Assessing the approaches to diagnosing and treating proximal suspensory desmitis

Article by Connor Parsons DipWCF

Diagnosing proximal suspensory desmitis in the hind limb can be difficult. However, the modern diagnostic modalities available to the industry today makes it possible to isolate injuries, allowing both veterinarians and farriers to work together to achieve the best diagnosis and prognosis possible for the equine in question.

In this article, Connor Parsons reviews the anatomy and function of the suspensory ligament, causes and signs of proximal suspensory desmitis and whether there is an ideal procedure for diagnosing, treating and formulating a prognosis for the horse as part of his DipHE Farriery studies. 

ANATOMY

The equine limb is complex yet effective. The suspensory ligament is made up of dense white fibrous connective tissue which suspends the fetlock and prevents hyperextension.

Originating at the proximal, plantar aspect of the third metatarsal/carpal attaching to two palmar depressions distal to the carpometacarpal and tarsometatarsal joints descending the channel formed by the 2nd, 3rd and 4th metatarsal/carpal, bifurcating two thirds of the way down the 3rd metatarsal/carpal, making a firm attachment to the palmar aspect of the proximal sesamoids, pulling the sesamoids proximally, then travelling dorsally and distally at an oblique angle to merge with the common digital extensor tendon. This forms a sling to support the fetlock joint. The ligament and its branches are strong but only slightly elastic (Devereux, 2006).

The suspensory ligament also forms a part of the hindlimb stay apparatus which is a system of ligaments, tendons and muscles that work together to allow the horse to stand and doze with minimal muscular effort. Also known as the fright and flight mechanism (Colles & Ware, 2020).

DAMAGE TO THE SUSPENSORY LIGAMENT

Suspensory ligament damage can affect horses of all breeds and ages. However, it is most common in competition horses. Proximal suspensory desmitis (PSD) is inflammation or damage of the main body at the origin of the ligament at the proximal end of the third metacarpal/metatarsal.

The suspensory ligament can be inflamed or there can be changes to the fibre pattern of the ligament. These cases will present with lack of performance, being worse on soft surfaces. In more severe cases a core lesion (hole) can be seen on an ultrasound scan, where a number of fibres have ruptured. This type of injury will have a more sudden onset of lameness (Dyson, 1994). Injury can be solely within the ligament, involve tearing of the fibres of the ligament or be connected to avulsion fractures at the origin, involving the proximal 3rd metacarpal/tarsal (Baxter, 2020). Complete rupture is possible, however, very rare. The prognosis for a complete rupture is not favourable (Dyson, 1994).

Although the suspensory ligament has a slight elasticity to its make-up, if it is stretched it tends to heal with a loss of elasticity making it susceptible to recurrent damage (Colles & Ware, 2020).

SIGNS OF PROXIMAL SUSPENSORY DESMITIS

Proximal suspensory desmitis is a difficult condition to diagnose as the hind limb is complex and many of the functioning structures work in unison. A horse suffering with inflammation or damage to the main body of its hind suspensory can present one of three ways. It may have a unilateral lameness, a bilateral lameness or just a general decrease in performance (Dyson,1994).

CAUSES OF PROXIMAL SUSPENSORY DESMITIS OF THE HINDLIMB

Although there has been extensive research into proximal suspensory desmitis, there is no primary cause in all cases. 

Proximal suspensory desmitis is a common injury in both front and hind limbs of the equine athlete. Usually bilateral in the hind limb (Dyson, 2016). All types and breeds of horses are susceptible to this type of injury. Poor conformation is a contributing factor to proximal suspensory desmitis.

Conformational defects such as straight hocks, sloping pasterns and long-toe, low-heel conformations would be at higher risk to injury. These conformational defects will all apply unnecessary pressure to the suspensory ligament. Horses that have suffered with this condition will be predisposed to a repetitive strain injury of this ligament (Devereux, 2006). Overextension of the tarsus as a result of overextension of the fetlock has been linked to proximal lesions. The higher the severity of trauma, the higher the severity of ligamentous lesion. Working horses on deep, soft surfaces will increase the risk of this injury (Baxter, 2020).

The hindlimbs are more frequently affected with this condition than the forelimbs with a much lower success rate of the horse returning back to performance prior to rest (69% hind vs 80% forelimb) (Colles & Ware, 2020).

