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Every effort should be made to help a recumbent patient stand and walk unless there is suspicion of bone fracture. By so doing, one can learn as much or more about voluntary effort and lesion localization than one can from reflex testing (Figure 2.20). Heavy animals should be moved early in the course of recumbency to avoid secondary problems such as decubital sores, decreased blood supply to limbs and dehydration, which makes evaluation difficult.

A patient that has recently become recumbent but uses the thoracic limbs well to get up likely has a lesion caudal to C₆, most often caudal to T₂. If such an animal cannot attain a dog‐sitting posture, the lesion is likely to be in the cervical spinal cord (Figures 2.13 and 2.20). If only the head, but not the neck, can be raised off the ground, there is probably a severe cranial cervical lesion. With a severe caudal cervical lesion, the head and neck usually can be raised off the ground, although thoracic limb effort decreases, and the animal usually is unable to maintain sternal recumbency. Assessments of limb function cannot be relied on while a heavy animal is lying on the limb being tested. Muscular tone can be determined by manipulating each limb. A flaccid limb, with no motor activity, is typical of a final motor neuron lesion to that limb, but in heavy recumbent animals there can be poor tone and little observable voluntary effort in a limb that has suffered pressure damage from been lain upon. A severe central motor pathway lesion to the thoracic limbs at C₁–C₆ causes poor or absent voluntary effort, but there will be normal or sometimes increased muscle tone in the limbs. This is because there is a release of the final motor neuron that is reflexly maintaining normal muscle tone under the calming influences of the descending central motor pathways. Interestingly, such a spastic (hypertonic) paralysis only in the pelvic limbs can also be seen with lesions between C₆ and T₂ if little or no thoracic limb gray matter is affected. A Schiff–Sherrington phenomenon of short duration (hours to a few days), with excessive extensor tone in the thoracic limbs in the presence of good voluntary activity and normal reflexes, has been seen rarely in horses and usually follows a cranial thoracic vertebral fracture.³⁶

Finally, spinal reflexes are tested in the thoracic limbs. The flexor reflex in the thoracic limb involves stimulation of the skin of the distal limb with needle holders and observing for flexion of the fetlock, knee, elbow, and shoulder (Figure 2.21). This reflex arc involves sensory fibers in the median and ulnar nerves, spinal cord segments C₆ to T₂, and motor fibers in the axillary, musculocutaneous, median, and ulnar nerves. Lesions cranial to C₆ may release this reflex from the calming effect of the central motor pathways and cause an exaggerated reflex with rapid flexion of the limb. The limb may remain flexed for some time and even show repetitive movements or clonus. Such lesions may also result in a crossed extensor reflex, with synchronous extension of the untested limb. This usually occurs only with severe and chronic central motor pathway lesions. Thus, an animal affected by such a lesion may demonstrate considerable reflex movement following stimuli, but usually will have little coordinated voluntary motor activity in the limbs being tested. A spinal reflex can be intact without the animal perceiving the stimulus, and the latter must be observed independent of the local reflex movement. Cerebral responses associated with the perception of the skin pinch include changes in facial expression, head movement, and phonation. Conscious perception of the stimulus will be intact only if the afferent fibers in the median and ulnar nerves, the dorsal gray columns at C₆–T₂, and the central sensory pathways in the cervical spinal cord and brainstem are intact.

Figure 2.20 Complete paraplegia with good function in the thoracic limbs is seen in these young ruminants (A to D). This will often be consistent with a lesion caudal to T₂ and sometimes (B) the tone in the pelvic limbs will be increased indicating a lesion most probably from T₃ to L₃. In this case, the pelvic limb reflexes were hyperactive, also consistent with spastic paraplegia due to a lesion from T₃ to L₃. Such a patient often will struggle around using the thoracic limbs (C). However, when a young ruminant postures and moves around (D), with the thoracic limbs not extended, the possibility of an additional lesion cranial to T₃ must be considered.

Figure 2.21 The only important spinal limb reflexes to perform on any patient that can be placed in lateral recumbency are the flexor reflexes in the thoracic limbs (A) and the pelvic limbs, and the extensor or patellar ligament reflex in the pelvic limbs (B). All other reflex testing can be problematic in interpretation, and results of such tests rarely change an anatomic diagnosis. Appropriate hyperactive reflexes and crossed extensor reflexes were present as expected in this normal neonatal calf. Reflexes should be tested in both pairs of limbs while uppermost, and while dependent, the most prominent result being taken as real, with prominently asymmetric reflexes helping to lateralize a lesion. Rarely, a reflex cannot be elicited in a normal patient, usually bilaterally.

