Knee clicking, or crepitus, is a common occurrence. Although it sounds abnormal, it 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 your knee pops when squatting, this does not necessarily indicate a more serious condition. However, knee popping and pain can be a sign of injury or underlying conditions. See a doctor or physical therapist for a diagnosis if this occurs frequently.
Read more: Why Do My Knees Crack When I Do Lunges?
Knee Clicking, No Pain
Strength imbalances in the knee muscles can cause knee clicking, but no pain, 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.
Treatment for runner's knee includes strengthening exercises to correct tracking of your kneecap during movement.
Arthritis and Clicking
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 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.
Treatment for osteoarthritis often includes physical therapy and cortisone shots to reduce inflammation. However, these interventions do not correct the underlying problem. Over time, as cartilage wears away, osteoarthritis can become very painful, and your joint might need to be surgically replaced.
Torn Knee Cartilage
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. However, more severe meniscal injuries can cause your leg to give out, and often require surgery to repair the damaged cartilage.
Crepitus and Synovial Plicae
Soft tissue surrounding your knee joint is called synovium. Folds in the synovium, called plicae, can develop and cause clicking in your knee, particularly when you're squatting.
Synovial plica syndrome might not cause problems other than clicking. However in some cases they become inflamed and painful. This pain typically occurs in the front of the knee and can be accompanied by crepitus and clunking. In these cases, they might be surgically removed.
Read more: Ew, Why Are My Joints Cracking and Popping?