Effectiveness and Safety of the Facet Fixation (FFX®) Implant in the Treatment of Degenerative Lumbar Spinal Stenosis

Inclusion Criteria: * Age ≥ 50 years. * Radiographic confirmation of clinical symptoms of at least moderate degenerative spinal stenosis, of 1 to 3 adjacent segments in the L1-S1 region with the need for surgical decompression. * Radiographic confirmation of no translational instability in main segment as well as in adjacent segments (dynamic translational instability ≤3 mm); * Visual analogue scale (VAS) back pain score ≥ 50 mm (on a 100-mm scale). * Minimum of 3 months of conservative therapy without improvement of symptoms. * Mental \& physical ability of the subject to follow the protocol (i.e., compliance with time schedule \& treatment plan, able to fill in questionnaire \& to undergo further study procedures). * Personally signed and dated informed consent document prior to any study-related procedures indicating that the subject has been informed of all pertinent aspects of the clinical investigation. Exclusion Criteria: * Prior lumbar spine surgery. * Radiographically confirmed damage of a vertebral body (e.g., osteoporotic compression fracture or because of tumours), at any lumbar level. * Isthmic or degenerative spondylolisthesis (anterolisthesis; retrolisthesis ≥ grade II) or spondylolysis (pars fracture). * Degenerative lumbar scoliosis (Cobb angle \> 25°). * Adipositas (obesity); defined as a body mass index (BMI) \>40. * Pregnancy, or wish to get pregnant during the course of the study, or breastfeeding. * Known allergy or sensitivity to titanium, titanium alloys, or MRI contrast agents. * Active or chronic infection-systemic or local. * History of significant peripheral neuropathy. * Significant peripheral vascular disease (e.g., with diminished dorsalis pedis or posterior tibial pulses). * Paget disease, osteomalacia or other metabolic bone disorders. * Cauda equina syndrome. * Known or documented history of transmissible disease, including AIDS, HIV and active hepatitis. * More than 3 vertebral levels requiring surgery. * Disc herniation at any lumbar level requiring surgical intervention. * Known osteoporosis (bone mineral density, BMD \< 120 mg/cm3). * Chronically taking medications or any drug known to potentially interfere with bone/soft tissue healing (e.g., steroids), not including a Medrol (methylprednisolone) dose pack. * Fixed and complete motor, sensory, or reflex deficit. * Rheumatoid arthritis or other autoimmune diseases. * Active malignancy: a subject with a history of any invasive malignancy (except non-melanoma skin cancer) unless he/she has been treated with curative intent and there has been no clinical signs or symptoms of the malignancy for at least 5 years. Subjects with a primary bony tumour are excluded as well. * Subject with a history of substance abuse (e.g., recreational drugs, narcotics, or alcohol). * Bone destruction, demineralisation or any affection potentially affecting fixation of an implant. * Spondylodiscitis or spine tumour. * Currently seeking or receiving workman's compensation. * In active spinal litigation. * Subjects who participate(d) in another clinical trial (within the last 4 weeks) that might influence the safety \& effectiveness assessment of this trial. * Subjects who are lawfully kept in an institution. * Subject who, in the opinion of the investigator, will be inappropriate for inclusion in this clinical trial or who will not comply with requirements of the study. * Subject under supervision or legal guardianship, or judicial protection. * Subject deprived of liberty by judicial or administrative decision. * Subject not covered by a social security scheme.