Page 1077 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1052 CHAPTER 10

VetBooks.ir PHASE 6 – GAIT AND POSTURE more consistent and predictable pattern of behav-
Usually horses with orthopaedic disease show a

This part of the neurological examination involves
of pain, in comparison to the unpredictable and vari-
a systematic assessment of the horse standing, walk- iours (e.g. head nod) associated with a focus or foci
ing and trotting. The aim is to determine whether able gait of an ataxic horse.
the horse’s gait is normal or abnormal, and to detect
any apparent musculoskeletal disease. At each point Assessment of gait
the observer is asking: is this behaviour normal or is The examination begins with assessment of the
there evidence of weakness, pain or an irregular and horse’s posture, looking for evidence of a wide-based
unpredictable gait (ataxia)? It can be challenging to stance or inappropriate placement of the limbs.
differentiate weakness from ataxia or from multil- Attributing significance to postural reflexes (plac-
imb lameness due to orthopaedic pain. ing the foot in an unusual position and watching to
see whether the horse resists and places it back in a
Defining weakness more ‘normal’ position) can be difficult. Stoic or dull
Severe weakness in all four limbs, without evidence horses may leave a limb in an unusual position for
of ataxia or spasticity, suggests neuromuscular dis- minutes, with conscious perception that the limb’s
ease. A weak horse is consistently not strong enough position is not quite right, but without the willing-
to walk normally, and so they drag their limbs, wear ness to move it. It is helpful to assess the horse’s
the dorsal aspect of the hooves and have a low arc of voluntary range of movement in the neck with ‘car-
the swing phase of their stride. Profound weakness rot stretches’. A reduced range of neck movements
in one limb is suggestive of a peripheral neuropathy is most commonly seen in horses with degenerative
or a muscle lesion in that limb. joint disease (DJD) of the articular processes of the
cervical vertebrae. Although there is not total agree-
Defining ataxia ment amongst neurology specialists, most authors
Normal body movement and spatial orientation are report that horses show most discomfort when flex-
controlled by the general proprioception system, ing laterally away from the location of a unilateral
and deficiencies of this system result in clinical signs DJD lesion of the cervical vertebrae.
collectively termed ataxia. General proprioceptive The muscles of the standing horse should be
information is passed from the receptors in muscles, observed for any evidence of muscle tremors;
joints and tendons spread throughout the body, and when seen at rest these are a sign of muscle weak-
the afferent nerves are the spinal nerves and trigemi- ness (UMN disease). While the horse is standing
nal nerve. square, their resistance to being pushed over should
When the general proprioceptive system is defec- be checked. Normal horses will react and push back
tive, the horse shows poor coordination of movement against the clinician’s steady, firm pressure on the
and inappropriate placement of limbs, trunk, head shoulder or hip, and pull back against the standing
and neck at rest. The most important descriptive fea- tail pull test. If the horse can be easily pushed, or
tures of a horse that has ataxia are that their move- pulled over by their tail, this is suggestive of pare-
ments are inconsistent and unpredictable – their stride sis. It can be helpful to assess the horse’s ability to
may sometimes be exaggerated and at other times may tolerate weight bearing while the contralateral limb
have a reduced range of movement. Signs of ataxia is held up – exaggerated muscle tremors or stum-
may develop purely due to a problem with commu- bling on the weight-bearing limb may be a sign of
nication of the sensory information to the brain, not weakness.
the motor pathways. However, in some circumstances Next the horse can be assessed in motion. The
such as spinal cord compression or trauma, both path- author looks at the horse walking and trotting in
ways tend to be affected simultaneously because of the a straight line, looking for stumbling, mis-steps,
juxtaposition of the ascending (proprioceptive) and knuckling, toe-dragging or a low arc of the cra-
descending (motor) tracts in the spinal cord. nial phase of the stride. Hypermetria, defined as an