity.
While the condition is named bursitis, the surrounding tendons can also become inflamed, leading to tendinopathy. This overuse syndrome develops gradually, unlike the sudden onset of a ligament or traumatic meniscus tear. Tightness in the hamstring muscles or underlying issues like existing knee osteoarthritis can predispose an individual to this medial knee irritation. The tenderness is usually concentrated about two to three inches below the knee joint line.
Long-Term Degeneration
A cause of inner knee pain is Medial Compartment Osteoarthritis (OA), the most common form of knee arthritis. The medial compartment bears a substantial portion of the body’s weight during activities like walking. This condition involves the gradual breakdown of the articular cartilage, the protective tissue covering the ends of the bones.
When this cartilage degenerates, the underlying bones begin to rub against one another, a process known as bone-on-bone friction. This friction generates pain and inflammation, which is exacerbated when weight is applied to the joint during the walking cycle. The pain from medial compartment OA worsens over months or years, distinguishing it from an acute injury.
In addition to a deep, aching pain that increases with activity, individuals often experience stiffness in the joint, particularly after periods of rest or in the morning. This morning stiffness usually lasts for less than thirty minutes. A grating, crackling, or scraping sound, medically termed crepitus, may also be heard or felt as the roughened joint surfaces move.
Since walking involves repeatedly loading the joint, each step places mechanical stress on the damaged medial compartment. This degeneration makes activities requiring full weight-bearing, such as walking or standing for long periods, increasingly difficult and painful.
When to Seek Professional Help and Immediate Care
While many causes of inner knee pain can be managed conservatively, certain signs indicate the need for immediate medical evaluation. You should seek professional help if you experience any of the following:
- Sudden, severe pain that prevents you from bearing any weight on the leg.
- A visible deformity of the knee, which could signal a fracture or dislocation.
- A feeling that the knee is unstable and keeps giving way.
- Systemic symptoms like a fever, or if the knee feels hot, swollen, and red, indicating a possible joint infection.
- Mechanical symptoms, such as the knee locking up or a persistent catching sensation, suggesting a structural tear.
- Persistent pain that does not improve after a week of self-care.
Immediate self-care can help manage initial pain and swelling while waiting for a diagnosis. Applying the R.I.C.E. principle is a helpful first step: resting the knee by avoiding painful activities, applying ice for fifteen to twenty minutes several times a day to reduce inflammation, and using gentle compression and elevation to control swelling.