sentences:  The prosthesis is indicated for back and leg pain caused by central or lateral spinal stenosis, degenerative disease of the facets with instability, and grade 1 degenerative spondylolisthesis with objective evidence of neurological impairment.Patents related to facet replacement have been around since the 1980s; more intense research into artificial facet replacement as an effective and marketable prosthesis has been ongoing since the mid-2000s.Prominent researched options include