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- Spondylolysis is a unilateral or bilateral defect in the pars interarticularis portion of the vertebrae.
- It is a stress fracture mostly seen in the lumbar vertebrae, and most commonly L5.
- Pain is relieved with rest and worsened by lateral bending or extension (NOTE: most back pain is worsened by flexion).
- If neurologic symptoms and/or radiculopathy are present, an alternative diagnosis should be considered, because they are rarely associated with spondylolysis.
- Diagnostic imaging should start with plain radiographs with added oblique views.
- Classically, oblique views show the Scotty dog sign with a crack on the dog’s neck/collar, the pars.
http://www.gentili.net/signs/images/400/spinescottyparsdefectdrawing.JPG
The Scotty dog’s head (superior articular facet), nose (transverse process), eye (pedicle), neck (pars interarticularis), and body (lamina) should be easily identified on the oblique radiograph.