Page 87 - Canine Lameness

4.3 The Neurologic Examination 59

Similar to the pelvic limb, all reflexes of the thoracic limb are performed in lateral recumbency.
The biceps reflex is elicited by placing an index finger firmly on the tendinous insertion of the biceps
muscle on the radius. While extending the elbow and pulling the thoracic limb caudally, the index
finger is gently struck with the plexor. To elicit the triceps reflex, the antebrachium is held with the
elbow maintained in flexion and rotated slightly outward (elbow abducted). The triceps tendon is
struck with the plexor, just above the olecranon. To elicit the extensor carpi radialis reflex, the ante-
brachium is supported with the elbow and carpus resting passively in flexion. The muscle belly of
the extensor carpi radialis is struck with the pleximeter, just distal to the elbow on the medial aspect.
4.3.7.2 Flexor (Pedal and Withdrawal) Reflexes
In the normal animal, the flexor reflex is meant to serve as protection against noxious stimuli that
would be potentially damaging to the skin. For example, if the animal steps on a sharp object, the
foot is immediately withdrawn even before pain is consciously perceived. The flexor withdrawal
reflex is more complex than myotatic reflexes; because the response involves flexion of all the mus-
cles in the limb, several spinal cord segments are activated. The receptors of the withdrawal reflex
are specialized nociceptors that respond only to noxious stimuli (pressure, heat, and cold). As
such, the stimulus used during reflex testing must be strong enough to discharge these nerves. A
sufficient noxious stimulus applied to a digit should cause the joints to flex (i.e. the limb with-
draws). Which afferent nerve is assessed depends on the specific area of skin being stimulated (for
applicable cutaneous areas, please refer to Table 4.4). The flexor reflex is a spinal reflex and there-

Table 4.4 Cutaneous sensory testing and autonomous zones used in the pelvic and thoracic limbs.

Nerve tested Cutaneous sensation Site used for testing autonomous zone
Thoracic limb
Radial Dorsal surface of the paw Dorsal surface of digits 1, 2, 3, and 4
Dorsal surface of digits 1, 2, 3, and 4
Musculocutaneous Medial aspect of the antebrachium Medial aspect of the antebrachium
Ulnar Caudal and palmar surfaces of the Caudal aspect of the antebrachium
antebrachium and paw; including digit 5 and lateral aspect of digit 5
Median Palmar surface of the paw None exist
Pelvic limb
Lateral cutaneous Craniolateral surface of the thigh Craniolateral surface of the thigh
femoral
Caudal cutaneous Caudal aspect of the proximal thigh Caudal aspect of the proximal thigh
femoral
Genitofemoral Proximal medial surface of the thigh and Proximal medial surface of the thigh
prepuce/vulva and prepuce/vulva
Saphenous Medial aspect stifle to hock Medial aspect; stifle to hock
Digits 1 and 2
Sciatic Caudal aspect of the distal thigh and caudal Caudal aspect of the distal thigh and
surface of the tarsus caudal surface of the tarsus
Tibial Plantar surface of the paw Plantar surface of digits 3, 4, and 5
Plantar surface of digits 3, 4, and 5
Fibular (peroneal) Dorsal surface of the paw Dorsal surface of digits 3, 4, and 5
Dorsal surface of digits 3, 4, and 5