A radiologic sign in spondylolisthesis.

Isolated lateral deviation and rotation of a spinous process seen in anteroposterior radiographs of the lumbar spine seems to be associated with pathology in the pars interarticularis. This radiologic sign was present in 57 patients with spondylolisthesis and five cases of spondylolysis. It was absent in 165 patients with radiologically normal pars interarticularis. There were no false positives, but the sign could not be demonstrated in the radiographs of four cases of spondylolisthesis and one of spondylolysis. An explanation of the mechanism of this sign is offered.