What defines a bifacet dislocation?

A bifacet dislocation is characterized by a complete anterior dislocation of the cervical vertebrae, specifically involving both facets of the affected segment. The crucial detail is that this dislocation results in the anterior displacement of the vertebra, exceeding 50% of the anteroposterior (AP) diameter of the involved vertebra. This degree of displacement is significant as it leads to instability in the cervical spine and can often be associated with neurological deficits due to potential spinal cord compression.

In this context, the other choices describe scenarios that do not meet the criteria for a bifacet dislocation. A complete anterior dislocation with less than 50% of AP body diameter is insufficient for this classification. A partial dislocation, as outlined in one of the options, does not signify a bifacet dislocation, which requires complete dislocation. Furthermore, a stable position without neurological symptoms would not correspond to a bifacet dislocation, which is inherently unstable and poses risks for neurological injury. Thus, the correct choice precisely describes the mechanism and nature of a bifacet dislocation.