[Atlanto-axial rotation and distance in small children. A postmortem study].

The aetiology of atlanto-axial rotatory subluxation is obscure. Therefore, a post mortem investigation was designed in order to evaluate the C 1-2 rotation and translation mobility and to clear the borderline between mobility and instability and to clear the role of the atlanto-axial joints in atlanto-axial rotatory subluxation. C 1-2 specimen of 2 months, 9 months and 53 months old children were used. In the intact specimen and after sequential decision of the atlanto-axial joint capsule, the atlanto-axial membrane, the transverse ligament of the atlas, and eventually the alar ligaments, the atlas was rotated and anteriorly translated over the axis. The end point of the movements was recorded radiographically. Decision of the anatomic structures increased the rotation of up to 25 degrees. The joint capsules are lax and wide thus allowing rotation with almost complete subluxation. The subluxation of atlanto-axial joints probably stays within the normal range of motion and is not a factor of atlanto-axial rotatory subluxation. Interlocking of the facets could not be observed. In atlanto-axial rotatory subluxation the atlanto-dental interval becomes asymmetric. Its radiographic projection is variable and therefore ist does not present a valuable radiographic parameter.