Biomechanics of the Spine II

Abstract

Spine biomechanics represents a traditional area of research by orthopaedists, neurosurgeons, bioengineers and physicists. Working in an emergency setting and managing spinal traumas every day we began a study on extended literature devoted to biomechanics of the spine, to see beyond the usual static evaluation of neuroimaging patterns. After our earlier paper on biomechanics of the spine16, we have reviewed and broadened some topics such as the role of the ligaments and introduced the main mechanisms of primary spinal traumas and deformations. The spine is a multiarticular complex structure controlled by the muscles whose correct function presupposes its stability. Several “stability factors” ensure spinal stability and correct movements. A number of biomechanical studies analysed the contribution of individual bony and soft spinal elements to stability and the effects of traumas. Several theories have been derived from these studies to account for the distribution of loads and vector forces, including failure-producing loads, among the components of functional spinal units (FSU). Holdsworth's initial two column concept, the three column models by Louis and Denis up to most recent four column theory by Cartolari all represent evolutions in assessing the distribution of loads and the presence and degree of instability in spinal traumas. Whether acute or chronic spinal instability means a partial or complete loss of one or both functions of the spine: load-bearing and cord protection. The diagnosis of spinal instability is crucial to establish the most appropriate strategy of management, namely in acute conditions. Biomechanical concepts are fundamental to understand the factors deciding the type, location and extent of spinal traumas, possible instability and the primary mechanism of the main types of injuries.