The Equine Spine--Back To Work
Think of your fondest memory of a time spent with a horse. Chances are you were going for a ride, enjoying the scenery and the companionship that exists between horse and human. It is no wonder that with the time we endeavor to spend on our horses' backs, we spend thousands of dollars each year to pamper them--gel pads, foam pads, air pads, saddles with wide trees, narrow trees, and adjustable trees. We use hot and cold therapies, acupuncture, electrostimulation, massage, magnets, and chiropractic techniques to help our horses' backs. Yet only a few specialists understand the complexities of the equine spine.
Jean-Marie Denoix, DVM, PhD, of the Centre d'Imagerie et de Recherche sur les Affections Locomotrices Equines (CIRALE) is one of the world's few specialists in equine locomotion. He has been studying the equine back for more than 15 years, collecting countless images and anatomical specimens, and discovering unique ways to help practitioners and horse owners visualize what is going on beneath the skin of our horses.
Denoix took some time out of his schedule of clinical cases and teaching at CIRALE, lecturing around the world, and writing scientific articles and books to relate some of his vast knowledge of the equine spine to readers of The Horse. He wants us all to understand how the equine spine is made, how it moves, and what can go wrong.
First, how can we visualize and understand what's going on under that hair, skin, and muscle? Denoix has diagnostic steps to examine a horse with performance problems that he believes might stem from the spine.
Inspection -- First, he examines the horse's spine at rest, looking at the topline for any asymmetrical areas and lumps or bumps. He also palpates the horse's spine, and encourages the horse to stretch his neck to see where there might be limitation in the animal's movement.
Thermography -- This tool is used to locate any abnormal thermal (hot or cold) areas on the back. This is done before watching the horse's performance while exercising. CIRALE has a special mirror that is mounted on the ceiling above the stocks in one examination room. This mirror reflects thermal changes in a horse's back to a thermography camera. The thermal images then can be saved in a computer.
Fabrice Audiegie, DVM, PhD, Maitre de Confèrences (Associate Professor) at CIRALE said that thermography is used on every horse which comes for a clinical examination. "It's simple," he said, "and it can allow us to determine more precisely which examination could be done on the horse and reduce the cost of the exam. Is there a hot spot on a particular section of the back? We'll look at the movement of the back closer. With some horses it will give us another hypothesis about the problem."
Exercise -- The horse is taken and worked both in-hand and on the longe on a hard surface, medium surface, and in soft sand. Denoix, his students, and his colleagues look for any obvious gait abnormalities.
Radiography -- Denoix was one of the first researchers who didn't use general anesthesia in radiographing the equine spine. "Under general anesthesia," he said, "you have to put the horse down, and control anesthesia and recovery. This increases time and cost. X rays in the standing horse began at Alfort (the veterinary school at Alfort is the parent university of CIRALE)."
Denoix had the strong feeling that back pain and injuries don't necessarily result from injury to the superficial surface of the spinal vertebrae, as many practitioners believed, but that clinical signs of back injuries are caused by lesions deep within the spine.
With computerized radiography at the Center, Denoix is able to view X rays immediately after capturing them, changing the exposure and resolution so that certain areas of the vertebral column can be seen in the most advantageous way. It is not uncommon to see Denoix showing a horse owner a radiograph of the horse's back, while illustrating with specimens how two vertebrae should fit together and how they are abnormal in the owner's horse. CIRALE has a complete spinal column in the radiograph viewing room, which is used for illustration with clients and students.
Ultrasonography -- Ultrasound is used to gather information about underlying bone and tissue in some areas of the spine. The echogenicity (how the sound waves reflect off of or are absorbed by an object) of the area can tell a clinician with a thorough understanding of anatomy whether or not there are lesions or articular changes in the spine. After pinpointing a problem spot in a radiograph, Denoix is able to more accurately target an area for ultrasonography.
Scintigraphy -- After injecting a special radioactive material, a gamma camera is used to detect fractures, bony lesions, and abnormalities within the spine. (It also can be used for soft tissues.) This technique is particularly useful in identifying bony lesions that cannot be detected with radiography since it identifies areas where bone is remodeling.
