The Bare Bones: a Primer with Dr. Bramlage

He hasn't got all day; nor, doubtless, do you. So let's cut to the chase. We won't dwell on the journey that has made Dr. Larry Bramlage a doyen of orthopedic science, in its daily application to the racehorse: not the alphabet soup of honors and distinctions, nor the long experience that has honed the sharpest diagnostic eye in the business through 23 years with Rood and Riddle. We have simply dropped into the clinic, on a recent visit to Lexington, to direct a brief sunbeam of his knowledge and insight into the practices of those who depend for a living on the miraculous but fragile equilibrium of the bones that support a Thoroughbred.

“Racehorses are so good because they produce their skeleton based upon what they do,” Bramlage begins. “They're not born with it. Their skeleton is the minimum weight that they can produce and still carry them around the racetrack. So they have a big engine, but their undercarriage is no heavier than it needs to be. And that's why they're fast.”

That's true, in some evolutionary measure, of all horses–and other animals, too, people included.

“The skeleton is different than hearts and lungs and muscles,” Bramlage explains. “Those train to a volume of work that you're doing. Skeleton trains to the level of work that you do.”

He recalls a series of experiments conducted on turkeys some years ago, where one wing was restricted and the fowls learned to flap the other to get food. The idea was to establish how many cycles of this activity were required to stimulate bone.

“Well, it's interesting,” Bramlage says. “Because when you reach 36 cycles in a day, that's the maximum the bone will respond to. You can go to 2,000 and it won't get any stronger than in those 36. And that's what makes a trainer's job tough. Because they have to push the horses hard enough, that they get strong enough to carry themselves around the racetrack. But if you do too much, then those extra cycles begin to be destructive.”

Those 36 cycles, for our purposes, apparently equate to about a furlong. Which, Bramlage explains, means that your fastest eighth will be the level for which your horse produces bone. Obviously that doesn't happen overnight, albeit bone is far more dynamic than most laymen assume.

“But the stimulus is there that it'll try to reach that next level before the exercise does,” Bramlage explains. “And then you repeat that over and over, and eventually the skeleton gets appropriate enough that you don't acquire any damage during those 36 cycles. So while there's some always ongoing wear-and-tear, the most important part of making a racehorse is usually up to four or five races. Once they get there, their skeleton is virtually made.”

The living nature of bone, however, does mean that the “made” skeleton can regress once taken out of training. But Bramlage is keen to address a misapprehension, which took root maybe a decade ago, that persistently galloping a young horse creates the foundation for a strong skeleton.

“Galloping a horse a lot helps the heart and lungs–but once you go past those 36 cycles in a day, the rest of them are just wear-and-tear,” he explains. “A lot of horses were actually harmed by excess galloping.”

Previously there had also been the attempt to extrapolate the principles of interval training, in human athletes. “I knew a couple of people who, as runners themselves, were going to interval train and beat everybody,” he recalls. “And they ended up with 4-year-old maidens with splints on their hind legs. Because the skeleton just can't take that that many fast intervals. In people, the limiting system is the heart and lungs, not the skeleton. Horses have such great heart and lungs that, unless they're bleeders, they virtually never limit. The horse's heart and lungs can respond to anything you throw at them. But the skeleton has to do it in little stair steps. And that's how, in young horses especially, the heart and lungs often get ahead of the skeleton.”

Though the tibia also registers trouble here–it absorbs a lot of force, in locking the reciprocal motion of stifle and hock–the most familiar symptom is shin trouble.

“You go too fast, the wear-and-tear begins to exceed the response and you get bucked shins,” Bramlage continues. “Shins have to triple in size. The front cortex of a cannon bone in a 'made' racehorse is three times thicker than in the yearling that started training.”

So how does this translate, ideally, into building up a young horse towards a race? Bramlage suggests a pretty familiar scenario: one or two furlongs at a rather higher level than the rest of the exercise, in effect showing the skeleton where it's going to be asked to go in three days' time. The real skill, in training, is monitoring attitude.

“People ask, what makes a good trainer?” he says. “For me, it's an easy question. It's being able to understand when the horse is happy and when he's not. When horses are adapting well, they're happy to train. When a horse starts not wanting to go to the track in the morning, not wanting to load in the gate, those are the kind of things you need to look out for. It's a real art for trainers to understand when to push a horse and when to back off.”

