Tuesday, February 18, 2020

Supporting limb laminitis: Dr. Scott Morrison's case review of Kentucky Derby winner Country House

Kentucky Derby winner laminitis Rood & Riddle Equine Hospital

Red roses show up twice a year: on Valentine's Day, and on the first Saturday in May, Kentucky Derby Day.

But this year, those two rose-filled days collided. On February 14, the world learned that 2019 Kentucky Derby winner Country House will not be returning to the races as a four year old, after all. As it turns out, the Derby was his last race.

The Valentine night announcement had a punchline: His owners revealed that the big chestnut son of Lookin at Lucky has been under treatment for supporting limb laminitis by Scott Morrison, DVM, of Rood & Riddle Equine Hospital in Lexington, Kentucky, since mid-summer. 

Dr. Morrison kindly agreed to share his insight into the management of this horse's six-month facedown with supporting limb laminitis, a medical complication which, according to laminitis overviews of the Grayson-Jockey Club Research Foundation, ends in euthanasia for 50 percent or more of horses afflicted. 

So that is where this story begins.

Country House on his way back to the barn after the confusing stewards' decision that crowned him the winner of the 2019 Kentucky Derby.

The most important thing to know about Country House is that he is alive and well today in a paddock at his owners' Blackwood Stables outside Versailles, Kentucky.

The last time most of us saw the horse was when he was led back to the barn at Churchill Downs. Country House did not run in any of the followup Triple Crown races. In fact, he never raced again.

The Blood-Horse quoted trainer Bill Mott remarks as far back as on June 16, five weeks after the Derby, suggesting that the horse probably wouldn't run again in 2019.

Two weeks later, on June 29, the colt arrived at Rood & Riddle Equine Hospital in Lexington, Kentucky for a thorough lameness examination. He was diagnosed with proximal suspensory desmitis (PSD) in both front legs. 

PSD is a common sport injury in both racehorses and performance horses. Its diagnosis requires thorough imaging of the suspensory ligament in the lower limb. The treatment is based on rest, along with various adjunctive therapies.

The horse was sent home to recover, but soon developed an infection in his right leg.

Laminitis is a risk for all horses; it has several "pathways", from medical to hormonal to mechanical, but all types of laminitis carry the potential to either suddenly or slowly destroy the health of the horse's foot and handicap its future athleticism. The amount of damage to the lamina, those tiny but strong fibers that tether the hoof wall to the large "coffin" bone (P3) within the foot, may vary in severity, case by case. When the horse bears weight on detached or diseased lamina, the bone may partially or fully detach from the hoof capsule that surrounds it.

Dr Scott Morrison, Rood & Riddle Equine Hospital
Dr. Morrison kindly shared some information about how Country House endured this very painful form of laminitis.

Veterinarians suggest that laminitis may be the most excruciatingly painful disease in the animal world. Imagine ripping off your toenail, and then standing with all your weight on that toe, like a ballerina.

Even though some forms of laminitis may be "manmade", the research of Australia's Brian Hampson, PhD, documented histological evidence of laminitis in hoof wall samples of some feral ("wild") horses, believed to be caused by nutrition or trauma.

This video from the van Eps Laminitis Laboratory at PennVet's New Bolton Center shows a time lapse representation of the detachment of lamina and resulting "rotation" of P3:

One of the laminitis pathways is called "supporting limb laminitis". It is not fully understood but is typically seen when horses have unequal weightbearing as a result of injury or infection in one leg. It can happen when a horse has major leg fracture surgery, or something as simple as a puncture wound. 

In favoring the injured leg, the horse overloads the presumed "good" leg. The resulting laminar breakdown may be more serious and life-threatening than the original injury or surgery; the horse is literally left without a leg to stand on. 

supporting limb laminitis Scott Morrison

Discomfort from the infection in Country House’s right front leg probably made him overload his left front foot and leg; supporting limb laminitis set in. In July he began an expanded, months-long treatment program which included sequential imaging evaluation, standing surgery, and various mechanical support solutions under the direction of Rood & Riddle’s Scott Morrison, DVM. 

