BACK TO BASICS: FOUNDATIONAL CLINICAL SKILLS FOR EQUINE PRACTICE


brisk extension of the back and pelvis without disen- gagement of the stay apparatus of the pelvic limb, fol- lowed quickly by return to normal posture. Next, stroke the hemostat caudally along the skin over the gluteal muscles. This should elicit spinal flexion, fol- lowed by relaxation of the lumbar spine and pelvis, again without release of the patella from the medial femoral trochlear ridge. Common abnormal reactions to these tests include (1) partial collapse in the pelvic limbs, (2) wobbling of the pelvis from side to side, and (3) no response, all ofwhichmay be observed in horses with truncal and pelvic limb weakness and/or ataxia caused by spinal cord disease.


Tail and Anus


Assess tail strength by lifting (extending) the tail. Prod or pinch the skin adjacent to the anus and observe the anal contraction and tail-clamp reflexes. If these reflexes are abnormal or if the history sug- gests possible cauda equina syndrome, perform a rec- tal examination to assess rectal tone and bladder size and tone. Assess muscular symmetry of the tail and test cutaneous sensation over the tail and caudal structures. Anesthesia and areflexia of the tail, penis, and peri-


neum and paralysis of the anus, rectum, bladder, and penis are signs of cauda equina syndrome. Lesions of the spinal cord or nerve roots caudal to the S2 spinal cord segment cause some or all of the signs of cauda equina syndrome.


5. Gait Evaluation


Examination Have the handler walk the horse in straight lines while keeping the horse’s head and neck as straight as possible during walking. Follow directly behind the horse. From this vantage point, evaluate leg position and stride symmetry. Also, watch for excessive (1) side-to-side (wobbling)movement of the pelvis, (2) up- and-down movement of the tuber coxae (pelvic roll), and (3) side-to-side rotation of an imaginary line from the tailhead to the tuber sacrale (pelvic yaw). Next, watch the gait from the side while walking in stride with the pelvic and then thoracic limbs. Note any toe dragging, knuckling, stride-length asymmetries, and abnormal protractive movements such as hyperflex- ion, stiffness (hypometria), or excessive range ofmove- ment (hypermetria). Often, these signs are most obvious as the horse transitions from standing still to walking. Repeat this part of the examination with the horse’s chin lifted and with the horse walking up and down a modest slope. These maneuvers exacerbate most gait abnormalities, especially stiffness of the tho- racic limbs. Take extreme caution when walking ataxic horses up and down slopes as they are more likely to stumble or fall on uneven ground. Back the horse briskly, observing for limb coordina-


tion and willingness to move backward. Normal horses should readily back in a straight line in two-


202 2022 / Vol. 68 / AAEP PROCEEDINGS


beat fashion, with diagonal limb pairs moving in syn- chrony (e.g., left thoracic and right pelvic limbs). A horse with spinal cord disease may sag backward before moving and slide its hooves along the ground rather than picking themup and placing them. Take the horse in hand for the next part of the ex-


amination. Hold the lead rope with the left hand and, by walking backward, lead the horse in counterclock- wise circles. It is very important that the horse is always walking forward in these circles. Vary the di- ameter, making the circles alternately small and large. Carefully observe the motion of the right (out- side) pelvic limb by looking under the horse’storso. This limb will often arc out widely on the outside of the circle (i.e., circumduction) in horses with spinal cord disease. In mirror-image fashion, lead the horse fromthe right side in clockwise circles. Next, pull the horse sideways in tight circles in ei-


ther direction. To do this, position yourself slightly behind the shoulder and walk backward while pull- ing the lead rope caudally and downward. The goal is to have the horse pivot around its center of gravity, with the forelimbs coming toward the examiner and the hind limbs moving away. If done correctly in nor- mal horses, the opposite thoracic limb should cross in front of the supporting limb and the pelvic limbs should move reciprocally, causing the horse to pivot around a point midway between the thoracic and pel- vic limbs. Horses that are weak and ataxic tend to sag backward in the hindquarters before they start to move and then pivot the front part of the body around one or both pelvic limbs. There is often also interference between or otherwise inappropriate placement of thoracic limbs. Horses with caudal neck pain will often display reluctance or refusal to cross one forelimb over the other. Signs of limb weakness and ataxia suggest spi-


nal cord (or, rarely, peripheral nerve) damage at or cranial to the affected limb. If there is obvious ataxia and weakness in thoracic and pelvic limbs, there likely is at least one lesion in the spinal cord somewhere between the front of the C1 and back of the T2 spinal cord segments. In cases where the signs are caused by external compression of the cervical spinal cord (e.g., cervical vertebral stenotic myelopathy), signs in the pelvic limbs are usually worse than those in the thoracic limbs. When, in such cases, the pelvic limb signs are mild, thoracic limbs may appear normal. In contrast, when tho- racic limbs are normal but there is moderate or severe ataxia and weakness in the pelvic limbs, there likely is at least one lesion caudal to T2 and cranial to S3. If one or both thoracic limbs are abnormal in a horse that has normal pelvic-limb gait, the gray matter of the C6 to T2 spinal cord segments (without white matter involvement), the roots or nerves of the brachial plexus, or the periph- eral nerves to the limbs are likely affected. Asymmetric lesions in the spinal cord cause signs that are more severe on the side of the lesion. Occasionally, there are signs of weakness without


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