Obviously you would hope that trial and error, over the generations, should have brought horsemen's intuitions pretty close to where they might land through learned science.

“If you go back to when Aiken, South Carolina, was the winter training center–because that's how far the railroad went south–they would have the Aiken trials and those 2-year-olds, early on, would be breezing an eighth,” Bramlage says. “Those short breezes were actually very useful to the horses. Especially when you're making the horse, it's a matter of trying to train heart and lungs–because you have to do that–without overtraining the skeleton.”

When a horse is past that stage, but has to be laid off training, the skeleton will not lose much strength through the first month but the situation will change pretty rapidly after two months. And a more significant spell, say four months, notoriously invites humeral or tibial stress fractures in a small number of horses: again, because heart and lungs train back so much faster than the skeleton.

Needless to say, by the time a horse is sent into the clinic, they have typically signaled a loss of form.

“If a horse has swelling in a knee or ankle, those guys at the racetrack pick it up,” Bramlage says. “These horses [sent into the clinic] don't have any obvious pain, heat or swelling, but their form has gone down. And a lot of times they have either bilateral lameness–two fronts or two hinds, sometimes all four–or they're just early wear-and-tear injuries. I think most of the really successful trainers today understand better than they did 10 years ago that the horse is subject to that wear-and-tear; and that whenever a horse is not giving you what it can, then you need to start looking.”

Parallel advances have been made in imaging technology. It is barely 30 years since radiographs were still processed on celluloid. Digital radiographs have themselves improved dramatically, and now scanning in three dimensions via CAT and MRI and ultimately PET is available.

“Nuclear imaging was a huge tool because those scans allowed us to look for stress fractures that didn't have any outward clinical signs,” Bramlage says. “But whenever regulators think in terms of needing a PET scan to monitor horses at the racetrack, that's not really true. You need to look at them and identify the horse that needs to be looked at, not scan them all. Most of those can be unraveled using all the tools we currently have. It's just a matter of knowing when you need to look. And so more than we need more equipment, we just need to look more often.”

The role of regulatory veterinarian is a contentious and evolving one. The process is being aided, however, by a growing injury database to succeed anecdotal assumption. Already Bramlage can see where this might take the profession.

“It may not hit during my lifetime, but I think the next really exciting revolution, which is going to totally change our care of racehorses, is digital timing,” he says. “It just makes sense that it will eventually move away from clockers and all be done passively, automatically, by the equipment. Well, when you have that data, it's not a real hard step to write an algorithm that identifies [problems that may be brewing].

“You could look at a horse's exercise fingerprint because stride length and stride cycle is pretty stable for individual horses. When the length begins to shorten, he's protecting something. And so each horse will have his own digital fingerprint, and this will be automatically recorded every time a horse works, every time they race. And all of a sudden you can say, 'This horse is getting into trouble.'”

Some early research has detected patterns that might anticipate injury as many as three races ahead. Bramlage can see a future where every horse will transmit data to central monitoring for red flags. For now, until the necessary technology is available, it falls to people like Bramlage to determine the level of risk that warrants its prohibitive cost.

“But I think that in the next generation beyond me, that will become automated,” he predicts. “And that will revolutionize the prevention of injuries. It'll be the best thing that ever happened.”

And that's one of the things that maintains such youthful enthusiasm in a septuagenarian who has already witnessed such transformation in the tools of his trade: the curve is only going to steepen.

Aside from digital radiography, the biggest leaps forward have been internal screws and plates; plus arthroscopy and its adaptation from diagnosis to treatment. For internal fixation, the initial debt was apparently to a Swiss cost-benefit analysis of chronic disagreement between tibias and ski-boots. Of arthroscopy, meanwhile, Bramlage muses: “Surgery never used to happen until there wasn't anything else you could do. Then with the arthroscope it became easier, quicker, better. And so now that is the first line of defense. The horse gets a chip fracture, they take it out right away. The joint doesn't degenerate, they go back to normal.”

Horsemen nowadays have gained faith that condylar fractures can be routinely secured. One of Bramlage's most celebrated patients, Personal Ensign, went a long way to changing perceptions. Nowadays you'll find many a Breeders' Cup winner with a screw lurking somewhere in its skeleton. It's a very different world from when Bramlage started out, and yet he feels we have barely started.

“Yeah, we were dipping X-rays in chemical solutions when I was a student,” he reflects. “But the young veterinarians right now will probably see the same explosion. Probably in the biologic areas: the understanding of cell biology, and cell communication, is doing the same ramp up. The ability to treat is going to be much more pointed and effective than now.”

