Knee pain when bending is common, interfering with daily activities like walking, climbing stairs, or sitting comfortably. While often temporary, this symptom can signal underlying conditions. Understanding these causes is a first step toward relief and mobility.
Patellofemoral Pain Syndrome
Patellofemoral Pain Syndrome (PFPS), frequently called “runner’s knee,” involves pain around or behind the kneecap. This condition is a common reason for discomfort when bending the knee, squatting, or navigating stairs. It often develops from repetitive stress on the knee joint, particularly in activities that involve repeated bending and straightening, such as running, cycling, or jumping.
PFPS pain can also arise from issues with how the kneecap moves within the groove of the thigh bone (femur). If the patella does not track smoothly, it can lead to irritation of the surrounding tissues and the underside of the kneecap. Factors contributing to this poor tracking include muscle imbalances or weakness in the quadriceps and hip muscles. When the kneecap is pushed out of its normal alignment, it can cause friction and discomfort, especially during movements that load a flexed knee.
Knee Osteoarthritis
Knee osteoarthritis (OA) is a degenerative condition where cartilage cushioning the knee joint gradually breaks down. This “wear and tear” process leads to pain, stiffness, and reduced flexibility, which are particularly noticeable when bending the knee or bearing weight. As cartilage erodes, bones can rub, causing friction and discomfort during movement.
The loss of this protective cartilage directly impacts the knee’s ability to bend smoothly and without pain. Individuals with knee OA often experience a dull, aching pain that worsens with activity and improves with rest. While more common with increasing age, it can affect younger individuals, especially those with previous knee injuries or excessive joint stress. The reduced cushioning makes everyday actions like squatting or climbing stairs especially challenging.
Meniscus Tears
The meniscus consists of two C-shaped cartilage pieces in the knee joint that act as shock absorbers between the shinbone and thighbone. Tears can occur acutely from a sudden twisting motion, or develop gradually due to degeneration. A torn meniscus causes significant pain, particularly when the knee is bent, twisted, or squatted.
Beyond pain, a torn meniscus can also lead to mechanical symptoms within the knee. People often report a clicking, popping, or catching sensation during knee movement. A torn piece of cartilage can interfere with joint motion, leading to locking or giving way. These symptoms are a direct result of the damaged cartilage impeding the smooth function of the joint.
Tendinitis and Bursitis
Tendinitis and bursitis are inflammatory conditions that can cause pain when bending the knee. Tendinitis is inflammation of a tendon, the fibrous tissue connecting muscle to bone. In the knee, patellar tendinitis (below the kneecap) or quadriceps tendinitis (above the kneecap) are common, often resulting from overuse or repetitive stress from activities like jumping or running. The pain typically intensifies with knee bending and activity.
Bursitis, on the other hand, is inflammation of a bursa, a small fluid-filled sac cushioning bones, tendons, and muscles around a joint. Prepatellar bursitis, affecting the bursa in front of the kneecap, is common, often caused by direct trauma or prolonged kneeling. When inflamed, a bursa causes localized pain and swelling that is aggravated by direct pressure or by bending the knee, as this compresses the irritated sac.
When to Seek Professional Help and Initial Home Care
Persistent knee pain, especially when bending, warrants professional medical evaluation. Seek prompt medical attention if pain is severe, you cannot bear weight, or notice significant swelling, deformity, or fever. A doctor’s visit is also advisable if the pain began suddenly without a clear cause or if it does not improve with initial home care measures.
For immediate, mild knee pain, some home care steps can provide temporary relief. The RICE method (Rest, Ice, Compression, and Elevation) is often recommended. Resting the knee, applying ice packs for 15-20 minutes several times daily, and using a compression bandage can help reduce swelling and discomfort. Elevating the leg above heart level can also assist in minimizing swelling. Over-the-counter pain relievers can help manage pain and inflammation, but these measures are not a substitute for a professional diagnosis if symptoms persist or worsen.