Lumbar Spinal Instability: An Updated Rewiew

According to the American Academy of Orthopaedic Surgeons, instability was defined as an abnormal response to applied loads, characterized by movement in the motion segment beyond normal constraints in 1989. Segmental instability has been defined as occurring in patients with low back problems and whose clinical status is unstable, with symptoms fluctuating between mild and severe symptoms in response to even minor provocations. The validity of these clinical definitions has not been demonstrated. Frymoyer et al defined segmental instability as “a condition where there is loss of spinal stiffness, such that normally tolerated external loads will result in pain” [1,2].