A Clinical Study of the Dynesys(R) Spinal System

Inclusion Criteria: * Patients having degenerative spondylolisthesis or retrolisthesis (up to Grade 1) AND/OR Patients having lateral or central spinal stenosis or other stenosing lesion as diagnosed by radiculopathic signs, neurogenic claudication or imaging studies; * Candidate for single-level or contiguous two-level PLF between L1-S1; * Patients have a predominate component of leg rather than back symptoms; symptoms include pain, muscle weakness, and/or sensation abnormality as evidenced by patient history and diagnostic studies. * Patients may require decompression at the levels considered for treatment * Pre-operative leg pain score greater than or equal to 40 mm on a 100 mm Visual Analog Scale (VAS); * Leg pain must be unresponsive to conservative (non-surgical) management for minimum of 3 months; * Pre-operative Oswestry score greater than or equal to 30 indicating at least moderate disability; * Skeletally mature individual between ages 20 and 80; * Must be willing and able to comply with study requirements; including willing and able to sign a study-specific, IRB-approved informed consent form, complete necessary study paperwork and return for required follow-up visits. Exclusion Criteria: * Primary diagnosis of discogenic back pain at affected levels as evidenced by a larger back than leg pain component. In the event of multi-level pathology a discogram should be considered; * Patients with leg pain due to etiologies other than those listed above, such as trauma, peripheral vascular disease and neuropathy should be excluded; * Degenerative scoliosis greater than 10 degrees at the affected motion segment; * Supplemental interbody column support (e.g., bone graft, spacers or fusion cages) is planned at the affected level(s); * Greater than Grade I spondylolisthesis or retrolisthesis at the affected level(s); * Radiculopathic signs from more than two contiguous or two noncontiguous vertebral body segment(s); * Previous lumbar fusion attempt(s), previous total facetectomy or trauma at the affected level(s); * Gross obesity defined as exceeding ideal weight by greater than 40% (measurement details are given in Appendix A); * Active local or systemic infection; * Advanced osteoporosis as evidenced by plain film radiographs or history of fractures and confirmed by DEXA scan to confirm adequate bone density; * Receiving immunosuppressive or long-term steroid therapy; * Active hepatitis (viral or serum) or HIV positive, renal failure, systemic lupus erythematosus, or any other significant medical conditions which would substantially increase the risk of surgery; * Documented history of titanium alloy, PET or PCU allergy, or intolerance; * Active malignancy or other significant medical comorbidities; * Current chemical dependency or significant emotional and/or psychosocial disturbance that may impact treatment outcome or study participation as evidenced by three or more positive Waddell Signs; * Pregnancy; * Incarceration; * Severe muscular, neural or vascular diseases that endanger the spinal column; * Missing bone structures, due to severely deformed anatomy or congenital anomalies, which make good anchorage of the implant impossible; * All concomitant diseases that can jeopardize the functioning and success of the patient; * Vertebral fractures; * Treatment of the thoracic and cervical spine; * Severely deformed anatomy due to congenital anomalies; * Paralysis