Bramlage is acutely aware of our industry's exposure to an ever more urban society that professes ever fiercer vigilance on behalf of animals with which it typically has little interaction, certainly compared with generations past. In that respect, veterinary regulation manifestly has a front-line role. He's excited, then, that a digital fingerprint might give mute animals a new way of telling doctor what's wrong.

Even with the advent of such tools, however, Bramlage believes that the essential mystique of the Thoroughbred will endure. We might be able to explain how everything fits together, and learn how to put things back together, but the key to performance will remain elusive.

“And actually I hope we never do get to that point where we understand everything about a horse,” he admits. “Because I think that's what's intriguing to people. You can improve your odds by improving your breeding. You can keep the horse healthy, you can have a trainer that's capable to that level. You can do all those things, but you still can't just go buy a Derby winner.

“Every horse is a product of a dip out of the gene pool. It's not a one-to-one combination of the mare and the stallion. There are all sorts of units. Like you've got four genes that cause eye color in people. There are all those different combinations of things. So to combine whatever comes out of that gene pool with the mental capacity, to train hard enough and compete hard enough, you never know which horse is going to have it.”

He chuckles, and asks whether you ever heard of a racing mule named Black Ruby?

“Well, she was on the California fair circuit for about 10 years and there was only one other mule could occasionally beat her,” he explains. “But they cloned her several times, and none of them could beat me. They had the exact same genetic makeup, but none of them would run like that. So that elusive factor, I think, is what keeps people intrigued. And I hope we never identify that.”

Even his exceptionally intimate professional relationship with horses, ranging from Personal Ensign to claimers at Ellis Park, has only marginally clarified the enigma.

“I don't know that there's any one thing,” he says with a shrug. “Good horses are always physically attractive, well balanced. They're almost always smart, they're very intelligent, very adaptable.”

Does that make better horses better patients, too?

“Absolutely,” he replies. “But racehorses are the best patients anyway, in my opinion. The worst patient is the 4H horse that's never felt anything but a rub rag, because when they have to deal with pain, you never know how they're going to handle it. But racehorses are just like people who train hard: you're stiff and sore next day and then it goes away and you feel better than you did before you started. They have better survival instinct.”

And while recruitment to equine practice is becoming harder, given the reduced social exposure nowadays between young people and horses, Bramlage guarantees endless fascination to the next generation. The measure of your work, he says, is so much more gratifying than in small animal practice.

“I think equine practitioners tend to practice a lot longer because there's another level of assessment,” he says. “Your horses have to go back and run. They have to win barrel races. They have to win ribbons, if they're a backyard horse they have to trail-ride. There's a couple of books I read, discussing why do armies fight? It's mostly not for abstract ideals. They fight for the people next to them, the people they trained with, the things they know and the fear of failure. And I think this level of assessment, with the possibility that you'll fail, but the rewards when you succeed, it's higher in horses.”

And there are literally hundreds of horsemen in the Bluegrass who will be relieved to hear him say that. “I could easily be retired,” he says. “At some point, physically it's not going to be possible to continue. But I think that's why people stick around. I mean, when the success barometer is the dog being able to get up on the sofa? That's not quite as intriguing!”

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Stronach Group Funding Surgeries On Injured Horses, Amid Controversy

Everyone at a racetrack holds their breath when a horse pulls up. It was true before the fatality spike at Santa Anita Park in 2018-19, and it's even more true now that every on-track injury feels like a liability for the sport. Veteran horsemen have long felt they could guess, as they get closer to the solemn scene, whether they think the injured horse is going to make it or not. In those moments when they believe there is no salvation to be had, most of them say the kindest thing to do is to end the horse's suffering as quickly as possible.

A recent initiative at The Stronach Group racetracks has been pushing the boundaries of that assumption – but not everyone is happy about it.

Taking the finances out of the equation

Two years ago, Stronach Group management was looking for whatever solutions it could find to the breakdown problem at Santa Anita. Facing what was an enormous public relations crisis, the company needed fewer dead horses. Its executives implemented a flurry of new protocols, including rolling back administration times for various therapeutic drugs, increasing veterinary oversight, and reducing whip use. Around that time, the company also began exploring the idea of funding surgeries on injured horses.

