Advance Access: C1 Lateral Mass Displacement and Transverse Atlantal Ligament Failure in Jefferson’s Fracture: A Biomechanical Study of the “Rule of Spence”

The incidence of atlas fractures has doubled in the past few decades according to a recent epidemiological study, accounting for approximately 11% of all cervical fractures and 25% of craniocervical injuries.1,2 Jefferson’s fracture, a type of atlas fracture, was first described in 1927 and represents a burst fracture of the atlas with disconnection of the anterior and posterior arches resulting in lateral spreading of the lateral masses (Figure 1).3 In 1970, Spence et al4simulated Jefferson’s fractures in 10 cadavers and determined that if the total lateral mass displacement (LMD) exceeds 6.9 mm, there is high likelihood of transverse atlantal ligament (TAL) rupture. Heller et al5 subsequently studied open-mouth (odontoid) view X-rays and redefined the value to 8.1 mm based on an inherent magnification of 18% on odontoid films.

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