Sunday, March 16, 2008

Proximal suspensory desmitis: A common lameness in sport horses

Disclaimer: The information in this article is summarized from the list of resources that is included below. I tried to be as accurate as possible. However, I'm not a vet and the article itself hasn't been proofed or fact-checked by anyone other than me. If you are considering treatment for your own horse, please consult the original sources or your own vet.

Tendon/ligament injuries are all too common in performance horses. The things we value in in equine movement -- suspension, engagement, and a ground-covering stride -- depend on the delicate suspensory mechanism in horses' legs. As a horse propels himself forward, the tendons and ligaments in the back of the leg work like a bungee cord to capture and release the energy. Horses who work for a living -- passageing, jumping, galloping, and whatnot--put a lot of stress on the suspensory apparatus.

What is proximal suspensory desmitis?
Proximal suspensory desmitis (PSD) is an injury to the upper suspensory ligament in either the front or hind legs. Proximal in this case refers to the upper part of the ligament near the hock or knee, and desmitis means "inflammation of a ligament." The suspensory ligament, or interosseous medius, is actually a mixture of tendon and muscle fibers. Overloading of the ligament leads to tearing of fibers and the small blood vessels. There is bleeding within the ligament and a hematoma forms. The horse experiences pressure and pain. In the hind limb, this ligament is surrounded by bone, which complicates diagnosis and treatment.

Some facts about PSD:

  • It tends to occur in highly trained horses, especially dressage and event horses.
  • Straight-hocked horses are more prone to PSD.
  • Horses with foot pain or unbalanced feet are more prone to PSD.
  • PSD often occurs bilaterally (in pairs of legs).
  • Symptoms tends to be subtle, with little or no heat or swelling, and often without outright lameness. More typical symptoms are poor performance, changes in gait, or resistance/evasiveness that are mistakenly atrributed to arthritis and other ailments.
  • PSD symptoms worsen when the horse is trotted on a circle with the affected leg on the outside.
  • PSD gets worse with exercise and it gets worse in soft footing.
  • PSD can be caused by working a horse too hard or beyond his level of conditioning.

Nerve blocks can help a veterinarian identify the proximal suspensory ligament as the source of lameness. However, nerve blocks alone can seldom conclusively diagnose PSD. Radiographs are primarily useful to see if there is a fracture or bony remodelling associated with PSD that could affect the healing process. Thermography can provide a glimpse of the heat pattern of the area. Diagnostic ultrasound the gold standard for assessing the suspensory ligament. The vet looks for ligament enlargement, poor definition of the margins, or some disruption of its internal architecture. In some cases, no lesions show up on ultrasound but are visible on MRI. MRI is increasingly used to make a definitive diagnosis.

Sometimes I read about a therapy or drug, and ask my vet about it. Her reply is sometimes positive, but occasionally she'll scoff, "Eh, No one does that," and then she'll proceed to tell me why it's such a loser treatment. So keep in mind as you read the summary of options below, this is just a census of available treatments as reported in various sources at a given time--not any sort of recommendation:
  • Stall rest and proper, unrushed, rehabilitation is essential.
  • Thermography or ultrasound may be performed at two-week intervals can help a veterinarian evaluate healing.
  • For recent injuries, anti-inflammatory corticosteroid drugs may help. Sometimes hyaluronic acid is injected.
  • High energy shock wave or radial pressure wave treatments relieve pain and stimulate ligament repair. These are most effective if employed within the first thirty days of the injury.
  • Stem cell therapy promotes remodelling and regeneration of tissue and shows promise for tendon injuries generally. There are several methods available. Cells can be extracted from the injured horse's own bone marrow, or from stem cells extracted from their bone marrow. After lab processing, cells are then injected into the area of injury. Read more about bone marrow therapy in The Horse. Stem cells can also be extracted from the injured animal's fat (adipose tissue) --about a tablespoon is needed. The company Vetstem uses this method. Read a case study of success using Vetstem to treat PSD. Yet another method uses cells from a pig's bladder. Urinary bladder matrix (UBM), is sold under the name ACell Vet. You can read about it in a presentation by the originator of the technique or in a recent article published in The Chronicle of the Horse.
  • Platelet-rich plasma contains something called "growth factors" -- sorry, can't explain much beyond this. But apparently when the plasma is injected into the lesion, the growth factors promote healing. To date there is only anecdotal evidence of success -- no research.
  • Surgical options include two approaches. Neurectomy, or surgically removing part of the nerve associated with the suspensory ligament, offers some pain relief without treating the primary injury. The plantar neurectomy cannot produce a greater degree of improvement than that seen after local anaesthesia, so nerve blocks should be performed first. Newer techniques such as desmoplasty with fasciotomy (tendon-splitting to you and me) have been successful in relieving pain and pressure. The tendon splitting procedure is primarily used for "core" injuries where there is a pocket of injury inaccessible to circulation. The splitting opens the area to the healing process. While it stimulates healing, surgical techniques do not speed healing. One study that tracked horse's training and performance following surgery found that 85% were able to return to full work after surgical treatment.
  • Counter-irritant therapy. One example used occasionally with success for PSD is the infiltration of the suspensory ligament with iodine in oil. Most of the evidence "for" this treatment is anecdotal.

There is short answer to how well horses "come back" from these injuries, but injuries treated quickly and agressively have better results, and foreleg injuries tend to have a better prognosis. Shock therapy is a proven technique that should be considered. Surgical treatment, while invasive, does seem to yield positive results in most cases.



