3 Case Studies

By Dr. Lauren MacLeod

The musculoskeletal system of the horse is an incredible machine — strong, fast, efficient, and capable of performing feats as varied as jumping obstacles and roping cattle. However, horse owners are all too aware of the fact that despite this amazing athletic ability, the equine body can be remarkably fragile. If one owns horses long enough, he or she is bound to encounter a disorder of the equine musculoskeletal system. For most of us, this conjures the image of a lame horse and many hours of cold hosing, bandaging, and veterinary visits. This is not without good reason as traditionally, the limbs have been the focus of equine musculoskeletal injuries. Veterinarians and horsemen alike have long considered lameness to be the hallmark of equine locomotion disorders. The limbs comprise the appendicular skeleton, and are complex, delicate structures that are often subject to injury, resulting in heat, pain, and visible lameness.

But what if a horse isn’t lame, but is also “not quite right?” Perhaps he just doesn’t perform as well as he used to, or is acting unfavourably under saddle. This vague and sometimes perplexing complaint is a common one presented to veterinarians when a horse fails to perform to his previous standard. While there are many medical or behavioural reasons why a horse may not be performing well, one of the more common causes is pain originating from his axial skeleton, or more specifically, the spine.

Spinal pain in the horse can present with a variety of clinical signs, depending on which part of the spine is involved (see Equine Skeleton). Head tossing, inverting the neck, or resisting lateral or longitudinal flexion while being ridden are characteristic of pain in the cervical spine. Horses with thoracic and/or lumbar discomfort may resent being groomed or saddled, and may buck or rear when asked to collect in an attempt to escape the added pressure on their painful back. The signs of sacral pain include reduced engagement of the hindquarters, dragging the hind toes, or a “bunny-hopping” gait at the canter in which the hindlimbs move together rather than in a true three-beat canter. Occasionally, horses with primary spinal pain do present with a true lameness. These cases can be difficult to diagnose, as an appendicular cause of lameness must be ruled out prior to assuming primary spinal pain. Sometimes, all that is reported in a horse with spinal pain is a decreased athletic ability when compared with his previous level of performance.

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When any of these signs develop in a horse, it is important to rule out physical discomfort as a cause of poor performance. Having a thorough veterinary assessment to achieve an accurate diagnosis is crucial to determine the best course of treatment for the individual horse. The goal of this article is to describe some common equine spinal problems that may be encountered by the horse owner, and how they are best treated to get the horse back on track.

CASE STUDY 1

The Cervical Spine – Wobbler Syndrome

The neck, or cervical vertebrae, represents the first area of the axial skeleton where abnormalities can develop. The cervical region is amazingly similar across all mammals - shrews, humans, giraffes, and horses all have seven vertebra! While the length and anatomy obviously varies significantly among these species, the function of the spine in this area remains the same: to provide structural support for carriage of the head, and provide a protective tube for the spinal cord as it travels to the body. 

While there are several conditions affecting the neck area, one significant spinal issues we see is “wobblers.”

Neck radiographs of normal spinal cord (green) and abnormal angle with spinal cord compression (red). Photos: Agwest Veterinary Group Ltd.

Wobbler disease is a common name for a specific condition called cervical vertebral malformation, or CVM. This vertebrae malformation results in spinal cord compression. While all breeds are represented in case reports of wobbler syndrome, Thoroughbreds are the most commonly affected breed, with some studies estimating up to two percent of horses being affected to some degree. Both females and (more often) males are affected by this condition.

Typically this problem is characteristic of young, rapidly-growing horses less than two years of age. Clinical signs may not be apparent until the horse is several years old; however, a careful neurological examination can often detect subtle abnormalities that are present early in the course of the disease. While often attributed to young foals or yearlings just “being clumsy or learning where their feet are,” specific movements under different postures may be needed to differentiate the normal, unpredictable acrobatics of an excited yearling from the early stages of wobbler syndrome. Additionally, the age of clinical onset will vary with the specific type of wobbler disease the horse has.

The abnormal proprioception (the ability to detect where you are positioning your body, feet, and legs), gait movements, and balancing reactions seen with wobbler syndrome come from spinal cord compression. Generally, we do not see any overt pain at the site of spinal cord compression. Over time this compression does eventually cause some tissue damage and inflammation, which itself can be painful, but the abnormal movements of the horse are from direct interference with normal functioning of the spinal cord signals. Other causes of neck-region related “lameness” may absolutely be accompanied by pain, including soft tissue damage and facet joint arthritis.

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As a veterinarian, listening to the presenting complaint of the owner or trainer is one of the most valuable parts of the visit. Astute, knowledgeable owners spend the most time with the horse, and their history will often present that “golden nugget” of information if we listen carefully. This rings true with wobblers history as the syndrome often presents as two distinct forms of the disease: static or dynamic. 

