Segmental instability of the lumbar spine can be defin ed as anabnormal motion between one or more vertebrae. This motion may causemechanical irritation of the intraspinal nervous tissue, thus, inducing painand/or neurological deficits.The clinical presentation of lumbar instabilityis characterized by chronic local low back pain. Mechanical lumbarinstability could be diagnosed radiologically by neutral radiograph eitherby moderate disc degeneration with mild narrowed disc space associatedwith osteoscelerosis or osteophytosis, presence of traction spur va cumphenomenon. It also could be diagnosed by functional ra diographs, CT orfunctional CT and M.R.I .Treatment either nonoperative as weightreduction, exercise, physiotherapy and medication or operative treatmentwhich is indicated in failed nonoperative treatment or capacitatingmanifestation by fusion.