Neurologic injury because of trauma after Type II odontoid nonunion

Abstract

Background context

Treatment of Type II odontoid fractures remains controversial, whereas nonoperative treatment is well accepted for isolated Type III odontoid fractures. Little is known about long-term sequelae of nonoperative management or risk of recurrent injury after nonsurgical treatment. We hypothesize that a substantial proportion of odontoid fractures assumed to be acute are actually chronic injuries and have a high rate of late displacement resulting in neurologic injury.

Purpose

To identify patients presenting with previously unrecognized odontoid fracture nonunions and to document the incidence of new neurologic injury after secondary trauma in this population.

Study design

Retrospective case series.

Patient sample

One hundred thirty-three patients with Type II odontoid fractures presenting to a Level I trauma center.

Outcome measures

Computed tomography (CT) and magnetic resonance imaging (MRI) scans, American Spinal Injury Association Motor Score (AMS), and neurologic examination.

Methods

All patients presenting after traumatic injury to a Level I trauma center from May 2005 to May 2010 with a Type II odontoid fracture on CT scan were included. Patients aged less than 18 years and those with pathologic fractures were excluded. Fractures were classified as chronic or acute based on CT evidence of chronic injury/nonunion including fracture resorption, sclerosis, and cyst formation. Magnetic resonance imaging was then examined for evidence of fracture acuity (increased signal in C2 on T2 images). Patients without evidence of acute fracture on MRI were considered to have chronic injuries. Computed tomography and MRI scans were interpreted independently by two reviewers. Chart review was performed to document demographics, AMS, and new-onset neurologic deficit associated with secondary injury.

Results

One hundred thirty-three patients presented with Type II odontoid fractures and no known history of cervical fracture with an average age of 79 years. Based on CT criteria, 31/133 (23%) fractures were chronic injuries. Nine additional fractures appeared acute on CT but were determined to be chronic by MRI findings. The overall number of chronic fractures was therefore 40 (30%). Interobserver reliability analysis for classification of fractures as chronic demonstrated κ=0.65 representing substantial agreement. Of the 40 chronic fractures, 7 patients (17.5%) had new-onset neurologic deficits after secondary injury including 4 motor deficits, 2 sensory deficits, and 1 combined deficit. Although the chronic injury group as a whole had similar AMS to the acute injury group (89 vs. 84, p=.27), the seven patients with new-onset neurologic deficit had an average AMS of 52.4.

Conclusions

A substantial proportion of patients presenting after cervical trauma with Type II odontoid fractures have evidence of nonacute injury. Of these patients, 17% presented with a new neurologic deficit caused by an “acute-on-chronic” injury.

Introduction

Evidence & Methods

The authors aimed to assess whether some Type II odontoid fractures seen acutely are actually acute-on-chronic injuries representing old nonunions.

Using their defined CT and MRI criteria, the authors found that 30% of acutely diagnosed fractures might actually be acute-on-chronic injuries.

Assuming the radiographic criteria are accurate, the findings are quite interesting. It is unclear, however, whether the conclusion can be drawn that surgery should be recommended for all presenting Type II fractures in order to avoid the risk of neurological injury due to secondary trauma. There may be a very high prevalence of individuals with nonunions who may never have a problem after subsequent falls. The study design does not lend itself to answering this question. That said, the findings might be useful during shared decision-making in acute presentations.

—The Editors

Odontoid fractures have been reported to represent between 9% and 19% of cervical spine fractures [1], [2], [3] and are most common in the elderly. According to the classification developed by Anderson and D'Alonzo [4] and modified by Grauer et al. [5], Type II fractures are the most common type, representing between 56% and 85% of odontoid fractures [1], [4], [6], [7], [8], [9]. Despite the location of the fracture in the proximal cervical spine, where a spinal cord injury can be devastating, neurologic deficit after odontoid fracture is uncommon, although the overall complication rate remains high [10]. The incidence of neurologic deficit after odontoid fracture has been reported to range from 13% to 25% [1], [2], [8], [9], [11], [12], with tetraparesis seen in only 2% to 8.5% [1], [2], [8], [9], [11], likely because of the relatively capacious spinal canal in the upper cervical region adjacent to the odontoid process.

Management of Type II odontoid fractures is controversial, and high rates of fracture nonunion after conservative treatment using an orthosis are well documented, exceeding 75% in some hard collar series [7], [11], [13]. Similarly, treatment with halo-vest immobilization results in nonunion rates reported as high as 54% [14]. Although high rates of nonunion occur after conservative treatment and immobilization, the long-term clinical significance of odontoid nonunion is not well characterized and has rarely been investigated in a systematic manner.

In this study, we sought to identify previously unrecognized odontoid fracture nonunions to document the rate of nonacute injuries in patients presenting with Type II odontoid fractures and report the incidence of new neurologic injury after secondary trauma in patients with odontoid nonunions. We hypothesize that a substantial proportion of odontoid fractures assumed to be acute are actually chronic injuries and that these chronic injuries have a significant rate of later displacement resulting in neurologic injury.