The combination of these diagnostic techniques gives clinicians, students, and clients a better look at the spine. Denoix explained, "My philosophy: The way you are considering a medical problem is totally dependent on the technical means you can use to investigate the disease."
It's All In The Joints
The spine contains the smallest joints of the equine locomotor system, which are moved by some of the thickest muscles of the body (over the back). You can see the broad range of spinal movement in all types of equine athletes -- in the agility of the Grand Prix jumper clearing a line of obstacles or the cutting horse maneuvering low to the ground, mirroring every minute move of a cow. To help better understand this complex series of joints, Denoix took us on a tour of the spine.
The vertebral column can be divided into five regions: the cervical (consisting of seven vertebrae), thoracic (18), lumbar (six), sacral (five), and coccygeal (15-21). They are numbered cranially to caudally (head to tail) by type (T1, T2; S1, S2, etc.). The first two cervical vertebrae -- the atlas and the axis -- have specialized functions for side-to-side and up-and-down movement. The thoracic vertebrae begin at the point of the shoulder and continue to where the last rib attaches to the vertebral column. The thoracic vertebrae closer to the neck have prominent dorsal spinal processes (projections) for attachment of muscles that support the front legs, head, and neck. The vertebrae of the sacral area help support the hind legs, and their ligaments form broad attachments to the bones and muscles of the pelvis.
Denoix explained more on the form and function of the back. "In the back there are 48 small synovial joints," he said. "There are 18 thoracic vertebrae and six lumbar -- two in each joint space (2 small joint spaces with synovial fluid and articular cartilage for each intervertebral joint). These joints are exposed and often over-stressed, especially when the horse has fast movement over a wide range."
The spinal processes are high in the wither area, and wide in the lumbar area. "In the lumbar area, the processes are very congruent and finely engineered," explained Denoix. "This variation in anatomy explains the different types and amount of movement in each area of the back." For example, "More flexion and extension occurs in the thoracic area. "
"A lot of people and practitioners consider treatment of back problems often, if not always, secondary to or associated with lameness, especially hind limb injuries," explained Denoix. "My approach is totally different. I consider that back problems are primarily due to lesions in the back. I have a lot of clinical cases to demonstrate that."
He acknowledged that taking standing radiographs is not always an option for veterinarians, and in those cases, it is difficult to observe the back problem as the primary issue.
"There have been a lot of X rays taken of the spinal processes," Denoix said, "and a lot of papers on the disease of spinal processes. But often, lesions of the spinal process (surface) are the tip of the iceberg. Most of the thoracolumbar lesions are located at the base of the spinal processes."
This last statement is a revelation to many owners and practitioners. Denoix continued, "Both the anatomy and the biomechanics can explain why pathology occurs in particular parts of the thoracolumbar area."
According to Denoix, there are four major "syndromes" of the spine that include le-sions. These include thoracolumbar (thoracic) overstress, especially osteoarthrosis of the articular processes and epiaxial synovial intervertebral articulation (AP-ESIVA, see below); kissing spines; lumbosacroiliac pain; and lumbar stiffness. Lesions can occur in the cervical vertebrae, but Denoix focuses on the more common problems that are caudal to (behind) the shoulder.
Thoracolumbar Overstress -- Lesions often are found in the articular processes and epiaxial synovial intervertebral articulation (AP-ESIVA) complex. These are common problems in the equine spine, and are a result of overstress.
"The AP-ESIVA is the key to explaining a lot of back pain in horses," said Denoix. The AP-ESIVA complex is located on top of and parallel to the vertebral canal, and consists of the ends of two vertebrae and the joint space and cartilage between them. The joint spaces in the thoracolumbar and lumbar regions appear less defined. Radiography and ultrasonography both are effective for diagnosing problems with the AP-ESIVA.
Abnormal findings identified with AP-ESIVA include asymmetry, fractures, density changes of the articular processes, periarticular proliferation (extra bone formation), and ankylosis (stiffness or fixation of a diseased joint) signified by little joint space or a dorsal bridge between vertebrae. Osteoarthrosis also is common in AP-ESIVA complexes, characterized by degenerative changes in the bone and cartilage of the joints and a progressive wearing of opposing joint surfaces.
