Let's Talk: Sesamoiditis

Sesamoiditis may be a 12-letter word instead of a four-letter one, but it often can seem like the latter to consignors and buyers alike. For many veterinarians, it has become a term that is used too broadly. The good news is that recent research findings are helping everyone understand the issue better.

Although there is a great deal of anxiety about having sesamoiditis appear on a sales report, a new study has shown that oftentimes it does not compromise future racing ability. However, any finding of sesamoiditis can impact a horse's desirability at the sales, which is one of the reasons why understanding more about it has 
become increasingly important. 

"It is one of those things that we look at pretty hard," said Dr. Scott Hay, president of Teigland, Franklin and Brokken Equine. "The reason is because if you have enough sesamoiditis that you end up with a suspensory branch lesion that is painful to the horse, then those are not always really easy things to fix.

"An ankle chip or a knee chip, you take the chip out, and you might have a little arthritic change involved with the surgery, but at least you can address it pretty well. Some suspensory lesions can be much more serious and much more difficult to get back to being right. That is one of the reasons we worry so much about it."

A key to sesamoiditis is understanding when the term is appropriate to use and when it is not. In horses, it specifically refers to variability in the radiological appearance of canals or channels within the equine proximal sesamoid bones. These are pairs of small triangular bones located at the back of the fetlock, and lameness can result from inflammation in the area. 

Variability can cover a lot of ground, and the veterinary community is looking to become more specific when it comes to diagnosing sesamoiditis. 

"Sesamoiditis is too broad of a term," said Dr. Kathleen Paasch of Rood & Riddle Equine Hospital. "If you think about it, not to be pedantic, but -itis, the suffix, is inflammation. When you say sesamoiditis, you are implying inflammation, when it may just be a change in the vascular canals. There may not be any inflammation at all. The word, by its very definition, is inflammatory. 

"The second problem is that we use it as a huge umbrella. When you have a fetlock chip, well a fetlock chip is a fetlock chip, but with this, there is a generalized unhealthy-looking bone. We use it as a catch-all term, and that's probably not fair to the horse. We would like to get away from that and toward describing how many vascular channels are enlarged, is there bone proliferation, is there a giant lucency? More specific things like that."

The equine fetlock is a complex but important area to understand, especially when it comes to sesamoiditis, which is typically first diagnosed using 
radiography. Researchers have found that alterations in vascular channel number, size, and shape are considered possible indicators of pathological change, whether to the bone itself or to the adjacent suspensory ligament branch. These channels carry branches of the palmar or plantar digital arteries. 

"When you see vascular channels with bone proliferation, you are seeing the changes in the bone," said Paasch. "That is secondary. It probably means that there is a strain or an insult to the suspensory branch. You can imagine how that suspensory branch, that ligament, comes down and it attaches there at the back of the fetlock on the sesamoid. When that gets strained, some of the 
little fibers can pull out from the 
sesamoid bone and that can cause an increase in the vascular canals or a bone proliferation. There is also likely an injury to the suspensory branch, so soft tissue.

"If there are some sesamoid changes, the first thing most vets are going to want to do, whether it is a spring survey or a sale horse, is say, 'We need to get an ultrasound and see what the suspensory branch ligament looks like.' I think people who see a lot of films are better about saying, 'We used to call this sesamoiditis, but I am not really sure this is a really big deal.' In the past 5-8 years, we have gotten a lot quicker to ultrasound them to know what we are dealing with."

Potential Causes

Studies have found that around 20% of yearlings have some degree of sesamoiditis, but the cause of the issue can vary. Sometimes, it is simply the result of horses being horses. They can overdo things when turned out in a field as a foal. Some of it can be attributed to conformation and growth rates, and sometimes it is less than ideal management. 

"Certainly, one of the big reasons is rapid growth phases and maybe excessive exercise at a stage of growth where things are more susceptible to strain," said Hay. "You have that suspensory insertion pulling on that sesamoid. A heavy body, fast growth, and excessive exercise are probably the main culprits."

Understanding the natural ways that horses move as well as the fact that each horse will handle growing spurts differently can help mitigate risk when it comes to managing future racehorses properly. 

"Essentially, if you are putting too much stress on the bone for whatever reason--whether it is an inappropriate form of exercise or perhaps the horse is growing at a rate where that level of exercise is too much--it could have consequences," said Dr. Jeffrey Berk of Equine Medical Associates. "Horses are individuals. All bone in young horses is undergoing a process. It is a maturation process, but it is a process that is responsive to the stresses that are placed on the bone. Are those stresses within the limits of the bone being able to do the requisite healing and remodeling to keep that horse moving forward in its training schedule or has it exceeded that?

