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Information for horse owners

HOW CAN STANDING EQUINE MRI HELP?

MRI has been the imaging method of choice in human medicine for many years, making it the gold standard for diagnosing orthopaedic pathology. Hallmarq’s standing equine MRI system offers equine vets the same diagnostic capability.

Often during a lameness work-up, your vet will use 'nerve blocks' to locate where the pain is coming from. This may then be followed with X-ray or ultrasound examinations, but because these imaging tools only show bone or some soft tissues your vet may not be able to see any abnormalities.

Standing equine MRI offers unique insight into equine lameness, identifying the specific cause in over 90% of cases. With no general anaesthesia required the inherent risks associated with anaesthesia and recovery can be avoided and an early, safe and accurate lameness diagnosis will save you time, money and worry.

Don't consider MRI as a last resort, get the answers that you need sooner rather than later.

Early - MRI can be undertaken as soon as nerve blocks confirm the location of lameness.

Safe - Hallmarq's system offers the choice of standing MRI, giving your vet the quality images needed whilst your horse remains under light sedation avoiding the risks of general anaesthesia.

Accurate - Each scan generates between 300-500 images per foot, offering a 90% likelihood of conclusive diagnosis. Targeted treatment can then be recommended, a prognosis can be clarified, and a more satisfactory outcome reached.

 

WHAT IS DIFFERENT ABOUT MRI?

MRI images show information about both bone and soft tissue, whereas x-rays only show bone and ultrasound only shows soft tissues. The clear images from MRI allow vets to make an accurate and precise diagnosis in 90% of cases.

 

Foot x-ray

 

Foot MRI


FURTHER INFORMATION

 

Information for horse ownersHOW SAFE IS STANDING MRI FOR THE HORSE?

MRI is widely used in both human and veterinary medicine, valued for its high image quality of bone and soft tissues with no ionising radiation. The technology used to create the images is unobtrusive and poses no known risk to the patient.

Hallmarq equine MRI systems have been used for over 60,000 standing sedated horse examinations, during this time there have been no fatalities. Had general anesthesia been necessary around 300 of these cases would have died as a result of the normal approximately 0.5% mortality rate following general anesthesia.

Hallmarq firmly believes that the standing MRI product has revolutionised the diagnosis and treatment of lameness by making MRI safe, affordable, and widely accessible to veterinarians and horse owners and has made a significant contribution to equine health and welfare.

Information for horse ownersIS IT THE SAME AS A HUMAN MRI SCANNER?

The underlying principle is exactly the same. But a horse is a very different shape to a human and does not fit well inside a scanner designed for people. The Hallmarq standing equine MRI has been specifically designed for imaging the standing horse - the scanner operates close to floor level, and the horse can immediately step out of an opening in the magnet if it moves. Because the Hallmarq scanner is smaller (the size of a horse leg, not a whole horse) it is also much quieter than a human scanner, only making a quiet ticking or buzzing noise during the scan.

Information for horse ownersWHAT IS THE DIFFERENCE BETWEEN HIGH FIELD AND LOW FIELD SCANNERS?

Both high field and low field scanners have been used in human clinical medicine for many years. Both have their own applications in clinical imaging.

High field:

  • Stronger magnetic field
  • Higher resolution images
  • Shorter scan time
  • Tubular or doughnut shaped
  • Requires general anesthesia
  • More expensive scan costs
  • Very noisy

 

Low field:

  • Smaller 'C' or 'U' shaped system
  • Less claustrophobic
  • Lower resolution images but still of diagnostic quality
  • Lower scan costs
  • Quite (only makes a quiet ticking or buzzing noise during a scan)
  • No general anesthesia required (standing MRI)

 

Information for horse ownersISN'T HIGH FIELD ALWAYS BETTER?

Images from high field scanners include a lot of detail and can cover a larger region in a single scan. However, this does not necessarily make for a better diagnosis, in much the same way as a veterinarian may choose to use a smaller x-ray or ultrasound machine in circumstances where it is diagnostically appropriate, even if a more powerful machine would give a higher quality image. The Hallmarq scanner can image a region approximately 13cm across with a typical resolution of 0.8mm x 0.8mm in-plane. This is ample detail to allow visualisation of the important structures of a horse limb.

Given the option of standing and high field, many horse owners prefer the lower cost and the ability to scan the horse without general anesthesia.

