Friday, October 12, 2012

Hallmarq Standing MRI: Hoof Conformation from the Inside Out

This sponsored blog post is the latest in a series produced in partnership with Hallmarq Veterinary Imaging. Thanks to Hallmarq for their support of The Hoof Blog. This video explains the process known as "Standing MRI" of the equine foot using a Hallmarq system. The units are in use around the world.

Which came first: the chicken or the egg? 
Forget everything you “know” or think you know, about the relationship between foot shape and lameness. What matters in this age of evidence-based veterinary medicine is 1) what can be demonstrated and measured; 2) reliably repeating what was demonstrated; and 3) documenting the data of the measures.

If some hoof research makes you yawn and seems to be proving what is already obvious to you, remember that building a better tower of knowledge means that we know we can count on the blocks at the bottom of the tower. They must be proven before we can move on.

Hoof science is shy a few blocks. The tower is still on the drawing board. In order to document what you "know"via the scientific process, it is necessary to approach it from different angles so that it can be measured.

The deep digital flexor tendon (DDFT) is the most common site of damage in the foot identified by standing MRI scanning of sport horses. As you know, this tendon runs down the leg and attaches to the bottom of the coffin bone (P3). The three arrows added to this scan are directing the eye to the portion of the DDFT which, in this Irish horse, has a lesion that looks like a split. Normally tendon would be solid black. The recent study in England looked at a group of horses with similar injuries of the DDFT and measured for similarities in the conformation of foot structures. (Photo courtesy of Troytown Equine Hospital, Co. Kildare, Ireland.)
When researchers at Great Britain’s Royal Veterinary College wanted to get to the bottom of this age-old conformation to lameness relativity issue, they used Hallmarq standing MRI images to collect data that could be measured. The group of investigators worked under the direction of Renate Weller Dr Med.Vet, PhD, MRCVS, FHEA, senior lecturer in diagnostic imaging and locomotor biomechanics, at the RVC's Structure and Motion Laboratory.

Tim Mair, BVSc, PhD, DEIM, DESTS, DipECEIM, MRVCS is an author of the paper and a partner in England's Bell Equine Veterinary Clinic, where Hallmarq Standing MRI scans were sourced by Hallmarq's Nick Bolas. Also from the private sector, and a recent RVC graduate, Jonathon Dixon BVetMed MRCVS of Rainbow Equine Clinic was involved with the study.

The premise of the study is an inside-out refinement of hoof confomration. Instead of measuring the circumference of the hoof capsule and the contour of the coronet, they measured or calculated characteristics of the structures inside the foot. The availability of real-world lameness cases' standing MRI scans meant that the researchers had the luxury of a library of almost 200 images of injured or lame feet that met the study's criteria.

The MRI would have been originally made to assist in a definitive diagnosis on a lame horse. The clinician noted that the MRI showed a lesion in the deep digital flexor tendon or injury to the navicular bone, etc.

The researchers from the Royal Veterinary College undertook the project of evaluating these standing MRI scans not in the context of a single lame horse, but in the hopes that they would find other similarities in the feet of horses that had received the same diagnosis.

Once again: don’t assume anything, but see what the MRIs had to say.

If you overlaid a dozen images of the same type of injury from a dozen horses’ hooves, would the hoof capsules line up and show similar characteristics?

The researchers found that there indeed was similarity in the measurements of feet with the same diagnosed injuries.

What type of horses and lameness?

The mean age of horses in the study was between ten and eleven years; the average grade of lameness was approximately a “3” on a scale of 1 to 10. Breeds included 37 Warmbloods, 51 Thoroughbreds and Thoroughbred crosses, 22 Irish sport horses, 15 Irish draft horses and Irish draft crosses, 11 Cobs and 43 horses of other various breeds.

The horses had been diagnosed with many types of injuries, including lesions of their deep digital flexor tendon (DDFT), navicular bone (NB), collateral ligaments of the distal interphalangeal joints and
25 other structures.

What was measured? C, sole angle; D, toe angle; H, heel angle; N, deep digital flexor tendon angle; PL1, plumb line 1;  PL2, plumb line 2;  MA1, proximal moment arm; MA2, distal moment arm; SI, distal phalanx length; LC, toe length.