"In my opinion, I think we are 
seeing less sesamoid pathology now. In the past, some level of sesamoid change may have inadvertently been created by inappropriate prepping for sales. Specifically, I mean too much time on a walking machine. People seemed to have backed off that. They are letting horses spend more time in turn out, and when they are walking them, they are usually hand-walking them in a straight line in a field. I think that has contributed to what I perceive as a decrease in 
sesamoid findings. It is only my personal experience, but I am seeing less now than I was a few years ago."

Critical Research

Berk is one of several respected veterinarians who worked on the major study "Radiological findings in the proximal sesamoid bones of yearling and 2-year-old Thoroughbred sales horses: Prevalence, progression and associations with racing performance," which was published in the Equine Veterinary Journal this January. The study concluded that there was no evidence of reduced performance associated with Grade 1 or Grade 2 vascular channels. 

"When we are talking about an enlarged vascular channel, it is well-defined in this study as being greater than or equal to 2mm wide for more than one-third of its visible length," said Berk. "There is such a thing as a normal vascular channel in the sesamoid, so you don't count those. Everyone used to say, 'Oh there is a vascular channel. Oh my god, this horse has sesamoiditis.' No. That is actually a completely normal sesamoid.

"Most of the findings we are seeing in sesamoids are not complete deal breakers. Some of them are statistically relevant in terms of racing performance and many are not. That's why we can't have a blanket term like sesamoiditis being used indiscriminately. Some of what we used to call sesamoiditis has some importance with regards to racing outcomes, but most of the things we talk about with sesamoiditis don't have any associated risk from a statistical standpoint."

The study required a good deal of industry cooperation, and researchers were clear from the beginning that the results were not the only thing they were interested in. They noted that radiological findings in the proximal sesamoid bones are a persistent source of controversy at Thoroughbred sales, due to inconsistent classification and conflicting assignment of potential clinical importance, and that they wanted to get away from the blanket term.

"There is no question that defining what sesamoiditis actually is was as important, if not more important, than any of the data that compared grades or lesions," said Dr. Wayne 
McIlwraith of Colorado State University, who also worked on the study.

Researchers sought consent for study inclusion from consignors at the 2016 Keeneland September Yearling Sale and from the five major subsequent North American 2-year-old Thoroughbred sales in 2017: Fasig-Tipton Gulfstream, Fasig-Tipton Maryland, Ocala Breeders' Sales March, OBS Spring, and OBS June. 

All told, radiographs for 2,508 yearlings were included, representing 10.9% of the annual Thoroughbred foal crop in the United States and 36% of all North American yearlings sold at auction in 2016. Repository radiographs for 436 2-year-olds were included, representing 19.7% of the 2-year-old Thoroughbreds sold at auction in North America in 2017. Racing performance data collection 
continued until the completion of the horses' 4-year-old racing season.

The study concluded that sesamoiditis is oftentimes statistically 
irrelevant in terms of future racing performance. However, it did find that Grade 3 vascular channels, abaxial new bone alone, and apical or abaxial fragments reduced the likelihood of racing when present in forelimb sesamoids, whereas Grade 3 vascular channels only delayed the start of racing when present in hindlimb sesamoids. 
Additionally, sesamoiditis is more likely to occur in forelimbs than hind.

"The big thing from the study is that with sesamoiditis, the bottom lines are very clear," said McIlwraith. "With Grade 3 vascular channels, there was a reduced chance of racing, and the horses that did race had fewer starts and delayed time to racing. Those are all definites. That doesn't mean that every Grade 3 shouldn't be purchased. The positive is that Grade 1s and Grade 2s constituted the majority of the horses with a valid lesion. There is also Grade 0, of course. A lot of Grade 0s have 
vascular channels that are under 2 mm. If they are less than 2mm for two-thirds of the length, they are considered zero and clean.

"Over 80% of your cases are not going to be significantly affected in their racing careers by the existence of that radiographic change. Those are the things that we found. That means that a buyer should be more relaxed, and a consignor will be happier. Everybody wins, including the horse, and that horse goes on and has a chance at having a real career."

Because of the specific parameters on measurements and the grading system used in the study, the results can serve as a beneficial tool for veterinarians out in the field.

"Studies like this are very helpful for the general population, and they are really helpful for general trends," said Hay. "They show us some of the things that maybe we shouldn't worry about so much. I think that the most helpful part of this study is that it will do a better job of characterizing what sesamoids are concerning and what ones shouldn't be as concerning. 

