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PubMed1993

Mice homozygous for a targeted disruption of Hoxd-3 (Hox-4.1) exhibit anterior transformations of the first and second cervical vertebrae, the atlas and the axis.

Gene targeting in embryo-derived stem (ES) cells was used to generate mice with a disruption in the homeobox-containing gene Hoxd-3 (Hox-4.1). Mice homozygous for this mutation show a radically remodeled craniocervical joint. The anterior arch of the atlas is transformed to an extension of the basioccipital bone of the skull. The lateral masses of the atlas also assume a morphology more closely resembling the exoccipitals and, to a variable extent, fuse with the exoccipitals. Formation of the second cervical vertebra, the axis, is also affected. The dens and the superior facets are deleted, and the axis shows 'atlas-like' characteristics. An unexpected observation is that different parts of the same vertebra are differentially affected by the loss of Hoxd-3 function. Some parts are deleted, others are homeotically transformed to more anterior structures. These observations suggest that one role of Hox genes may be to differentially control the proliferation rates of the mesenchymal condensations that give rise to the vertebral cartilages. Within the mouse Hox complex, paralogous genes not only encode very similar proteins but also often exhibit very similar expression patterns. Therefore, it has been postulated that paralogous Hox genes would perform similar roles. Surprisingly, however, no tissues or structures are affected in common by mutations in the two paralogous genes, Hoxa-3 and Hoxd-3.

Animals↗
PubMed1998

[Radiologic description of the growth plates of the atlas and axis in foals].

Fractures of the first two cervical vertebrae, atlas and axis, may occur in foals for different reasons, e.g. in cases of a fall, going head over heels or when being hit by a hoof. The tentative clinical diagnosis can be confirmed by x-raying the standing animal, with aid of computed tomography in the anaesthetized foal respectively. The growth plates however, and their time of closure have to be considered when interpreting radiographs. In the atlas there are two ventrolateral plates and one dorsomedian cartilagineous plate. Only the dorsal plate, however, can be found in the dorsoventral projection up to an age of about 12 months. The ventrolateral growth plates which have closed at about six months of age cannot be seen in either ther dorsoventral or laterolateral projection. In transversely oriented CT-scans all of the three centres of ossification can easily be made visible in the atlas. In the axis the cartilagineous gaps between the dens axis and the cranial epiphysis as well as the cranial and caudal epiphyseal growth plate can be shown in normal x-radiographs in both planes of projection. Besides this there are growth plates between the corpus vertebrae and the arcus vertebrae in the axis which cannot be seen in either radiographic projection. They become clearly visible in transversal CT-scans and are ossified at the age of three to four months. At the end of the first year the growth plates between the dens axis and the cranial epiphysis have closed. The cranial and caudal epiphyseal plate are gone at an age of about four to five years.

Animals↗
PubMed1985

Axis fractures: a comprehensive review of management and treatment in 107 cases.

The combination of movement, location, and anatomy of the axis predisposes it to multiple and varied fracture/dislocations distinct from other vertebrae. We examine all forms of axis fractures and address the appropriate treatment for each specific fracture type. In a retrospective review of 625 cervical spine fractures during an 8-year period, we found 107 axis fractures. There were 25 hangman's fractures (23%), 59 odontoid fractures (55%), and 23 miscellaneous fractures (22%). Each case was characterized by age, sex, the presence of associated injuries, presenting symptoms and findings, initial treatment, and results of that treatment. Excluding 6 early deaths, 90 of 101 patients were located for a median follow-up of 3.2 years. We found that 17% of cervical fractures involve the axis. Axis fractures have a high association with head and other cervical spine injuries, 40% and 18%, respectively. Few neurological deficits result from a fracture of the 2nd cervical vertebra. Hangman's fractures are effectively treated with external stabilization, preferably with a halo vest. We noted a shorter period of treatment using the halo vest as compared to the SOMI brace. Nonunion occurred in 26% of odontoid Type II fractures, but occurred in 67% of those with dens displacement of 6 mm or greater, regardless of age or direction of dislocation. We recommend early surgical therapy for this subgroup. There is no correlation between age and the rate of nonunion. In patients with odontoid Type II fractures with dens displacement of 0 to 5 mm, fusion occurs with external stabilization alone. Odontoid Type III fractures are one-half as common as Type II fractures, and all heal well with external stabilization. Twenty-two per cent of acute axis fractures are not hangman's or odontoid fractures. Miscellaneous fractures of the axis generally do well with external stabilization and immobilization.

Adolescent↗
PubMed1976

[Clinic of the upper cervical spine and review of the medical history of the regional osteology (author's transl)].

After a brief review of the systematic clinical work up of this region within our century, the medical history of the osteology of the occipito-cervical junction is given special attention. It is looked upon the illustrations of the first printed anatomical textbooks that are linked with such famous names as Berengario, Dryander, Estienne, Vesal and Eustachius. Leonardo da Vinci's concept of the first two vertebrae is also mentioned.

Anatomy↗
PubMedDate not supplied

Os odontoideum in children: neurological manifestations and surgical management.

The os odontoideum is a congenital anomaly of the 2nd cervical vertebra. It is an ossicle that is separated from the body of the axis by a variable transverse gap. This weakens atlantoaxial stability. When ligamentous support also fails, subluxation ensues. Compressive myelopathy and vertebral artery obliteration may occur. Eight cases, all in children, were studied prospectively. The neurological manifestations and surgical indications and treatment are discussed.

Adolescent↗