DISCUSSION

In a study of six horses, this is an extremely small cohort of horses to be able to state an average age a horse is likely to present with this condition. This study also shows that all of the horses studied were of varying fitness levels, therefore stating that this does not affect the likelihood of injuring the hind suspensory ligament. There was only one horse in this study that was unfit and overweight. The rest were all competition fit with good muscle mass, showing that fitness doesn’t necessarily decrease the risk of this injury happening. The case history of the six horses studied did not include which discipline or level the horse was working at. This would be an interesting factor to consider when looking at which horses would be more susceptible to proximal suspensory desmitis.

Each individual case was being looked after by different veterinarians, giving a clear picture of different approaches on how to diagnose and treat this condition. Although for the purpose of a study the varying opinions will make the comparison more difficult. All horses presented with a reduction in performance prior to veterinary contact. Only one horse was reported with a bilateral lameness behind. Flexion testing appeared to aggravate the lameness making it more prominent to see. Local analgesia has been shown to be effective in isolating the area to be investigated. Also, showing lameness on the other hind once the worse limb has been blocked out.

Using digital diagnostic modalities such as ultrasonography to diagnose this condition allows the veterinarian to study the changes in the fibre pattern of the suspensory ligament. This will allow the veterinarian to see the severity of damage caused and allow them to provide the best treatment plan possible. In this study only one horse had a lesion while the other five horses had thickening and slight changes to the fibre pattern. Horse 2 had lesions on both hind limbs however the veterinarian didn’t medicate, box rest was recommended. His prognosis was guarded.

Although radiographs of the feet don’t directly help with the diagnosis of proximal suspensory desmitis, they do allow the farrier to trim accordingly to restore the hoof back to correct hoof pastern axis and mediolateral foot balance. This will reduce lever arm forces thus reducing any unnecessary pressures on the plantar aspect of the limb.

Horses were radiographed for foot balance to aid with remedial trimming and shoeing. This will increase the equines prognosis allowing the farrier to have a clear picture of what is being dealt with. All of the horses that were radiographed presented with a negative sole plane and weak heels.

The question is whether this foot conformation is because the horses are wanting to apply more pressure to the caudal aspect of the hoof in the landing phase, reducing the movement of the metacarpophalangeal articulation. This is an attempt to reduce the loading forces applied to the suspensory ligament. However, it will also cause the heels to become weak. Or, if this conformational defect has caused the suspensory ligament to become inflamed or damaged, thus causing proximal suspensory desmitis.

Proximal suspensory desmitis can be secondary to other conditions such as hock conditions or sacroiliac problems which cause the horse to adopt a different gate. Therefore causing unnecessary loading on the suspensory ligament. It is important that the primary cause is diagnosed and treated when treating proximal suspensory desmitis. This is where scintigraphy can be a useful tool to get a clear picture of the cause involved in individual cases. Scintigraphy is an expensive diagnostic modality which carries significant health and safety risks, this must be taken into consideration when dealing with cases.

All horses studied were worse on a soft surface where it is harder for the horse to guard itself from soft tissue injuries. Horses that are worse on soft surfaces generally are suffering from soft tissue pain. However, nerve blocks will help the veterinarian pinpoint the structures involved when diagnosing lameness.

Although it is possible to have a unilateral lameness with proximal suspensory desmitis in the hind limb it is most common for the lameness to be bilateral. All of the horses in this study had a bilateral lameness, generally worse on one limb than the other. Although presenting prior to veterinary contact as lack of power or struggling to strike off on the correct canter lead.

When a veterinarian is deciding on a treatment plan, the horse is looked at carefully including its previous history as some treatments come with higher risks, although can be extremely effective for reducing inflammation. Shockwave treatment comes with minimal risks involved and is effective; however, many racing authorities require a mandatory 5 day Stand-Down period from racing following the administration of extra-corporeal shockwave therapy. Findings from this study show that the horses with the best prognosis of getting back to competitive work have undergone surgery. Understandably this is the last resort treatment as it is invasive and expensive for the client. 

Only one horse from this study did not have any medical intervention and this horse had the least favourable prognosis. This would suggest that box rest alone is not generally enough if the horse is expected to get back to full athletic fitness. The most common veterinary treatment is steroidal injections into the area of interest and shockwave therapy with rest. However, the use of corticosteroids in horses in training often adopt a clear 14-day exclusion on the use of intra-articular (joint) injections before racing in line with different racing authority regulations.

Water based therapy can also be considered as part of the recovery process when bringing the horse back into work. It’s known to reduce limb oedema, stimulate nerves, and improve circulation, which speeds the healing process and provides pain relief. It also aids in joint stability, providing all-around support to the limbs. 

