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The Basics of Nerve Blocks

By Grant Miller, DVM, September 16, 2014

palpating-nerves-to-prepare-for-a-block
Palpating nerves to prepare for a nerve block.

Ever feel lost when your veterinarian starts talking about nerve blocks?  Nerve blocks are a basic diagnostic tool that veterinarians can use to localize lameness to a certain area of the body- usually this is the “distal extremity” also known by most of us as the “lower leg.”  Here are the answers to some common questions that stump horse owners from time to time.

 

What exactly is the vet doing when he or she places a nerve block?

 

The horse has sensory nerves going down the legs that lie just under the surface of the skin.  These nerves send information about stimuli up to the brain.  If the veterinarian anesthetizes (“numbs”) these nerve at a certain location, everything on the leg below that location will cease to feel stimuli- including pain.  A nerve block consists of the veterinarian placing a small amount of numbing agent (usually lidocaine or carbocaine) strategically near nerves to selectively anesthetize an area of the leg.  This is done by wiping the skin with some rubbing alcohol and then using a very small needle to inject the agent under the skin.

 

Once the area is numb, how does the vet determine if it is the location of the lameness?

 

Prior to placing a nerve block, the veterinarian will observe the horse moving- usually at the trot but sometimes even at the walk.  Once the vet sees which leg is lame and the degree of lameness, he or she can use this as a comparison point for after the nerve block is place.  So, for instance, if a horse is lame at the trot prior to a nerve block being placed, but then trots sound following the nerve block, the vet knows that the source of the lameness is coming from the location that was just anesthetized.

 

Speaking of degrees of lameness, how does the vet quantify them?

 

Most veterinarians use a lameness grading system developed by the American Association of Equine Practitioners (AAEP.)  It grades lameness on a score of 0 to 5 with the following descriptions:

0: Lameness not perceptible under any circumstances.

1: Lameness is difficult to observe and is not consistently apparent,

    regardless of circumstances (e.g. under saddle, circling, inclines,

    hard surface, etc.)

2: Lameness is difficult to observe at a walk or when trotting in a

    straight line but consistently apparent under certain circumstances

    (e.g. weight-carrying, circling, inclines, hard surface, etc.)

3: Lameness is consistently observable at a trot under all   

    circumstances (e.g. trotting in a straight line.)

4: Lameness is obvious at a walk.

5: Lameness produces minimal weight bearing in motion and/or at  

    rest or a complete inability to move.

 

If my horse’s leg is numb, how come he can still move it?

 

When the vet places a nerve block, he or she is blocking sensory nerves. But sensory nerves are different than motor nerves, which innervate muscles in order to get them to move.  Even when a sensory nerve block is placed, the leg will continue to be able to move because the deeper motor nerves are unaffected by a nerve block.   

 

How long do nerve blocks last?

 

About 45 minutes to 1 hour.

 

Are there any risks?

 

Risks are minimal however some nerves run close to synovial structures such as tendon sheaths or joints.  For that reason, infection is possible as a result of the introduction of the needle into that area.  Therefore, for certain nerve blocks, the vet will take a few extra minutes to wipe betadine and rubbing alcohol on the leg.

How many nerve blocks are there?

 

There are about a dozen areas of the body that can be nerve blocked.  Most nerve blocks are performed on the legs, but they can also be performed on the jaw and face to anesthetize teeth for dental procedures or on the eyelids to permit eye exams.  The most common nerve blocks are as follows:

 

  

·        Palmar Digital “PD”- anesthetizes the heel and bottom of the foot.

·        Abaxial- anesthetizes the foot and pastern.

·        Low 4-point- anesthetizes the foot from the fetlock down.

·        High 4 or 2 point – anesthetizes the leg from just below the carpus or hock 

         down.

·        Radial/ Ulnar (front) or Peroneal/ Tibial (hind)- anesthetizes the leg from the

         carpus down on the front or the hock down on the hind.

 

 

If my veterinarian places a nerve block and my horse goes sound, does that mean we have a diagnosis?

 

No.  The nerve block just tells you the area that the lameness is coming from.  Next your veterinarian will need to look at the bone and soft-tissue structures within that region to figure out the exact source(s) of the lameness.

 

Now when the vet starts talking about nerve blocks - you will be in the know! 

