Hindlimb lameness is frustrating to deal with, regardless of the type of equine discipline we are involved with. Proximal suspensory desmopathies of the hind limb can be challenging to treat.
One of the more common causes of chronic lameness is hindlimb proximal suspensory desmopathy (HPSD). Chronic referring to the continuous nature of the problem, as this is seldomly a problem diagnosed, treated, and resolved within a couple of weeks. It can start as an acute (sudden) lameness, but persist as an ongoing, performance-limiting lameness that may never resolve completely. Desmopathy equates to the disease of a ligament.
The hindlimb suspensory ligament (SL) is a ligament that attaches to the back of the cannon bone, just below the hock joint, and extends down the cannon where it bifurcates into medial (inside) and lateral (outside) branches, that each insert onto their respective sesamoid bones at the back of the fetlock. It is well tucked in between the hind splint bones and is covered by the superficial and deep digital flexor tendons. The body and the branches of the hindlimb SL are easily palpated but the proximal (upper) origin of the hind SL is not. The SL is part of the suspensory apparatus that is responsible for supporting the fetlock during movement.
Hind SLs are less commonly affected with pathology compared to the SLs in the forelimbs, but once affected they are often harder to manage than forelimb SL injuries.
Whilst many horses performing different forms of athletic activities suffer HPSD, horses with straight hindlimb conformation with hyperextended fetlock joints have been found to have an increase in the incidence of HPSB and a decrease in the success rate of treatments. A hyperextended fetlock is a fetlock that looks to be dropped lower behind when standing than a fetlock in the “ideal” position, and this conformation puts added strain on the ligament.
HPSD can be challenging to deal with as clinically it can present in different ways and can cause lameness or poor performance that persists for weeks to months. Sometimes, HPSD affects both hind SLs simultaneously, so lameness is not detected, but instead the horse loses hindlimb impulsion, shows poor transitions or stiffness when ridden. Other times the horse may just show behavioural changes and be reluctant to work, or bolt when ridden. Lameness, if present, may settle with time and then resurface when the work intensifies, or in some cases persist even with box rest.
“No treatment exists
that uniformly resolves
all cases of HPSD.”
No treatment exists that uniformly resolves all cases of HPSD. Furthermore, the origin of the hindlimb SL is not readily visible or palpable, even to the experienced handler, making it difficult to detect the early stages or monitor the progress of HPSD without having to rely on lameness as a guide to success or failure. A diagnosis typically requires a positive response to a nerve block of the deep branch of the lateral plantar nerve, the nerve that innervates the proximal suspensory ligament. An ultrasound examination of the ligament can aid with the diagnosis of HPSD but is not always conclusive as the fibres may not always be clearly disrupted.
Unlike forelimb suspensory ligament desmopathy, where the lesions are usually restricted to the SL and clearly seen on ultrasound, HPSD can involve the SL, the bone at the back of the upper cannon where the SL attaches, the nerve that innervates the ligament, and the connective fascia that surrounds the SL. Therefore, the clinical diagnosis of HPSD can be due to multiple sites of pathology, all within the same anatomical region, but all differing in their precise etiology, making the treatment and management of HPSD variable in its success between patients.
There are a multitude of treatment options available to treat HPSD, but these could be described as management options, as they commonly don’t cure the injury completely and only offer short to midterm relief.
NON-MEDICAL MANAGEMENT
Treatments that avoid the use of therapeutic medications include cold water/ice of the limbs, corrective shoeing, and rehabilitation exercises.
Using ice boots and standing in cold water to reduce inflammation is a lot easier to do for injuries in the forelimb than the hindlimbs in my opinion, which makes this option less practical for many horse owners. It is difficult to apply ice boots that go up high enough, and that the horse tolerates for long enough to offer good relief in many horses. Ice spas are good at allowing the cold therapy enough time to reduce inflammation, but due to their cost very few owners would have access to them. Standing horses in large containers of cold ice water is fraught with danger for both the horse and the handler unless the horse is heavily sedated or incredibly compliant.
Horses with long toes and low heels have an increased association with HPSD, but whether this is the poor hoof conformation causing HPSD, or as a result of HPSD changing the way the hind foot adapts, is difficult to say. Suffice to say, the farrier should be consulted in HPSD cases to ensure the hoof is carefully balanced and excess toe is removed to help these horses improve.
Rehabilitation for any tendon or ligament injury is important and should always be considered when the horse is recovering from an injury. In most cases, rehabilitation is used in conjunction with medical and or surgical treatments to maximise the chances of recovery and a successful return to competition.
For acute cases of HPSD, box rest for a month or so is recommended to allow the inflammation to settle and prevent the horse from incurring further damage. The horse then undergoes a walking program for several months with a slow resumption back to full exercise, as governed by the veterinarian.
Chronic cases don’t require box rest unless there has been a sudden increase in lameness due to re-injury. Instead, they require slow, steady work on a well maintained, even surface to reduce the risk of overextension of the fetlock or uneven foot placement. Treadmill exercise can be very useful to help the horse regain fitness without over-straining the ligament. As each horse is different, a program should be mapped out with joint consultation between the veterinarian, the trainer, and the owner so everyone is aware of the time and effort involved.
Shockwave therapy is a very popular treatment modality for treating HPSD and does give medium-term results for many cases. Treatment protocols will differ between veterinarians, but I would normally use an initial course of three sessions, each two weeks apart, and then follow up with a ‘’booster” every 3-6 months. Shockwave treatment is not cheap, however, and costs in the vicinity of $900 for the initial course (three sessions using a focus shockwave machine).
