FLXfit Post Market Outcome Study Protocol

Inclusion Criteria: * Adult (age 18 - 70 years) patient (male or female) with the following conditions of the lumbar spine as confirmed by advanced imaging (CT or MRI), who is a candidate for primary spinal fusion procedure according to acceptable criteria for such medical conditions: * Degenerative disc disease * With up to Grade I spondylolisthesis * Failure of at least 6 month conservative treatment BMI \< 40. * Patient to approve no pregnancy during the 24 months of study and no participation in other studies in parallel to this one. Exclusion Criteria: * This device is not intended for cervical spine use. PI may exclude patient from study Contraindications include, but are not limited to: * Infection, local to the operative site * Signs of local inflammation, * Fever or leukocytosis, * Morbid obesity, * Pregnancy, * Mental illness, * Any other condition which would preclude the potential benefit of spinal implant surgery, such as the presence of tumors or congenital abnormalities, fracture local to the operating site, elevation of segmentation rate unexplained by other diseases, elevation of white blood count (WBC), or a marked left shift in the WBC differential count, * Suspected or documented allergy or intolerance to implant's materials, * Any case not described in the indications, * Any patient unwilling to cooperate with postoperative instructions. * These devices must not be used for pediatric cases, nor where the patient still has general skeletal growth. * Any case where the implant components selected for use would be too large or too small to achieve a successful result. * Any patient having inadequate tissue coverage over the operative site or inadequate bone stock or quality. * Any patient in which implant utilization would interfere with anatomical structures or expected physiological performance. * Prior fusion at the level to be treated.