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New Therapies to Help Your Horse

By Grant Miller, DVM, September 08, 2014

Every time I think I have a handle on the therapy options that are available to horse owners, new ones pop up.  They probably have been around for longer than I realize, but they are new to me nonetheless.  Many seem to be adapted from the human physical therapy realm, which I find somewhat comforting because humans can actually testify to their efficacy.  Plus, they are likely to be safe if they have been used on humans.  Here are a couple that I would like to share with you:

 

Functional Electrical Stimulation (FES) Therapy

fes-pad
Credit: www.equinew.com 
FES Pad
 

Functional Electrical Stimulation (FES) was originally developed for use in humans with debilitating injuries that prevented them from being able to move. And, of course, muscles that are not used begin to atrophy, or shrink.  This phenomenon could occur in patients with neurologic disease, spinal-cord injury, or in those who were bed-ridden. However, FES therapy could be used to maintain muscle mass and function.  

 

Essentially, FES is the application of computer-regulated electrical impulses to the muscles through electrodes affixed to the skin. The therapy invokes a rhythmic contraction and relaxation of muscles.  It is like an electronic deep-tissue massage.  Results reported among human patients and horse owners alike include pain reduction, increased range of motion, and an all together “good” feeling afterward.

 

FES can be useful in horses, particularly in the deep pelvic muscles, because machines can generate an electrical signal that can penetrate up to 6 inches into the body. That allows it to reach the deep muscle, tendon and ligament tissues. This ability is of great value when dealing with spinal and pelvic problems such as iliopsoas muscle strains. Horse owners report that horses enjoy the sensation and often start to show extreme relaxation during treatment.  Therefore, sedation is seldom needed for this therapy to be applied.

 

FES is generally used for the following purposes:

  1. To stimulate muscles, tendons and ligaments so that normal movement is returned to injured tissue.
  2. To promote edema reduction and tissue healing through increased circulation of blood and lymph due to the movement of muscles.
  3. To stimulate muscle movement and sensory nerves for the treatment of pain.
  4. Reversal of the wasting of muscle (used in EPM rehabilitation).
  5. Reduction of scar tissue.
  6. Increasing range of motion.
  7. Wound healing.

Novobrace

Horses with tendon and ligament tears will undoubtedly be laid-up for months, and many owners remain forever timid for fear of injury recurrence.  Now, veterinary researchers have developed a therapy to stabilize soft-tissue injuries to halt their advancement and aid in healing. Novobrace is a patented injectable bioadhesive that forms an internal brace using a chemical crosslinking agent that is injected directly into the torn tendon or ligament, immediately adding mechanical support to the injury. 

Although flexible (elastic), the brace prevents further advancement of the lesion, which results in improved healing. Novobrace may be used as a standalone therapy and also as an adjunct therapy with other tissue healing therapies including stem cells and growth factors. Over 90% of the horses treated with Novobrace to date have returned to work within seven months with zero percent of re-injury.

Horses with tendon or ligament injuries can receive the injection as soon as 10 days following the injury.  A veterinarian will sedate the standing horse, disinfect the injection site, provide local anesthesia to the area being injected using lidocaine, and then inject the agent using ultrasound guidance.  The whole process can take less than 30 minutes but can shave months off of lay-up and help ensure strong, healthy healing.

We're always looking for new treatments or modalities that make a positive difference in our horses' lives. 

Editor's Note: Read Dr. Miller's article on tendon injuries here.

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Looking a Horse in the Mouth

By Grant Miller, DVM, September 02, 2014


The horse in the photo above is likely 6 or 7 years old.

 

Do you ever wonder what your veterinarian is looking at when he or she opens your horse’s mouth to the estimate its age?  It is intricate, and can take years of practice to really get good, but that doesn't mean that you cannot at least get a general idea of what to look for.  Here are a few basic rules that you can follow to at least estimate an age range in a horse by oral examination. 

 

1)  Horses tend to object to having their lips pulled apart and mouths opened.  For this reason, standing off to the side when you open the mouth will help you avoid being injured since they often try to throw their head up in the air when you open their lips.

 

2)  As you curl up the upper lip, look for a tattoo.  If the horse has one, it is simple to determine its age since The Jockey Club assigns a letter to each year that a horse is born.  For instance, all thoroughbreds that race on the track born in 2006 have a tattoo that begins with the letter “J.” 

jockey-club-tattoo-age-chart
Credit: The Jockey Club

3)  Check for “baby” teeth (also called deciduous teeth.)  They are caps that will eventually be replaced by permanent adult teeth.  Horses will have them up until the age of 5.  Sometimes you will see missing caps which can hone you in on an age range.

