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Epiduroscopy: an exciting window into back pain in horses

VETERINARYWeb Master
  Back pain is a well known cause of lameness, gait alterations and poor performance in sport horses. Up to 25% of dressage horse owners report back problems in their animals, but not only sport horses are affected. Although racehorses compete at a younger age than other equine athletes, they might suffer from back pain more often than we think, autopsy studies have identified pathological changes in the back of the majority of examined young thoroughbreds. Until recently, it has been very difficult to investigate back pain and it is easy to overlook this as a cause of disappointing performance. A novel surgical technique which has recently been reported in Equine Veterinary Journal, may change all this.      an adult racehorse of average size, the complete sacral, lumbar and a small part of the thoracic spinal canal can be reached with a 60 cm endoscope.      How can epiduroscopy help veterinarians to find the source of pain in a horse with back problems?     While the spinal cord sends and receives signals directly from the brain, the spinal nerves are the communication pathway between the spinal cord and the body. Spinal nerves are, among other things, responsible for the movements of the muscles in the back and legs and for sending information about pain in the back and legs back to the brain. Injury to a spinal nerve can result in dysfunction of muscles or in pain. Fortunately, the spinal nerve roots are well protected from injury, first by the surrounding bony vertebrae and, after leaving the spinal canal, by a thick muscle layer. However, the nerve can be injured at the point where it exits the spinal canal. The spinal nerves exit the canal through the openings between two adjacent vertebrae. The opening is called the intervertebral foramina. Each opening is in close proximity to the facet joints that connect the vertebrae. Inflammation of these joints (facet joint arthritis) causes back pain and results in irregular growth of bone around the arthritic joint.        While severe bony changes can be picked up on radiographs, subtle changes can easily be missed. Unfortunately, even relatively small bony growths can impinge on the passing nerve and cause irritation and inflammation. Nerve root impingement is a recognized cause of lower back and leg pain in people and now that we have epiduroscopy available for horses, it will be possible to identify the prevalence and importance of this condition in equine athletes.  This will be especially interesting for young racehorses, where facet joint arthritis can be found in the thoracolumbar spine of up to 97% of cases that undergo autopsy but currently there is no information about the effects of this arthritis on passing spinal nerves.     << Fig 7 near here>>           Will epiduroscopy lead to better treatments?     Epiduroscopy can not only identify an inflamed nerve root, it can also be used to treat the inflammation through targeted injections of steroids via the working channel of the endoscope. There is a lot more work to do before this approach becomes commonplace for back pain. However, at North Carolina State University, the approach has used epiduroscopy to diagnose and successfully treat nerve root inflammation in the neck of an adult horse with chronic forelimb lameness. With help of the recently described lumbosacral epiduroscopy, it is now also possible to introduce this approach for therapy for inflammation in the spinal nerves located in the lower back. At North Carolina State College of Veterinary Medicine, we are currently developing a protocol to identify horses with back pain and unknown causes of hindlimb lameness that are suitable candidates for lumbosacral epiduroscopy. The findings of these examinations should shed more light on unknown or underestimated causes of back and leg pain in horses.          Back pain is a common and well-recognised problem in sport horses and may be an underestimated reason for poor performance in young racehorses. Autopsy findings suggest that especially young thoroughbreds frequently suffer from lesions in the muscles and joints of the lower back, but diagnosing these abnormalities is difficult in living horses. Some cases     << EVJ logo near here>>        The trouble with back pain     In people, “lower back pain” is the most common cause of job-related disability and a leading contributor to missed workdays, and it could be an underestimated problem in horses. Although several studies have shown a high incidence of pathology in the equine backbone, more correctly called the thoracolumbar and lumbosacral spine, and most of these findings were made during autopsies and not in clinical cases or live horses. Diagnosing the reason for back pain in a living horse is difficult, this is due to the complex anatomy of the horse’s back and the large size of an adult horse. The currently available diagnostic tools often fail to accurately identify the source of pain in clinical cases, the heavy back musculature limits the value of x-rays, while the wide range of scintigraphy (bone scan) findings in healthy horses makes it difficult to distinguish normal variations from clinically relevant problems. Ultrasonography for detecting bony anomalies in the equine back is also of limited value.       In people, the diagnostic tools of choice are magnetic resonance imaging (MRI) and computed tomography (CAT Scan, CT). But currently, because of the large size of adult horses, these tools cannot be used to assess the equine back. Consequently, veterinarians are often unable to pinpoint the underlying lesion in horses with clinical signs of back pain and thus cannot develop a targeted treatment plan.         