“As we looked around, we said, 'If we take the financial piece out of it, what decisions do people make?'” said Dr. Dionne Benson, chief veterinarian for 1/ST Racing, The Stronach Group's racing brand. “You look at a horse like ArchArchArch, who broke down in the Derby, got a fetlock arthrodesis and [became] a breeding stallion. Those are no-brainers for people because they want the residual value of the stallion. But often if you've got a gelding that's running for $5,000, there's an economic decision that's made. We wanted to allow people to make the decision for the horse while taking some of the economic burden away.”

Orthopedic surgery and subsequent care can cost thousands of dollars, and costs increase exponentially based on the complexity of the injury and the smoothness of recovery.  Benson and others worried that there were cases of owners or trainers looking at the prospect of operating on an injured horse as a money-loser, and choosing to euthanize – even in cases where the horse might have had a productive life in retirement. She also wondered how many horses were euthanized without significant diagnostics to even find out if they could be saved. Benson said she heard of one case – not at a Stronach track – where a horse was euthanized after pulling up lame with a sizable bump in the leg, which veterinarians assumed was a serious fracture. Only upon conducting a necropsy did they learn it was a hematoma.

Santa Anita is unique in that it has a fully equipped equine hospital on-site, so it's logistically easy to assess and operate on a horse with an orthopedic injury. Benson consulted the best orthopedic surgeons in the country, including Dr. Larry Bramlage at Rood and Riddle Equine Hospital in Kentucky and Dr. Ryan Carpenter, who operates at Santa Anita, looking for guidance on what makes for a good surgical candidate and what doesn't.

Then, the racetrack began funding veterinary care in cases where owners wouldn't or couldn't. In the past year and a half, Benson said The Stronach Group has paid for veterinary care on a variety of injuries, including some serious wounds, a bilateral condylar fracture, cannon bone fractures, and sesamoid fractures. The track was willing to pay for surgery even in cases where a referring veterinarian may have suggested euthanasia. So far, it has paid for surgery for 17 Santa Anita-based runners since the start of 2020, and 13 are alive and well – which Benson considers a solid success rate, assuming those horses may have otherwise been euthanized by their connections. From those 17, there were 11 fetlock arthrodesis surgeries, where a serious sesamoid fracture is repaired by fusing the bones in the ankle joint. Eight of those horses are still alive and doing well. For horses who would otherwise be dead, Benson said she's comfortable with those outcomes.

That early success rate prompted The Stronach Group to expand its surgical assistance program to its tracks in Maryland and Florida. In lieu of on-site surgery suites at the racetracks there, The Stronach Group has implemented partnerships with Rood and Riddle and the University of Pennsylvania to refer surgical candidates.

Currently, Benson said if a horse sustains an injury on track, the horse's treating veterinarian and trainer will typically put a splint on the injured limb, administer sedation and pain relief, and take the horse back to its stall for evaluation. Someone from The Stronach Group veterinary team will reach out and ask for diagnostic images on any horse who does not have a fracture coming through the skin and does not have injuries to more than one limb (with one exception in California). Horses with those injuries are not considered good surgical candidates. The track then offers to send those images to Drs. Carpenter, Bramlage, or Rood and Riddle surgeon Scott Hopper for a consult. If the surgeon tells the racetrack and connections they think the horse has better than a 50/50 chance at eventual pasture soundness with surgery and the horse's owner doesn't want to proceed, they are offered the opportunity to sign the horse over to The Stronach Group.

Dr. Ryan Carpenter

All of this takes time, but it's time Carpenter says he would normally give a horse anyway before deciding whether to proceed with surgery. Perhaps surprisingly, he says that the main indicator of whether a horse will do well with surgery isn't a matter of how gnarly their radiographs look – it's about the amount of swelling and blood supply they have to the area. Independent of this program, he often waits until the day after an injury before assessing a horse's fitness for surgery because that's when it'll be most clear how the blood supply responded to the injury.

Carpenter said he has learned from the past two years of the track-funded surgery in California that the responsiveness of on-track emergency personnel is key to a horse's chances. While a horse with a fracture wears a Kimzey splint in the trailer ride from the track to the barn, Carpenter prefers to remove it at the barn, take the necessary images, then wrap the leg and put the Kimzey back on as quickly as possible. That extra compression and support from the bandage can significantly reduce swelling, and even a few minutes' difference can have a massive impact on how the horse's blood supply reacts to the injury later.

