South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
reflex of the thoracic limb may be reduced in recumbent animals, whereas that of the pelvic limb
may be exaggerated.
Thoraco-lumbar lesions (T3-L3)
An animal that has no thoracic limb involvement, but pelvic limb ataxia and weakness will have a
lesion caudal to the brachial plexus, between T2 and L3. Look closely for symmetry over the
gluteals and pelvic limbs, to help differentiate between these lesions and more caudal lesions
involving the pelvic outflow. The panniculus or cutaneous trunci reflex (segmental afferent –
efferent C8-T1) is tested by lightly stimulating the skin of the lateral thorax. It is easiest to detect
asymmetry since horses vary in their response to this test. The withdrawal reflex in the pelvic
limb may be exaggerated.
Flexibility of the thoracolumbar spine is assessed by firmly stimulating the skin of the
longissimus musculature and observing for a lordotic movement over the thorax and cranial
lumbar region and a kyphotic movement over the caudal lumbar region and gluteals.
Pelvic outflow (L4-S3)
Horses with lesions between L4 and S3 (the lumbosacral outflow) may exhibit muscle atrophy of
one or more muscles of the pelvic region. They may be easy to pull over when standing and will
be unwilling or unable to take weight on the affected side when the other limb is lifted. With
more caudal lesions, there may be involvement of the anal and perineal reflexes, tested by lightly
stimulating the skin surrounding the anus and observing for a reflex contraction of the anal
sphincter. There may also be paresis of the tail. Withdrawal reflex may be reduced or absent in the
pelvic limb in recumbent horses.
Bladder function and control of defaecation
Damage to the sacral spinal cord segments can be manifest as bladder incontinence. The bladder
is reflexly controlled primarily by the pelvic and pudendal nerves, via higher order neurones in the
caudal brainstem and cerebrum. The smooth muscle (detrusor) of the bladder wall is innervated
by parasympathetic fibres that leave the spinal cord in the sacral segments and then combine to
form the pelvic nerve. The pudendal nerve innervates striated muscle of the bladder neck; during
micturition, this striated muscle is relaxed, and stimulation of the pelvic nerve causes the detrusor
smooth muscle to contract and the bladder to evacuate. Lesions in the sacral region may also be
manifest as faecal incontinence. In horses, lower motor neuron (pelvic nerve) problems (faecal
retention) are usually identified.
Further reading
De LaHunta A. & Kent M. Veterinary Neuroanatomy and clinical neurology. 3 rd Ed. Saunders 2008
Furr M. and Reed SM. Equine Neurology. Blackwell Publishing. 2007
Mayhew, J. Large Animal Neurology. Blackwell Publishing. 2009
Olsen E, Dunkell B, Barker W, Finding E, Perkins J, Witte T, Yates L, Baiker K, Piercy RJ. Agreement and validity
of gait assessment in equine neurological examinations. J Vet Intern Med. 2014 Mar-Apr;28(2):630-8.jmc
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