[Degenerative instability of the lumbar spine].

Degenerative instability is difficult to define, diagnose, and treat. Diagnosis and treatment of degenerative instability are based on the biomechanical stability of the functional spinal unit as well as on the pathologic diagnosis of the disease. Recent advancements in biomechanical studies on the functional spinal unit and radiological diagnostic methods have introduced new diagnostic criteria. In this review, biomechanical stability of the functional spinal unit, changes in stability associated with degeneration and diagnosis, and treatment of degenerative instability are discussed..