If the athlete has Down syndrome, Special Olympics requires a full radiological examination establishing the absence of Atlanto-axial Instability before he/she may participate in sports or events which, by their nature, may result in hyperextension, radical flexion or direct pressure on the neck or upper spine.  The sports and events for which such a radiological examination is required are: judo, equestrian sports, gymnastics, diving, pentathlon, butterfly stroke and diving starts in swimming, high jump, alpine skiing, snowboarding, squat lift, cheerleading, and football team competition (soccer).