Page 269 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

244 CHAPTER 1

VetBooks.ir 1.462 Fig. 1.462 A 6-year-old Warmblood gelding with
its neck in a fixed low position bent to the left,
a posture typical of the neck locking syndrome.
The horse had patchy sweating on the right side at
the level of the articulation between the sixth and
seventh cervical vertebrae. The horse was reluctant to
move. Manual manipulation of the neck relieved the
clinical signs. The horse had moderate enlargement
of the articular process joints between the fifth and
sixth cervical vertebrae and marked enlargement of
the articular process joints between the sixth and
seventh cervical vertebrae, with ventral buttressing.
These radiological abnormalities are consistent
with osteoarthritis. The neck locking syndrome is
postulated to be associated with intermittent nerve
root compression.

from right to left and left to right permits best evalu- Lameness may be accentuated by local analgesic tech-
ation of the articular process joints. The diagnosis niques performed in the lame limb. Rarely, there are
of the clinical significance of OA of the articular episodic signs of lower motor neuron dysfunction,
process joints is often achieved by exclusion of other such as severe stumbling. Lameness characterised by
potential causes of the clinical signs. Intra-articular a hopping-type forelimb gait, only seen when ridden
analgesia performed under ultrasonographic guid- (Fig. 1.464), may be noted in a subset of horses with
ance can be used; however, there is a risk of inducing nerve root compression. Although many horses do
transient paresis. Myelography and, more recently, have advanced OA of caudal cervical articular process
CT, either standing or under general anaesthesia, joints and/or subluxation (Figs. 1.461, 1.465, 1.466),
can be used in horses with ataxia and weakness if some affected horses have no detectable radiological
surgical intervention is being considered. abnormality.
Painful OA causing neck pain and stiffness is not Locking neck syndrome is characterised by a sud-
common but does occur. Although neck pain may be den onset low neck posture, unwillingness to move
present, the primary presenting clinical problem is and sometimes marked pain (Fig. 1.462). There may
sometimes alteration in behaviour (e.g. bolting, rear- be focal patchy sweating on one side in the caudal
ing, stopping and refusing to go forwards). There neck region. The condition usually resolves sponta-
may be localised muscle atrophy in the caudal neck neously within 24 hours. In some horse the clinical
region and focal pain on palpation. Marked pain may signs can be resolved by manipulation of the neck.
reflect fracture of an articular process. It is speculated that the syndrome reflects transient
Nerve root compression is an unusual cause of fore- nerve root compression and evidence of chronic
limb lameness. Lameness is often worst when ridden nerve root pathology has been found.
and may only be present under these circumstances. Dermatomal sweating (Fig. 1.458) is the result
It may be influenced by whether the horse is ridden of neural compromise and may also be accompanied
to a contact or on a long rein. The lameness can be by some change in hair coat colour. Branches of the
highly variable in presence and severity. When lame- vertebral nerve join the spinal nerve roots as they
ness is severe, affected horses are usually less willing leave the intervertebral foramen, providing auto-
to go forwards and they change their facial features, nomic fibres locally. Dermatomal sweating is the
reflecting pain (e.g. ears back, glazed expression in the result of impingement on the vertebral nerve or its
eyes, mouth open) (Figs. 1.463, 1.464) and may tilt branches, which run alongside the vertebral artery
the head consistently in one direction (Fig. 1.463). in the paravertebral foramina. Articular process