Cold water therapy is typically prescribed when the goal is to reduce heat and inflammation. Applying cold water or ice reduces the amount of accumulating fluid to an injured area and can somewhat numb the area, causing a topical analgesic effect. 

Underwater treadmills are often used for horses with tendon and ligament injuries to provide a gradual transition back into exercise and regain the range of motion. Swimming is also used to condition the horse without putting a load on the skeletal system. It is often used in the early stages of tendon and suspensory injuries due to no pressure being placed on the lower limb. Trainers who use swimming as part of their routine often find that, in addition to the cardiovascular workout, it also helps the horse relax and settle its mind.

This is not always successful and horses are then admitted for surgery. While the surgery for this condition is successful, there must be consideration taken into the fact that it is not legal to compete at certain levels once this surgery has taken place.

The study shows that the farriery treatment involved when dealing with this condition is varied, depending on which veterinarian the horse is being looked after by. However, the author has had positive results from many different shoeing styles. The main importance of trimming and shoeing for this condition has been shown to restore the best possible hoof pastern axis through trimming, supporting the entire limb and fitting a shoe with an early breakover. This will reduce the lever arm on the metacarpophalangeal articulation, thus minimising unnecessary pressure on the suspensory ligament.

CONCLUSION

Having such a small cohort of horses in a study makes it difficult to finish with a conclusive result. This small study however, has given a positive result in the diagnosis stages of dealing with this condition. At this stage nerve blocks are invaluable along with ultrasonography. In less obvious cases MRI is useful to gain a diagnosis and occasionally scintigraphy will be used to locate the problem. Radiography is a useful tool when dealing with PSD and checking the origin area for avulsion fractures.

This study has also shown that there is a link between a negative solar angle and proximal suspensory desmitis. However, this would need to be studied further and on a greater scale to determine why there is a link between this conformational defect and this condition.

It is paramount that correct foot balance is achieved by the farrier. To achieve this foot balance radiographs are required. This study has shown that there is no definitive way to shoe for this condition, however it has shown a positive result from an early breakover shoe, allowing the horse relieve pressures on the caudal aspect of its hoof. Horses that had the best prognosis underwent surgery, allowing them to get back to competitive fitness.

REFERENCES

Baxter, G. M., 2020. Adams and Stashak's Lameness in Horses. 7th Edition ed. Hoboken, NJ: John Wiley & Sons.

Colles, C. & Ware, R., 2020. The Principles of Farriery. 2nd edition ed. Marlborough: J.A.Allen. 

Devereux, S., 2006. The Veterinary Care Of The Horse. 2nd Edition ed. London: J.A.Allen. Dyson, S., 1994. Proximal suspensory desmitis in the hindlimb: 42 cases. British Veterinary Journal, 150(3), pp. 279-291.

Dyson, S., 2016. American Association of Equine Practitioners. [Online] Available at: https://aaep.org/horsehealth/lowdown-high-suspensory-disease-proximal-Suspensory-desmitis [Accessed 19 11 2022].

Smith, M., 2022. Newmarket Equine Hospital. [Online] Available at: https://www.newmarketequinehospital.com/media/pm1beabc/hah349-Vet_susp_desmitis-final.pdf [Accessed 9 April 2023].

The X Factor - Growth spurts in young horses: What can we learn from 'human' research into growth and maturation in sport and exercise?

By Alysen Miller

Ask anyone to list five famous Belgians, and odds are that Kevin De Bruyne’s name will make an appearance. The Manchester City midfielder is widely regarded as one of the best footballers of his generation. Yet you might not have heard of him at all were it not for an innovative talent development scheme in his home country that could influence the way we select, train and manage racehorses.

Traditionally young footballers, like racehorses, are grouped age. By contrast, bio banding is the process of grouping athletes on the basis of attributes associated with growth and maturation, rather than chronological age. “Whether you mature earlier or later has quite a lot of bearing in sport, where greater speed, strength or power can be important,” explains Professor Sean Cumming, an affable Orkney Islander based at the University of Bath who studies growth and maturation. “When you look at children in sport, we group them by age for competition and for training. And while age groups are great in so far as it allows you to match kids of similar cognitive development, motor skills and experience, the challenge is that kids can vary hugely in terms of their biological maturity.” Although the effect of this ‘maturity bias’ doesn’t kick in until pubertal onset at around 11 or 12 years of age, the variance in biological maturity can already be anything up to five or six years by that point.

