Anatomic variability of 120 L5 spondylolytic defects.

Study Design Adult human osteologic specimens were assessed for spondylolytic defects and characterized. Objectives To characterize and determine the prevalence of spondylolytic defects in an osteological collection. Methods Lumbar vertebrae from the Hamann-Todd Osteological Collection at the Cleveland Museum of Natural History were examined. Digital images of specimens with L5 isthmic spondylolytic defects were analyzed, examining the distance of the pars defect in the sagittal plane in relation to the caudal aspect of the pedicle. Results There were 95 bilateral complete (BC), 16 unilateral incomplete (UI), 5 unilateral complete (UC), and 4 unilateral complete defects with an incomplete defect on the contralateral side. The mean distance of BC defects from the pedicle and inferior vertebral end plate was 4.03 mm and 4.88 mm, respectively. The mean distance of the defect from the inferior end plate on the left and right sides were 5.31 mm and 4.44 mm, respectively (p = 0.001, correlation coefficient = 0.56). The mean distance of UI and UC defects from the inferior end plate was 6.38 mm and 2.6 mm, respectively. Conclusion L5 spondylolytic defects were found in 3.87% of the sample. This large-scale description of isthmic spondylolytic defects reveals that significant variability exists in the location of the defect. The anatomic location of the pars defect likely plays a role in the development of L5 nerve root compression and radiculopathy in this clinical scenario. Classifying these defects might allow surgeons to better identify those patients who might benefit from fusion alone without posterior decompression.