Front Matter

Chapter 17 Diagnosis of and Treatment Options for Disorders of the Spine 429

limited flexibility of the spine allows for fluid
movement once propulsion is initiated.
The tail, like the head, is cantilevered from
the body. The apparatus necessary to carry this
weight is not extensive but the tail has a role in
balance and fine movement that has been
extremely well documented in the cat (Walker
et al., 1998). Although not as well studied, the
canine tail also serves to help with balance dur­
ing locomotion (Wada et al., 1993).

Conformational considerations

Each vertebra interlocks with the adjacent verte­

bra cranial and caudal to it. Except for the first

and second cervical vertebrae (Figure 17.3B), the

components of each individual vertebra are sim­

ilar but each varies as the morphology of that

site is determined by its functional requirements

(Figure 17.6).

The first few thoracic vertebrae have the tall­

est dorsal spines, as they are the scaffold that

carries the weight of the head. These forces are

transmitted through the vertebral joint, muscle,

and ligamentous structures. The arch of the

thoracolumbar spine is greatest usually at the

point at which the 10th thoracic and 11th tho­

racic dorsal spines meet. At this site, the dorsal

spines acutely reverse direction from a caudal

sweep (T10) to a dorsal sweep (T11). The anti­

clinal vertebra is the one where this change

occurs and is usually, but not always, T11.

A fibrous ring, the fibrous annulus, which is

composed of strong cross fibers that firmly

attach one vertebra to another, interconnects

the vertebral bodies. The central portion of this

ring is filled with a gelatinous substance, the

nucleus pulposus, a remnant of the phyloge­

netically primitive notochord. The nucleus pul­

posus absorbs forces created between the

vertebral endplates and dynamically transfers

those forces to the surrounding fibrous ring in

response to dorsoventral and lateral move­

ments of the spine. We do not usually appreci­

ate the dynamic nature of these structures as

they are often viewed through still‐motion

studies such as radiography, CT, and MRI. With

motion the gel becomes compressed at the side

of narrowing of the disc space and expanded at

Figure 17.5 Ventrodorsal radiograph of the pelvis and
femurs showing the box‐like nature of the pelvis and the
ball and socket joints of the femurs.

Figure 17.6 From left to right, the cervical, thoracic, and lumbar vertebra showing the tremendous variation in
conformation in the same animal.