Radiography of the lumbar spine is limited by its inability to detect stress reactions in the pars interarticularis that have not progressed to complete fracture.

• On lateral views, which are most sensitive, spondylolysis appears as a linear lucency in the pars interarticularis.
• The lucency seen in the pars interarticularis on oblique radiographs (which are most specific) has been described by Lachapelle to form the appearance of a collar on the neck of the Scottie dog.  

     If plain radiographs are negative or inconclusive, patients can be referred for MRI, CT, or single-photon emission computed tomography (SPECT) bone scintigraphy.