Sir,

I read with interest an article entitled "Late cervical dislocation - causes and prevention" by Haj Ali, et al.2 The authors must be appreciated for their superb study on a very important topic ie. delayed dislocation of occult cervical spine injuries, which was hitherto alluded in the literature.

I agree with the authors that facet fractures are potentially unstable injuries and therefore, need more aggressive management than the conventional use of collars. This is clearly evident in their study that 5 out of 7 patients of facet fractures without dislocation treated with cervical hard collars subsequently developed dislocation. Hereby, I would like to elaborate a little further on the concept of delayed manifestation of cervical spine instability with particular reference to the facet fractures.

Unstable injuries may jeopardize the spinal cord and nerve root function in the acute phase or lead to late instability with pain and/or neurological deterioration in the chronic phase. Late instability is much more common than frequently realised because ligamentous structures do not reconstitute normally, even after prolonged rigid external fixation. Conventional radiography is not foolproof for the diagnosis of all cervical spine injuries. Woodring and Lee reported that fractures were missed in 23% of patients and in half of those, there was an unstable cervical spine injury.8 Approximately 10% of patients with spine trauma who have normal clinical findings at an initial neurological examination incur neurological deficits subsequently.5 Herkowitz and Rothman reported six patients who developed neurological deficit and radiographic evidence of cervical spine instability within 3 weeks of cervical spine injury when none was present initially. Such an entity is termed as subacute instability that becomes apparent weeks after an injury when the muscle spasm has subsided and is thought to be due to elastic and plastic deformation of the ligamentous structures and discs of the cervical spine.3

Unilateral facet fractures represent 3-11% of all cervical spine injuries.7 Facet fractures occur most commonly at C6 and C7 and result in radiculopathy in 6 to 39% of patients.7 Facets of superior and inferior articular processes articulate with each other forming the facet joints providing segmental stability to the cervical spine. Panjabi, et al. in their experimental work with the cadavers observed that horizontal translation of the vertebra increased significantly after removal of the facet joint.4 They concluded that the facet joint acted as a couple between horizontal translation and sagittal plane rotation. Cusick, et al. found that unilateral facetectomy diminished the strength of the spine by 31% and that bilateral facetectomy diminished the strength by 53%.1 As facet fractures result in the fracture of the bony buttress, even with reduction in traction there is residual rotatory instability. The residual rotatory instability of a facet fracture, however, is not well controlled with a halo vest and thus nonsurgical treatment always results in malrotation, although union may occur. Bilateral facet fractures lead to bi-directional rotational instability.

Fractures of superior process are either at the apex or base. Apical fractures are usually associated with transient high-grade bilateral facet subluxation and cord injury. The fracture fragment may be small enough that the remaining part of the superior process provides an adequate bony block. Basal fractures are typically associated with root or cord deficit because the vertebral subluxation cannot be resisted by the incompetent superior articular process. Flexion of the superior vertebral body usually does not occur because the subluxing inferior articular process does not have to ride up an intact superior process. Inferior process fractures are typically at the base of the process and tend not to be associated with neurological deficit, because the neuroforamen is not narrowed. Typically there is no flexion with the anterior subluxation of the superior vertebral body. Inferior process may also be fractured vertically by the impaction of the superior process of the subjacent vertebra.6

A small apical fracture of the superior process without subluxation on dynamic lateral radiographs may be treated with an orthosis. Other articular process fractures are typically managed with posterior wiring and grafting, because an othosis including the halo vest may not maintain the reduction and prolonged traction may not be practical. Vertical split fracture of inferior process can successfully be treated conservatively leaving the rotational displacement uncorrected, provided impaction is adequately deep and there are no radicular and spinal symptoms.6 The ultimate clinical decision is not whether or not the injured spine is stable, but which treatment is best.