Article 125 © Argospine and Springer-Verlag France 2011 - DOI 10.1007/s12240-011-0016-8 - ArgoSpine NEWS&JOURNAL - quarterly september 2011 - Vol. 23 - N°3 Type D fractures of the odontoid process ARTICLE D.S. Korres 1* , A.F. Mavrogenis 2 , P. Gratsias 2 , M.J. Posantzis 3 , E.A Giannakopoulos 1 , N.E Efstathopoulos 4 1 Third Department of Orthopaedics, KAT Hospital, Athens, Greece 2 First Department of Orthopaedics, KAT Hospital, Athens, Greece 3 Sixth Department of Orthopaedics, KAT Hospital, Athens, Greece 4 Second Department of Orthopaedics, KAT Hospital, Athens, Greece Corresponding author: dkorres@med.uoa.gr Abstract: Type D fractures of the odontoid process are rare and usually occur in the elderly. The mechanism of fracture is unclear. Non-operative treatment is indi- cated provided that adequate immobiliza- tion using skull traction followed by either a collar or a halo vest can be achieved. The prognosis is usually favorable for this type of fractures. We present 6 patients with complex (type D) fractures of the odontoid process admitted and treated at our institu- tion since 1970. There were five men and one woman with a mean age of 57.7 years (range, 16-81 years). Although there were concomitant injuries no neurological deficits due to the odontoid process fracture was detected. All patients were treated non-oper- atively using skull traction or a halo vest for 8 to 12 weeks. One patient deceased two days after the injury. At the latest examina- tion, all the remaining five patients had complete union of the odontoid process fracture; three of them had excellent range of motion and two had painful or restricted range of motion of the upper cervical spine. Keywords: axis vertebra, odontoid process, fractures, classification I - INTRODUCTION Odontoid process fractures account for approximately 10-14% of cervical spine fractures [3, 6, 20]. Because of the unique anatomy and architecture of the odontoid process, upper cervical spine injuries lead to specific pattern of odontoid process fractures. The under- standing of the mechanism of the frac- tures and the biomechanics of the odontoid process is important for treat- ment and prognosis [11, 22]. Based on the anatomy, the internal archi- tecture and the biomechanical properties of the odontoid process, we have distin- guished 4 types (types A to D) of odontoid process fractures, and recog- nized a neutral zone at the level of the transverse ligament where practically no fractures are ever noticed (Fig. 1 and 2) [19]. Type D fractures of the odontoid process are complex (split, vertical, double or burst) fractures; the fracture line may extend through 2 or more anatomical areas of the dens (Fig. 3-5). The purpose of the present study is to present 6 patients with type D fractures of the odontoid process admitted and treated at our institution over a time period from 1970 through 2008. II - PATIENTS AND METHODS From 1970 to 2008, 110 patients (13.5% of all cervical spine fractures and 4.3% of all spinal fractures) were admitted and treated at the authors’ institution for an odontoid process fracture. There were 69 men and 41 women with a mean age of 46.7 years. A motor vehicle accident was the main cause of injury in 74 patients (66.6%), a fall from height in 30 patients (27.4%), and other causes in the remaining 6 patients (5.75%). The fractures were classified according to the Anderson-D’Alonzo [2], the Roy- Camille [23, 24], and the authors’ classi- fication [19]. According to the authors’ classification, 2 patients had a type A fracture, 36 patients had a type B fracture, 40 patients had a type C fracture (type C1 in 12 patients and type C2 in 28 patients), and 6 patients had a type D fracture of the odontoid process [17-19]. Figure 1: Schematic presentation at the open mouth radiograph of the four types of odontoid process fractures (types A to C) and the neutral zone. Figure 2: Overview of (A) type A, (B) type B, (C1) type C1 and (C2) type C2 fracture of the odontoid process. Figure 3: Type F fracture at the tip and the base (arrows) of the odontoid process (Patient 5).