Atlantoaxial instability in Down's syndrome.

Some issues related to participation in certain sports by persons with Down syndrome require clarification. Since 1965 there have been occasional reports about a condition described at various times as instability, subluxation, or dislocation of the anticulation of the first and second cervical vertebrae (atlantoaxial joint) among persons with Down syndrome.’’5 This condition has also been found in patients with rheumatoid arthritis,’6”7 abnormalities of the odontoid process of the second cervical vertebra,4’5’12”3’15 and various forms of dwarfism.’8 Atlantoaxial (C-i, C-2) instability has not attracted general attention because clinical manifestations are rare and the condition is limited to a small portion of the population. The incidence of atlantoaxial instability among persons with Down syndrome has been reported by various observers to be 10% to 20%2,9,15 When atlantoaxial instability results in subluxation or dislocation of C-i and C-2, the spinal cord also may be injured. This is a rare but serious complication. In March 1983, the Special Olympics, Inc, sponsors of a nationwide competitive athletic program for developmentally disabled persons, without prior announcement, mandated for participants with Down syndrome special precautions to prevent Senious neurologic consequences from stress on the head and neck in sports competition.’9 Although thousands of persons with Down syndrome have taken part in sports events during the 15-year history of the Special Olympics without a known occurrence of neurologic complications due to participation, the new directive requires all persons with Down syndrome who wish to participate in certain sports that might involve stress on the head and neck (gymnastics, diving, pentathlon, butterfly stroke in swimming, diving start in swimming, high jump, soccer, and warm-up exercises that place undue stress on the head and neck muscles) to have a medical examination, lateral-view roentgenograms of the upper cervical region in full flexion and extension, and certification by a physician that the examination did not reveal atlantoaxial instability or neurologic disorder. Failure either to cornply or to have medical certification would result in exclusion from the above-specified sports. Parents, physicians, and sports authorities were understandably surprised by the immediacy of the edict. Many parents were resentful because of the short time for screening, the cost of the examinations, and discovery that most physicians did not know about the directive or were not aware of the atlantoaxial syndrome. Some radiologists were not familiar with exact procedures for screening. In general, physicians were perplexed by the sudden concern about a condition that had never been a problem among the largest group of disabled participants during 15 seasons of the Special Olympics. There are no national statistics to confirm the extent of screening in 1983, but valiant efforts were made to comply with the directive during the 6week interval allowed for the procedures. It has been stated that there were no reported casualties due to atlantoaxial instability in the Special Olympics last year. However, some participants were barred from the specified events. Atlantoaxial (C-i, C-2) instability is a manifestation of the generalized poor muscle tone and joint laxity commonly found in persons with Down syndrome. The instability is due to (1) laxity of the transverse ligament that holds the odontoid process of the axis (C-2) in place against the inner aspect of the anterior arch of the atlas (C-i), maintaining integrity of the C-i, C-2 articulation or (2) abnormalities of the odontoid, such as hypoplasia, malformation, or complete absence.4’5’9”3”5 These conditions allow some leeway between the odontoid and the atlas, especially during flexion and extension of the neck. This results in a “loose joint.” In extreme cases, the first cervical vertebra slips forward and the spinal cord is vulnerable to compression by the odontoid process of C-2 anteriorly or by the arch of C-i posteriorly. Measurement of the distance between the odon-