Craniovertebral Junction Instability and Mechanisms of Injury

The chapter deals with the concept of post-traumatic instability of the craniovertebral junction (CVJ). Comprehension of the normal anatomy and native biomechanics of the CVJ is essential to recognize the post-traumatic injuries and potential instability which may result into catastrophic neurological complication. Biomechanically, the cranio-cervical junction supports the weight of the head and represents one of the most mobile segment of the spine. Physiological range of motion must be understood with approximately 25–30° of flexion-extension at C0-C1 and C1-C2 and around 35–40° of rotation each side at C1-C2. The stability is ensured by both soft tissues including joint capsules, membranes and ligaments, and sub-occipital muscles with the key-role played by the transverse ligament, and also bony structures including lateral masses of C1 and C2 and the odontoid process. According to the mechanisms of injury (compression, distraction, translation, rotation), it is possible to categorize specific injury patterns that is helpful to assess the stability of the injury and may influence the treatment option. CT-scan is very effective to detect injuries of bony structures and look for abnormal displacements whereas MRI is useful to objective and confirm the presence of ligamentous lesions.