Knee snapping, popping, or grinding

A knee that snaps or pops when you walk, exercise, twist, or turn may be annoying but usually is not a cause for concern if you don't have any pain and your knee feels stable.

A knee that snaps or pops at the time of a painful injury may be caused by:

• Sprains, strains, or other injuries to the ligaments and tendons that support the kneecap.
• A torn ligament, such as the torn anterior cruciate ligament (ACL) or the medial collateral ligament (MCL).
• A tear in the rubbery cushions of the knee joint (menisci).
• Breaks (fractures) of the kneecap, lower portion of the femur, or upper part of the tibia or fibula. (See an illustration of the structures of the knee.) Knee fractures most commonly are caused by abnormal force, such as a falling on the knee, a severe twisting motion, severe force that bends the knee, or when the knee forcefully hits an object.
• Kneecap dislocation. Pieces of bone or tissue (loose bodies) from a fracture or dislocation may get caught in the joint and interfere with movement.

Grinding may occur with joint movement because of other conditions, such as:

• Degenerative joint disease (osteoarthritis).
• Wear and tear on the material that absorbs shock and provides a gliding surface (articular cartilage) on the underside of the kneecap (chondromalacia patellae).

Prompt treatment is important to promote healing and prevent complications.