The pars interarticularis, or pars for short, is the part of vertebra located between the inferior and superior articular processes of the facet joint. In the transverse plane

Transverse plane

The transverse plane is an imaginary plane that divides the body into superior and inferior parts. It is perpendicular to the coronal and sagittal planes....

, it lies between the lamina

Lamina of the vertebral arch

The laminæ are two broad plates, extending dorsally and medially from the pedicles, fusing to complete the roof of the vertebral arch.Their upper borders and the lower parts of their anterior surfaces are rough for the attachment of the ligamenta flava....

 and pedicle

Pedicle of vertebral arch

The pedicles are two short, thick processes, which project dorsally, one on either side, from the superior part of the vertebral body at the junction of its posterior and lateral surfaces. They connect the body of the spinal vertebra to the arch...

. In other words, in the axial view, it is the bony mass between the facets that is anterior to the lamina and posterior to the pedicle. It is abnormal in spondylolysis

Spondylolysis

Spondylolysis is a defect of a vertebra. More specifically it is defined as a defect in the pars interarticularis of the vertebral arch. The great majority of cases occur in the lowest of the lumbar vertebrae , but spondylolysis may also occur in the other lumbar vertebrae, as well as in the...

, either due to fracture or congenitally. Bilateral C2

Axis (anatomy)

In anatomy, the second cervical vertebra of the spine is named the axis or epistropheus.It forms the pivot upon which the first cervical vertebra , which carries the head, rotates....

 pars fractures are known as the hangman's fracture

Hangman's fracture

A Hangman's fracture is the colloquial name given to a fracture of both pedicles or pars interarticularis of the axis vertebra .The mechanism of the injury is forcible hyperextension of the head, usually with distraction of the neck. Traditionally this would occur during judicial hanging, when the...

.

On an anterior oblique radiograph of the lumbar spine, the pars is the neck

Neck

The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...

 of the imaginary Scottie dog;
the Scottie dog's eye is the pedicle, its hindlegs the spinous process, its nose the transverse process, its ear the superior articular facet and its forelegs the inferior articular facet.
Stress fractures of the pars interarticularis are known to be associated with playing volleyball, although the mechanism is somewhat unclear.