pars interarticularis

{{Short description|Part of the vertebra}}

Image:Gray84.png

The pars interarticularis, or pars for short, is the part of a vertebra located between the inferior and superior articular processes of the facet joint.{{cite book |author=WebMD |chapter=spondylolysis |chapter-url=https://books.google.com/books?id=t8UfI3BH78wC&pg=PA399 |page=399 |year=2009 |title=Webster's New World Medical Dictionary |edition=3rd |publisher=Houghton Mifflin Harcourt |isbn=978-0-544-18897-6}}{{cite web |last1=Mansfield |first1=J. T. |last2=Wroten |first2=Michael |title=Pars Interarticularis Defect |url=https://www.ncbi.nlm.nih.gov/books/NBK538292/#:~:text=of%20young%20athletes.-,The%20pars%20interarticularis%20(pars)%20lies%20between%20the%20superior%20and%20inferior,and%20one%20inferior%2C%20zygapophyseal%20joints. |website=StatPearls |publisher=StatPearls Publishing |access-date=15 October 2023 |date=2023}}

In the transverse plane, it lies between the lamina and pedicle. 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, either due to fracture or congenitally. Bilateral C2 pars fractures are known as a variant of the hangman's fracture.

On an anterior oblique radiograph of the lumbar spine, the pars is the neck of the imaginary Scottie dog; the Scottie dog's eye is the pedicle,{{cite journal |vauthors=Macleod S, Hendry G |title=Congenital absence of a lumbar pedicle. A case report and a review of the literature |journal=Pediatr Radiol |volume=12 |issue=4 |pages=207–10 |year=1982 |doi=10.1007/BF00999313 |pmid=6752854}} its hindlegs the spinous process, its nose the transverse process, its ear the superior articular facet and its forelegs the inferior articular facet.Capobianco JD. OMM Board Review. Available at: [https://archive.today/20121203045037/http://www.md-do.org/NewOMMBoard%20Review02-REV.htm www.md-do.org]. Accessed on April 9, 2007.{{dl|date=January 2020}}

Stress fractures of the pars interarticularis are known to be associated with playing sports such as volleyball, although the mechanism is somewhat unclear.{{EMedicine|article|309106|Physical Medicine and Rehabilitation for Stress Fractures}} Patients with spina bifida occulta have an increased risk for spondylolysis.{{EMedicine|article|395916|Physical Spondylolysis Imaging}}