Dalley, 10th Edition

91

Vertebrae

Vertical compressive force transmitted to occipital condyles

Occipital condyle

2

Dens of axis (D)

Lateral mass of C1 (LM)

Occipital condyle AO

D

D

LM

LM

C1

Wedge of lateral mass squeezed laterally

Anterior arch of C1 (Ar) C2

AA

C2

(B) Anterior view of coronal section of craniovertebral (atlantooccipital [AO] and lateral atlantoaxial [AA]) joints. Compare with CT in E.

(A) Anterior view of occipital condyles, atlas and axis

Lateral mass (LM) of atlas

Center of anterior arch (Ar)

compressing the lateral masses between the occipital con dyles and the axis drive them apart, fracturing one or both of the anterior or posterior arches (Fig. B2.3A, B). If the force is suf cient, rupture of the transverse liga ment that links them will also occur (Fig. B2.3C). The re sulting Jefferson or burst fracture (Fig. B2.3C–E) in itself does not necessarily result in spinal cord injury because the dimensions of the bony ring actually increase. Spinal cord injury is more likely, however, if the transverse ligament has also been ruptured (see the Clinical Box “Rupture of Trans verse Ligament of Atlas” in this chapter) indicated radio graphically by widely spread lateral masses. Fracture and Dislocation of Axis Fractures of the vertebral arch of the axis (vertebra C2) are one of the most common injuries of the cervical vertebrae (up to 40%) (Yochum & Rowe, 2004). Usually the fracture occurs in the bony col umn formed by the superior and inferior articular processes of the axis, the pars interarticularis (see Fig. 2.8C). A frac ture in this location, called a traumatic spondylolysis of C2 (Fig. B2.4A, B, D), usually occurs because of hyperextension of the head on the neck rather than the combined hyperex tension of the head and neck that may result in whiplash injury . Whiplash injury generally produces strains of mus cles and/or ligaments instead of fractures. While whiplash is painful and debilitating in the short term, it is unlike verte bral fracture, which is potentially life-changing. Such hyperextension of the head was used to execute criminals by hanging, in which the knot was placed un der the chin before the body suddenly dropped its length through the gallows oor (Fig. B2.4C); thus, this fracture is called a hangman’s fracture . In more severe injuries, the body of the C2 vertebra is dis placed anteriorly with respect to the body of the C3 vertebra.

LM

Transverse ligament of atlas (C1)

(C) Inferior view of Jefferson (burst) fracture of C1

Ar

LM

LM

(D) CT of Jefferson fracture

SUPERIOR

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LM

LM

Ar

LEFT

C2

RIGHT

INFERIOR

(E) Reconstructed CT image, anterior view, of Jefferson fracture showing fragment of anterior arch (Ar) and outward (lateral) shift of lateral masses of C1 (LM)

FIGURE B2.3. Jefferson fracture of atlas.