SPONGIT: Comparison of Two Surgical Approaches in the Treatment of Degenerative Spondylolysthesis

Inclusion Criteria: * Adults aged less than 75, * Having been informed about clinical trial objectives and risk, * Covered by health insurance system, * Suffering from degenerative spondylolisthesis (whatever the grade and intervertebral disc height) needing one-level surgical fusion due to either invalidating lombalgia/radiculalgia despite 6-month optimal medical treatment and/or motor neurological symptoms. Exclusion Criteria: * Previous lumbar fusion, * Previous spine traumatism, * Presence of at least one major contraindication to surgery and/or general anaesthesia (ie, non controlled coagulopathy, active infection, or serious underlying disease, auto-immune affection). * Presence of at least one contraindication to either TLIF or GPLI, * Severe radiological osteoporosis. * Active cancer at time of inclusion into the study. * Unlikely to comply with the requirements of the study and/or to complete the study for psychological, social, familial or geographical reasons. * Under any administrative or legal supervision.