The current management of type II odontoid process fractures is controversial. Type II odontoid process fractures have a one-year mortality rate of 18% in patients over 65 years of age. Type II odontoid process fractures are fractures through the waist of the odontoid process, between the level of the transverse ligament and C2 vertebral body. Anderson and D’Alonzo classified odontoid process fractures into three types in 1974. Odontoid process fractures are the most common fractures of the axis. They can be devastating injuries with associated neurological injury in 2–27% of patients and the acute mortality rate is 2.4%. There is a bimodal distribution with low-energy fractures in the elderly and high-energy fractures in young patients. Introduction Sixty percent of spinal injuries affect the cervical spine and 9–20% of cervical spine injuries involve the axis (C2). Key words: Odontoid process, Odontoid process fracture, Ligament, Biomechanical, Cadaveric. If the MRI determines that there is associated ligament injury it is likely that the fracture is unstable and we would suggest operative management. We suggest magnetic resonance imaging (MRI) of the soft tissues in the acute setting of a minimally displaced odontoid process fracture to plan management of the injury. Discussion: We have found that the odontoid process itself may account for up to 37% of the stiffness of the C1-C2 complex and that soft tissue structures account for further resistance to movement. These differences did not reach statistical significance ( p > 0.05). The mean Young’s modulus in anterior displacement decreased proportionally (compared to the previous dissection) by the following percentages when the structures were divided: facet joint capsules (bilateral) 16%, ligamentum flavum 27%, anterior longitudinal ligament 10%. Results: The mean Young’s modulus in anterior displacement decreased by 37% when the odontoid process was fractured ( p = 0.038, 95% confidence interval 0.04–1.07). Biomechanical analysis of stiffness, expressed as Young’s modulus, was performed under right rotation, left rotation and anterior displacement. The C1 and C2 blocks were mounted and biomechanical analysis was performed to test the stability of the C1-C2 complex after cutting the odontoid process to create an Anderson and D’Alonzo type II fracture then successive division of the atlantoaxial ligaments. Methods: We dissected eight fresh-frozen cadaveric cervical spines to prepare the C1 and C2 vertebrae for biomechanical analysis. St George’s, University of London, Tooting, London SW17 0RE, UK St George’s, Healthcare NHS Trust, Tooting, London SW17 0RE, UK Received 6 March 2015, Accepted 29 April 2015, Published online 15 June 2015 Abstract – Aims: We wished to investigate the role of the cervical ligaments in maintaining atlantoaxial stability after fracture of the odontoid process. A biomechanical, cadaveric study Oliver Richard Boughton1,2,*, Jason Bernard2, and Matthew Szarko1 1 2 Odontoid process fractures: the role of the ligaments in maintaining stability. SICOT J 2015, 1, 11 Ó The Authors, published by EDP Sciences, 2015 DOI: 10.1051/sicotj/2015011 Available online at: OPEN

Odontoid processes