A trick knee, as it is often called, is called a luxating patella in medical terms. The patella is the kneecap, which is one of three bones that make up the knee joint. The patella or kneecap sits in the front of the knee. The patella glides up and down during leg movement in a groove on the front of the femur that is called the trochlear groove. The patella is held in place by tendons and ligaments. Luxation or subluxation describes the situation when the affected body is moving abnormally out of place. A complete luxation or subluxation is called a dislocation. Therefore, a luxating patella is a kneecap that moves too far out of the trochlea. The subluxation or dislocation forces the patella to the outer side of the knee usually during bending or pivoting activities. A “trick knee”, or knee that spontaneously gives way or collapses, can occur while playing sports or during normal activities of daily living. Unstable or subluxating kneecaps are one of the main causes of a trick knee. Other knee instability scenarios, such as anterior cruciate ligament (ACL) deficiency can also cause knee giving way and instability; these knees can also be described as a “trick knees”. Dr. Riley J. Williams, orthopedic knee specialist, serving Manhattan, Brooklyn, New York City, NY and surrounding areas, has extensive experience in treating a luxating patella, ACL tears, and other issues related to knee buckling, or trick knee issues.