Biomechanics of the Craniovertebral Junction

The craniovertebral junction (CVJ) consists of the occiput and the first two cervical vertebrae, and functions as an articulation point capable of complex motions distinct from the remainder of the spinal column. These unique features make the CVJ more mobile than any of the other joints in the cervical spinal column, and important biomechanical properties must be understood in order to properly accommodate instrumentation to stabilize the spine after trauma, neoplasm, or degenerative disease. Each joint (Occiput-C1 and C1-C2) has its own unique biomechanical properties; at the occiput-C1 joint, bony structures are most responsible for stability and motion, while at the C1-C2 joint, ligamentous structures provide greater stability and motion compared to the bony elements. A fundamental understanding of the biomechanics of the CVJ is important for spinal surgeons, physical therapists, and biomechanical engineers. In this chapter, we will review basic biomechanical and physiological properties of the CVJ, and then discuss common changes in biomechanics that occur via trauma and degenerative disease. This will provide the foundation for a brief discussion on techniques for the fixation of the craniovertebral junction.