The concept that relative age can play a determinative role in future sporting success is not new. It explains why broodmares are covered in spring to produce foals in February and March. A winter-born colt running in the Derby in early June of its three-year-old year may be up to 10% of its life older than a spring-born animal—an unquestionable advantage. Or is it?

Indeed, it’s not only in horse racing where the orthodoxy around the so-called ‘relative age effect’ holds sway. In his book Outliers, Malcolm Gladwell notes that a disproportionate number of elite Canadian hockey players are born in the earlier months of the calendar year. 

The reason, he posits, is that since youth hockey leagues determine eligibility by calendar year, children born in January are pitted against those born in December. Because the earlier-born children are likely to be larger than those born later (at least until somatic factors kick in), they are often identified as better athletes. 

This, in turn, gives them more exposure to better coaching, and the gap between the two groups widens. Sociologist Robert K. Merton has dubbed this the ‘Matthew Effect’ after a verse in the Gospel of Matthew: "For unto everyone that hath shall be given, and he shall have abundance. But from him, that hath not shall be taken away even that which he hath.”

But, cautions Professor Cumming, this only tells part of the story: “What even a lot of the academics get wrong is that relative age and maturity are not one and the same. In fact, our data shows that only about 8% of the relative age effect in academy football can be explained by physical maturity. It’s quite possible to be the oldest kid in the age group but also the least mature, or the youngest kid in the age group but also the most mature.” 

The focus on relative size and strength alone, in other words, can create a bandwagon effect. “If you’re looking to identify and develop the most talented young athletes, then it’s going to cloud your vision. It’s going to make some kids look fantastic and some kids look quite poor.” Perhaps tellingly, the last January-born Derby winner, Pour Moi, came in 2008. The youngest winner of the last 10 years, Anthony Van Dyck, was born in mid-May.

Machester City and Belgium superstar midfielder Kevin De Bruyne is the Royal Belgian Football Association’s Programme of the Futures’ most famous graduate

Enter De Bruyne. The Royal Belgian Football Association’s Programme of the Futures, as it is known, allows late-developing players to hone their skills by playing mostly friendly matches against teams of the same physical maturity level, irrespective of age. De Bruyne is the scheme’s most famous graduate. Other members of the late-developer club include Dries Mertens, Thomas Meunier and Yannick Carrasco. By deliberately creating a climate in which late-maturing players get a second bite at the cherry, a country with a population of just 11 million has become a global footballing superpower. Unsurprisingly, other nations are starting to catch on, and several similar programmes have sprung up across the UK and Europe.

Every professional football club has a story about the one who got away—the player that was cut from their programme for being too physically small, from Jamie Vardy (released by Sheffield Wednesday at 15) to Harry Kane (the now 6’2” striker was released by Arsenal at the age of nine). But the consequences are more far-reaching than just missing out on the next footballer superstar. There is compelling evidence to suggest that tailoring the training load to the stage of the athlete’s biological maturity can reduce injuries. The amount of time spent off through injury during an athlete’s formative years is thought to be one of the single biggest factors that determines future professional success. 

Since overuse injuries and stress fractures all peak when the athlete is going through their pubertal growth spurt, it is important to identify when an athlete is entering this phase and adjust the load accordingly. As Professor Cumming explains, “Because we know the growth spurt typically takes off at around 85-86% [of the athlete’s predicted adult height] and peaks at around 90-91%, as soon as they move into that phase we can change the training prescription to more developmentally focused stuff—coordination, balance, core strength—all things that are going to help the child transition to a phase when their body is changing rapidly, when they’re more at risk of certain types of injuries.” Early evidence from clubs using the method has pointed to a 72% reduction in injuries.

Daniel & Claire Kubler have been bio-banding their horses using knee x-rays, among other metrics, to determine when to increase a horse’s workload

And it’s not just football clubs that are starting to understand the benefits of bio-banding. Daniel and Claire Kübler have been bio-banding their horses using knee x-rays, among other metrics, to determine when to increase a horse’s workload. “We back most of our own horses and train them away to where they can canter relatively comfortably at a normal speed,” says Daniel. “Once a horse can canter away, that’s when we go in and do that first set of x-rays.” The horses are given a grade based on the degree of fusion in the growth plates in the knee, with A being an open growth plate, B being partially closed and C being a closed growth plate. “Those really open ‘A’ horses, you might say, ‘OK, there’s no point—give it a break,’” says Daniel. The C’s, likewise, tend to be easy cases. “It’s really the B horses that are the interesting ones, where you have to make a bit more of a decision,” says Daniel. “What we don’t want to be doing is increasing the workload on a horse that’s relatively immature.”

