Page 822 - Adams and Stashak's Lameness in Horses, 7th Edition

788 Chapter 6

around the spinal structures; medication with systemic Clinical Signs
corticosteroids and DMSO may be indicated. Due to the contribution of the spine to the normal
VetBooks.ir Prognosis gait pattern in the horse, as described earlier in this
chapter, horses that suffer from vertebral facet joint
The prognosis for nondisplaced vertebral fractures syndrome are often presented for lameness. In acute
without neurological symptoms is favorable, as is the cases, the pain in and around the facet joints can be so
prognosis for most stress fractures. When neurological severe that the horse does resist all movement and stand
symptoms are present, the amount of time needed to with the hindfeet parked out and the back lowered. This
reduce these symptoms with medication is a good indi- position closes the facet joints in the thoracic and lumbar
cator for future expectations. The longer it takes for the spine, causing less tension in the joint capsules. The
recovery of neurological functions, in general, the poorer muscles of the back and hind end are contracted. This
the prognosis. attitude can be difficult to differentiate from tying‐up
syndrome; however, with vertebral facet joint syndrome,
the serum levels of creatine kinase (CK) and aspartate
aminotransferase (AST) are within normal limits or only
FACET JOINT ARTHRITIS AND VERTEBRAL FACET slightly elevated.
JOINT SYNDROME With severe pain in the thoracic or lumbar spine,
signs can be similar to those of colic, with restlessness,
Etiology pawing, looking back, or standing with the hindlegs
When facet joint osteoarthritis is present in the thora- parked far out, giving the impression of wanting to uri-
columbar spine, similar to this process in humans, 31,32 a nate. In those cases, the heart rate can be as high as
complex of processes in and around the vertebral facet 60–80 beats per minute, but an examination for colic
joints can lead to a painful condition known as facet reveals that the horse is within normal limits.
joint syndrome. In the cervical spine, however, osteoar- In more chronic cases, the locomotion of the horse
thritis of the facet joints seems to be less frequently can be altered and a stiff back noticed. At the trot, the
related to facet joint syndrome than in the thoracolum- propulsion of the hindlimbs can be reduced unilaterally
21,25
bar spine, and the accompanying muscle spasms in the or even bilaterally. Due to the attachment of the
segmental muscles are absent. This gives the impression front limbs with ligaments, tendons, and muscles to the
of an isolated joint disease with a reduced range of thoracic vertebrae, motion of the front limbs also affects
motion and pain in just the affected joint. However, the position of the thoracic facet joints. At the trot, due
compression of nerve roots due to proliferation of the to the diagonal gait, the thorax moves between the scap-
bone around the facet joints is a more common observa- ulae, with a maximum extent of motion in the dorsal
tion in the cervical spine than in the thoracolumbar processes of the withers of 1–3 cm to left and right. Pain
spine. in the facet joints of the thorax thus can lead to less
The initiating incident in facet joint syndrome is dam- mobility in the thoracic spine, and an altered gait pat-
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age to the facet joint, primarily to the joint capsule and tern in the trot is best described as stiff or shortened.
the adjacent connective tissue, or else to the cartilage During the canter the thorax moves less, except in
and/or subchondral bone. In the horse, this primary inci- downward transitions (changing from canter to trot or
dent quite often is trauma, caused when the horse slips, trot to walk) when there is more loading of the facet
falls, flips over, gets cast, or injures itself in any other joints, as well as in landing after a jump or going down-
way. Due to the rich innervation of the facet joint tis- hill. Therefore, when thoracic facet joints are involved,
sues, the inflammation reaction caused by the primary signs mentioned by the owner or rider can include stiff-
trauma starts a cascade of reactions that is more obvi- ness, reluctance to go downhill or jump, and refusal or
ous than in the joints of the limbs. difficulty in extended trotting. Especially in jumping, a
One of the first reactions of the horse is stabilization trainer or rider may note a preference of the horse to go
of the spine by muscular contraction and spasm of the left or right after a jump, and this is quite often thought
epaxial and subaxial muscles. This can occur in just the to be related to an injury to the distal limb but in fact is
segment that is related to the injured vertebral facet caused by facet joint problems.
joint, but a larger portion of the vertebral column may Because lateral bending is a prominent mobility fea-
be involved. This muscle contraction can be short, last ture of the thoracic vertebrae, lateral bending of the
hours to days, or last weeks or even months. It is very horse may be reduced when thoracic vertebrae are
likely that the prolonged contraction or spasm is very involved with facet joint syndrome. This can be observed
painful and partially immobilizes the spine, as is the sit- during circles and serpentines and in lateral exercises
uation in humans. 31,32 such as shoulder in, travers, and half pass of dressage, as
As a consequence of this immobilization, the facet well as in turns in barrel racing, polo, and eventing, or in
joint is more or less fixed in one position, which between fences when jumping. Tightening the girth or
makes regaining later mobility a painful experi- putting the saddle on also can reveal an adverse reaction
ence. Due to the muscle spasm, no normal sequence of the horse, because these actions can load the thoracic
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of contraction–relaxation occurs in the muscle, and facet joints.
the normal supportive function is less effective. When lumbar facet joints are involved in facet joint
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Consequently, when excessive force is applied to the syndrome, the most affected gait is the canter, because it
spine again, repetitive injury to that facet joint can is then that the dorsoventral flexion of the lumbar spine
be the result. is most prominent. The lateral exercises—shoulder in,