LUMBAR SPONDYLOLYSIS WITHOUT SPONDYLOLISTHESIS - RECOGNITION OF ISOLATED POSTERIOR ELEMENT SUBLUXATION ON SAGITTAL MR

PURPOSE: To document the occurrence of isolated dorsal subluxation of posterior elements in cases of lumbar spondylolysis without spondyloli sthesis both quantitatively (using spinal canal measurements) and qual itatively (by visual inspection) on sagittal MR images. METHODS: Retro spective analysis identified 63 patients with lumbar spondylolysis (co nfirmed by CT or conventional radiography) who had undergone MR imagin g. From these we identified 12 patients with pars interarticularis def ects but no evidence of spondylolisthesis. Measurements of anteroposte rior spinal canal diameters were performed in these 12 patients to asc ertain whether the sagittal canal diameter at the level of the spondyl olysis exceeded the normal range as determined from 100 control subjec ts, RESULTS: In 9 of 12 patients the spinal canal was abnormally widen ed at the level of the spondylolysis because of dorsal subluxation of posterior elements. In 5 of these patients, the subluxation was readil y visible on midline sagittal MR images. In 4 patients, spinal canal m easurements were necessary to document this phenomenon. CONCLUSION: In the majority of patients with spondylolysis but without spondylolisth esis, sagittal MR images can show isolated dorsal subluxation of poste rior spinal elements.