While the program has been going full strength in California for a year and a half, it was implemented much more recently at Stronach Group facilities in Florida and Maryland. In Maryland, three horses have been sent to surgery at New Bolton Center by the track, and all three have lived. One was a spiraling medial condylar fracture on a hind limb that needed a plate. The referring veterinarian suggested euthanasia, but the surgeon said the horse had a 50 to 60 percent chance to return to racing. After seeing the surgeon's report, Benson said the horse's connections decided to proceed with the surgery themselves.

In Florida, Benson admits the results haven't been as strong; surgical success rate is at about 50 percent.

Not everyone is on board

The Paulick Report has interviewed a number of horsemen and veterinarians with direct and indirect knowledge of The Stronach Group's program to fund surgeries. All declined to speak on the record for fear of retribution from racetrack management, and most expressed serious concerns about the ethics of the program.

For horsemen who had not had a horse injured on track since the program came to their state, there seemed to be little concrete information provided by the racetrack about how it would work. Many had the impression the track was strong-arming trainers into signing over ownership of the injured horses (an allegation Benson denies), playing on their fears of losing stalls. They also had no access to information about the outcomes of injuries they'd witnessed and believed or assumed all or most horses trailered to nearby clinics for surgery had died.

People who had been involved with an on-track injury confirmed the track is not exerting pressure on connections to sign horses over, but did say they had serious concerns about whether the decision to send particular horses to surgery had been fair on the animal.

For horses that go through a complex surgery and long recovery from a procedure like a fetlock arthrodesis, many people questioned those horses' short- and long-term quality of life, along with the associated cost to care for them. Benson said that horses who had been saved by track-funded surgeries in California were placed via the California Retirement Management Account (CARMA) if they were only pasture sound. The track has committed to following those horses throughout their lives to ensure that, given the relatively limited vocational options for some, they didn't fall into a bad situation.

Carpenter said skepticism of the program in the case of serious injuries like sesamoid trauma likely comes from an outdated notion of what a surgical repair, like a fetlock arthrodesis, entails. Dr. Dean Richardson at New Bolton has perfected the procedure in recent years with new materials, cables and locking plates, and new approaches to the incision sites that make the surgery shorter, less complicated, and more likely to achieve a positive outcome than it did a decade ago.

“You have to acknowledge that just because we're done things a certain way for a long time, that doesn't mean that's the way we will continue to do them or should continue to do them,” said Carpenter. “An arthrodesis done today has a far better chance of survival than an arthrodesis done 10 years ago. but the perceptions of people today are often based on the perceptions of the past.”

This horse suffered serious wounds in a freak accident at Laurel when he reared and fell onto an iron fence. The Stronach Group funded his care, and he is ready to leave the hospital and begin rehabilitation.

He's also troubled by the number of people who seem intent on euthanasia in cases he thinks don't warrant it, including career-ending sesamoid fractures on horses without residual value in the breeding shed. While the critics of the program believe they are coming from a place of kindness, Carpenter believes he is, too.

“This is one where if it was American Pharoah, everyone would be cheering 'Give this horse a chance,' but when it's a $10,000 claimer, everyone's cheering 'Put it down,'” he said. “That, I don't understand. A horse is a horse. If it's good enough for American Pharoah and humane enough for American Pharoah, then it's good and humane enough for the $10,000 claimer that no one knows their name.”

But as the program expands to other states and continues over a period of years, a greater success rate will mean there will be more horses that need that kind of care and monitoring. Some have wondered whether it's fair to salvage a horse for pasture soundness, only to pass on the costs for the remainder of its 15 to 20 years of life to a non-profit or a well-meaning adopter. Private home placements for pasture ornaments are hard to come by, which is why there are so many retired horses in sanctuary facilities already.

The question asked independently by nearly everyone who expressed concerns to this publication was also – is The Stronach Group doing this out of the kindness of its corporate heart, or to reduce fatality numbers? Horses are considered racing or training fatalities for the purposes of the Equine Injury Database (EID) if they are euthanized due to injury within 72 hours of incurring the injury.

Benson said this isn't the motivation behind the program, and that horses vanned off and euthanized in the 72-hour window are reported by The Stronach Group to the EID as racing or training fatalities. In California, the horse racing board keeps its own records on racing and training fatalities and follows up with necropsies and post-mortem reports as part of state regulations. In Florida, on-track deaths are supposed to be reported to the Division of Pari-Mutuel Wagering, but it seems from public records as though those reports are made voluntarily by a trainer or treating veterinarian, not a state representative keeping independent track of deaths.

