Tuesdays with Tony – Tendinitis

Around my clinic, horse legs sure do hold a lot of fascination for my docs. They spend a whole lotta time looking at them and talking about them. I have to admit, it is kind of amazing that those big ol’ horse bodies have such spindly legs, and they don’t even seem to rest them 23 hours a day like I do.

Horses evolved with the bulk of their muscles in the upper part of their limbs, in order to reduce the weight of their lower legs and make them more efficient for locomotion. Put simply, horses are fast because they have long, skinny legs, and a lot of muscle up top. (This is why we don’t race hippos). Because of their anatomical construction, the tendons in a horse’s lower legs are long and carry large weight bearing forces. The tendons are used to store energy to propel the horse through his next stride and they also act as a shock absorber for the limb. Those long tendons that make your horse awesome for running away from predators (lions, wolves, or plastic bags) also makes him great at the stuff you want to do with him, like racing and jumping. But surprise, surprise, their design also makes them prone to injury.

The basics

Tendons and ligaments are made of pretty similar material, the main difference being that a tendon attaches a muscle to a bone and acts to move that bone, while a ligament attaches a bone to a bone (usually) and works to maintain bones in alignment and keep the joint stable. There are a whole bunch of tendons and ligaments in the horse, but there are some that we talk about frequently, because they are easy to observe, and among the most commonly injured – specifically, the flexor tendons and ligaments on the back of the lower leg. The big 4 in that area are the superficial digital flexor tendon (SDFT), the deep digital flexor tendon (DDFT), the check (accessory) ligament of the DDFT, and the suspensory ligament. In some places where a tendon changes direction over a joint, the tendon is enclosed in a fluid-filled tendon sheath. Think about a tendon sheath like a water balloon wrapped around the tendon that allows it to glide smoothly over a bony point.  If you have an injury to a tendon, it’s called tendinitis. Injury to a ligament is called desmitis. Unlike muscles, tendons and ligaments don’t have a very good blood supply, which can be an important difference when injuries occur.

How injuries occur

Injury can happen as a sudden overload of a previously normal tendon, such as might happen if your horse takes one bad step. An injury like this often happens during exercise. The chances are increased if the horse is unfit for the job he’s being asked to do, but even a fit horse can be injured if he is fatigued and not protecting himself properly or if he is ridden on poor footing. Another contributing factor is having long toes and low heels, which places extra stress on the tendons on the back of the leg. Injury can range from a minor tearing of the tendon fibers to a complete rupture.

Frequently though, an injury doesn’t just come out of nowhere but is actually the result of cumulative damage that progressively weakens the tendon. There may not be much clinically evident inflammation, but small amounts of damage are occurring without being noticed, and the body isn’t able to keep up with repairing it. The tendon eventually becomes weak enough for a significant injury to occur. Tendons tend to be injured in this kind of progressive, degenerative way, while ligaments are more likely to be injured in the sudden overload way.

 What you might notice

This will depend on how bad the injury is. The basic signs of a tendon injury are heat, swelling, and pain around the area of the injury. Because of the inflammation, the injured leg will feel warmer than the uninjured one and the tendon may feel thicker. When you squeeze the tendon, the horse may flinch or try to pull his leg away. If there is bad enough damage to the superficial digital flexor tendon, you may see a thickening giving the leg a “bowed” appearance if you look at the leg from the side. This is the origin of the term “bowed tendon” you have probably heard.

If there is only minor damage, you might only see a mild lameness. You may not even notice it when the horse is walking, and it only becomes evident at the trot. In a severe injury, the horse may be unable to bear weight on the limb at all.

 How will my doc diagnose an injury?

While heat, pain, or swelling may help to make a diagnosis, subtle tendon and ligament injuries may not have obvious localizing signs and may need to be identified by performing a lameness examination with nerve blocks. Extensive injuries also need to be evaluated to see what structures are involved and how bad the damage is. Once my doc has this info, she can recommend the appropriate treatment.

My doc has a super cool ultrasound to allow her to see the tendon and ligament fibers within your horse’s leg. She can do this at my clinic or right at your farm! The ultrasound can show which tendon or ligament is injured and how far within that structure the injury extends. She uses her ultrasound to measure the size of the injury, to recommend therapy, and to monitor healing. It’s also very useful to follow the injury over time to determine when the horse is ready to resume an exercise program. It’s suuuuper important to use a controlled exercise program when your horse goes back to work, to avoid re-injury.

Treatments

The old acronym for how to treat a tendon or ligament injury is taken from human medicine – R.I.C.E.. That is, Rest, Ice, Compression, and Elevation. Good luck convincing your horse on the elevation part, but the first 3 still apply. Rest will mean a period of restricted activity. Whether that means stall rest or paddock rest, and for how long, depends on the injury and the stage of healing. My doc will figure that one out for you. Ice means cold therapy, which is often cold hosing (or cooled wraps if you’re fancy). This is usually employed in the early parts of the injury while there is a lot of inflammation. Compression means bandaging, used to support the area and keep swelling down. (For a tutorial on how to apply a stable bandage, see my previous blog.) My doc may also prescribe an anti-inflammatory medication to reduce swelling and pain.

Those are the old standbys, and while they are still useful, the problem is that tendon and ligament just aren’t tissues that naturally heal well (unlike bone). They tend to heal with scar tissue instead of well organized, elastic tissue like the original. So the healed tendon is weaker and prone to re-injury.

Nowadays, my doc has some pretty cool tools to help improve the quality of the healing. Even better, they use materials from your horse’s own body to do it! I’m talking about a field called regenerative medicine, and specifically, Platelet Rich Plasma and Stem cells. The idea behind these things is that they improve the way the tendon or ligament heals so there is less scar tissue and less risk of re-injury.

Platelet-Rich Plasma (PRP) is taken from your horse’s own blood. Blood contains platelets, which are the cell fragments that form blood clots when an injury occurs. The cool thing about platelets is that they are little bags of molecules called growth factors. So my doc can take some blood, and process it to get the platelets in a super-concentrated form. She then injects the PRP right into the injured part of your horse’s tendon where the growth factors get to work stimulating regeneration of your horse’s tendon/ligament fibers. We use a lot of PRP at Springhill Equine, because it works really well and is a bit more economical than stem cells.

Stem cells are cells with the ability to turn into many types of tissue, according to what signals they receive. They are also collected right from your horse. My doc can take them from either bone marrow or fat and then send them to a lab to be cultured up to a high number. The lab then sends them back and my doc will inject them into the injured tendon. Similar to PRP, the stem cell injection also has growth factors. Those stem cells, now sitting in the tendon, will get the signal to become tendon cells, so the repair will have more quality material and less scar tissue than if it were left to heal by itself. Modern medicine is pretty cool, huh?

There are a few other therapies used to treat tendon and ligament injuries in certain circumstances, such as extracorporeal shock wave therapy, laser therapy, or even surgery in certain circumstances. My docs have done a lot of training in this stuff, so they’ll know what to recommend if your horse gets injured. Give them a call if you have any questions, I’m sure they would looove to talk to you about those fascinating horse tendons. As for me, I’m ready to rest my own legs and take a nap now.

Until next week,

Tony

P.S. Looking for more information on Tendinitis? Look no further than our podcast page, Straight from the Horse Doctor’s Mouth. Did you know that Dr. Lacher & Justin have a weekly podcast. It’s filled with tons of useful knowledge. Be sure to chek it out.