Dalley, 10th Edition

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Vertebral Column

Superior articular process (ear)

Pedicle (eye)

L3

Transverse process (snout)

Pars interarticularis (neck)

2

Inferior articular process (anterior limb)

(A) “Scotty dog” sign in lumbar vertebra Posterolateral view

L4

Broken neck of “Scotty dog” indicates spondylolysis ( red arrows )

L5

(C) Transverse CT

(B) Posterolateral oblique radiograph, spondylolysis and spondylolisthesis ( green arrow ) of L5

FIGURE B2.17. Spondylolysis.

Fracture of Dens of Axis

spondylolisthesis of the L5 vertebral body relative to the sa crum (S1 vertebra) due to the downward tilt of the L5/S1 IV joint (Fig. B2.18). Spondylolysis of L5, or susceptibility to it, probably results from a failure of the centrum of L5 to unite adequately with the neural arches at the neurocentral joint during development (see “Ossi cation of Vertebrae” in this chapter). Spondylolisthesis at the L5–S1 IV joint may (but does not necessarily) result in pressure on the spinal nerves of the cauda equina as they pass into the superior part of the sacrum, causing lower back and lower limb pain.

The transverse ligament of the atlas is stronger than the dens of the C2 vertebra. Fractures of the dens make up about 40% of fractures of the axis. The most common dens fracture occurs at its base—that is, at its junction with the body of the axis (Fig. B2.19A). Often these fractures are unstable (do not reunite) because the transverse ligament of the atlas becomes interposed between fragments (Crockard et al., 1993) and because the separated fragment (the dens) no longer has a blood supply, which

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S1

L5

S1 L5

Median MRI

FIGURE B2.18. Spondylolisthesis ( arrows ) secondary to spondylolysis of L5 vertebra.