46 Anomalies in Posterior Spinal Segments of the Axis
Anomalies of the axis vertebra are common and involve primarily the odontoid process and, relatively less frequently, the vertebral body.1–10 Anomalies of the posterior elements are extremely rare.4,11 We encountered three cases where the posterior elements of the axis were absent, the body of the axis was dislocated anterior to the body of the C3 vertebra, and the posterosuperior lip of the C3 vertebral body caused severe compression of the spinal cord.12,13 The remarkable similarity of these three cases suggests that the absence of the posterior elements of the axis and spondyloptosis is a well-defined clinical entity and that treatment options in such cases need to be crystallized.
Incidence
Congenital absence of the posterior elements of the axis is extremely rare. In our three cases, there was complete absence of the posterior elements of the axis, and the body of the axis was dislocated and positioned anterior to the C3 cervical vertebra. The body of the C3 vertebra caused severe cord compression. We could locate only two additional reports of patients with partial defect in the posterior elements of the axis.11,14 Morizono et al. detected the defect in the spinous process and lamina of the second cervical vertebra during a roentgenographic study of the cervical spine for investigation of headache and neck pain following trauma.11 This patient responded to conservative therapy. Clinical details of the second case labeled as spina bifida of the axis are not mentioned in the report.14 In contrast, anomalies related to the defects in the development of the posterior arch of the atlas have a reported incidence of 3 in 1000 persons.15
Development
Embryologically, the arch and the spinous process of the axis are formed from a pair of left and right primordial cartilages.16 The cause of a defect may be either malformation of the primordia or failure of ossification3,17,18 of the normally developed cartilage. Complete absence of both the cartilaginous and bony components of the posterior elements of the axis implies a very early fault in embryogenesis.17 O’Rahilly et al.19 studied the cervical spine of nine embryos. They found that by stage 23 of embryogenesis (8 postovula-tory weeks), the neural arches of the axis extended laterally from the centrum and formed a complete or incomplete foramen transversarium. During the same period of embryo-genesis, the neural arch proceeds directly backward to a variable extent, forming pedicles, articular facets, and part of the lamina. A developmental defect in our cases could have occurred during or before this stage of embryonic development. The exact cause of the defect in our patients cannot be known. There was no evidence of consanguinity or obvious teratogenic events in utero.
Clinical Features
The clinical and radiological features of all three cases encountered by us have remarkable similarities ( Table 46.1 ). There was no history of major trauma to the neck or head. In the first two patients, there was a partial reduction of the dislocation after the application of traction. However, our third patient did not tolerate traction and showed clinical symptomatic worsening.
Treatment
An attempt to fix the spine by interlaminar instrumentation after partial reduction of the dislocation with traction resulted in neurological worsening in our first patient. Transcervical decompression, which was followed by posterior fixation, resulted in satisfactory clinical improvement in the second patient. In the third, anterior transoral decompression and plate and screw fixation resulted in immediate and sustained clinical improvement. This case is illustrated below. Although there is the risk of infection following placement of a metal plate via a transoral route, the ease of exposure and decompression and fixation by this route can be employed to great advantage.
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