The situation is different with small animals such as cats and dogs. Here the finer anatomical structures and the different nature of the pathology (generally brain and spine, rather than limbs) mean that high field has some important advantages. Hallmarq makes a high field MRI for companion animals.

Information for horse ownersWHAT IS THE DIFFERENCE BETWEEN STANDING AND ANAESTHETISED SCANNERS?

All high field scanners require anesthesia. For low field there are two types of scanners: one also requires anaesthesia, the other (the Hallmarq system) uses a smaller magnet which fits around the leg and is normally used with the horse standing and sedated but not anesthetised.

Information for horse ownersDOESN'T THE HORSE MOVE?

In a high field scanner, the heartbeat and breathing of the horse can produce motion of the leg in the scanner, which is normally reduced with padding and careful positioning. In the Hallmarq scanner the standing horse stands on a solid floor and is supported by a chest rail, but it may still sway during the scan. This can affect images acquired higher up the leg. Special software developed by Hallmarq corrects the effect of the motion to produce diagnostic quality scans.

Information for horse ownersHOW SAFE IS IT?

There are no known biological hazards of static magnetic fields, and MRI does not use any ionising radiation or toxic chemicals. There are international safety standards for MRI operators relating to the RF and gradient fields generated during the imaging process, but the low field Hallmarq system falls well within all relevant safety standards. The most significant safety concerns are from magnetic metal objects (eg tools, horse shoes) being allowed too close the magnet, and the normal hazards of working around horses.

Information for horse ownersWHAT ARE THE MOST COMMON DIAGNOSES OF FOOT PAIN?

Lameness is notoriously difficult to diagnose properly. The usual procedure involves a series of "trial and error" steps using nerve blocks, x-rays and other methods for diagnosis followed by treatment, waiting to see if the treatment is effective and if not, going round the loop again. Each individual step in this process may cost a few hundred pounds, but each time round the loop only has a low (about 30%) chance of getting a clear diagnosis so the total cost soon adds up. This is illustrated in the diagram below. During this process the owner also has other costs (farrier, livery, etc) and there is a risk that the problem may get worse while left untreated. MRI does on average work out as an economic option for all but the most straightforward cases.

The most common MRI diagnoses in the foot are:

- Navicular bone degeneration
- DDFT tendonitis
- Collateral ligament desmitis
- Traumatic arthritis
- Phalangeal bone bruises
- Navicular collateral desmitis
- Fractures

All of these diagnoses appear as pain in the foot and thus lameness in the horse, which is blocked by injection of local anaesthetic to the heel area (palmar digital nerve) and/or the coffin joint. They can all, therefore, be described by the catch-all term "navicular disease" or "navicular syndrome" which should be heard less and less these days as MRI leads to a more specific diagnosis.

Information for horse ownersHOW ARE THE CAUSES OF LAMENESS NARROWED DOWN AND WHAT IS THE ROLE OF 'NERVE BLOCKING'?

Normally a vet will be able to tell which leg a horse is lame on (or at least which leg is worst) by watching how the horse moves. They then narrow down where the problem is by injecting small amounts of local anaesthetic to numb specific regions. The anaesthetic is applied just where certain nerves are known to go. Once a nerve is blocked everything "downstream" will go numb, so the vet will start at the furthest point and work back toward the body. The most common starting point is the nerve that goes to the heel area of the foot, the palmar (or plantar) digital nerve (often abbreviated to PD) -the back half of the lower leg is called palmar for the front legs, and plantar for the back legs. There are branches of this nerve on both the inside (medial) and outside (lateral) sides. Sometimes vets will try to numb just one side or the other, but as the nerves branch out further down this is not a very reliable way to localise the source of pain to one side or the other.

If the horse moves more freely when this area is blocked the vet knows that the pain is coming from somewhere in the foot, most likely the back half. Traditionally pain in this area has been believed to come from the navicular bone or the surrounding tissues so the lameness has been labelled first "navicular disease" and then more recently, as it has been recognised that it is not always actually the navicular bone causing the problem, "navicular syndrome". Today with MRI showing that many different structures can be involved and other research showing that the PD nerve block will numb most of the foot, even the label "navicular syndrome" is becoming less used.

