Healing process of Type II odontoid fractures after C1-C2 posterior screw fixation: Predictive factors for pseudoarthrosis
- Department of Neurosurgery, University of Iowa Hospitals and Clinics, Iowa City, United States,
- Department of Neurosurgery, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima City, Hiroshima, Japan,
- Department of Anesthesiology, Far Eastern Memorial Hospital, New Taipei City, Taiwan.
Satoshi Yamaguchi, Department of Neurosurgery, University of Iowa Hospitals and Clinics, Iowa City, United States.
DOI:10.25259/SNI_198_2022Copyright: © 2022 Surgical Neurology International This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, transform, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.
How to cite this article: Satoshi Yamaguchi1, Brian J. Park1, Masaaki Takeda2, Takafumi Mitsuhara2, Kiyoharu Shimizu2, Pei-Fu Chen3, Royce W. Woodroffe1. Healing process of Type II odontoid fractures after C1-C2 posterior screw fixation: Predictive factors for pseudoarthrosis. 31-Mar-2022;13:116
How to cite this URL: Satoshi Yamaguchi1, Brian J. Park1, Masaaki Takeda2, Takafumi Mitsuhara2, Kiyoharu Shimizu2, Pei-Fu Chen3, Royce W. Woodroffe1. Healing process of Type II odontoid fractures after C1-C2 posterior screw fixation: Predictive factors for pseudoarthrosis. 31-Mar-2022;13:116. Available from: https://surgicalneurologyint.com/surgicalint-articles/11502/
Background: The healing process after C1-C2 posterior screw fixation (C1-C2 PSF) for odontoid fractures is not well understood. Here, we evaluated such processes and identified factors potentially contributing to pseudoarthroses following fusions for Type II odontoid fractures.
Methods: Pre- and post-operative cervical radiographs and computed tomography (CT) images from 15 patients with preoperative Type II odontoid fractures who underwent C1-C2 PSF were retrospectively reviewed.
Results: CT images identified three areas of bone fusion: The primary fracture site in the dens (9/15 patients, 60%), the atlanto-dental interspace (ADI) (10/15, 67%), and C1-C2 interlaminar space after onlay bone grafting (4/15, 27%). All patients showed bone fusion in at least one of three areas, while only one patient (6.7%) achieved bone fusion in all three areas. With these overall criteria, nine of 15 patients (60%) were considered fused, while six patients (40%) were determined to exhibit pseudoarthroses. Univariate analyzes showed that the preoperative C2-C7 SVA for the nonunion group was significantly larger versus the union group, and bone fusion at the level of the ADI was significantly more common in the nonunion versus the union group.
Conclusion: CT studies identified three anatomical areas where bone fusion likely occurs after C1-C2 PSF. Increased sagittal balance in the cervical spine may negatively impact the fusion of odontoid fractures. Further, bone fusion occurring at other sites, not the primary fracture location, through stress shielding may contribute to delayed or failed fusions.
Keywords: Bone fusion, C1-C2 posterior screw fixation, Odontoid fracture
Anderson and D’Alonzo Type II odontoid fractures are the most common among three types of odontoid fractures.[
This was a retrospective IRB approved review of 15 cases of Anderson and D’Alonzo Type II odontoid fractures treated with C1-C2 PSF by one surgeon (2011-2015).[
Clinical patient data
There were 15 patients who underwent C1-C2 PSF for Anderson and D’Alonzo Type II odontoid fracture.[
Use of CT studies to document fusion
We examined pre- and post-operative CT characteristics associated with fracture nonunion using Hounsfield units at the odontoid base and fractured odontoid tip (i.e., regarding bone density) and maximum bone gap of the fracture site [
Radiological parameters examined as possible factors associated with fracture union/nonunion from preoperative images. Left: (a) region of interest (ROI) for Hounsfield unit (HU) of fractured odontoid process, (b) ROI for HU of the base of odontoid process, (c) maximum separation of the fracture. Right: (d) cervical lordosis measured by C2-C7 Cobb angle, (e) C2-C7 sagittal vertical axis, (f) T1-slope, (g) Occiput-C2 angle.
Out of 30 total C2 screws inserted, 24 screws were placed in the pars interarticularis, and six screws in the C2 lamina (i.e., due to high-riding vertebral arteries). After the installation of screws and rods, the laminae of C1 and C2 were decorticated for the subsequent placement of onlay bone grafting. In the first five cases, cancellous bone was harvested from the ilium, while in the last ten cases, we utilized allograft/demineralized bone matrix (DBM). Patients were instructed to use a cervical collar for 6 weeks after the surgery.
Statistical analysis was performed by a computer software (SPSS Inc., IBM, Chicago, IL). Tests utilized included: the Shapiro–Wilk test, Student’s t-test, nonparametric Mann– Whitney U-test, and the Fisher’s exact test.
Incidence of bone fusion in 1–3 areas
Bone fusion was seen in three different areas in the atlantoaxial cervical spine [
Three anatomical areas where bone fusion occurred. Top row: white arrow indicates bone fusion in the odontoid fracture. Middle row: Black arrow indicates bone fusion in the atlanto-dental interval space. Bottom row: asterisk indicates bone fusion in the C1-C2 interlaminar space after onlay bone grafting.
Of note, all four of five patients receiving iliac autograft fused versus none using allograft/DBM.
Only 1 (6.7%) patient showed bone fusion in all three areas while six patients fused in two areas, while eight patients had bone fusion in only one area, (i.e., either at the primary fracture [n = 2] or ADI [n = 6] sites) [
Differences in SVA and ADI fusion rates
The preoperative C2-C7 SVA was significantly greater for the nonunion versus union group patients and these patients were typically older [
Stress shielding effect in ADI as a possible cause of fracture nonunion
Considering that the directions of the screws in C1-C2 PSF are not perpendicular to the fracture line but more parallel to the axial plane of the C1 lamina, those screws appear to press fractured odontoid process toward the anterior arch of the atlas more than its basal part. Once a bone fusion in ADI is established, it may lead to a stress shielding effect to the fracture site with subsequent delayed or failed fracture union. This hypothesis may explain why a bone fusion in ADI was significantly more common in the fracture nonunion group (100%) than union group (44%).
The union rate of fractured odontoid process after C1-C2 PSF evaluated by CT scan
Several studies used CT scans to evaluate the union rates of odontoid fracture safer C1-C2 PSF.[
Cervical sagittal balance and bone union in odontoid fractures
The influence of cervical sagittal balance on the fracture angle in odontoid fractures and postoperative fracture union rate has rarely been discussed. Wang et al. revealed that advanced age (>45 years), long duration of the fracture (>2 months), and preoperative separation of the fractured dens (>4 mm) were independently associated with fracture nonunion after C1-C2 PSF.[
Our study identified three anatomical areas where bone fusion likely occurs after C1-C2 PSF. Increased sagittal balance in the cervical spine may negatively impact the fusion of odontoid fractures. Bone fusion occurring at other sites besides the primary fracture location may causing stress-shielding effect to the odontoid fracture and may contribute to delayed or failed fusions.
Institutional Review Board (IRB) permission obtained for the study.
There are no conflicts of interest.
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