The occasional click or pop from a knee joint is a common experience. These sounds can occur during everyday movements like walking, squatting, or climbing stairs. While often a normal bodily phenomenon, understanding their causes helps determine when they are harmless or signal a significant concern.
The Sounds Your Knees Make
The knee joint can produce a range of sounds, including clicking, popping, grinding, and cracking, collectively referred to as crepitus. These sounds are quite common. Sounds alone, without pain or discomfort, are generally not indicative of a problem. However, when clicking or popping is accompanied by pain, swelling, or a feeling of instability, it may point to an underlying issue within the joint.
Common, Harmless Causes
One frequent and benign reason for knee clicking is cavitation, involving the formation and bursting of gas bubbles within the synovial fluid. Synovial fluid lubricates the joint. Changes in pressure during movement cause dissolved gases to form small bubbles. When these bubbles rapidly collapse, they produce a popping or cracking sound, similar to cracking knuckles. This process is typically painless.
Another common cause of knee sounds is the movement of tendons or ligaments. Tendons connect muscles to bones, and ligaments connect bones to other bones, providing stability. As the knee moves, these fibrous bands can momentarily glide or snap over bony prominences or scar tissue, creating a clicking or snapping sensation. This is a normal part of joint mechanics and usually presents no concern unless associated with pain or swelling.
Articular cartilage, the smooth tissue covering the ends of bones within the joint, can also contribute to knee sounds. While designed for smooth movement, its surface can become slightly uneven with age or wear. When these rougher surfaces glide past each other, they may produce grinding or crackling noises. This alone does not signify a problem if pain is absent.
When to Be Concerned
Knee clicking accompanied by symptoms can signal an underlying issue. Pain, swelling, or a feeling of the knee getting stuck, catching, or locking warrant medical attention. A reduced range of motion, where bending or straightening the knee becomes difficult, also indicates a potential problem.
Several conditions can cause problematic knee clicking:
A meniscus tear, damage to the C-shaped cartilage that cushions the knee, often presents with pain, swelling, stiffness, and a clicking or catching sensation.
Osteoarthritis, a degenerative joint condition where cartilage wears down, can lead to painful clicking or grinding as bones rub against each other.
Chondromalacia patellae, or “runner’s knee,” involves the softening and deterioration of cartilage under the kneecap, resulting in pain and popping noises, especially with activities like climbing stairs or squatting.
Ligament injuries, such as tears to the anterior cruciate ligament (ACL) or medial collateral ligament (MCL), can cause a popping sound at the time of injury, followed by instability, pain, and swelling.
Next Steps and Management
If knee clicking is accompanied by pain, swelling, locking, catching, or a reduced range of motion, consult a healthcare professional. A doctor can diagnose the cause through physical examination and, if necessary, imaging tests like X-rays or MRI scans. Early diagnosis allows for timely intervention and management.
For knee sounds without symptoms, general knee health practices are beneficial. Maintaining a healthy weight reduces stress on the knee joints. Regular low-impact exercises, such as walking, cycling, or swimming, strengthen surrounding muscles like quadriceps and hamstrings, contributing to joint stability. Stretching exercises also improve flexibility and range of motion.