Sole angle

Sole angle is a relatively new term in the lexicon of foot anatomy. It is not the angle formed where the sole meets the wall, as documented in some studies. Its number is not describing the sole at all, in fact, rather the concavity of the coffin bone.

Dr. Weller took the time to explain it for Hoof Blog readers as the concave sole surface of the coffin bone to horizontal angle. Check the diagram to see the point on the mid-sagittal MRI scan where this angle is measured.

Dr Weller explained: "The issue we have in practice is that the sole angle we measure on radiographs does not correspond to the angle at which the DDFT actually attaches, but (rather we measure) the lateral and medial coffin bone borders.

"This (angle of the coffin bone) can be taken as an approximation at best, since the concavity of the coffin bone differs between horses. So some may have little concavity and in those horses the radiographic measurement will correspond quite well to the insertion angle of the DDFT, (however) some horses may have (a) very concave coffin bone and in these the radiographic measurements will not represent the DDFT insertion angle.

"The reason we care about this angle is that it is strongly related to the strain the DDFT experiences and hence the pressure this tendon exerts on the navicular bone," she concluded.

Measurement results

  • A larger sole angle was associated with combined deep digital flexor tendon (DDFT) and navicular bone (NB) lesions, but not with NB lesions alone.
  • A more acute angle of the DDFT around the NB was associated with DDFT and NB lesions.
  • A lower heel height index was linked with DDFT injury.
  • The larger the sole angle, the smaller the likelihood of a DDFT or NB lesion.
  • Measurements of the feet in the study contradicted findings of other studies.

Why is this study important?

Taking measurements from diagnostic images is not a new idea, so why is this study newsworthy? 
Previous studies have shown that certain conformational traits--sole angle in particular--increase forces acting on the DDFT and NB in sound horses. This study supports these findings by showing that conformational parameters are associated with DDFT and NB lesions in lame horses.

Standing MRI is done with the horse
bearing weight on the injured limb
The researchers noted that while this study shows an association between certain conformation parameters and foot lesions, foot conformation cannot be identified as causative factor of lameness. "Foot conformation may change as a consequence of lameness," they concluded.

Which brings us back to the chicken and the egg.

Future studies at the RVC will focus on dynamic conformation by investigating foot-surface interaction in lame versus sound horses, which may eventually open a preventative and/or therapeutic window for horses in the process of developing specific lesions within the foot.

Relevance of this study

The study's findings emphasize the deep digital flexor tendon's influence on the conformation of the foot and that it plays a leading role in many foot lameness problems. The DDFT's angle within the foot and the relative concavity of the distal phalanx (P3) (as measured by sole angle) may become routinely documented in the future.

Studies like this one are changing the way that foot structures are evaluated and measured. Standing MRI scanning provided three-dimensional evaluation of the foot, expanding the diagnostic field for the most precise possible examination of foot tissues and for the most accurate measurement protocols for scientific relevance. 

But Weller’s team’s emerging protocols for evidence-based hoof evaluation provide the sport horse and racing worlds with a basic building block that could one day be used on important studies to answer questions on equine welfare, prevent pain and increase a horse’s useful years. The hoof is one of the last frontiers of equine science, and the Royal Veterinary College is dedicated to learning more about it.

Research can’t be any more relevant than that.

To read the full paper: Kate Holroyd, Jonathan J. Dixon, Tim Mair, Nick Bolas, David M. Bolt, Frederic David and Renate Weller; Foot conformation in lame horses with different foot lesions diagnosed, published online in The Veterinary Journal, September 2012.

 To learn more about Hallmarq Veterinary Imaging and standing MRI technology for horses:

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Disclosure of Material Connection: Hoofcare Publishing contracted to receive compensation for compiling this post but the veterinary expertise and opinions in the article were provided by John Peloso DVM and Hallmarq Veterinary Imaging.  The information contained in this article is for informational purposes only, and should not be used to replace professional veterinary advice for your horse. Visitors to the website are responsible for how they choose to utilize this content. I am disclosing this in accordance with the Federal Trade Commission’s 16 CFR, Part 255: Guides Concerning the Use of Endorsements and Testimonials in Advertising.

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