There is little known about the association of ligament injuries with odontoid process fractures. They recommended operative treatment for older patients, in fractures with posterior displacement and when the displacement of the fracture is greater than 4–6 mm. They looked at the primary outcome measure of bone fusion after operative (either C1-C2 fusion or anterior screw fixation) versus non-operative management (halo vest immobilisation or cervical collar). A meta-analysis was performed of operative versus non-operative management of Anderson and D’Alonzo type II odontoid process fractures by Nourbakhsh et al. Opinion is divided as to whether these fractures should be treated non-operatively (halo device or cervical collar) or operatively (anterior screw fixation or posterior C1-C2 fusion). 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. Sixty percent of spinal injuries affect the cervical spine and 9–20% of cervical spine injuries involve the axis (C2). This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 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. These differences did not reach statistical significance ( p > 0.05).ĭiscussion: 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. 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. * Corresponding author: We wished to investigate the role of the cervical ligaments in maintaining atlantoaxial stability after fracture of the odontoid process. St George’s, Healthcare NHS Trust, Tooting, London St George’s, University of London, Tooting, London Oliver Richard Boughton 1 ,2 *, Jason Bernard 2 and Matthew Szarko 1
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