Radiological Characteristics of Low-Grade Lytic Spondylolisthesis: Similarity to Dysplastic Spondylolisthesis

STUDY DESIGN: Retrospective case-control study. PURPOSE: This study aimed to analyze the etiology of low-grade lytic spondylolisthesis based on the radiologic features of the vertebra. OVERVIEW OF LITERATURE: According to the Marchetti-Bartolozzi classification scheme, high-grade lytic spondylolisthesis (Meyerding grade 3–5) is classified as dysplastic. However, determination of the etiology for low-grade lytic spondylolisthesis as developmental or traumatic remains controversial. METHODS: Patients admitted and treated for one-level (L4/5 or L5/S1) low-grade spondylolisthesis were included in the study. A total of 135 patients were divided into the degenerative or lytic spondylolisthesis groups according to their condition (81 patients [degenerative group] vs. 54 patients [lytic group]). To assess the level of similarity in the radiological findings between low-grade lytic spondylolisthesis and dysplastic spondylolisthesis, the pedicle diameters and vertebral heights of the L4 and L5 vertebrae were measured on computed tomography images. Measurements were then converted to each vertebra’s ratio to reduce confounding factors among individuals. RESULTS: The affected vertebra had a smaller sagittal pedicle diameter/transverse pedicle diameter ratio in the low-grade lytic spondylolisthesis group compared to the degenerative group, and the posterior vertebral height/anterior vertebral height ratio of L5 was smaller in the L5/S1 lytic spondylolisthesis group compared to the degenerative spondylolisthesis group. CONCLUSIONS: Low-grade lytic spondylolisthesis and dysplastic spondylolisthesis demonstrated similar radiological findings. Hence, surgeons should be attentive to the morphology of the vertebral body and posterior column during preoperative planning for the treatment of low-grade lytic spondylolisthesis.