Nerve and Nerve Root Biomechanics

Together, the relationship between the mechanical response of neural tissues and the related mechanisms of injury provide a foundation for defining relevant thresholds for injury. The nerves and nerve roots are biologic structures with specific and important functions, and whose response to mechanical loading can have immediate, long-lasting and widespread consequences. In particular, when nerves or nerve roots are mechanically loaded beyond their mechanical tolerance for injury, motor and/or sensory deficits can result. The severity and persistence of the symptoms are modulated by the profile of the mechanical insult. In this chapter, the relevant anatomy, and structure are reviewed in the context of biomechanical data describing the mechanical behavior of nerves and nerve roots. While both nerves and nerve roots have components of their anatomic organization that protect the axons of their neurons, there are distinct differences in their structure and composition. These variations contribute to differences in their mechanical response to loading owing to their strength and stiffness. However, both tissues are time-dependent and exhibit viscoelastic behavior. These time-dependent characteristics in mechanical responses imply that, in addition to the magnitude of force or deformation, the rate of loading and duration of applied mechanical insult can modulate physiologic outcomes associated with mechanical loading to these tissues. This chapter reviews all of these concepts in the context of biomechanics and physiologic outcomes. In addition, a review of current work studying nerve and nerve root loading in animal models is provided in order to relate these outcomes to clinical symptoms.