 

4)  If you open the mouth and look down at the occlusal (table) surface of the lower incisors, they will have a characteristic shape.  In general, horse incisor teeth progress through different shapes as the horse ages.  Here is the progression:

–     Oval (0 to 5 yr) to

–     Round (5 to 9 yr) to

–     Triangular (10-15) to

–     Square (15 to 19)

 

5)  When you look at the incisors from the side, the contour and angle between the top and bottom incisors will change over time so that it becomes more angled as the horse ages.

tooth-angles-by-age
Tooth Angles by age

 

6)  In the upper corner incisor, most horses will have a marker called the Galvayne’s Groove.  Here is how it progresses over time:

•      Appears at the gumline at 12 years

•      ½ way down tooth at 15 years

•      All the way down tooth at 20 years

 

 

7)  Remember, the term “long in the tooth” refers to an aged animal. Therefore when examining the upper corner incisor, the overall length of the tooth can give you a general idea as to age range.  Here are general rules:

 

•      Between 5 and 9 years, the tooth is wider than it is tall

•      From 9 to 10 it is perfectly square (equal height and width)

•      Gets longer than it is wide from there

 


The upper corner incisor goes from wide to long as the horse ages

 

There are several more markers that the veterinarian examines to help hone in on an estimated age, but these are a good start to get you in the ballpark.  Generally, it is difficult to age a horse past 23 years no matter who is looking, but the general shape and length of the incisors, as well as their angle and the presence of the Galvayne’s Groove can get us close to knowing “young,” “middle-aged” or “older.”

 

For more information, you may want to consider purchasing the American Association of Equine Practitioners Guide to Determining the Age of the Horse.

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OsPhos Now Available

By Grant Miller, DVM, August 25, 2014

 osphos
Credit: OsPhos
Courtesy Dechra

For years we have heard about the wonder drug Tildren and its ability to make horses with navicular syndrome, hock arthritis and ringbone go sound.  Until recently, Tildren was not available in the United States.  Just a few weeks back, that changed when CEVA, the manufacturer or Tildren, gained FDA approval for its use in the United States.  But did you know that drug manufacturer Dechra also recently came out with a competitor to Tildren?  It is called OsPhos and it is showing some promising results!

What is OsPhos?

OsPhos is an injectable bisphosphonate solution for the control of clinical signs associated with navicular syndrome in horses four years and older. OSPHOS inhibits bone resorption (disappearance) by inhibiting cells called osteoclasts.  Osteoclasts grab onto calcium crystals which comprise bone and dissolve them.  By stopping osteoclast activity, OsPhos slows bone degradation.  Sound familiar?  That is because this drug has the same mechanism of action as Tildren.  See how they compare here.

Does it work?

Clinical trials conducted by Dechra in order to comply with FDA testing requirements found that 75% of horses treated with OsPhos showed a significant reduction in lameness by 56-days post injection.  Here is a more direct way of putting it: horses that were grade 3 out of 5 lame (3= lame at a trot in the straight line) pre-OsPhos ended up being only a grade 2 out of 5 lame (lame at a trot in a circle but sound in a straight line) two months post administration.  More information can be found here in the FDA freedom of information summary on OsPhos. 

Are there side effects?

Nothing significant to speak of.  One in 10 horses showed signs of abdominal discomfort (pawing, fidgeting, cramping) about 2 hours post-injection, but got over it after a 15 minute walk.  Some were given a dose of banamine but none had serious or lasting reactions.  More information can be found here.

How is it given?

OsPhos is administered as three 5 cc intramuscular injections given in three locations on the body all at once.  It can be given every 3 to 6 months depending on the severity of the lameness, but ultimately should only be repeated as needed when signs of lameness recur.  In other words, some horses may only need it once, while others many need it two or three times per year.

How does is stack up to Tildren?

In many ways, OsPhos holds its own against Tildren:  

  • OsPhos is currently available through veterinary supply distributors while Tildren is on backorder.
  • OsPhos costs about $300 to $350 per treatment while Tildren will usually run around $1,100 to $1,300.
  • OsPhos can be given intramuscularly while Tildren has to be given intravenously.  In addition, Tildren has been reported to be most efficacious when it is diluted in a bag of IV fluids and administered over a period of hours.  This requires a catheter and more time under veterinary supervision while it is being given.
  • OsPhos shows similar results to Tildren in terms of reduction in lameness and in time of onset.  Tildren definitely exerts a long term effect, with many owners reporting that it reaches full performance 3 months following administration and continues to work for years thereafter.  Because OsPhos is so new, we will have to wait and see how it measures up to Tildren over the long haul.

