Type 2 Dens Fracture
Updated: Apr 1, 2023
93 F with trauma from a fall. Neck pain • Xray of the Week
Figure 1. What is the important finding on this CT scan.
Figure 2. CT scan of Type 2 dens fracture. Red arrow is pointing to the fracture line at the base of the dens.
Figure 3. Anderson and D’Alonzo dens fracture classification system. Diagram by Neal Joshi.
Type I: Avulsion fracture of the tip of the dens, usually stable.
Type II: Fracture of the base of the dens, usually unstable.
Type III: Fracture involving the body of C2, usually stable.
The odontoid process, otherwise known as the dens, is a bony projection from C2 (axis). The most commonly utilized classification system for fracture of the odontoid process is the Anderson and D’Alonzo system, which identifies three types of fractures (1) (Fig. 3). C2 fractures can be classified into Odontoid and Hangman’s and most common C2 fractures are the type II odontoid fractures. These can pose issues due to a greater than 50% rate of non-union. These fractures occur during hyperextention and hyperflexion injuries to the cervical spine (falls, motor vehicle accidents). Type II odontoid fractures are most common and can occur at any age but mostly in the elderly due to increase risk of falls and decreased bone mineral density.
A type I odontoid fracture is described as an avulsion fracture of the tip of the dens. A type II fracture is one that occurs at the base of the dens and is considered unstable due to high rates of non-union. Type III fractures involve the body of C2 and may even involve the facets (Fig. 2). For odontoid fractures, radiographs can be very useful, but a negative result does not exclude a fracture. Therefore, if there is clinical suspicion a CT scan should be obtained (Fig. 1) (3). Non-contrast MRI is useful for viewing ligamentous structures which may be injured. In non-displaced type II odontoid fractures for example, the transverse ligament needs to be intact for certain surgical procedures and would require an MRI for evaluation (4). Complications of odontoid fractures include malunion, non-union, and pseudoarthrosis. Type II fractures are unstable and have a higher rate of nonunion mainly due to the lower surface area of the fractured bone compared to type III fractures. Radiological parameters such as displacement and angulation are important and can determine surgical planning of type II odontoid fractures. Using CT, it was determined that diagnostic classification of displacements and angulation had good observer reliability using review systems and tools in image processing software (5).
Figure 4. Fluoroscopic guided placement of an odontoid screw.
For treatment of type I and III odontoid fractures, external fixation via a rigid cervical collar may be sufficient. For type II fractures, surgical fixation is usually required if there is greater than 4-5 mm of displacement due to high risk for non-union (3) (Fig. 4).
Korres DS, Chytas DG, Markatos KN, Efstathopoulos NE, Nikolaou VS. The "challenging" fractures of the odontoid process: a review of the classification schemes. Eur J Orthop Surg Traumatol. 2017;27(4):469-475. doi:10.1007/s00590-016-1895-3
Montemurro N, Perrini P, Mangini V, Galli M, Papini A. The Y-shaped trabecular bone structure in the odontoid process of the axis: a CT scan study in 54 healthy subjects and biomechanical considerations [published online ahead of print, 2019 Feb 1]. J Neurosurg Spine. 2019;1-8. doi:10.3171/2018.9.SPINE18396
Chutkan NB, King AG, Harris MB. Odontoid Fractures: Evaluation and Management. J Am Acad Orthop Surg. 1997;5(4):199-204. doi:10.5435/00124635-199707000-00003
Löhrer L, Raschke MJ, Thiesen D, et al. Current concepts in the treatment of Anderson Type II odontoid fractures in the elderly in Germany, Austria and Switzerland. Injury. 2012;43(4):462-469. doi:10.1016/j.injury.2011.09.025
Karamian BA, Liu N, Ajiboye RM, Cheng I, Hu SS, Wood KB. Reliability of radiological measurements of type 2 odontoid fracture. Spine J. 2019;19(8):1324-1330. doi:10.1016/j.spinee.2019.04.020
Neal Joshi is a medical student and aspiring diagnostic radiologist at Rowan University School of Osteopathic Medicine in New Jersey. Prior to medical school, he did research with mouse models for Parkinson’s disease and L-DOPA induced dyskinesias. He also did an internship at Kessler Institute for Rehabilitation in a stroke lab analyzing MR images in ischemic stroke patients with hemispatial neglect. During his time at Rowan, he did research with animal models for traumatic brain injury with an emphasis on electrophysiology of neurons. He graduated from William Paterson University where he completed his studies in biology and biopsychology. Apart from medical school, Neal loves to read, skateboard, go on hikes, and spend time with his friends.
Update July 2022: Dr. Joshi is a Radiology Resident at Thomas Jefferson University in Philadelphia.
Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who Dr. Rice has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson.
Follow Dr. Rice on Twitter @KevinRiceMD