Pars Defects – Spondylolysis

History: young adult male with back pain. 

Pars defects – lateral radiograph of the lumbosacral spine reveals a pars interarticularis defect at L5-S1 (yellow arrow), with mild anterolisthesis of L5 on S1. This is also referred to as spondylolysis with spondylolisthesis.

This is a case of a pars interartcularis defect with anterolisthesis, also called spondylolysis with spondylolisthesis. These injuries are thought to be due to chronic repetitive stress at the pars interarticularis, and most commonly occur at the L5-S1 level. It is best demonstrated on oblique radiographs of the lumbar spine where discontinuity of the neck of the Scotty Dog is demonstrated, which you can read about here.

X-ray of a grade 4 spondylolisthesis at L5-S1 with spinal misalignment indicated (Photo credit: Wikipedia)

On the frontal view, spondylolysis with spondylolisthesis can be diagnosed by the inverted Napolean hat sign, which you can read about here.