Although the growth rate in horses varies somewhat by breed, most horses do not reach full physical maturity until around six years of age, with larger breeds like draft horses still growing until eight years of age. A two-year-old horse is an adolescent; it has reached approximately 97% of its mature height by 22 months but critically, its bones will not fully fuse for another four years. 

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Like humans, horses grow distal to proximal—that is, from the feet up—with the pasterns developing first, fusing at around six months, followed by the cannons at around the one-year mark. The pelvis and spine fuse last. It is during the horse’s two-year-old year that the major leg bones—the radius, ulna and tibia—will fuse. It is therefore important to understand when a horse is entering its growth spurt and tailor its regime accordingly. “It’s about injury reduction,” argues Daniel. “Young athletes are highly susceptible to injury, and by recognising and identifying the growth spurt, you’re massively reducing the injury rate by adapting the training load.”

“The knees are the most delicate bit,” he goes on. “That’s where most of your injuries occur that can cause problems down the line. When you’ve got one with poor grading on its knees, it’s being pre-emptive in your training,” he continues. “You would train that horse a bit more conservatively and not push it quite as hard. You might spend more time on an incline gallop, or you might introduce swimming into the horse’s routine so that you’re putting a bit less concussion through those joints. And hopefully you’re getting the benefit down the line, because they haven’t been pushed too hard, too young.”

Joint licence-holders Daniel and Claire have long advocated for the role of science in training racehorses. “We’re not scared of it,” says Claire, who holds a degree in physiology from Cambridge University. “Having the additional awareness of it gives you a greater understanding,” she asserts. Coming from a non-racing background, meanwhile, has allowed Daniel to approach training with something of a fresh perspective: “It’s the critical questioning. A lot of things in racing are done because that’s the way they’ve always been done, and you can work backwards and find that the reason they work is because, scientifically, it stacks up. But there’s other things where you actually go and look at the science, and it doesn’t make any sense to do that.”

“I love reading about human sports science and listening to podcasts to get ideas,” he explains. “Essentially we’re all mammals, and although there are some differences, there are also a lot of similarities.”

Following the science has not only allowed the Küblers to produce happy, healthy horses—“I’d like to say our horses are very sound and durable,” notes Claire—it has helped them manage owners’ expectations. “Owners enjoy the insights and better understanding themselves as to how the horses progress and develop,” she says.

Feedback from work riders is just as important as the science and can provide and can provide as much insight into the horse’s state of growth as an x-ray

“As a trainer, sometimes you can look at a horse and you can see it’s backwards and it needs time,” says Daniel. “What’s helpful about having the knee x-rays is that it’s a very visible thing to show to someone who doesn’t necessarily understand horses particularly well or isn’t used to them. It’s a simple way to say, ‘Your horse is immature.’ That’s a helpful tool as a trainer in terms of being able to communicate very clearly with your owners.” Posting regularly on social media, meanwhile, has attracted interest from outside the sport—including from Professor Cumming himself, who reached out to Daniel through Twitter. 

The science is certainly compelling. But, emphasises Daniel, you cannot rely on data alone. “You can’t solve the challenge of training racehorses purely with numbers in the same way that I don’t think you can solve it purely just by looking anymore, because you’re not looking at bits of information. It’s an example of using a scientific, data-driven, analytical approach to enhance the welfare and time the horse’s development in the right way for that individual,” he says.

“The numbers don’t lie, but still you need the horsemanship,” agrees Claire. Feedback from the work riders, she says, can provide as much insight into a horse’s state of growth as an x-ray. “They can pick up on the horse, whether it’s still maturing and doesn’t quite mentally understand what it’s doing. Then you can come up with ideas together as a team,” she says.

In a climate where racing, and equestrian sport in general, is the subject of increasing scrutiny—both from outside the sport and from within—t is submitted that any sports science techniques that can deliver tangible welfare benefits to the horse should be embraced.

“At the end of the day, they have to go out and race, and they all have to be sound enough to do that,” says Daniel. 

“You’re always trying to find ways to help get an edge on the track—to get more winners,” agrees Claire. “But you also just want to do the best for the horse so you’re getting a sound horse to achieve its optimum best.”

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