Knee clicking is a common symptom and does not always indicate cause for concern. A complex interworking of ligaments, tendons and muscles support your knee joint. These must support your body weight during normal activities and added force when you exercise, particularly for high-impact activities like running. If you experience a clicking or popping sound when you squat or bend the knee, this does not necessarily indicate a more serious condition. However, clicking can be a sign of injury or underlying conditions.
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Strength imbalances in the knee muscles can cause clicking, particularly while squatting. Your quad muscles are responsible for keeping your kneecap in line as you bend and straighten your knee. Outer quad muscles are often stronger than the inner quads, pulling the kneecap off track as you move. This condition -- called runner's knee -- can cause clicking in your knee.
Osteoarthritis is a condition that commonly occurs as you age. The knee joint is composed of three bones: your patella or kneecap, the end of your femur or thighbone and the top of your tibia or shinbone. These bones fit together and are supported by cartilage, ligaments, muscles and tendons. When the membranes and cartilage that support your knee begin to wear down, you may experience a clicking, crunching or grinding sound in the knee when you squat as parts of the bones are rub against each other. While you may not initially experience pain with osteoarthritis, you may find the clicking is accompanied by joint stiffness. This condition tends to develop slowly, and may affect one knee or both.
Cartilage called the meniscus protects and cushions the knee joint. Meniscal tears are a common athletic injury that occurs when your knee twists while you bear weight. This injury is often characterized by a clicking or popping sound. Mild meniscal tears may result in knee weakness or continual clicking that can go away as the meniscus repairs itself.
Soft tissue surrounding your knee joint is called synovium. Folds in the synovium, called plicae, can develop and cause clicking in your knee, particularly as you bend it. These plicae may not cause problems other than clicking, however in some cases they become inflamed and painful.