No matter how you look at it, OsPhos is a welcome addition to the horse world in the U.S.  If it can help our horses be more comfortable, while saving us some time and expense, then pop open the champagne!

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Corneal Ulcers

By Grant Miller, DVM, August 18, 2014


A large, severe corneal ulcer that has been stained with fluorescein dye.

Have you ever shown up to the barn to find your horse’s eye swollen closed and dripping excessively?  Sometimes they bump their heads, or even get flicked in the eye by a neighbor’s tail.  No matter what the cause, early and appropriate medical management is crucial for eye injuries.  Most veterinarians will not put off an appointment to look at an injured eye- even if the owner reports that it appears mild.  So many things can go wrong with eyes, especially when the horse decides to rub the eye repeatedly on the inside of his front legs!  Once this cycle starts, what originally was a minor injury can rapidly progress to a very serious condition.  Therefore - as vigilant owners, we really have to “keep an eye” on eyes!

 

Horse’s corneas are vulnerable to injury because of their convex contour.  The cornea is the outer most layer of the globe - or the “glassy” surface which we can touch with our fingers.  They protrude off the horse’s face in order to accommodate a wide field of vision, but this added benefit of panoramic vision also comes with an increased risk of injury.  Horse corneas protrude so far that some veterinarians will joke that “a horse’s cornea enters the room before it does.” 

 

Corneal scrapes (also called ulcers) are nothing to sit on since horses will reliably advance their severity by rubbing their eye.  The initial signs of an injury to the cornea are: 

 

·        Squinting and sensitivity to bright light (photophobia)

·        Excessive tearing (epiphora)

·        Swelling of the tissue around the eye (conjunctivitis)

·        Pain (blepharospasm)

 

We can’t always see the injury on the corneal surface just by looking at it.  Most of the time, the veterinarian needs to put a special dye in the eye called fluorescein stain.  The stain will run off the surface of a healthy, in-tact cornea.  But, if any layers of the cornea are scraped away, as is the case with ulceration, the dye will saturate the area and then show up in direct light. 

 

Corneal ulcers are painful and extremely aggravating for the horse (and the owner for that matter!)  The pain sensation can be overridden by applying pressure to the eye or by rubbing it.  But the trauma induced to the corneal surface by rubbing only results in a worsened condition of the ulcer since it causes more layers of the cornea to peel away.  For this reason, it is imperative that owners prevent their horse from rubbing the eye during the ulcer rehab period. 

 

Here are some effective management tips:

 

1.    The veterinarian will usually prescribe antibiotic eye ointment to treat the ulcer.  Unfortunately, the eye ointment is not very user friendly and must be given usually 4 to 6 times per day.  And by “day”- we mean a 24 hour period!  If the antibiotic ointment can be effectively given on a 24-hour basis, the healing period will be shortened significantly.  If 24-hour dosing is not possible, then giving doses “first thing in the morning, and last at night” will be of added benefit.

 

2.   When working on the horse, wear gloves.  The bacteria on human hands are the strongest on the body, and often are resistant to some antibiotics.  If we inoculate these bacteria into the horse’s injured eye during the course of trying to treat it, they will compound the problem and impede healing. 

 

3.    Keep your horse in a darker stall since light is a painful stimulus.  Use of a fly mask is also helpful.  Some people actually place a duct tape patch on the fly mask over the affected eye to provide an additional shield.

 

4.    In addition to eye medications, the veterinarian will put the horse on an anti-inflammatory medication such as banamine.  Make sure that anti-inflammatories are given at the exact interval and amount that the veterinarian prescribes.  This way, you will maximize the comfort of the horse, and thus minimize the change of him rubbing his eye to alleviate discomfort.

 

5.    Finally - DON’T dig through the tack trunk and find an old tube of eye medication to put in the eye yourself.  Not all eye medications are the same and using the wrong one can have disastrous consequences.  For instance, did you know that there is a kind of eye medication that, if applied to an eye with an ulcer, will stop the ulcer from healing for several months?  In addition, there is another kind of eye medication that can cause severe colic and induce blindness by dilating the eye.  Don’t take risks by trying to “self-treat”!  Your horse needs his eyes and the risk is unacceptably high if you gamble on mystery medications.

 

When you find your horse with a squinting and watery eye, get him out of the light, put on a fly mask, stop him from rubbing the eye and call the vet.  You and your horse will be glad that you did!

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