It's also true that the track's desire to give an injured horse a chance does, by default, create the opportunity to reduce fatality numbers – and those numbers are better in all three states since the surgical program and other reforms were implemented.

“We have reduced the number of racing related fatalities in Florida and they are consistent year over year in Maryland to date,” said Benson. “In training, we have reduced horse fatalities (on-track musculoskeletal and sudden deaths) by about half in both Maryland and Florida year over year. Additionally, while I cannot speak for Florida generally, we enter all fatalities and injuries to horses in the EID for our tracks and training facilities located there. Moreover, every horse that dies or is euthanized at Gulfstream Park or Palm Meadows is sent to necropsy at our expense. This has been the case for over a year.”

Benson and Carpenter agreed that those concerns voiced by horsemen in Florida and Maryland are nothing new – they heard them when they launched the program in California. Both now say that referring veterinarians and horsemen in California are on board with the program, largely because they've seen horses move on to second careers or achieve pasture soundness. They remain confident that eventually, their success at other facilities will convince the naysayers.

“I acknowledge the fact that what we're doing here in California is not going to be widely accepted in other states,” said Carpenter. “I think we're a little bit ahead of the curve and part of that is because of what we endured in 2019.

“What I saw very quickly in interacting with people who don't know anything about racing, is that every single fatality is significant. When you make the comment that 'This year we've only had 30 [fatalities]' — which from an industry standpoint is amazing — the people are still appalled because that's still a very, very big number.”

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Sesamoid Bones: They Take A Lot Of Pressure And Raise A Lot Of Questions For Researchers

As racing continues its quest to reduce injury rates, one key area of interest for many experts is the proximal sesamoid bones.

Most racing fans who have heard of sesamoid bones know about the two small, triangular bones held inside the suspensory ligament that form the back of the equine ankle, but horses (and humans) actually have other sets of sesamoids in the body. The two that form each ankle are called the proximal sesamoid bones. The human kneecap or patella is present in the horse as a component of the stifle and is also considered a type of sesamoid bone. The navicular bone in the internal structures of the hoof is also a type of sesamoid. Sesamoids exist because they reduce friction on joints by gliding over the joint's surface, helping to pull the limb back and forth.

The proximal sesamoid bones are part of the ankle or fetlock, which drops down toward the racing surface to absorb the horse's weight during a footfall. The joint flexes farther down the harder the foot falls. The elastic tendons and ligaments (particularly the suspensory ligament) are crucial during this shock absorption procedure, and the proximal sesamoids are hard at work in this moment too – which may mean it's not surprising that they're a common source of injury.

Existing research suggests that sesamoid fractures or suspensory apparatus failures are associated with 30 to 50 percent of fatal injuries in Thoroughbred racehorses. At a recent virtual session of the University of Kentucky's annual Equine Showcase, researchers said that makes them a crucial area of study – but we have to start from the beginning.

Scientists would like to know how the structure of the proximal sesamoids changes in response to intense exercise like racing. We know bones change their shape and structure in proportion to the amount and types of forces placed on them through exercise in a process called bone remodeling. (You can learn more about bone development and remodeling here.) It would be helpful to know if somewhere in that process, sesamoid bones undergo abnormal changes that could signal or predispose an upcoming fracture.

According to Dr. James MacLeod, researcher and faculty member at the Gluck Equine Research Center, scientists first need the answers to more basic questions about proximal sesamoids. In order for researchers to know what is considered an abnormal structural change, they have to know what's normal for these particular bones – what size, shape, and internal structure is typical? How do they develop? When do they develop? How much variation is there in size, shape and structure between individuals, between breeds and between sports?

Unfortunately, MacLeod said, existing science is somewhat light on the answers to these questions.

“It turns out that in the horse, very little information was published about proximal sesamoid bone development and maturation in a normal sense,” he said.

When trying to answer the basic question of when these bones develop, MacLeod and his colleagues dug up two publications in textbooks suggesting that these particular bones don't begin to form in a developing equine fetus until very late in gestation, between Day 290 and 330 in what's typically a 340-day gestation. The end of ossification (hardening) for the bones was, according to these textbooks, complete at around month three or four of the foal's life.

“We had evidence right away that there was much more to know about the development of proximal sesamoid bones,” he said.

