Page 1118 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Nervous system 1093

VetBooks.ir anaesthesia or recumbency, although myopathy involvement results in a horse that has great dif-
may complicate the clinical picture. Spinal cord
ficulty rising from a recumbent position and has
lesions of the ventral grey matter or nerve roots at
L4 and L5 can also result in femoral nerve paralysis a crouching posture when standing, because of
flexion of the joints of both hindlimbs. The patel-
and these have been seen in horses with EPM. The lar reflex will be depressed or absent, but a normal
femoral nerve innervates the quadriceps femoris, flexor reflex will be present if the sciatic nerve is
which is the major extensor muscle of the stifle, in intact. The prognosis is guarded in cases of femoral
addition to providing sensory innervation via the nerve paralysis unless the nerve can be repaired.
saphenous nerve to the medial aspect of the limb
(Fig. 10.52). Paralysis of this nerve results in an Tibial
inability to extend the stifle. Reciprocal flexion of Tibial nerve paralysis is uncommon because the
the tarsus and digits when the stifle flexes means nerve is well protected by the muscles and bones
that femoral nerve damage results in extensor paral- of the limb. This branch of the sciatic nerve pro-
ysis, with the affected limb resting in a flexed posi- vides motor innervation to the gastrocnemius and
tion and the ipsilateral hip in a lower position than digital flexor muscles. Paralysis causes the limb to
the contralateral hip. There is no weight bearing be held with the tarsus flexed and the fetlock rest-
on the affected limb during locomotion. Bilateral ing in a flexed or partly knuckled position. This
results in the hip being held lower on the affected
side. Flexion of the hock and extension of the digits
are unopposed and result in over-flexion of the limb
10.52 when walking, with the foot raised higher than nor-
mal. Controlled extension of the hock is absent at
the completion of the advancing phase of the stride
and results in the foot being dropped straight to the
ground. This gives the gait a similar appearance to
‘stringhalt’. There is anaesthesia of the caudomedial
aspect of the leg.

Peroneal
This branch of the sciatic nerve is most vulnerable
to injury where it crosses the lateral condyle of the
femur. Injury from kicks and lateral recumbency is
most common, but the nerve is not usually severed,
and these horses eventually improve. The peroneal
nerve supplies the flexor muscles of the tarsus and
extensor muscles of the digits. Paralysis results in
extension of the tarsus and flexion of the fetlock
and interphalangeal joints. At rest this results in a
horse that holds the limb extended caudally, with the
dorsum of the hoof resting on the ground. During
locomotion the hoof is dragged along the ground. If
Fig. 10.52 This Shire horse was presented with the limb is advanced manually and the toe extended,
a 3-week history, following a traumatic episode in the horse can bear weight on the limb. It is impor-
a field, of right-hind lameness and rapid profound tant to support and protect the limb while the ani-
quadriceps muscle atrophy. Subsequent clinical mal is given time to improve. Hypalgesia is reported
examination confirmed this was due to femoral nerve to occur on the craniolateral aspect of the hock and
damage. (Photo courtesy GA Munroe) metatarsal regions.