Page 70 - November 2020

EQUINE HEALTH
TENDON AND TENDON SHEATH INJURIES
by Heather Smith Thomas
Horses in strenuous athletic careers are often injured by stress and strain on leg structures. Soft tissue injuries (ten-
dons and ligaments) often take the longest time to heal. Tendon injuries range from
mild inflammation to ruptures, says Duncan Peters, DVM, DACVSMR, ISELP Certified Member, East-West Equine Sports Medicine, Lexington, Kentucky. “Most of these occur in the superficial digital flexor tendon. We see this in racehorses and in performance horses like jumpers, event horses, etc. Usually, there has been some degeneration of the tendon and weakening of the tendon over time—and then there’s an incidence that suddenly overloads and injures that tendon,” he says.
“More commonly we see some swelling in
There’s usually something that makes an astute observer suspect that something is not right, but then maybe the problem disappears, and the horse seems fine for a while. Then it may happen again, and the horse has a poor workout or doesn’t want to train as well—and maybe there’s a little heat in that leg again. “Eventually we realize something isn’t right and we do a physical exam and maybe an ultrasound examination. In many cases, we can verify the problem with diagnostic imaging like ultrasound--or possibly an MRI may be needed to pick up subtle changes. We try to find and treat these problems before they get too seri- ous,” says Peters.
Tendon sheath swellings are common in racehorses. “Often, we’ll find a hint of what
that holds the sesamoid bones together at
the back of the fetlock. If this is injured or irritated, it can also cause filling of the sheath. If there is swelling in the digital sheath, this can be an indication that there is injury or inflammation of other structures associated with this,” says Peters.
“It is rare that we just see what is called tenosynovitis (inflammation of the tendon sheath), but possible. In some cases, we’ll see a horse that has a workout or a race and the next morning there is a little filling in that digital sheath in spite of bandaging. It may be that the horse simply overdid a little. The fluid
is a sign that there is some inflammation. Trainers and grooms pay a lot of attention to these things and may pick up an indication
the mid-cannon region or down around the fetlock/pastern region with associated tendon sheath swelling. These swellings may be large, hot and painful when palpated. The area will be inflamed and there can be a wide variety
of damage—anything from little micro-tears to core lesions or margin lesions where there
is actually some significant damage to the tendon, which can be seen on ultrasound. We may use ultrasound to visualize the extent of the damage. It may be just small areas of what we call hypoechoic regions within the tendon, or more significant areas in which 50 to 70% of the tendon cross-sectional area is damaged,” he says.
“There are a wide variety of things that can be seen with acute injuries that occur when a horse is working. In many cases, however, we just see a gradual change in the tendon, espe- cially in some of the horses that may not show much lameness or discomfort. They may just have poor performance. They may have mini- mal changes associated with the tendon, but the tendon looks a little bigger than it used to, or perhaps it gets some heat in it now and then.”
may come, before the actual injury, seeing a bit of swelling in the digital sheath—from just above the fetlock and on down into the pastern region. Another area of swelling may occur in the distal carpal sheath with high tendon injuries. We may see some early filling in those areas, if there is some inflammation of the tendon or some of the other struc- tures that are within or close to that tendon sheath,” he says.
“The digital sheath runs from just above the fetlock and down to the heels of the hoof, and there are a variety of structures there. The main ones are the superficial and the deep flexor tendons that run through that area. If they are injured or inflamed, there will be some filling/swelling in that sheath,” he explains.
The other structures in that area that can be injured and cause problems are the distal sesamoidean ligaments, the cruciate, oblique and the straight ligaments. “If any of those are injured or inflamed, there will also be swelling of that area. The other structure that may be involved is the inner sesamoidean ligament
early on that this horse needs to take it a little easier. There may be something starting to show up and the horse needs to be watched more closely when he works. The extra filling in that sheath can be an early warning sign,” he explains.
If there is an actual injury and the tendon sheath does blow up extensively, it’s very com- mon to see that area always carry some extra swelling. “The tendon sheath is distended
and stretched and will never completely tighten up again, and this is the situation we call windpuffs. It’s not uncommon for older campaigners to carry a little more fluid in those tendon sheaths, just from wear and tear over the years. They may have a windpuff that goes up or down with work. It may actually shrink a bit and get tighter when the horse is worked, compared to when the horse is just standing around, or you may see one that goes the other direction and has more fluid/swell- ing after being worked. You have to know the horse and know whether something like this should be a cause of concern or not. Attention to detail is important,” says Peters.
“The rule of thumb is that it takes one month per letter, i.e. bone takes four months to heal, tendons take six months and ligaments eight months. It’s an easy way to remember it, and ligaments are the slowest to heal—because there is less blood supply to a ligament.”
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