The articular processes are projections from the junction of the pedicle and the lamina, bound superiorly and inferiorly by their smooth articulating facets. Fusion of the superior and inferior articular processes forms the articular pillar, or articular mass. The apposing articular facets form the apophyseal joint (synovial joint) that has a postero-inferior inclination of approximately 35º.
Most articular pillar fractures are due to a hyperextension rotation mechanism of injury. Simultaneous hyperextension and rotation, produces axial loading on the side of rotation. This axial loading force occurs in a sagittal plane along the cervical articular masses. The force is initially transmitted first to the superior the inferior articular process of the articular mass, then to the tips of the spinous process, and finally to the lamina and the pedicle. The result is an oblique or vertical fracture through the articular pillar.
Due to the difficulties of radiographic visualization of the articular pillars and laminae on routine AP, oblique and lateral views of the cervical spine, isolated articular pillar fractures may be missed. Incongruity of the lateral margin of the pillar or a radiolucent line through the pillar on an AP projection is suspicious for this type of fracture. On the lateral radiograph, the “double outline sign” has been described and is formed by the superimposition of the normal articular mass over the smaller image of the collapsed pillar. CT assists in identifying the fracture, determining fracture extension into adjacent structures, and assessing for the presence of a free-floating pillar fragment. MRI is used to assess the integrity of the ligamentous structures.
Case courtesy of Associate Professor Pramit Phal.