[Unilateral locking of cervical facet joints. Frequency and value of roentgenologic signs].

Unilateral locking of cervical facet joints is often misdiagnosed and inadequately treated, because it is not readily detected on plain radiographs. Primary radiographs of 17 patients were analysed to evaluate radiographical signs with reference to frequency and significance. Direct signs of locking were present in no more than 53% of cases. Of these, an abrupt change in laminar space width, seen in 88.2%, proved to be the most reliable sign. Displacement of the spinous processes above and below the lesion was found in the same percentage of cases, but it carries less diagnostic weight. While present in all cases, anterolisthesis is only diagnostic if additional oblique views show evidence of lateralized cervical anterolisthesis. Clearly less reliable indirect signs included: the bow tie sign (29.4%), dehiscence of the spinous processes (23.5%), differences in the sagittal diameters of the vertebral bodies above and below the lesion (35.2%), double facet contour (47%) and tilting of the cranial segment of the cervical spine away from the locked facets (58.8%). Abnormalities of disc shape were not seen on a.-p. projections. Those detectable in axial views are irrelevant to locking, as are empty facets. If more than one indirect sign is present and if unilateral locking is suspected but cannot be established unequivocally even on additional oblique views, computed tomography is indicated, because reduction continues to be the first step in the management of fresh injuries.