The flexor reflex is evaluated by pinching both the lateral and medial toes at the base of the nail of the nonrecumbent limb.
Complete limb flexion is expected (Figure 6). The afferent pathway of the reflex is mainly from the sciatic nerve and part of the femoral nerve on the medial toe, and
the efferent pathway evaluates the integrity of the sciatic nerve (L6-S1 segments of the spinal cord). When evaluating the
flexor reflex, make sure that there is maximal flexion of all joints before concluding that the reflex is normal. In many
patients with sciatic paresis (e.g. polyneuropathy, lumbosacral compression), flexion of the hocks might be incomplete. Because marked joint pain can result
in poor flexion and lead to a wrong assessment, it is important to evaluate the limb for any sign of pain before testing the
flexor reflex by performing a good orthopedic examination.
5. Evaluating muscle tone. 6. Testing the flexor reflex.
For the thoracic limbs, the most reliable myotatic reflex is the extensor carpi radialis. With the patient in lateral recumbency,
support the nonrecumbent thoracic limb at the level of the elbow. With the elbow and carpus in slight flexion, strike the
extensor carpi radialis muscle with a plexor. A slight extension of the carpus is expected, although it cannot be elicited
in some patients. The afferent aspect of the extensor carpi radialis reflex is mediated mainly by the radial nerve for the
medial toe and the ulnar nerve for the lateral toe. A complete and prompt normal reflex requires the proper function of many
nerves of the brachial plexus coming from the C6-T2 segments of the spinal cord (axillary, musculocutaneous, median, ulnar,
and radial nerves). Other tendon reflexes can be evaluated, but they are not always reliable.2 A good description of these reflexes can be found elsewhere.1
The perineal reflex is evaluated by gently touching the perineal area with a pin or forceps (the afferent pathway is the pudendal
nerve). The normal response is flexion of the tail and contraction of the anal sphincter mediated by the S1-S3 and caudal
segments of the spinal cord. Evaluate the reflex on both sides.
The cutaneous trunci reflex allows evaluation of the superficial sensation of the thoracolumbar spinal cord along with the
cutaneous trunci muscle, innervated by the lateral thoracic nerve (spinal cord segment C8-T1). The afferent nerve comes from
the stimulated segment, enters the spinal cord at the level of the stimulation, and travels cranially (bilateral). A synapse
occurs at C8-T1 causing a bilateral contraction of the cutaneous trunci muscle. With the animal standing or in sternal recumbency,
gently pinch the skin lateral to the spine from caudal to cranial. As mentioned previously, the stimulation of one side should
stimulate a bilateral contraction of the cutaneous trunci muscles. In cases of a unilateral C8-T1 involvement, the cutaneous
trunci reflex will be absent unilaterally on the side of the lesion, regardless of the side of the stimulation. In cases of
a transverse myelopathy, the cutaneous trunci reflex may be absent bilaterally, caudal to the lesion. In normal animals, the
reflex gradually disappears in the middle to lower lumbar area. It can be difficult to elicit in some animals, especially
Conscious proprioception reactions
You first evaluate the conscious and unconscious proprioception while evaluating the gait (e.g. knuckling, dragging of the toes); however, it is worth further evaluation. Conscious proprioception is a reaction and, thus,
requires normal function of all the ascending and descending pathways in the spinal cord up to the contralateral somesthetic
cortex. In dogs, evaluate conscious proprioception with the animal standing. For the hindlimbs, I like to support the patient's
weight under the pelvis and gently place the foot on its dorsal surface (Figure 7). A normal patient will quickly and properly replace the foot on its plantar surface. Some animals are more relaxed with
support under the abdomen. Also, a submissive or painful dog may be slow to replace the limb even if the proprioceptive pathway
is intact. For the forelimb, I like to stand over the dog and support the patient under the chest with one hand (Figure 8). Gently place the front paw on its dorsal surface. It is not unusual that a pet won't let you place the dorsal surface on
the floor before attempting to replace it.