Spinal Stabilization: Is Fusion the Right Way?

Abstract

This chapter discusses current concepts of spinal stabilization from the anatomic, biologic, and biomechanical point of view. Stability must be defined, understood, and referenced to the functional spinal unit. The functional spinal unit is defined as two adjacent vertebra with intervening soft tissues, disc, and articular structures that connect them (30). This functional unit must remain intact as it has forces applied to it creating various stresses and strains on its component. In order to maintain stability, its components move relative to each other. Each element in the construct has individual biomechanical and viscoelastic properties, but the unit as a whole has separate properties distinct from its component parts. Stability, therefore, may be defined as the ability of the functional spinal unit in which, under physiologic load, no abnormal strain or excessive motion occurs and the neural elements are protected. The proper word in this context should be equilibrium. Normal physiologic motion is part of the definition. When forces are excessive, the range of motion exceeds normal tolerance and instability results. Instability may be acute, such as in fractures or dislocations from a motor vehicle accident or chronic, such as the segmental lumbar instability that results with progressive degenerative disc and facet articular disease. It may produce pain, and it may result in neurologic injury. Scoliosis and kyphosis represent a specific type of instability with impairment of normal coronal and sagittal balance.