What Is the Pars Interarticularis?

A facet joint is a pair of bony masses, looking much like a yoke, interlocking with articular processes that together connect vertebra to vertebra along the spinal column. The pars interarticularis in the cervical portion of vertebrae are articular superior and inferior pillars that arise out of the junction of the pedicle in front and anterior to the lamina behind. Locking with facet joints, they form what are called the spinal motion segments and are responsible for keeping the vertebrae stable and guiding and limiting the motion of the vertebrae. Congenital abnormalities of the pars interarticularis can bring on problems and injuries from dislocations, fractures, degenerations, or surgeries can cause severe conditions.

Adolescent athletes can suffer from lower back pain caused by unilateral or bilateral stress or fatigue fractures of the bridge between upper or lower pars interarticularis. It has been said that as many as 30% of adolescent athletes have this injury revealed when it reaches a level known as spondylolsis. Intense training and repeated small traumas received at an early age, before the skeletal structure is fully formed, are believed to be the root of the fractures.

Spondylolsis is termed a defect of a vertebra and thought to result from continuous overtraining. Football linemen often suffer from it due to bending over at the line and hard contact while the vertebra are extended. In persistent cases of spondylolsis, the condition can progress to spondylolisthesis, where one vertebra slips forward in relation to the adjacent vertebra. Spondylolisthesis happens in adolescents, as it is harder for this kind of slip to happen in a fully formed skeleton.

The pars articularis may become so degenerated due to congenital disc degenerative disease that they break apart. This is called lysis, or prolapse, of the pars interarticularis. Yet, it has been noted in studies of those with slipped discs that enlarged central spinal canals — as in those who have a pars interarticularis defect — may be a protection from spinal cord damages due to the disc lesions.

Surgery for spondylolisthesis of the pars interarticularis is often advised for continuous pain. For those who do require surgery, it is a fusion spinal surgery. Most other pars interarticularis defects, fractures, or conditions can be treated with more conservative measures. Lessons in biomechanics, rest, ice to reduce inflammation, gentler exercises, and physical therapies must replace the sport for several weeks. It may be necessary to give up any sport requiring hyperextensions of vertebrae.