The Lowdown on High Suspensory Disease (Proximal Suspensory Desmitis) from AAEP.

Proximal suspensory desmitis in veterinary textbook Adams lameness in horses.
Lots of statistics and info on the prognosis fo for PSD.

Proximal Suspensory Ligament Disease of the Forelimb from The Horse Magazine.

Dealing with suspensory injuries by Heather Thomas Smith for an October 2003 issue of California Thoroughbred.
Excellent description of the surgical procedures available for PSD.

Morris, D., et. al. Treatment Options for Hindlimb Proximal Suspensory Desmitis. Compendium Equine, October 2007. p. 266-272.
Restricted access, but a terrific article! Covers treatment options. You can get it via interlibrary loan from your public library, but if you are having trouble, email me for a copy.


Horse owners guide to the suspensory ligament
This article talks about the healing process for ligament injuries.

Suspensory brochure from UC Davis
A primer on tendon and ligament injuries, with fantastic illustrations.

Proximal suspensory desmitis in the horse: extracorporeal shock wave therapy compared to injections according to Dr. Müller-Wohlfahrt.

Crowe, O. Treatment of 45 cases of chronic hindlimb proximal suspensory desmitis by radial
extracorporeal shockwave therapy
. Proceedings of the Annual Convention of the AAEP 2002.
This study showed that of the forty-five horses treated, 41% percent of cases were sound and returned to their previous or greater level of exercise 6 mo after diagnosis. EWST improves the prognosis for this type of injury.
Restricted access.

Proximal Suspensory Desmitis (PSD) of the Forelimb from University of Florida's MEDS Newsletter, vol. 1, issue 3.

Authors: Crowe, O.M. Treatment of chronic or recurrent proximal suspensory desmitis using radial pressure wave therapy in the horse, Equine Veterinary Journal, Volume 36, Number 4, May 2004 , pp. 313-316(4).

White,N. Surgical treatment of suspensory desmitis. Virginia Tech document.

Hewes, C. and White, N. Outcome of desmoplasty and fasciotomy for desmitis involving the origin of the suspensory ligament in horses: 27 cases (1995-2004). Journal of the American Veterinary Medical Association. 2006 Aug; vol 229 (issue 3) : pp 407-12.
Study of 27 horses with PSD who underwent "tendon-spitting survery." 85% of horses returned to full work.

Suspensory ligament injuries from Petlearn.

Chronic suspensory injury from Eggleston Equine, LLC. December, 2006 article.

He's lame again! from Metamora Equine.
Has a nice illustration.

All about suspensory ligament injuries from Horse and Hound

Les, Sellnow. Tendons and Ligaments from The Horse, September, 2006.


  1. When our horses have soft tissue injuries (which is rare- good farrier) we tend to put them on te side of a hill for a year and let them heal temselves. The hill keeps them active while they rehabilitate, and a year is a very long time for a horse to heal. It's not very scientific but it works really well.

  2. I know people who have done both shock wave therapy and stem cell therapy. Both have worked very well to heal suspensory injuries. I also know people who have done hand walking and rest also, which works if you stick with it and don't ride too soon.

    Growth factors are proteins that are produced by tissues to help other tissues to grow, repair, or change in some way. There are many, many growth factors and they all have slightly different actions. Often these proteins are secreted by one type of cell so that a different type of cell can use them. The cell that uses the growth factors will often have surface receptors (think electrical socket) on the outside of the cell that the growth factor (the plug end of an electrical cord, without the cord) can attach to (so the gorwth factor plugs into the socket). When the growth factor is attached to the cell surface it then can trigger certain genes or cell processes within the cell to turn on. Probably more info than you wanted to know!

  3. The problem with PSD injuries is that it doesn't heal with rest :(

    Thank you for all the information!

  4. Hmm, just to add to my previous comment - after reading through some of the resources I wonder why some vets in the UK say PSD doesn't heal from rest alone? The statistics mentioned in one of the resources above seem to claim otherwise.

  5. i'm guessing a little here, but having read through a bunch of the articles, I think part of the discrepancy might be...

    a) Forelimb has a far better prognosis than hindlimb. They really need to be discussed separately.
    b) Recurrence rates for suspensory injuries of this type are really high. There aren't that many studies that track long term soundness.
    c) There are so many new treatments, perhaps some of the articles are older and therefore aren't able to compare rest/rehab to new treatments.

  6. Seems like this is becoming more common all the time. Generally in this area we see shock wave therapy and stall rest followed by private turn out. Most cases I have seen it is usally at least a year before horse is under saddle again. I think that the studies of nutrition based healing for both horse and human are very interesting.

  7. Suspensory injuries are very common in STB racehorses. Generally 6 mos. to a year of turnout heals them nicely. Of course, their training upon return must be slow and steady. Unfortunately, like many other injuries, this kind of injury frequently leads to the same condition in other limbs due to the stress caused by the original injury. STB's also have a possible (not confirmed) genetic predisposition to this injury, as it occurs with them - particularly geldings - above the norm.

  8. Thanks for including Vet-Stem in all of this information! You've started a great forum on the topic. Just a little FYI, Vet-Stem is located in California, not Britain.

    Cheers- Callan Green, PR rep for Vet-Stem."

  9. I can see that you are an expert at your field! I am launching a website soon, and your information will be very useful for me.. Thanks for all your help and wishing you all the success in your business. Castlebrook Barns


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