With static CVM there is compression of the spinal cord in a specific area that causes clinical signs regardless of the neck position. Most commonly this occurs in the lower neck involving the vertebral joints C5-C6 or C6-C7. Nerve deficit symptoms are noticed even when the neck is in a neutral position and are not typically worsened during flexion or extension of the neck. 

Dynamic CVM occurs when the clinical signs become apparent with specific neck movements. This can occur with either flexion downwards, extension upwards, or lateral flexion either to the left or right. The golden nugget in the owner’s history is the complaint of lameness, tripping, or abnormal posture only when specific movements are being performed. This may be described as the young weanling walking funny downhill, or the three-year-old warmblood gelding tripping in the left canter lead. Since the spinal cord compression is a process that takes time to develop, initially the cord may have adequate space within the vertebral column in a neutral position only. Eventually, the movement of the vertebral joints pinches the cord enough to cause the symptoms.

Clinical signs

Horses with clinical signs of CVM may exhibit tripping, abnormal toe wear, asymmetrical limb movement, and proprioception deficits where the horse appears to be “searching” for where to place its feet. As the severity progresses, there can be swaying or leaning of the body to one side, and weakness or loss of muscle tone in affected limbs. As mentioned, since the compressive lesions can occur anywhere around the spinal cord, signs may be unilateral and affect only one side of the body. More commonly, the hindlimbs are affected first despite being quite far from the actual problem in the neck region. This occurs because the arrangement of grey and white matter nerve tissue within the spinal cord has the hindlimb white matter nerve fibres located around the most outside portion of the cord. As a result, they get compressed first.

Diagnosis and treatment 

History, physical examination, and diagnostic imaging with radiographs and ultrasound are the basis for CVM diagnosis. Abnormal vertebrae joint angles are the hallmark of spinal cord compression. Unfortunately, once clinical signs develop there are very few treatment options with long term success. Control of inflammation and pain may give short term relief, but the disease is progressive in nature. Retirement from riding and safe turnout is a common recommendation. 

CASE STUDY 2

The Thoracolumbar Spine - Overriding Dorsal Spinous Processes

In recent years, the term “kissing spines” has entered the common equestrian vocabulary, and many horses have received this potentially career-limiting diagnosis. But how common is this condition, and how is it treated?

Thoroughbreds are more likely to develop problems from ODSP than other breeds, which is attributed to their selection for back structure most suited to lengthening at a full gallop rather than collection. Photo: Shutterstock/Dennis W Donahue

Kissing spines, more correctly called overriding dorsal spinous processes (ODSP), is a condition in which the bony projections on the top of the thoracic and lumbar vertebrae are too close together, resulting in pain and inflammation when they make contact with each other. In a normal spine, the dorsal spinous processes are evenly spaced and separated by connective tissue. 

Overriding dorsal spinous processes, or “kissing spine.” Photo: Agwest Veterinary Group Ltd.

Clinical signs

In horses with overriding dorsal spinous processes, the bones contact each other and “kissing lesions” develop at these points of contact. These kissing lesions are characterized by bone resorption and remodelling, which is visible on radiographs. The inflammatory response at these sites of impingement contributes to pain, muscle spasm, adverse behaviour, and decreased ability to perform.

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A 2011 veterinary study found that over one-third of horses with no sign of back pain have radiographic evidence of ODSP. That is: Normal, non-painful horses can have so-called “kissing spines.” Therefore, simply finding these lesions on radiographs is not sufficient for diagnosing this condition. However, the presence of ODSP lesions on radiographs is a predisposing factor for back pain, as horses with clinical back pain are almost twice as likely to have ODSP lesions than those with no back pain. It has also been noted that horses in dressage training are more likely to have clinical pain associated with ODSP, which is most likely due to the emphasis on collected work and engagement of the back muscles so desired in this discipline. Thoroughbreds are also more susceptible to this condition than other breeds. As a racing breed, the Thoroughbred has been selected for a back structure most suited to lengthening at a flat-out gallop. It is thought that when the Thoroughbred is then repurposed as a riding horse and expected to collect its frame, structural differences that promote galloping ability result in impingement of the dorsal spinous processes. Therefore, while more than one-third of horses have ODSP lesions, only some of them become painful, and they are more likely to become a problem in dressage horses and Thoroughbreds than in other horses.

Diagnosis and treatment

If a veterinarian suspects ODSP as a cause of back pain in a horse, he or she will use clinical examination and medical imaging techniques to confirm the diagnosis. This will likely include a standing musculoskeletal palpation examination, moving soundness evaluation, and radiographs. Depending on his or her findings, the veterinarian may also recommend further testing such diagnostic analgesia to confirm the source of pain, or more advanced medical imaging such as nuclear scintigraphy. Once the diagnosis of ODSP has been confirmed, a treatment plan can be instigated.