Trainers will be familiar with the principles of endoscopy as it is a procedure commonly used to assess the upper airway and to perform minimally invasive procedures in joints (arthroscopy) or the abdomen (laparoscopy), also known as keyhole surgery. In people, endoscopy is also applied to identify problems within the spinal canal that can cause chronic back pain.         Anatomy of the back     The spine is a “column of vertebrae”, hence the scientific name “vertebral column”, that provides the bony support for the neck and back. In horses, the vertebral column is typically formed by 54 vertebrae that are connected to each other by joints, muscles and ligaments.  Although slight variations of these numbers are common, typically, in the neck there are 7 cervical, in the back there are 18 thoracic, 6 lumbar, and 5 sacral vertebrae; and, in the tail, there are 18 (15-21) caudal vertebra.         <<Figure 1 near here>>         The lumbar vertebrae are connected to the “sacrum”, a bone formed by the fused sacral vertebrae. Both the lumbar spine and the sacrum should be included when examining a horse with lower back pain. Within the spine, a central canal spans from the head to the tail. This spinal canal contains the spinal cord and the roots of the large nerves that originate from the cord (spinal nerves). The spinal cord and the nerve roots are the pathway for transmission of information, in both directions, between the brain and the rest of the body. To protect this delicate nervous tissue, the spinal cord and nerves are enclosed in a protective layer, the dura mater. Located between the dura mater and the bone of the vertebrae is the epidural space, which is filled with loose connective tissue and fat. Through small gaps between certain vertebrae (e.g. between the first and second cervical vertebra or the sacrum and the first caudal vertebra), the epidural space can be accessed and explored with a thin, flexible endoscope. This procedure is called “epiduroscopy” and allows a direct viewing of the structures in the spinal canal.        Epiduroscopy     Epiduroscopy is used in people to, among other things, diagnose injury and compression of the spinal cord and the spinal nerves. In horses, the cervical spinal canal, located in the neck, and the lumbosacral spinal canal, situated in the lower back, can be examined with epiduroscopy. While anaesthesia is required to examine the neck, lumbosacral epiduroscopy is done in standing, sedated horses.      A specialised endoscope set-up is required and since sterility is critical, epiduroscopy should only be performed in referral hospitals. The instrument has to be long enough to allow examination of the complete lumbosacral spinal canal and thin enough to fit into this narrow space. Ideally, the endoscope is at least 60 cm long but no thicker than 4 mm      <<Figure 2 near here>>.         The epidural space is entered through a small gap between two vertebrae, just above the base of the tail (Figure 3). The endoscope is then slowly inserted while the surgeon injects small amounts of a sterile saline solution through its working channel (Figure 4). This is necessary to push the epidural fat and connective tissue gently out of the way and allow viewing of the structures of interest, as shown in (Figures 5 and 6): the spinal cord and spinal nerves (enveloped by the dura mater), blood vessels and the inside of the surrounding vertebrae. In can be diagnosed with the currently available diagnostic tools, including a thorough clinical examination, radiographs, ultrasound and bone scan. In cases where these methods have been exhausted and failed to provide a diagnosis, epiduroscopy might provide the missing piece of information.            Legends     Figure 1: Horse skeleton seen from above, outlining the different regions of the spinal column.        Figure 2: Tip of a flexible videoendoscope that is suitable for lumbosacral epiduroscopy. The instrument is 60 cm long and has an outer diameter of 3.8 mm (Olympus BF-C 160).     Figure 3: This horse has been draped for lumbosacral epiduroscopy. The site where the endoscope will be inserted is left uncovered and has been prepared for aseptic surgery.      Figure 4: With his right hand, the surgeon slowly inserts the endoscope through a white plastic sheath into the epidural space. With his left hand, he controls the moveable tip of the endoscope. In the background, the monitor depicting the endoscopy image can be seen (out of focus).      Figure 5: Prior to injection of sterile saline through the working channel of the endoscope, the ability to see the different anatomical structures in the epidural space is very limited. At the bottom of the image, the dura mater that covers the spinal cord can be seen, while the epidural fat (on top of the dura mater) prohibits viewing of other structures.     Figure 6: Following careful injection of sterile saline solution, the examination becomes more rewarding. A spinal nerve root (*) can be seen emerging from the spinal cord (covered by dura mater) and cross the epidural space. Epidural fat can be seen above (x).      Figure 7: Pipe cleaners have been inserted into the intervertebral foramina, the opening between adjacent vertebrae through which spinal nerves exit the spinal canal. Note the close proximity of the facet joints (arrowheads).         Video 1: Preparation and insertion of the endoscopy in a sedated horse.      If you would prefer to include a link to this video currently it can be found at: http://onlinelibrary.wiley.com/store/10.1111/evj.12591/asset/supinfo/evj12591-sup-0001-Item1.mp4?v=1&s=735ecdd6a1606af5023c32d0406c01ef5e6f2445        Video 2: Lumbosacral epiduroscopy in a healthy horse.      If you would prefer to include a link to this video currently it can be found at:     http://onlinelibrary.wiley.com/store/10.1111/evj.12470/asset/supinfo/evj12470-sup-0002-MovieS1.mov?v=1&s=188211909de8842a9c434f5d202e2e76d53690

