The purpose of this retrospective clinical evaluation is to compare VEO® single or multilevel results to XLIF® single or multilevel results relative to the safety endpoints. This study will collect retrospective data on subjects who were treated with VEO® and XLIF® at least 3 months prior to the initiation of this study. Given that fusion generally takes at least 6 months to determine, the aim of this study is not to determine fusion but to consider the short-term (out to 6 months) reported adverse events between the two cohorts.