Treatment of ODSP is multifactorial, and there is no single effective therapy. Initial medical management may involve prescription anti-inflammatories (such a phenylbutazone or firocoxib) and/or muscle relaxants to improve the horse’s comfort. The horse’s saddle should be assessed by a qualified saddle fitter to ensure it fits well and is not contributing to the back pain and muscle spasm. It is often recommended to slowly rehabilitate the horse by gradual return to work in a low, stretching frame on the longe line. This helps strengthen the core and back muscles without the added weight and pressure of a rider. Other adjunctive medical therapies that can help reduce back pain are mesotherapy, extracorporeal shockwave therapy, and acupuncture. Some horses will require direct injection of the painful areas of the back with corticosteroids, which are potent anti-inflammatories. Upon diagnosis of ODSP, the veterinarian will design a tailored treatment protocol for each patient to help maximize the chance of success.

For horses that do not respond to medical management of ODSP, surgical correction can be considered. A relatively new technique, called an intraspinous ligament desmotomy, involves cutting the short ligaments that run between the impinging dorsal spinous processes. This surgery can be performed in a standing horse, thus eliminating the risk of general anesthesia. In most cases, recovery takes a matter of weeks and postoperative care is minimal. Success rates for return to previous level of work have been reported to be as high as 80-95 percent with this procedure. While still new on the scene in the management of ODSP, this surgery appears to be a promising option. 

Although the diagnosis of kissing spines has been associated with career-limiting pain, veterinary research has led to better understanding of the development of this condition and its management. Today, owners of horses affected by kissing spines have a wealth of options in the treatment of this condition, and many horses can return to their previous level of work. 

CASE STUDY 3

The Pelvis

While the vast majority of hind-end related musculoskeletal abnormalities will involve the actual limbs themselves, the pelvis is becoming increasingly diagnosed as a primary problem. This is in part to more widespread comprehensive training of veterinarians and the incredible advances in diagnostic imaging available for horses. With the combination of radiographs, ultrasound, and nuclear bone scans, we are able to effectively image the majority of the equine pelvis. 

Photo: Thinkstock/GlobalP

The pelvis is comprised of several parts. There are five sacral vertebrae that are fused together to form the sacrum. At the front end of the pelvis the sacrum joins onto the lumbar (lower back) vertebra at the lumbosacral (LS) joint. This is where 90 percent of the vertical flexion and extension of the lumbar area occurs. Behind the sacrum is located the coccygeal or tail vertebrae, which vary in number. On each side of the spine, the sacrum joins onto the ilium (hip bones) at the SI joint. This SI area is a major cause of spinal pain in horses. 

SI disease involves the whole region around each SI joint. While there may be problems within the actual joint itself, the supporting soft tissue ligament structures are often involved in the disease process. Development of SI pain can occur from a point-in-time traumatic injury to the pelvic area such as a fall or collision, but more often it is a result of long term gradual stress-related damage to the region. This ongoing stress can be due to poor conformation, compensation for limb or lumbar back pain, or specific athletic movements based on riding discipline. 

Pelvic Palpation. Photo: Agwest Veterinary Group Ltd.

Presenting complaints

There are many consistent details when owners present horses with suspected SI disease. Back pain, stiff hind end gaits, and lack of propulsion for both flat and jumping disciplines are all commonly observed. Examination of the horse will reveal a painful response when palpating the tuber sacrale, reluctance for flexion of the hindlimbs, and flexion testing may actually result in worsening of an opposite hindlimb lameness.

SI disease may occur from long term compensation for a specific hindlimb lameness such as hock arthritis, but often it will present as the primary clinical problem with no additional limb issues. This will be determined based on the exam findings, diagnostic nerve blocks, and motion evaluation. Interestingly, one characteristic gait abnormality seen with SI disease is the hindlimbs “walking a tightrope.” This tracking of both hind feet landing near midline reduces pelvic rotation and is more comfortable for the horse. 

Diagnosis and treatment 

While diagnostic imaging with ultrasound, radiographs, and bone scans will help identify SI disease, the veterinary exam described above is the most integral part of the process. Treatment for sacroiliac problems is very rewarding. The gold standard method for relieving pain in this area are ultrasound guided injections of the SI region. Using long needles, we use the ultrasound to visualize delivery of medications to the front and rear aspects of the region. The joint and the surrounding ligaments are the general target area medicated. Additional therapies may also include acupuncture, mesotherapy, and extracorporeal shockwave therapy. 

Conditions of the equine spine that reduce comfort or function can have drastic effects on a horse’s performance. The first and most important step in diagnosing and treating these issues is the detection of signs that suggest the spine as the source of trouble. Keen observation of changes in a horse’s behaviour or locomotion should alert the rider or caretaker to developing problems. If spinal pain or dysfunction is suspected, veterinary assessment should be pursued in order to achieve an accurate diagnosis. From cervical vertebral malformation to sacroiliac pain, a wide range of conditions exist that affect the complex axial skeleton of the horse. Recent years have brought more awareness of equine spinal problems, both in the general equestrian public and in the veterinary profession. This awareness, together with the development of effective treatment modalities, has given many horses with spinal disease relief from pain, and a second chance at their performance careers.

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Main Photo: Shutterstock/Anastasia Popova