Dalley, 10th Edition

Chapter 2 ■ Back

92

With or without such subluxation (incomplete dislocation) of the axis, injury of the spinal cord and/or of the brainstem is likely, sometimes resulting in quadriplegia (paralysis of all four limbs) or death. Fractures of the dens are also common axis injuries (40–50%), which may result from a horizontal blow to the head, or as a complication of osteopenia (pathological loss of bone mass) (see the Clinical Box “Fracture of Dens of Axis” in this chapter). Dislocation of Cervical Vertebrae Because of their more horizontally oriented ar ticular facets, the cervical vertebrae are less tightly interlocked than other vertebrae. The cer vical vertebrae, “stacked like coins,” can be dislo cated in neck injuries with less force than is required to fracture them (Fig. B2.5A–F). Because of the large verte bral canal in the cervical region, slight dislocation can oc cur here without damaging the spinal cord (Fig. B2.5B). Severe dislocations, or dislocations combined with frac tures (fracture–dislocations), injure the spinal cord. If the dislocation does not result in “facet jumping” with locking of the displaced articular processes (Fig. B2.5F, G), the cervical vertebrae may self-reduce (slip back into place) so that a radiograph may not indicate that the cord has been injured. An MRI, however, may reveal the resulting soft tissue damage (Fig. B2.5F).

Body of axis (B)

Dens (D) of axis (C2)

Superior articular facet

Foramen transversarium Transverse process Pars interarticularis (fractured)

Inferior articular process

Lamina

Spinous process (SP)

(A) Posterosuperior view

Apical ligament of dens Alar ligament Facet for anterior arch of atlas Articular facet for transverse ligament Superior articular facet Foramen transversarium

D

Pars interarticularis (fractured)

SP

B

Inferior articular process

Body

Transverse process

(B) Lateral view

Rope under chin forces abrupt hyperextension

(C) Schematic

(B) Lateral view

(A) Lateral view

Cranium

Anterior arch of atlas (C1)

D

Posterior arch of atlas (C1)

(C) Lateral view

B

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(D) Lateral view

(E) Lateral radiograph, dislocation at C6–C7

FIGURE B2.4. Hangman’s fracture and dislocation of axis. A and B. The pars interarticularis of the C2 vertebra is fractured ( arrows ). C. The position of the hangman’s noose knot produces hyperextension during hanging ( arrows ). D. Radiograph demonstrating a hangman’s fracture ( arrows ). (D) Lateral radiograph

FIGURE B2.5. A–E. Dislocations of cervical vertebrae. A–D. Four stages of injury are shown. A. Stage I: exion sprain. B. Stage II: anterior subluxation with 25% anterior translation. C. Stage III: 50% translation. D. Stage IV: complete dislocation. E. Radiograph of a stage III dislocation with 50% translation ( arrow ).