Biomechanics of the Spine

Abstract

The field of modern biomechanics has deep historical roots from the ancient Egyptians, who documented the earliest accounts of spinal injury (2600-2200 BC), as well as from the ancient Hindus, who were noted for their treatment of spinal deformities (3500-1800 BC). Building on this foundation, the modern explosion of spinal instrumentation introduced the concept of internal fixation for spinal stabilization, further advancing the understanding of the mechanics of musculoskeletal motion. The spine is a complex mechanical structure complete with levers (vertebrae), pivots (facets and disks), passive restraints (ligaments), and actuators (muscles). Each of these elements merits special consideration and thus is addressed individually. Understanding actions and reactions, force vectors, related component vectors, and the movements and/or deformation that they cause allows the spine surgeon to apply fundamental physical principles to clinical practice. Kinematics is the application of these physical principles toward the study of the motion of rigid bodies. Knowledge of the principles and laws that are clinically relevant regarding spinal instrumentation is crucial to success. Clinical biomechanics requires the assessment of 3 key questions: 1) how do the components of the implant connect together, 2) how does the implant connect to the spine, and 3) how does the construct function biomechanically? The ability to apply basic biomechanical principles in the clinical arena provides a framework that the surgeon can use in the clinical decision-making process.