Soon after the research team began their inquiries, Dr. Emma Adam, assistant professor at Gluck, used advanced imaging to discover that the very beginnings of cartilage (which would eventually transition to bone) were beginning to form in what would become the fetlock at Day 46 of gestation. At that point the fetus was only three centimeters long, with a tiny forming limb only three millimeters long.

Currently, MacLeod and his colleagues are in the process of learning more about the variability of the bones in adults, assembling lots of samples from horses who have died for reasons independent of development or injury to the sesamoid bones. Researchers want to study them grossly (recording observations detectable without a microscope) as well as at a microscopic level. They're looking at elements like bone volume, which refers to the amount of a bone that is minerals. Researchers already know that sesamoid bone volume increases with age as an animal matures and the bone itself grows. Next, MacLeod said, we need to learn how bone volume may change when the horse grows old enough to begin exercise.

Another element that could be important in microscopic bone changes is the trabeculae, which are the bands or thin rods of tissue that together make up the hard structural elements of the bone. MacLeod hopes researchers will learn more about the orientation of these little beam-like supports – are they isotropic, meaning their orientation creates a look of sameness throughout a sample, or are they anisotropic, meaning many of them lie in a single, similar orientation? This matters because it impacts how easy a substance is to break. If you think about chopping an anisotropic piece of wood, he points out, it's easy to do with the grain because all the strands of the block's interior structure are pointing more or less the same direction. If you chop against that grain, it suddenly becomes tougher. With an isotropic substance like metal, its components are oriented in all different directions at a cellular level, making it equally difficult to cut or split no matter how you approach it — there's no area or angle of weakness on a microscopic level.

The initial step to understanding these elements of the bone's structure is to get as many samples as possible from a wide cross section of ages and breeds. Those breed differences could be really important, too — it won't help racehorses if the team develop their sense of normal sesamoid bones from Shetland ponies.

“You'd certainly expect [to see differences],” he said. “The skeletal system in general matures differently between different breeds. Small horses and ponies actually mature faster than larger horses.”

There could also be important differences in what's “normal” between male and female animals, as well as large, heavy-bodied and fine-boned horses within the same breed.

For now, MacLeod said his team has more questions than answers, but he is hopeful that soon – maybe even by next year's annual equine research showcase – he can provide some.

“I think as we ask the questions, as we generate quality data sets, as we advance imaging technologies, I think we will be able to answer those questions,” he said.

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Ask Your Veterinarian Presented By Kentucky Performance Products: What’s Bone Bruising?

Veterinarians at Rood and Riddle Equine Hospital answer your questions about sales and healthcare of Thoroughbred auction yearlings, weanlings, 2-year-olds and breeding stock.

QUESTION: What does it really mean when a veterinarian talks about a racehorse having “bone bruising”?

DR. A.J. RUGGLES: If you been around racehorses you likely have heard the term “bone bruising.” Despite its common use the term is really not entirely accurate in most cases. What your veterinarian is likely referring to is Non-Adaptive Stress Remodeling (NASR). You can see why the term bone bruising is more commonly used.  While a true contusion (bruise) of the bone–manifested by lameness and characteristic findings of edema in the bone on magnetic resonance imaging–occurs, it is much less common than NASR.

To understand NASR and its causes, an understanding of bone anatomy and physiology is necessary. Most people think of the skeleton as an inert frame that muscle, tendon and ligaments attach to allow movement or as protection for vital organs. While the skeleton performs these functions, it also is a very dynamic system than is undergoing a constant process of removal and replacement as the horse grows in size and is being trained.

Dr. Alan Ruggles

It is easy to realize the skeleton of a foal is different than the skeleton of a 3-year-old. Not only has the horse grown in stature, but the structure of the bone itself is altered to fit its athletic activity. For example, the front of the cannon bones in the front legs of a trained 3-year-old will be thicker and denser compared to a 3-year-old that has never trained and only exercised at pasture. Likewise, an older broodmare who has been out of training and has had many foals may have a relatively weaker skeleton compared to the actively trained racehorse due to the absence of training and the depletion of calcium from her skeleton due to multiple lactation cycles.

When an athlete trains, whether it is a person or horse, receptors between the cells within the bone recognize the changes in load in the bone and send a signal for the bone to change its geometry and replace damaged bone to fit this new activity. This normal process is called stress remodeling. During this process original bone is removed and new bone is produced to replace it. Imagine a long bone like the cannon bone as a cable of a suspension bridge and within the cable are multiple smaller wires cables.