"In our experience, AP-ESIVA lesions are much more likely to be associated with back pain than kissing spines or any other vertebral lesion," said Denoix.
Kissing Spines -- Kissing spines are exactly what they sound like -- spinal processes that touch or "kiss" one another at rest or in motion. Radiographic examination can reveal the contact and/or remodeling between two adjacent spinal processes, transverse (crosswise) thickening of the processes, and abnormal alignment of the processes. Denoix prefers to use ultrasonography to see accompanying supraspinal ligament (ligament that attaches to the dorsal spinal processes and extends from the withers to the tail) lesions, which usually are either insertion desmopathies (disease at the insertion of the ligament) on top of the spinal processes; or recent, old, or chronic desmopathies of the supraspinal ligament.
"The most common location of these lesions is in the vertebral segment between T10 and T18," said Denoix, "although kissing spines are not rare between L1 and L6."
Kissing spines can be found in horses with no back pain, and even with normal spinal movement, so careful assessment of the lesions must be performed. Pain is more consistently associated with kissing spines when acute or chronic ligament injuries are present.
Lumbosacroiliac Pain -- This pain stems from the enormous amount of flexion and extension in the lumbosacroiliac area, which is between the fifth lumbar vertebrae (L5) and the first vertebrae of the sacrum (S1). Denoix relies heavily on ultrasound techniques for diagnosis in this region, both externally and transrectally.
Externally (dorsally) Using an ultrasound probe externally in the lumbosacral area, Denoix can look at tears in the dorsal sacroiliac ligament (attaches pelvis to sacrum dorsally), bone surface irregularities of the ilium (which makes up part of the pelvis) and vertebrae, irregularities of the ligament insertion, and changes in fiber orientation.
Transrectally An internal exam via the rectum is required to assess the ventral sacroiliac ligament, the bottom parts of the sacroiliac and lumbosacral joints, and the ventral intervertebral foramina, which is the passage formed by adjacent vertebrae where the sciatic nerve (supplies the hind limb and pelvis) and vessels reside.
According to Denoix, a common abnormal finding in the lumbosacral area is the absence of discs. This finding is indicative of ankylosis, which is stiffness or fixation of a joint by disease.
"Lumbosacral ankylosis has been observed in horses demonstrating low back pain, and it's likely that the last lumbar intervertebral joints are overstressed when the more highly mobile joint of the area becomes fused."
Lumbar Stiffness Caused By Ankylosis -- Ankylosis often is seen between L2 and L5. Osteoarthrosis of the AP-ESIVA complexes leading to stiffness has been observed. Denoix explained that ankylosis often is found in horses presenting low back pain or abnormal lumbar conformation.
Supraspinal Ligament (SSpL) Injuries -- "Desmopathies of the SSpL have rarely been reported in the literature," said Denoix, and were "most commonly observed in the cranial lumbar region (toward the front), inducing thickening and pain." This information is in agreement with the studies of another prominent back specialist, Leo Jeffcott, BVetMed, PhD, FRCVS, DVSc, MA, DSc, Dean of the Veterinary School at the University of Cambridge (U.K.) and Chairman of the FEI Veterinary Committee.
Using ultrasound, Den-oix has confirmed occurrence of SSpL lesions in sport and racehorses. The most common location was between T15 and L3. Jeffcott found that avulsion fractures or bone remodeling and sclerosis (hardening) of the dorsal surface of spinal processes might be noted in these horses.
Lesions Of Vertebral Bodies And Discs -- Denoix refers to Jeffcott's studies, which explain that these types of lesions are not found commonly in horses and cannot be imaged ultrasonographically in the thoracolumbar area except caudally to L4 by way of the rectum. Horses with a history of back pain have shown these lesions, which include vertebral spondylosis (ossification of the longitudinal ligament), vertebral body deformation found in the last thoracic vertebrae, deformation of the vertebral head and fossa (groove), as well as "ski jump" deformation (a dorsal bony extension of the vertebral fossa) in the caudal thoracic area. Ventrolateral bony proliferation may be present in the lumbar area, he added.
