Biomechanics Research in Traumatic Spinal Injuries: “Everything Should Be Kept as Simple as Possible, but no Simpler”

Abstract

The vast majority of the knowledge in spinal biomechanics available today is derived from studies on cadaveric specimens (2). Nevertheless, every time a researcher intends to defend a position on the basis of biomechanical data acquired from such types of experiments, a well known set of criticisms arises. Several limiting factors for the validity of the results obtained in such research scenarios are usually mentioned: the room temperature and humidity (which, by differing from the in-vivo conditions, are thought to alter the stiffness of the constructs), and the influence of preservation processes (such as cooling or freezing) on the viscoelastic properties of the cadaveric tissues and the role of surrounding structures other than bone and joints (such as muscles and tendons), which provide a dynamic biomechanical effect in the in vivo condition (1). Moreover, although cadaveric models are useful for quantifying the results proportioned by different surgical strategies (such as the degree of spinal canal decompression provided by a full laminectomy in comparison to bilateral decompression through a hemilaminectomy) as well as for testing the biomechanical properties of different stabilization techniques, they are completely unsuitable for studying how instability affects the physiology of the spinal cord after traumatic injuries, and, therefore, of limited application in the field of spinal cord injury research. Although the majority of neurosurgeons do not find any major technical difficulty when facing the task of providing stabilization and fusion for a patient with a thoracolumbar fracture, inducing stabilization and fusion of adjacent vertebral segments in smallanimal models has always been a great challenge for laboratory researchers. The problem involves, besides other factors, the lack of appropriate instrumentation (such as screws, rods or wires) specifically designed to address the peculiarities of the anatomy of such animals. In fact, it would not be unfair to state that the difficulties associated with the several different methods that have already been tried as attempts to achieve stabilization of the spinal column in experimental models have significantly limited the amount of in-vivo research on the biomechanical variables involved in spinal cord injury as well as on the associated effects of such injuries to the normal physiology of the spinal cord (7). Although transpedicular screws and rods would be theoretically ideal, they are in practice not feasible due to the small size of rats’