When bone changes its shapes or repairs injured bone each of these original smaller wires (primary osteons) are removed and then replaced with new bone (secondary osteons). During this process the removal phase occurs at a rate 50 times faster than the replacement rate. The rate of remodeling is influenced by the stimulus of training and when it occurs successfully, the process is necessary and positive. Another response of bone is to make itself larger quickly to resist mechanical loads by putting down relatively weaker (woven not cortical bone) on the surface of a bone. This is what causes the bump in bucked shins.

Most of the adaptive process of the horse skeleton via stress remodeling occurs without incident but sometimes the process gets overwhelmed and manifests as lameness. If there is a failure of the normal stress remodeling process, there can be an accumulation of damaged bone which can cause lameness, micro fissures and fractures.

An image captured from a bone scan shows an area of concern

Sometimes the lameness is obvious and easily detected, such as a bucked shin of the front cannon bone. Sometimes the lameness is obvious but not easily detected on a physical exam as with humeral, tibial or ilial stress fractures. Most commonly, at least in our practice, the horse has clinical signs of poor performance: perhaps a “crabby gait” or not changing leads. The horse is often lame in more than one limb, which makes detection of the problem more difficult.

A careful lameness examination with diagnostic nerve blocks is recommended to ferret out the cause of the lameness. The nerve blocks help us localize the source of lameness and help us direct our diagnostic imaging such as radiographs, ultrasound, nuclear scintigraphy, MRI or computed tomography.

Nuclear scintigraphy (commonly known as bone scan) is very helpful in detecting stress remodeling since it is best suited to detect excess bone metabolic activity which occurs during stress remodeling and stress fractures.

Radiographs and computed tomography may reveal increased density of the bone with associated bone resorption especially in the condyles of the distal cannon bone. There also may be changes in the bone contour and the development of fractures. Magnetic resonance imaging with high field magnets (MRI) is helpful to determining the health of the cartilage as well as bone and associated soft tissue structures. Ultrasound is not generally helpful in diagnosis or management. Newer technologies such as standing computed tomography and PET scans give detailed 3D images of bone and show promise but are not yet available for widespread use and are still undergoing clinical validation in the management of stress remodeling.

An MRI shows an area of bone bruising

If your horse is diagnosed with bone bruising, it likely has a form of NASR. That is the bad news. The good news is most cases do not develop clinical fractures and therefore are not treated surgically and responds to rest. Horses that develop fractures such as dorsal cortical fracture of the cannon bone or condylar fractures of the cannon often are treated surgically for best outcomes. Other hairline fractures of the humerus and tibia are treated with rest alone. The majority of cases in racehorse affect the bottom of the cannon bone or the third carpal bone and are treated with rest.

An image from a radiograph shows bone bruising

Typically, they are given 60 to 90 days off and pasture activity is recommended. The purpose of the period of rest is to allow the skeleton to catch up with the signals that have been sent by training so the stress remodeling process can finish to better allow the bone to withstand the rigor of training and racing. Remember, during stress remodeling bone resorption is 50 times faster than production.

Timing on when to turn the horse out obviously depends on the degree of lameness. If the horse shows any potential for a fracture being present, negative follow-up radiographs are needed before turnout etc. All these decisions are unique for each horse and should and be made in concert with your veterinarian. Treatments such aspirin and isoxsuprine and some over the counter supplements may help during the process by improving blood flow to the bone. Drugs which inhibit the natural bone remodeling process such as bisphosphonates, in my opinion, should not be used in cases of NASR and should only be used as labeled.

The vast majority (80% plus) respond to a period of rest with turnout. This is a tried and true method of trainers who have for decades given horses time off usually in the winter. These methods still work today of course. Proper diagnosis of NASR is important in my opinion to make sure you know what you are treating and to make sure no other condition exists that might require a different intervention.

Next time you hear that a horse has bone bruising, remember it is likely a form of NASR and hopefully you will have a better understand of the natural process of bone turnover and how it is related to this syndrome.

Dr. Ruggles specializes in orthopedic surgery and lameness. In addition to his experience as a practicing veterinarian, he served as a faculty member at New Bolton Center and at Ohio State University before joining Rood and Riddle in 1999. He is a partner in the hospital and is part of the AAEP “On Call” media program.

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