Page 672 - Adams and Stashak's Lameness in Horses, 7th Edition

638 Chapter 5

nerve paralysis. There have been isolated reports of no areas of skin innervated only by either the radial or
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radial nerve paralysis included in a generalized distal the axillary nerves—the ulnar, median, and musculocu-
VetBooks.ir anesthesia on an operating table or while on the ground terizing the extent of nerve damage and can be used to
taneous nerves can be related to such areas.
axonopathy.
9
31
Electrophysiological studies can be helpful in charac-
Prolonged lateral recumbency while under general
may also produce a radial‐paralysis‐like syndrome in determine selective denervation of the extensor muscles.
the forelimb. 48,51 Episodes of ischemia are likely to cause However, because it takes approximately 7 days for the
neuropractic conduction changes and permanent nerve axon distal to the site of the damage to degenerate,
changes if prolonged. 51 EMG done before this time has limited usefulness.
3
Alternatively, faradic stimulation done 7 days after clini-
cal signs develop can be used to differentiate between
Clinical Signs
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neuropraxia and axonotmesis or neurotmesis.
The signs vary depending upon the extent or degree Radiography, ultrasonography, and laboratory analysis
and location of paralysis. When the portion of the radial of muscle enzymes may be needed in some cases to make
nerve supplying the extensors of the digit is affected, the an accurate diagnosis of radial nerve paralysis.
signs are characteristic. In the acute phase the horse is
unable to bear weight because of the inability to extend
the elbow, carpal, and phalangeal joints. If the limb is Treatment
placed under the horse and fixed in place, it can bear Treatment consists of systemic and local anti‐inflam-
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weight passively. While the horse is standing, the matory therapy, stall rest, application of a bandage
shoulder is extended and the elbow is dropped (dropped splint, and controlled exercise. A PVC bandage splint
elbow appearance) and extended while the carpus and applied to the caudal aspect of the limb from the proxi-
digits are flexed. The muscles of the elbow and the mal antebrachium to the fetlock will maintain the limb
extensors of the carpus and digit appear relaxed, and the in extension, permitting the horse to bear weight com-
limb appears longer than normal. The “dropped elbow” fortably. The splint is maintained until the horse can
appearance is not specific for radial nerve paralysis; this place the limb in extension without support. Controlled
appearance can be seen with many other conditions exercise can be started when clinical signs (neurologic
associated with the elbow, humerus, and shoulder function) begin to improve. The amount of exercise is
regions (Figure 5.43). Occasionally, radial nerve paraly- dictated by the horses’ capabilities. Electromyographic
sis is accompanied by paralysis of the entire brachial studies can be done at 4‐ to 6‐week intervals to access
plexus. In this case, the limb shows paralysis of the return of nerve function.
flexor and extensor muscles and is unable to bear
weight.
With complete radial nerve paresis, the horse is gen- Prognosis
erally reluctant to move, and at a walk the limb is EMG has been found to have a good prognostic value
dragged forward passively by the action of the proximal in assessing the extent of the injury in a small number of
pectoral, biceps brachii, and coracobrachialis muscles, cases. In most cases a guarded to poor prognosis is
15
with the dorsal surface of the hoof in contact with the given, 15,45 but compression and entrapment injuries
ground. Due to the physical distress associated with often lead to partial or complete recovery. Recovery
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radial nerve paralysis, some horses may sweat profusely may take a few weeks in pure neuropraxia to several
and have an elevated pulse and respiration. Milder months or years in axonotmesis. 45,58 Reinnervation is,
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cases of radial nerve paralysis present with varying however, unlikely with more severe nerve damage. 15
degrees of non‐weight‐bearing lameness and a dropped
elbow with mild flexion of the carpal, fetlock, and
phalangeal joints. At a walk the lameness is often char- ACKNOWLEDGMENT
acterized by a lowered foot flight arch and a shortened
cranial phase of the stride. 15 The authors thank Dr. Ted S. Stashak for his contri-
butions to this chapter in the previous edition.
Diagnosis
Many cases of radial paralysis are due to external References
trauma; therefore, the scapula, humerus, radius, and 1. Adams R, Turner TA. Internal fixation of a greater tubercle frac-
olecranon process should be examined radiographi- ture in an adolescent horse: a case report. J Equine Vet Sci 1987;
7:174–176.
cally. Radial nerve paralysis must be further differenti- 2. Anderson D, Allen D, DeBowes R. Comminuted, articular frac-
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ated from rupture of the medial collateral ligament of tures of the olecranon process in horses: 17 cases (1980 to 1990).
the elbow, elbow arthritis, and myopathy of the biceps Vet Comp Orthop Trauma 1995;8:19–23.
brachii, triceps brachii, anconeus, and extensor carpi 3. Andrews F, Reed S. Diagnosis of muscle disease in the horse. Proc
Am Assoc Equine Pract 1986;32:95–100.
radialis muscles. 70 4. Arthur R, Constantinide D. Results of 428 nuclear scintigraphic
It previously was believed that cutaneous sensation to examinations of the musculoskeletal system at a Thoroughbred
the craniolateral aspect of the antebrachium is lost with racetrack. Proc Am Assoc Equine Pract 1995;41:280–281.
complete loss of nerve conduction of the radial nerve or 5. Auer J, Watkins J. Treatment of radial fractures in adult horses: an
analysis of 15 clinical cases. Equine Vet J 1987;19:103–110.
brachial plexus and that if the sensation is present, it 6. Auer J, Struchen C, Weidmann C. Surgical management of a foal
indicates the lesion selectively affects the motor fib- with a humerus‐radius‐ulna fracture. Equine Vet J 1996;28:
ers. However, studies done in horses indicate there are 416–420.
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