Asian Spine J.  2017 Feb;11(1):15-23. 10.4184/asj.2017.11.1.15.

Biomechanical Assessment of Stabilization of Simulated Type II Odontoid Fracture with Case Study

Affiliations
  • 1Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
  • 2Musculoskeletal Education and Research Center (MERC), A Division of Globus Medical, Inc., Audubon, PA, USA. mhussain@globusmedical.com

Abstract

STUDY DESIGN: Researchers created a proper type II dens fracture (DF) and quantified a novel current posterior fixation technique with spacers at C1-C2. A clinical case study supplements this biomechanical analysis. PURPOSE: Researchers explored their hypothesis that spacers combined with posterior instrumentation (PI) reduce range of motion significantly, possibly leading to better fusion outcomes. OVERVIEW OF LITERATURE: Literature shows that the atlantoaxial joint is unique in allowing segmental rotary motion, enabling head turning. With no intervertebral discs at these joints, multiple ligaments bind the axis to the skull base and to the atlas; an intact odontoid (dens) enhances stability. The most common traumatic injury at these strong ligaments is a type II odontoid fracture.
METHODS
Each of seven specimens (C0-C3) was tested on a custom-built six-degrees-of-freedom spine simulator with constructs of intact state, type II DF, C1-C2 PI, PI with joint capsulotomy (PIJC), PI with spacers (PIS) at C1-C2, and spacers alone (SA). A bending moment of 2.0 Nm (1.5°/sec) was applied in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). One-way analysis of variance with repeated measures was performed.
RESULTS
DF increased motion to 320%, 429%, and 120% versus intact (FE, LB, and AR, respectively). PI significantly reduced motion to 41%, 21%, and 8%. PIJC showed negligible changes from PI. PIS reduced motion to 16%, 14%, and 3%. SA decreased motion to 64%, 24%, and 54%. Reduced motion facilitated solid fusion in an 89-year-old female patient within 1 year.
CONCLUSIONS
Type II odontoid fractures can lead to acute or chronic instability. Current fixation techniques use C1-C2 PI or an anterior dens screw. Addition of spacers alongside PI led to increased biomechanical rigidity over intact motion and may offer an alternative to established surgical fixation techniques.

Keyword

Type II dens fracture; Odontoid fracture; Atlantoaxial stabilization; Cervical biomechanics; Interarticular spacer

MeSH Terms

Aged, 80 and over
Atlanto-Axial Joint
Female
Head
Humans
Intervertebral Disc
Joints
Ligaments
Range of Motion, Articular
Skull Base
Spine
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