Interpreting results of testing the tendon reflexes—triceps, biceps, extensor carpi radialis, etc.—in the thoracic limbs is problematic and does not usually assist in defining the site of neurologic lesion, perhaps except for neonatal animals. Also, patients with profound diffuse neuromuscular paresis can have reflexes that are at least present. However, a general description of two of these reflexes follows—descriptions for the remainder being superfluous. To perform the triceps reflex, the relaxed limb is held slightly flexed, and the distal portion of the long head of the triceps and its tendon of insertion is balloted with a rubber neurology hammer in smaller patients or a heavy metal plexor in larger patients while observing and palpating for contraction of the triceps muscle, which causes extension of the elbow. The triceps reflex involves the radial nerve for its afferent and efferent pathways and spinal cord segments C₇ to T₁. The triceps reflexes, although present, can be extremely difficult to demonstrate in heavy, adult, recumbent patients. The musculotendinous portion of the extensor carpi radialis muscle can be balloted to produce an extension of the knee when the relaxed limb is held in a partially flexed position. This extensor carpi radialis reflex involves afferent and efferent fibers also in the radial nerve, but the reflex may not always be present in normal adult animals.

All these reflexes are usually active in normal neonates in which there is a prominent crossed extensor reflex present that subsides through the first weeks of life.

The pelvic limb spinal reflexes may also be evaluated in all animals that can be restrained in lateral recumbency and in all recumbent patients. In addition, the amount of voluntary effort and muscle tone present in the pelvic limbs is assessed in recumbent patients. As described for the thoracic limbs, this can be performed while watching the animal attempt to get up or by observing its struggle in response to stimuli while lying in lateral recumbency. Consideration must be given to possibly exacerbating a fracture.

The patellar reflex and the flexor reflex are the two most clinically important spinal cord reflexes involving the pelvic limbs. The patellar reflex is performed by supporting the limb in a partly flexed position, tapping the middle patellar ligament with a neurologic hammer or a heavy metal plexor, and observing a reflex contraction of the quadriceps muscle resulting in extension of the stifle (Figure 2.21). The sensory and motor fibers for this reflex are in the femoral nerve, and the spinal cord segments involved are primarily L₄ and L₅. The flexor reflex is performed by pinching the skin of the distal limb with needle holders and observing for flexion of the limb. The afferent and efferent pathways for this reflex are in the sciatic nerve and involve spinal cord segments L₅ to S₃ (Figure 2.16).

Although two other reflexes can be elicited in most neonatal animals, they are frequently not clearly reproducible in adult patients, and thus results of testing them do not usually contribute to defining the site of neurologic lesions. The gastrocnemius reflex is performed by balloting the gastrocnemius tendon and observing and palpating the contraction of the gastrocnemius muscle, which is accompanied by an extension of the hock. This reflex involves the tibial branch of the sciatic nerve and spinal cord segments L₅ to S₃. Second, the cranial tibial reflex results in contraction of the cranial tibial muscle with hock flexion occurring when the muscle is balloted and the relaxed limb is held partially extended. Variable limb movement and direct impact muscle contraction in response to mechanical stimulation may be interpreted falsely as a positive reflex muscle contraction when both these reflexes are tested.

Distinguishing characteristics of final motor neuron paresis and paralysis and central motor pathway paresis and paralysis are given in Table 2.5. Such distinctions can be straightforward in assisting to anatomically localize the site and extent of spinal cord and peripheral nerve lesions in many patients, but in recumbent heavy patients and those with chronic disease and disuse these classic characteristics can merge such that this distinction becomes problematic.

Table 2.5 Common clinical features with lesions involving central motor pathway and final motor neurons

Clinical sign	Clinical features with lesion in
Central motor pathway	Final motor neuron
Muscle tone	Normal to hypertonic	Hypotonic to flaccid
Muscle atrophy	None or disuse*	Significant
Muscle fasciculations	NOT present	Present
Reflexes	Normal to hyperactive	Hypoactive to absent

^* With lameness and disuse in fit horses, this becomes quickly evident in proximal muscles.

Skin sensation from the pelvic limbs should be assessed independently from reflex activity using the two‐pinch technique focussing on the autonomous zones (Figure 2.15). The femoral nerve is sensory to the skin of the medial thigh region, the peroneal nerve to the dorsal tarsus and metatarsus, and the tibial nerve to the plantar surface of the metatarsus and fetlock. As for the thoracic limbs, lesions of the peripheral nerves to the pelvic limbs, such as the femoral and peroneal nerves, result in specific motor deficits; however, the precise sensory deficits can be difficult to define.

The patellar reflex is hyperactive in newborn foals, lambs, calves and kids, and probably in all large animal neonates. Also, the cranial tibial and gastrocnemius tendon reflexes are easily performed in healthy, cooperative newborn patients. As with the forelimbs, these patients have normal, strong, crossed extensor reflexes. In addition, an extensor thrust reflex is obtained, in very young patients, by rapidly overextending the toe while the limb is already partially extended. This results in a forceful extension of the limb and possibly represents a Golgi tendon organ reflex that becomes suppressed as the animal matures.