"That's all on a statistical basis, of course. It's still a complex problem, and the horses are all still individuals. We can certainly predict things a lot better with these types of studies, but we still have to be aware there are outliers."

Different Needs

The trick with sesamoiditis is that often the best thing that can be done is giving the horse time. That is a luxury that pinhookers usually do not have compared to someone who is purchasing for themselves. The veterinary findings for each individual horse can often help people determine their next course of action.

"Absolutely there is a difference 
between the needs of a pinhooker and an end user," said Paasch. "A pinhooker is going to want a horse that is good to leave the sales grounds and start into a program. By the very nature of what they do, they have less time to get a horse ready. So, on a weanling or a yearling, pinhookers are wary of any abnormality. I think they are less 
critical at a 2-year-old sale because generally you can see that the horse has performed.

"When you look at a yearling and it has got changes, and we haven't really asked it to do anything yet, that is the great unknown. If you have an end user, maybe they are willing to turn a horse out for six months or just not start it as quickly as a 2-year-old. If a horse has mild or generalized sesamoiditis, we will often say break it in the spring but then kick it out for a bit and take your time. That is a horse to take your time with and not a 2-year-old racehorse."

No matter what part of the process a person plays, having a better understanding of what sesamoiditis is and what it isn't comes into play for both buyers and consignors alike. 

"It's pieces of a puzzle, and you are putting all of the puzzle pieces together," said Berk. "When you have a finding in a sesamoid, you have to determine how that affects the whole picture. That is what the research is for--to help you to do that. Clearly the study shows that there are many sesamoid findings in yearling and 2-year-old sales that have no bearing on the suitability of a horse for racing. I think that is important. 

"If a horse someone is considering buying at public auction does have some findings, people need to realize that some of these findings will only become a problem if the horse is rushed. So many of the sesamoid findings, if they are willing to give the horse a little bit of time, typically resolve themselves."

For those who are looking to pinhook, there are also some key takeaways from the study that work specifically in their favor. 

"Concave defects, which are usually on the inside sesamoid, had no effect on racing careers, and in most instances, they were healed by the time they were in a 2-year-old sale," said McIlwraith. "That means a pinhooker shouldn't prejudice a concave lesion in the sesamoid. It won't even be there at the 2-year-old sale. We know now that they don't cause a problem."

Continuing Education

True sesamoiditis is something that requires time and management. Different programs may allow for that time, while others cannot. Understanding the parameters of what is likely to impact athletic performance when it comes to sesamoiditis benefits each of the parties involved with the sale of a horse.

"I think everyone is looking to learn a little bit more about it," said Hay. "For end users, at the end of the day, if they see a horse that has a lot of talent, that is probably the number one predictor of if they are going to be a successful racehorse. If they have a little bit of sesamoiditis, they want a comfort level that they can still purchase that horse and go on with it. The 2-year-olds that have absolutely clean sesamoids but aren't 
talented don't make much money."

As veterinarians understand more about this complex issue, they are better positioned to help clients identify what findings are within the range of their personal comfort levels.

"As you learn more, you can be a lot more opinionated for your client," said McIlwraith. "I have talked to people who have said this study is really helpful, and not just in the United States. There is buy-in. When people understand how we define sesamoiditis, some of them, who are honest with themselves, are going to go, 'Wow, I was so wrong.' The more you know, the more helpful you can be."

With research highlighting why using sesamoiditis as a blanket term can be a disservice, veterinarians remain hopeful that the findings will improve the sales experience for everyone, including the horses.

"I think that we have gotten better at describing what it is," said Paasch. "We know a little bit more about the things that should be a true red flag. Most buyers, be they end users, pinhooker, or bloodstock agents, look at reports in the barns. Don't be scared if you see sesamoiditis on a report. Talk to your vet. Is it something you really need to be concerned about or something you can live with? Work with somebody that knows your level of risk." 

Berk echoed those sentiments, 
explaining that comprehending the issue better makes finding a productive path forward easier to achieve. 

"Education is a critical part of the equation when people are buying horses," he said. "People need to understand what the process is and how we go about making the assessment that we do. We are trying to get away from the catch-all term sesamoiditis and be a little bit more specific about what we are seeing in the sesamoids. 

"At the end of the day, whatever the finding is, we have to attach a level of risk to it that the client can understand. You can have some sesamoid findings that pose almost no risk, and there are other findings that might pose 
medium-to-high risk. If you label it all as sesamoiditis, and you don't educate the buyers, then they don't know the 
difference. They think they need to come off any horse that has anything to do with a sesamoid finding, and that's not the case at all."