"The foot just continued to slowly rotate over time," he said, thinking back to the early-summer months. "We took all the proper foot support precautions early on, but the left foot continued to rotate.”

This type of laminitis is monitored and evaluated through periodic radiographs and especially through a type of radiograph called a "venogram", which utilizes contrast material injected into the foot. Once the contrast is diffused, a radiograph is taken to discern whether there is damage to the blood supply, and if so, how serious, and hopefully reversible, the damage might be.

laminitis de-rotation Scott Morrison
post-tenotomy radiograph captions

"Sequential venograms showed significant perfusion (blood supply) deficits at the toe and sole corium," Dr. Morrison shared. "These deficits were not improving, even with significant shoeing mechanics." Equine podiatry employs what is called “mechanics” of width, length, thickness and angulation of horseshoes and boots, as well as the use of different materials, to affect a change that encourages healing and hoof growth.

In this case, Dr. Morrison turned to what is called a "derotation" method of trimming and then shoeing and supporting the foot, and elevating the heels, as well. "Rotation" in laminitis refers to the effect of slight movement of the coffin bone, that large, domed bone inside the hoof. Areas of the bone's attachment to the hoof capsule can be destroyed by laminitis, and the detached bone may shift within the foot.

External mechanics weren’t the only treatment; Dr. Morrison also perfused the colt's foot multiple times with stem cells.

The result, however, wasn’t a significant improvement.

Country House supporting limb laminitis

"He just continued to deteriorate," Dr. Morrison said. "The bone started to show some demineralization. We decided, with the owner's approval, to perform a tenotomy, which is a simple surgical procedure to sever the deep digital flexor tendon and relieve tension on the bone. 

"We followed this with what we call a ‘derotation’ shoe," he continued. This type of shoeing is designed to physically support the foot in a particular position deemed to be most therapeutic to encourage healing and growth.

On another front, Dr. Morrison needed to address the damage to interior structures caused by incomplete blood supply, as identified in the venography,. "I had to treat the necrotic tissue that developed secondary to the avascular and tissue compression with larval therapy." 

Scott Morrison laminitis radiograph Rood & Riddle
In the past two months, Country House has continued to recover from his laminitis. These radiographs show the improvement in sole depth, particularly under the tip of P3, and the continued hoof wall growth indicating how far down the coronary grooving mark has grown.

Larval therapy employs sterile maggots that are intentionally bred by medical suppliers for use in cleaning wounds or rectifying tissue damage where circulation cannot do its normal healing role.

As the summer turned to fall, Country House responded. "Through a lot of hard work and great care and management from the farm, we were eventually able to rehabilitate the foot," Dr Morrison concluded.

"Currently, Country House is doing great. He walks sound, and is almost sound at a jog. He is turned out again in a paddock, and he is off all medications. Unfortunately, his foot won't hold up to racing again, but I'm certain that it won't prevent him from living a long comfortable life.”

laminitis Rood and Riddle Equine Hospital
laminitis venography

Why were multiple venograms needed to evaluate Country House? The blood supply in the foot changes with loading and unloading.

In the short video below, also from the van Eps Laminitis Laboratory at PennVet's New Bolton Center, you see the blood supply in a representative (normal) weightbearing foot imaged through CT scanning. This is similar to the far left venogram in the Country House series above. 

A horse bears more weight than normal on its "good" leg to favor an injured one; the "good" leg is lifted less often because of the pain involved. The mechanism of support limb laminitis may involve "ischemia", the critical lack of blood to deliver oxygen to tissues, complicated by a foot that remains planted on the ground with the reduced blood flow pattern shown. (This horse does not have laminitis.)

When the foot is raised off the ground and captured by venography, you would see perfusion similar to this (below). Compare this with the middle still image of Country House's foot above. The blood supply in the colt's unweighted foot is compromised; restoring it was a key treatment goal.  (These videos were made with computed tomography (CT) and modeling software by Materialise in Belgium.)

