UNILATERAL LOCKING OF CERVICAL FACET JOIN TS - FREQUENCY AND SIGNIFICANCE OF RADIOGRAPHICAL SIGNS

Unilateral locking of cervical facet joints is often misdiagnosed and inadequately treated, because it is not readily detected on plain radi ographs. Primary radiographs of 17 patients were analysed to evaluate radiographical signs with reference to frequency and significance. Dir ect signs of locking were present in no more than 53% of cases. Of the se, 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 i t carries less diagnostic weight. While present in all cases, anteroli sthesis is only diagnostic if additional oblique views show evidence o f lateralized cervical anterolisthesis. Clearly less reliable indirect signs included: the bow tie sign (29.4%), dehiscence of the spinous p rocesses (23.5%), differences in the sagittal diameters of the vertebr al 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 o n a.-p. projections. Those detectable in axial views are irrelevant to locking, as are empty facets. If more than one indirect sign is prese nt and if unilateral locking is suspected but cannot be established un equivocally even on additional oblique views, computed tomography is i ndicated, because reduction continues to be the first step in the mana gement of fresh injuries.