Therapy Approaches At CIRALE
"When the site of the lesions is identified in X rays and ultrasound," Denoix explained, "we will do localized injections of steroids guided by ultrasound."
He next uses meso-therapy, which he explained as an injection of products within the skin (close to the idea of acupuncture), in order to remove deep pain.
"When these two techniques have removed pain, the horse must go back to work, and the training program should avoid any activity where the horse is reluctant or painful while building new muscle in the back. The trainer and rider are essential in the management of back pain in horses."
Physical therapy and chi-ropractics are useful in the back, according to Denoix. "The problem is that the technique reflects a technical specialization that needs to have a good, thorough ana-tomical, biomechanical, and pathological knowledge of the spine."
Saddles A Culprit?
Are we causing back problems in our horses? Denoix believes that saddle pressure is directly applied to the muscles and can induce some muscle ischemia (lack of blood flow) in areas beneath the saddle. "But I don't consider saddles as a cause of articular pain, or that they are responsible for the lesions that I am able to image or radiograph.
"I think it is justified to take care of the saddle. It can be a factor that increases the intolerance of the horse to a rider's weight, but the saddle is rarely a primary cause of back pain."
Above all, understanding the stresses our horses' spines undergo will help us to optimize care. Denoix supports the concept. "Knowledge of the normal functional behavior and mechanical properties of the vertebral column is important to understand the pathogenesis of back lesions, to identify the clinical manifestations of back pain, and to ensure a rational approach to physical therapy."
The Spine in Motion
Denoix explained how the anatomy of the spine accommodates typical horse movement:
Flexion and extension are associated with the cranial thoracic area.
Rotation and lateral flexion (side to side) are possible in the mid-thoracic area.
Flexion and extension are normal in the thoracolumbar junction.
The lumbosacral area is very specialized in its flexion and extension movement--rotation and lateral movement do not occur here. There is less movement in the lumbar area.
Cirale: Efficient Examinations
The objective of building CIRALE was to provide owners, trainers, and breeders with the equipment to diagnose and improve the performance of the horse, and therefore the equine market, in the highly horse-populated Normandie area of France. A total of 13 vets work at the center, which is an extension of the Veterinary School at Alfort in Paris.
CIRALE Director Jean-Marie Denoix, DVM, PhD said that builders combined every type of surface to get as much information as possible about the biomechanics of a patient. "We have different surfaces (for evaluation and diagnostics)," he explained. "We have a graded surface so horses can go up and down a hill, which is good for evaluating "wobblers," and a medium-surfaced (but firm) trotting lane." CIRALE also has areas for longeing: a hard surface, groomed grass, soft sand, and a medium rubber surface. The building currently consists of a series of examination rooms used for what Denoix calls a "dynamic exam." (It's easy to see why.)
Physical examination--An intern gives the horse a physical exam, looking at the horse's history, build and conformation, and for any abnormalities. This room has stocks, which are also used for transrectal ultrasound examinations and thermography exams.
Ultrasound--This room is kept very dark, for optimal viewing of the ultrasound screen. A raised area on which the horse can stand works nicely for examination of the distal limb, and also as a place for staff and students to stand out of "kicking distance" of the horses.
Radiography--"We print the im-ages and keep them on disk," said Denoix. "We can alter the density, size, and other details about the image (with computerized radiography)."
MRI--Magnetic resonance imaging is especially useful for the head, due to the complex anatomy of this area.
Scintigraphy--The final room is devoted to detection of abnormalities with nuclear imaging.
The second floor of CIRALE consists of office space, conference rooms, and lecture rooms. Adjacent to the exam rooms are a well-ventilated stable and hay/equipment storage areas. Another building, serving as the second wing to CIRALE, will house a treadmill for trotters and Thoroughbreds. There will also be an indoor schooling arena for working jumpers and horses on the flat.
About the Author
Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.
POLL: Managing Working Horses