Zygapophyseal joints

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Bones, ligaments and joints of the thoracic and lumbar spines.

The zygapophyseal joints, also called facet joints, are joints of the vertebral column that are classified as joints of the vertebral arches. More specifically, they are plane synovial joints between the superior and inferior articular processes on adjoining vertebrae.

The zygapophyseal joints extend between the axis (C2) and the first sacral vertebra (S1). Each joint is enclosed by a thin and loose fibrous capsule that attaches to the margins of the articular facets, which are covered in hyaline cartilage. The zygapophyseal joints are stabilized by accessory ligaments of the vertebral column, which firmly connect adjacent laminae, transverse processes, and spinous processes.

The size, shape and positioning of the articulating surfaces and the resulting joint planes depend on the region of the spine. The orientation of the articular surfaces, together with the size of intervertebral discs, determine the type and range of movements possible at each region.

In the cervical region, the superior articular facets are superoposteriorly placed while the corresponding inferior facets are anteroinferiorly oriented. Thus, the joint planes slope inferiorly from anterior to posterior, permitting flexion and extension.

In the thoracic region of the spine, the superior articular facets largely project posteriorly whereas inferior facets are mainly anteriorly positioned. The joint planes are therefore vertically placed, restricting flexion and extension, but allow for rotation movement.

The articular surfaces of the lumbar region are sagitally oriented with the superior facet facing posteromedially and the inferior facet facing  anterolaterally. The articular processes are interlocked, permitting mainly limited flexion and extension movements.