Total Facet Arthroplasty System®(TFAS®) Clinical Trial

Inclusion Criteria: * Degenerative spinal stenosis, central or lateral, at spinal levels L3-L4 or L4-L5 * Skeletally mature male or female between the ages of 50 and 85 years of age inclusive * No greater than Grade I degenerative spondylolisthesis at the index level * Persistent leg symptoms,including pain, numbness, burning or tingling for a minimum duration of six months * Operative candidates with no more than three levels of degenerative lumbar spinal stenosis requiring decompression * Failed to respond to non-operative treatment modalities for a minimum duration of six months Exclusion Criteria: * Male or female less than 50 or greater than 85 years old Grade 2 or higher spondylolisthesis or any retrolisthesis at the index level * More than 3 vertebral levels of degenerative spinal stenosis requiring decompression * More than 1 vertebral level of degenerative spinal stenosis requiring instrumentation * Not available for long term follow-up and interval visits * Prior or concurrently planned lumbar fusion or disc replacement at any level of the lumbar spine * Two or more previous surgeries to the lumbar spine at the same level to be implanted * Is being treated with other devices for the same disorder (e.g. pain control devices) * Active systemic infection or infection at the operating site * Osteoporosis * Known sensitivity to device materials * Has an immunosuppressive disorder * Has a medical condition that may interfere with clinical evaluations * Is obese defined by a patient body mass index greater than 40 * Has significant scoliosis (Cobb \>25°) * Is pregnant or planning to become pregnant within the proposed three year investigation