If the vet thinks the pain is in the foot they might try to narrow the location down further with one or two other blocks. Since both of these are "downstream" of the PD block the horse has to be left a little while for the local anesthetic to wear off before either of these are tried. The other two blocks are:

  • Injection of local anaesthetic into the coffin joint: This will help determine if the problem is in the joint itself or the surrounding tissue. However as research has again shown that anaesthetic injected into the joint can numb tissues in a large region, the block is not as specific as the traditional textbooks will have you believe. Because this injection is right into the joint fluid there is a risk of infection, so it is not normally used as the first test and strict aseptic procedures are needed.
  • Injection into the navicular bursa: This will detect if pain is coming from the navicular area. The navicular bursa is like a fluid filled plastic bag squished between the back of the navicular bone and the DDFT and extending above the navicular bone. It helps the tendon move smoothly over the bone. It can become inflamed, or damaged if the tendon or bone are diseased. However the navicular bursa is very difficult to inject accurately, with the needle having to go deeply into the heel, so again vets will not use this as their first test and many avoid it altogether.


If the PD block does not make the horse go sound then the vet will work back up the leg blocking nerves closer to the body. The next block up is the "abaxial sesamoid" which is used to detect pain in the whole foot, pastern, and to some degree the fetlock. Then even further up you get the "4 point" or, in the hind limbs "6 point" where there are so many nerve branches many different injections are needed to get them all. Then there are a whole range of different blocks aimed at different structures.

Very often when a horse is blocked in one foot it will then go lame on the other side, as the pain is actually in both feet but one is worse in one than the other. So then the other foot has to be blocked as well. This makes the whole process very complicated and time consuming. When watching the horse trot up, it can be really difficult even to see which leg is the problem let alone whether it has got better, stayed the same, or switched sides. The whole process of nerve blocks can take a long time and not be very reliable. However it is a critical first step to narrow down the painful area as MRI can only image a small region at one time (eg a foot, or a fetlock).

The vet might use a system such as a Lameness Locator to assist in gait analysis. The Lameness Locator consists of three small sensors that are attached to the poll, rump and one foot as the horse is trotted in hand. The sensors gather data on the horse's movement that can be used to spot subtle or multi-limb lamenesses. It's good at picking up small changes but it doesn't replace the skill of an experienced vet.

Information for horse ownersIS IT EXPENSIVE?

Lameness is a difficult disease to diagnose, and to treat. Conventional x-ray, ultrasound, rest, treatment, remedial farriery or other approaches may each cost less than an MRI, but add up to more in total and yet be ineffective. Hallmarq recommends a conservative approach is considered first, but if the lameness persists an MRI may well cost less than repeated cycles of different tests and treatments. In addition the results are with you within a few days, saving wasted time and preventing the problem getting worse. If your horse is insured for veterinary fees all UK insurance companies, and most in other countries, will fully reimburse the cost of MRI (subject to your policy details and confirmation with your vet that it was needed)

Information for horse ownersWHAT TO EXPECT WHEN YOUR HORSE HAS STANDING MRI

An MRI scan will usually include the following steps:

1. Initial examination
On arrival for the scan the horse’s overall health is evaluated for sedation and the clinic vets will briefly examine the horse's lameness.

2. Horse shoes
Metal horse shoes would degrade the quality of the images if left on as the MRI scanner contains a large magnet. Normally just two shoes, on the leg to be scanned and the adjacent leg, are removed.

3. Sedation
The standing MRI eliminates the need for anaesthesia, so removes the mortality risk and often allows for day patient scheduling. Top up doses may be applied during the scan, either on a drip or via a needle.

5. Positioning
The horse is walked into the MRI scanner, with the lame leg placed between the poles of the magnet. A radiofrequency coil is fitted around the injury site and the operator makes careful adjustments to ensure the horse and magnet are both in the right place.

6. The Scan
The scan takes around one to two hours, producing around 300-500 images at multiple angles of the limb or hoof, highlighting different types of tissue and pathology.

7. Recovery
After the scan the horse is given time to recover from the sedation, and in most cases can return home the same day.

8. Interpretation
The vet responsible for scanning will carefully review the images to arrive at an opinion about likely pathology or injury. This is communicated to the referring vet, who will then be able to take other case information into account when reporting back to the owner on the findings.

9. Treatment
The findings from the scan will enable an accurate diagnoses to be made. With precise information available the vet can prescribe the best possible treatment for the horse

Information for horse ownersI'D LIKE TO GET MY HORSE SCANNED, WHAT DO I DO NEXT?

Speak to your vet. MRI is not appropriate for all lameness cases, and your vet will know the particular details of your case.

To check the location of your nearest scanner click here