Pain on the inner, or medial, side of the knee during bending is a common complaint. The medial compartment contains ligaments, cartilage, and soft tissues that provide stability and smooth movement. When the knee flexes, these structures are compressed, stretched, or pinched, which can trigger discomfort. Understanding the location and nature of the pain helps distinguish between an acute injury, chronic inflammation, or progressive joint wear.
Acute Injuries to Supporting Structures
Sudden, intense pain on the inner knee, especially following a specific event, often signals damage to the primary stabilizing tissues. The Medial Collateral Ligament (MCL) is a band of tissue running along the inner side of the joint, and it prevents the knee from collapsing inward. An MCL injury typically results from a direct blow to the outside of the knee or a sharp, forceful twisting motion that overstretches the ligament. Pain from an MCL sprain is usually felt directly along the inner joint line and is accompanied by tenderness when the area is touched.
In severe MCL injuries, individuals may experience difficulty fully bending or straightening the knee due to pain and swelling. The knee might also feel wobbly or unstable, suggesting compromised joint alignment. While most people with mild to moderate sprains can still walk, they often do so with a noticeable limp due to discomfort under load.
Another frequent source of acute inner knee pain is a tear in the medial meniscus, a C-shaped piece of cartilage that functions as a shock absorber. Meniscus tears often occur when the foot is planted and the knee is suddenly twisted, causing the cartilage to be pinched between the thigh and shin bones. Pain from a meniscal tear is also localized along the inner joint line, but it is frequently paired with mechanical symptoms that are noticeable during bending.
These mechanical symptoms can include a distinct clicking or popping sensation as the knee moves, or a feeling that the joint is catching or locking. If a torn fragment of the meniscus gets lodged within the joint space, it can prevent the knee from achieving full extension. This pain may develop over several hours following the initial injury and can make activities like squatting or descending stairs difficult.
Inflammation of Local Soft Tissues
Pain that develops more gradually, often linked to repetitive activity or overuse rather than a single traumatic event, may stem from irritated soft tissues outside of the main joint. One of the most common causes of this discomfort is Pes Anserine Bursitis or tendinitis, which affects structures located a few inches below the joint line on the inner side of the shinbone. The pes anserinus is the convergence point of three hamstring and thigh muscle tendons: the sartorius, gracilis, and semitendinosus.
A fluid-filled sac, known as the pes anserine bursa, lies beneath these tendons, providing lubrication and reducing friction against the bone. When this bursa becomes inflamed, the condition is called bursitis, and the pain is concentrated about two to three inches below the knee joint. This discomfort is described as a burning or aching sensation rather than the sharp, joint-line pain associated with acute tears.
The pain is characteristically worsened when the knee is bent under load, such as when climbing stairs, standing up from a seated position, or during vigorous exercise. The inflammation results from excessive friction or strain, making it common in runners, athletes, or individuals who perform repetitive knee flexion movements. Tenderness upon pressing directly on the area, below the main joint, is a distinguishing feature of this soft tissue irritation.
Degenerative Changes in the Joint
Pain that progresses slowly over months or years, worsening with activity and age, suggests progressive wear within the joint itself. Medial compartment osteoarthritis (OA) is the most common form of knee arthritis and involves the gradual deterioration of the smooth articular cartilage. Since the medial compartment carries a significant portion of the body’s weight, it is often the first area to show signs of this breakdown.
As the cartilage thins, the cushioning effect is lost, leading to bone-on-bone friction as the knee moves and bends. This friction produces pain that is described as a deep ache or a grinding sensation, known as crepitus. The pain is exacerbated when putting pressure on the joint, such as when walking up or down an incline or when rising from a chair.
A distinguishing symptom of osteoarthritis is stiffness, particularly after periods of rest or in the morning upon waking. This stiffness is typically relieved within a half-hour as the joint warms up with gentle movement. While the pain may initially feel better with rest, it often returns and intensifies with prolonged activity, reflecting the progressive nature of the condition.
Recognizing Serious Symptoms and Seeking Care
While many causes of inner knee pain can be managed with initial at-home care, certain symptoms indicate a need for prompt medical evaluation. The inability to bear weight on the affected leg is a sign that a serious injury, such as a severe ligament tear or a fracture, may have occurred. Similarly, severe and rapid swelling, especially when accompanied by intense pain or a visible deformity, requires urgent medical attention.
If the knee locks persistently, preventing you from fully straightening or bending the leg, it suggests a mechanical obstruction, such as a lodged meniscus fragment, that needs professional assessment. For minor discomfort, initial steps like rest, ice application, and gentle movement may be appropriate. However, consulting a physician or physical therapist is necessary if pain lasts more than a few days, interferes with sleep, or if any concerning symptoms appear.
Symptoms Requiring Immediate Medical Attention
- Inability to bear weight on the affected leg.
- Severe and rapid swelling, intense pain, or a visible deformity of the joint.
- Persistent locking that prevents full straightening or bending of the leg.
- Systemic symptoms like a fever, chills, warmth, or redness over the joint, which can signal an infection.