It should be noted that there are two types of shockwave machines in use, a focus shockwave machine that focuses all the energy to a small point, and a radial shockwave machine that releases energy that radiates outward, like the ripple effect seen when a rock hits the water. Personally, I prefer the focus type shockwave as it more powerful and the energy is focused over a small area, giving better results overall. The downside is that the cost for focus shockwave treatment is significantly more expensive than the radial shockwave therapy due to the large difference in running costs (radial versus focal) of each pulse that is fired into the tissue.
Therefore, when comparing costs to perform shockwave treatment between various clinics, make sure you are comparing the same type of machine, and not the use of a focus shockwave versus the use of a radial shockwave machine. Shockwave treatment can give horses relief from clinical symptoms of HPSD for up to 12 months.
“Injecting medications…
is commonly used for
a short-term effect.”
MEDICAL MANAGEMENT
Anti-inflammatory medications such as phenylbutazone and other NSAIDs (non-steroidal anti-inflammatory drugs) are very good at reducing inflammation and alleviating pain. In the short term they are very useful at relieving lameness, but relying on them in the long term is far from ideal. Apart from the potential deleterious effects that long-term administration of NSAIDs can have on the horse’s health, their prohibited or restricted use in horses that are competing makes their use very limited.
NSAIDs should be used in the initial stages of an injury to minimise the effects of inflammation, but if the inflammation and lameness do not resolve, alternative management or treatment should be sourced. If long-term treatment with a NSAID is the only available option, then a NSAID from a sub-group of drugs called COX-2 inhibitors should be used, as their prolonged use has a far less detrimental effect on the horse’s health compared to phenylbutazone. The main two available for use in horses in Australia are fibocoxib and meloxicam.
Injecting medications around the insertion of the proximal SL is commonly used for a short-term effect. While cortisone is a potent anti-inflammatory medication that reduces pain and inflammation, it can slow down soft tissue repair, which is undesirable if the ligament itself has pathology. Cortisone injections offer good relief when the source of pain is due to the fascial swelling causing a compartmental pressure on the SL and/or pressure on the nerve. Some people prefer to use traumeel, a homeopathic remedy, instead of cortisone and have been happy with the results.
For cases of HPSD that are associated with pathology in the fibres of the SL that are clearly demonstrated on ultrasound, the use of biological products such as stem cell therapy and PRP (platelet-rich plasma) is useful.
The PRP provides growth factors that improve the quality of healing, whereas the stem cells are thought to provide cells that can differentiate into ligament tissue as well as provide growth promoting factors. The PRP or stem cells can be injected into a lesion in the SL if the there is sufficient damage of fibres to allow the product to be introduced.
In other cases, the PRP can be injected periligamentous, meaning around the damaged ligament, allowing the growth factors to move into the damaged area, and I have had success doing this. There are reports advocating that if you inject stem cells intravenously (straight into the blood), they will be directed to the damaged ligament and encourage healing, however, the amount of scientific literature to support this as a long-term success is limited.
Some veterinarians are using products known as bisphosphonates for the treatment of HPBS, but their efficacy has not been established for this injury. Bisphosphonate use in horses has been adopted from human medicine, where these medications are used to treat osteoporosis by slowing the resorption of bone. The two more common brand-named bisphosphonates available in Australia are Tildren and Osphos and they are marketed as treatments for navicular syndrome, with the potential for improving osteoarthritis such as degenerative joint disease in the hock.
As there is a close anatomical association between the tarsometatarsal (TMT) joint and the proximal insertion of the HSL, it is possible that the improvement seen is due to some hock pathology that co-exists with the HPSD that improves when bisphosphonates are administered, or it may be that it reduces bone pain in the proximal cannon where the PSL attaches.
SURGICAL OPTIONS
Surgery to cut the fascia surrounding the hind SL and/or cutting the nerve that innervates the proximal SL is the best option for cases of HPSD that are non-responsive to medical management. In the hindlimb, a strong band of fascia surrounds the SL, forming an anatomical compartment that limits the free space available for the ligament to swell. Once the SL swells excessively, the fascia effectively becomes a tight band, putting further pressure on the ligament and the nerve, causing further pain and inflammation (like “compartmental syndrome” in people). If the pressure is not released, the horse remains lame and further deterioration can occur in the SL, therefore, surgery is performed to cut this fascia, allowing the SL to swell without any impingement.
Surgeons will sometimes combine cutting the fascia with a procedure known as a neurectomy (cutting a nerve). There are two different nerves that have been targeted for this surgery – the deep branch of the lateral palmer nerve, and the larger tibial nerve. There are several studies that report many horses have remained free from lameness for two years or more following a neurectomy, without serious complications.
It should be noted, however, that many equine governing bodies believe that neurectomies can be detrimental to the welfare of the horse and therefore have outlawed it as a procedure, thus preventing horses that have had a neurectomy from competing.
Other surgeries that have been tried including SL desmoplasty (splitting the ligament) and osteostixis (small holes drilled into the back of the cannon bone). These surgeries, when performed, are frequently done in conjunction with a partial or full fasciotomy, so the success may be related to the cutting of the fascia as much as to the procedure itself.
This list of treatments for HPSD is not a complete list and there are many available products that people have advocated as cures, including using laser, therapeutic ultrasound, electromagnetic boots, and injections of 2% iodine. The ones I have mentioned early are treatments that appear to offer better results currently.
Therefore, if you suspect your horse has HPSD, have it assessed and diagnosed by your veterinarian. That way you can discuss all the treatment and management options available, and find the best option to help your horse return to its athletic career. EQ
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