Page 797 - Adams and Stashak's Lameness in Horses, 7th Edition

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CHAPTER

Lameness Associated with

the Axial Skeleton

THE AXIAL SKELETON

Rob Van Wessum

Back pain is increasingly recognized as contributing ventroflexion, and rotation. Any specific change in the
to or even causing equine lameness. 1,4,8,16,19 Previously posture of the horse causes a change in the direction in
back pain was generally considered to be a secondary one or more of these three planes. The cervical interverte-
problem, with the primary lameness of a limb causing bral joints allow a relatively large range of flexion
changes in movement and affecting the spine. In recent dorsiventrally as well as laterally, while the intervertebral
years, more and more primary spine injuries have been joint between the first and second cervical vertebra
acknowledged. 2,8,10,11,19 To understand the function of permits rotation. In the thoracic vertebrae the mobility is
the vertebral column, its attached tissues, and their rela- mainly lateral flexion, with some minor dorsiventral
tionship to the physics of equine locomotion, some basic motion. In addition, the mobility of the costovertebral
anatomical and biomechanical knowledge is necessary. joints is necessary for breathing. In the lumbar spine the
main mobility is in dorsiventral flexion with some rota-
tion. In the sacral region there is a small amount of
ANATOMY AND BIOMECHANICS dorsiventral flexion, while in the tail there is considerable
OF THE VERTEBRAL COLUMN dorsiventral and lateral flexion but no rotation. 3,4
The pattern of motion of the spine also is gait spe-
There are approximately 260 joints between the verte- cific. The support and the positioning of the spine are a
brae; the vertebrae and ribs, the sacrum and pelvis, and specific function of each gait, enhancing the range of
the head and the first cervical vertebra all contribute to motion of the extremities by facilitating optimal posi-
mobility in the entire spine. In most of these joints, the tioning of the limb relative to the spine and the other
total range of motion is limited in both direction and limbs. The axial muscles can function as a stabilizer of
degree, but the overall effect of all of the joints within the the spine and hold certain portions of the spine during
spine creates a significant amount of motion in the entire locomotion. The epaxial muscles are symmetrically
spine. Because of its connection to the limb, a major arranged between the transverse and dorsal spinous
3,9
function of the spine and the attached muscles is the posi- processes. The spinalis muscle, semispinalis muscle, and
tioning of the limbs. Some of the muscles controlling limb multifidus muscle form the most axial and deepest epax-
position have their origin at the spine and their insertion ial muscle group. The multifidus muscle consists of a
on an extremity; other muscles with both origins and large number of separate muscle units, each covering
insertions on the spine regulate mobility in the spine itself. only two to six vertebral segments along the entire ver-
Joints of the spine allow mobility dorsally, ventrally, tebral column. The middle epaxial muscular layer, called
and laterally, and some allow rotation. In particular areas the lateral system, extends from C1 to the pelvis and
of the spine, the vertebrae have specific ranges of motion sacrum. The iliocostal muscle forms the most abaxial
within the three basic axes: lateroflexion, dorsi‐ and part of this system, and longissimus muscle forms the

Adams and Stashak’s Lameness in Horses, Seventh Edition. Edited by Gary M. Baxter.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/baxter/lameness
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