Page 798 - Adams and Stashak's Lameness in Horses, 7th Edition

764 Chapter 6

medial part, which is very well developed in the lumbar Table 6.1. Mobility of the spine.
region. The splenius muscle in the cervical and cranial
VetBooks.ir ial muscles. Part of the spine
thoracic region forms the most superficial layer of epax-

Walk Gait Axis Cervical Thoracic Lumbar Sacral
In the walk, the main motion of the spine can be Walk DV ++ + + +
described as a “snakelike” motion. A sinusoidal pattern Lat + ++ − +
of motion is present in the spine with lateral flexion in
the thoracic region, some rotation in the lumbar spine, Rot +− − + −
and dorsiventral flexion in the cervical region, all con-
tributing to support the walk. Electromyographic eval- Trot DV + + − −
5
uation has shown the action of the splenius muscles is to
elevate the head and neck and facilitate forelimb pro- Lat − − − −
traction by the elongated brachiocephalicus muscle. The Rot − − − −
sternocephalicus muscle contributes to the stance phase
of the front limb. The longissimus dorsi muscle acts dur- Canter DV ++ + +++ ++
ing the stance phase of the hindlimb, whereas the rectus
abdominus muscle is not active at all but limits vertical Lat +− + − −
acceleration of the abdominal visceral mass. The multi- Rot − − ++ +
fidus lumborum muscle is active in the intermediate part
of the stance phase of the ipsilateral limb, and the
obliquus externus abdominal muscle shows intermittent DV = dorso‐ and ventroflexion, Lat = lateroflexion, Rot = rotation, − = not
activity. 4 present, + = minor mobility, ++ = major mobility, +++ = maximum
mobility.
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Source: Reprinted with permission from van Wessum, p. 469.
Trot
At the trot there is only modest dorsiventral flexion
in the thorax and the neck. The maximal thoracolumbar Table 6.1 is an overview of the degrees of mobility
extension occurs in the mid stance phase due to the vis- and their relationship to the three gaits. It is easy to
ceral inertia. The splenius muscle acts before and during understand that this relationship can make a lameness
the first part of the stance phase of each forelimb to limit examination more of a challenge. Some common symp-
lowering of the neck, and the sternocephalicus muscle toms are associated with specific parts of the spine, as
controls neck elevation. The brachiocephalicus muscle shown in Table 6.2.
acts to achieve protraction of the forelimb. The rectus
abdominus muscle limits the passive thoracolumbar
extension caused by the visceral mass inertia during the History
stance phase. The longissimus dorsi muscles act at the As in every examination, investigating the horse with
end of the stance phase and during the suspension phase back pain starts with the history. Taking time for a
12
to induce lumbosacral extension to facilitate hindlimb good interview with the client is the first step to better
protrusion. In the trot, most muscles act to stabilize the comprehend the problem. Listening to the information
spine, not to move it. 5,6
provided by the client is a good start. Asking guiding
questions such as whether there are time‐related changes
Canter in the quality of the gaits or difficulties in keeping the
correct lead can provide information about the gait in
There is more lumbar and sacral motion in the canter which the complaints are more evident. Common com-
than in any other gait, with lumbar rotation and dor- plaints from owners of horses with back problems
siventral flexion in the lumbar, thoracic, and sacral include resistance to bending to one direction more than
spine. In the neck, the splenius muscle is active during to another; not accepting the bridle; kicking and buck-
7
the trailing diagonal stance phase. It limits the neck to ing (especially in one gait, most commonly the canter);
lower and causes neck extension during the leading poor‐quality canter, cross canter, or switching leads; or
stance phase, and the sternocephalicus muscle shows generalized stiffness. The poor‐quality canter may be a
1
reciprocal activity. The brachiocephalicus muscle is no‐sound, 4‐beat canter, more “bunny‐hop‐like” with
mainly active during the stance phase. The longissimus less separation between the subsequent footfalls of the
dorsi muscles are active during the suspension phase hindlimbs.
and during the trailing hindlimb stance phase. The rec- Some complaints are specific to the discipline.
tus abdominus muscles act reciprocally during the sup- Complaints indicative of back pain in dressage horses
port phase of the non‐leading diagonal to support the include difficulties in the walk and canter pirouettes,
visceral mass and initiate thoracolumbar flexion. The a poor quality or a lateral walk, and unsatisfactory
sublumbar muscles, psoas major and minor, are active collection and “coming under” (carriage of the hind-
during the suspension phase and are part of the propul- quarters). In jumpers, common complaints are unsat-
sion forces in the canter. 4 isfactory bascule (balance above the fence), lack of