Front Matter

Chapter 20 Imaging in Canine Sports Medicine 511

Though ubiquitous in equine imaging, the
use of bone scintigraphy is not common in
small animal practice, likely due in part to the
availability of alternative imaging techniques
such as CT and MRI. Unlike CT and MRI, scin-
tigraphic exams can be performed in the awake
animal under light sedation, and the entire
skeleton can be imaged in a short time (Schwarz
et  al., 2004). Regulations surrounding the use
and handling of radiopharmaceuticals and the
patient postinjection have made it impractical
for many facilities to offer the procedure.
Despite these limitations, it is still a viable
option for use in canine diagnostic imaging,
especially in occult or complex lameness.

Electrodiagnostic testing

Electromyography and nerve conduction stud-
ies are used in conjunction with a complete
neurological exam to test function of the
muscles and nerves. A battery of tests includes:
electromyography; peripheral motor and sen-
sory nerve conduction; evaluation of nerve root
function with F waves, cord dorsum potential,
and H reflex studies; and assessment of the
neuromuscular junction with supramaximal
repetitive nerve stimulation and stimulated sin-
gle‐fiber electromyography (Cuddon, 2002).
Electromyography and motor nerve conduc-
tion studies are the most often performed
studies in human and veterinary medicine and
will be the focus of this section. More informa-
tion on the additional testing and their indica-
tions is available elsewhere (Cuddon, 2002).

Electromyography

Electromyography evaluates the insertional,
spontaneous, and voluntary electrical activity
of the muscle cell membrane in the motor unit
(Chrisman et al., 1972; Brown & Zaki, 1979). By
recording the changes in the electrical potential
of the muscle cell membrane, electromyogra-
phy can help differentiate between primary
myopathy and neuropathy, identify lesion
location, and determine severity of the injury
to the nerve (Chrisman et  al., 1972; Brown &
Zaki, 1979; Cuddon, 2002).

Electrode needles are placed in the muscle

unit to be evaluated. These electrodes are

connected to an amplifier which enhances the

electrical signal from the muscle cell mem-

brane. This electrical activity is shown on an

oscilloscope and projected through a speaker

providing both visual and auditory evaluation

of the signals. There are characteristic visual

and auditory signals that are produced by both

normally and abnormally functioning motor

units (Table 20.1). At rest, muscle is electrically

silent. Upon insertion of the electrode needle

there is a sharp spike in electrical activity that

should return to zero once the insertion is com-

plete and the muscle returns to rest. Incomplete

relaxation and voluntary contractions will also

produce characteristic electrical activity that

also returns to zero upon complete relaxation.

Abnormalities are detected with insertion or

movement of the electrode needle and observ-

ing the produced wave forms and sounds out-

lined in Table 20.1.

Motor nerve conduction

The focus of motor nerve conduction studies is

the function of the peripheral nerves. By calcu-

lating the speed of an electrical signal through a

muscle innervated by the nerve in question, the

integrity of that specific nerve (e.g., radial nerve)

can be evaluated. Nerve conduction studies are

typically used for differentiating between dis-

use and dennervation atrophy, as well as the

detection of axonal loss in the peripheral nerves.

These studies are typically performed in con-

junction with electromyography.

Using the same basic equipment as electromyo-

graphy, and a nerve/muscle stimulator, elec-

trodes are placed proximal and distal on the

motor unit to be tested. The compound muscle

action potential amplitude, duration, and area are

all measured and the velocity of the electrical

signal from the anode and cathode are measured

after stimulation is applied. The nerve conduc-

tion  velocity is then calculated from these data

using the equation: Nerve conduction velocity =

Distance between points/(Proximal conduction

latency  –  Distal conduction latency) (Cuddon,

2002). Normal values for conduction velocity