title: Biomechanical Assessment of Stabilization of Simulated Type II Odontoid Fracture with Case Study.
abstract: METHODS
  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.
  
  
  OBJECTIVE
  Researchers explored their hypothesis that spacers combined with posterior instrumentation (PI) reduce range of motion significantly, possibly leading to better fusion outcomes.
  
  
  BACKGROUND
  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.
authors.affiliation: Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
authors.forename: Roy T
authors.initials: RT
authors.lastname: Daniel
authors.affiliation: Musculoskeletal Education and Research Center (MERC), A Division of Globus Medical, Inc., Audubon, PA, USA.
authors.forename: Mir M
authors.initials: MM
authors.lastname: Hussain
authors.affiliation: Musculoskeletal Education and Research Center (MERC), A Division of Globus Medical, Inc., Audubon, PA, USA.
authors.forename: Noelle
authors.initials: N
authors.lastname: Klocke
authors.affiliation: Musculoskeletal Education and Research Center (MERC), A Division of Globus Medical, Inc., Audubon, PA, USA.
authors.forename: Soumya S
authors.initials: SS
authors.lastname: Yandamuri
authors.affiliation: Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
authors.forename: Lukas
authors.initials: L
authors.lastname: Bobinski
authors.affiliation: Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
authors.forename: John M
authors.initials: JM
authors.lastname: Duff
authors.affiliation: Musculoskeletal Education and Research Center (MERC), A Division of Globus Medical, Inc., Audubon, PA, USA.
authors.forename: Brandon S
authors.initials: BS
authors.lastname: Bucklen
keywords: Atlantoaxial stabilization; Cervical biomechanics; Interarticular spacer; Odontoid fracture; Type II dens fracture