In this new chapter of his life, Country House will join several stallions in Kentucky who have overcome laminitis. The first one that came to mind is Spendthrift Farm’s multiple graded-stakes winner Lord Nelson, who was also treated for laminitis by Dr. Morrison. His recovery from supporting limb laminitis required tenotomy surgery on one front foot and special shoeing on the other. In his first year at stud, Lord Nelson served 127 mares.

Support limb laminitis research has been supported at Penn Vet and The Ohio State University vet schools, thanks to funding over the last ten years from sources like the Grayson-Jockey Club Research and AAEP foundations. Research is difficult, since humane standards limit the intentional induction of such a deadly disease.

According to the Grayson Foundation, despite great advances in the treatment of even the most catastrophic limb fractures and infections in horses, "supporting limb laminitis remains the major cause of treatment failure in these cases. An effective preventative strategy would be a significant step forward for the welfare of horses and for the horse industry."

Country House recovering from laminitis
The Derby winner's left front foot is continuing rehabilitation at BlackWood Stables in Versailles, Kentucky. In this photo, the coronary grooving track is visible at the toe,just below the hairline. It would grow out over time as the foot regained its health. Country House now enjoys being turned out in a paddock. (Scott Morrison photo)

Dr. Morrison and his colleagues in the podiatry clinic at Rood & Riddle Equine Hospital are members of a small but effective (and growing) group of dedicated referral equine podiatry veterinarians working to help horses with supporting limb laminitis, as well as other forms of the disease. In 2019, Rood & Riddle hosted an international conference on equine podiatry with significant content on laminitis therapy, including radiography, venograms and de-rotation shoeing.

This month, a chapter on the clinical management of stress-induced laminitis, authored by Dr. Morrison, will be published in the new second edition of the reference book, Equine Fracture Repair, edited by Alan Nixon.

• • • • • 

This article about the 2019 Kentucky Derby winner may re-fuel a great debate, even though months have passed since the blanket of roses were somewhat begrudgingly laid across the  withers of Country House. But when historians list the Derby winners, the name of Country House will be there. 

And now Country House has won again, beating laminitis this time. It's one victory on his record that no one will ever question, since beating laminitis may be a more significant triumph than winning any race.

• • • • • 

To learn more about Dr. Scott Morrison's work on supporting limb laminitis:

Baxter, G.M. and Morrison, S., 2008. Complications of unilateral weight bearing. Veterinary Clinics of North America: Equine Practice, 24(3), pp.621-642.

Morrison, S., 2010. Chronic laminitis: foot management. Veterinary Clinics: Equine Practice, 26(2), pp.425-446.

Morrison, S., 2011. Long-term prognosis using deep digital flexor tenotomy and realignment shoeing for treatment of chronic laminitis. Journal of Equine Veterinary Science, 31(2), pp.89-96.

Morrison, S. (2020). Stress‐induced Laminitis. In Equine Fracture Repair, A.J. Nixon (Ed.). doi:10.1002/9781119108757.ch49

Also of interest:

Belknap, J.K. and Geor, R.J., 2017. Equine laminitis. John Wiley & Sons. (book)

Hampson, B., de Laat, M., Mills, P., Walsh, D. and Pollitt, C. (2013), The feral horse foot. Part B: radiographic, gross visual and histopathological parameters of foot health in 100 Australian feral horses. Aust Vet J, 91: 23-30. doi:10.1111/avj.12017

Wylie, C.E., Newton, J.R., Bathe, A.P. and Payne, R.J., 2014. Prevalence of supporting limb laminitis in a UK equine practice and referral hospital setting between 2005 and 2013: implications for future epidemiological studies. Veterinary Record, pp.vetrec-2014.

Learn more about Country House and Blackwood Stables, where he is currently in rehabilitation: https://blackwoodstables.com/

More about Fran: Fran Jurga launched this Hoof Blog in 2004; it has won many awards and now contains more than 1,800 articles on virtually every aspect of hoofcare and lameness. She also writes on a freelance and contract basis about things other than hooves for publications and corporations around the world. What can she write for--or about--you?

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