Dr Timo Prange

Read full study online here: 2016 Jan;48(1):125-9. doi: 10.1111/evj.12470

 

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Back pain is a well known cause of lameness, gait alterations and poor performance in sport horses. Up to 25% of dressage horse owners report back problems in their animals, but not only sport horses are affected.

Although racehorses compete at a younger age than other equine athletes, they might suffer from back pain more often than we think, autopsy studies have identified pathological changes in the back of the majority of examined young thoroughbreds. Until recently, it has been very difficult to investigate back pain and it is easy to overlook this as a cause of disappointing performance. A novel surgical technique which has recently been reported in Equine Veterinary Journal, may change all this.  

How can epiduroscopy help veterinarians to find the source of pain in a horse with back problems?

While the spinal cord sends and receives signals directly from the brain, the spinal nerves are the communication pathway between the spinal cord and the body. Spinal nerves are, among other things, responsible for the movements of the muscles in the back and legs and for sending information about pain in the back and legs back to the brain. Injury to a spinal nerve can result in dysfunction of muscles or in pain. Fortunately, the spinal nerve roots are well protected from injury, first by the surrounding bony vertebrae and, after leaving the spinal canal, by a thick muscle layer. However, the nerve can be injured at the point where it exits the spinal canal. The spinal nerves exit the canal through the openings between two adjacent vertebrae. The opening is called the intervertebral foramina. Each opening is in close proximity to the facet joints that connect the vertebrae. Inflammation of these joints (facet joint arthritis) causes back pain and results in irregular growth of bone around the arthritic joint.

While severe bony changes can be picked up on radiographs, subtle changes can easily be missed. Unfortunately, even relatively small bony growths can impinge on the passing nerve and cause irritation and inflammation. Nerve root impingement is a recognized cause of lower back and leg pain in people and now that we have epiduroscopy available for horses, it will be possible to identify the prevalence and importance of this condition in equine athletes.  This will be especially interesting for young racehorses, where facet joint arthritis can be found in the thoracolumbar spine of up to 97% of cases that undergo autopsy but currently there is no information about the effects of this arthritis on passing spinal nerves.

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