Connoisseurs of the crooked foal, let’s get into part 2 of our series – flexural limb deformities! Last time in part 1, we talked about angular limb deformities, which are inward or outward deviations of the leg from midline, when viewed from the front of the foal. A flexural limb deformity, on the other hand, means that the limb is abnormally flexed or extended when viewed from the side of the horse. You’ve probably already heard of one kind of flexural limb deformity – a club foot. We’ll get more into club foot and some other kinds of FLDs shorty.

First, there are 2 types of flexural limb deformities – hyperextension and hyperflexion. Let’s deal with hyperextension to start with, because it’s easy and I’m a lazy cat.

                                           Hyperflexion caused by tendon laxity

                                               Hyperflexion of the carpus (knees)

Hyperextension

This is common in newborn foals, especially when they’re premature. The flexor tendons that run along the back of the legs are weak and allow the leg to stretch too far. Both front or hind limbs can be affected. The great thing about hyperextension is that it usually fixes itself in a few days or weeks. But it’s important to have my doc out to make sure the bones in the legs are fully formed and there isn’t incomplete ossification to complicate the tendon laxity (see part 1 of crooked foals). As long as my doc says the bones are fine, the foal will need some controlled exercise to help strengthen the tendons. We don’t want to lock these guys up in a stall full time, but we also don’t want them overdoing it and galloping around in a pasture with mom. A small paddock is usually good to allow limited exercise. Resist the urge to put a splint or heavy bandage on the legs! That will make the tendons even looser and worsen the condition. If the baby’s heel bulbs are hitting the ground, a very light wrap around the pastern can protect the skin, or my doc can put a glue-on extension on the foot to help the foal stand. No heavy bandage, got it? Generally, hyperextension is pretty easy to deal with, so I don’t lose too much cat nap time over it.

                                                         A heel extention shoe

Hyperflexion

The hyperflexion kind of FLD is commonly called “contracted tendons”. This name really bristles my fur because it’s usually incorrect. The tendons are not usually “contracted” at all, just functionally too short compared to the bony column.  If a tendon is actually contracted, that means there is a defect in the tendon, and that can happen in adult horses after an injury but it’s usually not the problem in foals. Nevertheless, you will hear the term “contracted tendons” term used. But now you can feel superior and correct your friends if you hear it.

Hyperflexion can be present when the foal is born, or it can develop later. If it’s there at birth, the cause might be a toxin or disease the mare had during pregnancy, or it could have been caused by the position of the foal in the uterus. If it develops later, it may be caused by incorrect nutrition or excessive energy intake in the first weeks and months of life, causing rapid growth of the bones. If the bones grow longer quickly, the tendons can’t keep up and a flexural deformity results.

This is most often a problem of the front limbs, though rarely the hocks can be affected. It usually occurs at the level of the foot, the fetlock, or the knees. My doc will need to examine the foal and feel the tendons to determine which ones are affected and she’ll probably need to take X-rays of the legs. The structures involved determine which kind of deformity is present. Then the treatment plan will depend on the deformity. Let’s talk about the different kinds of deformities.

Club foot

Club foot is a flexural deformity at the level of the coffin joint in the foot. It’s caused by a deep digital flexor tendon that is relatively too short compared to the bones of the leg. Since the DDFT attaches to the back of the coffin bone (down in the foot), if the tendon is too short it pulls the coffin bone and the hoof wall backwards, creating an abnormal steep angle to the hoof. In a normal horse, the front of the hoof and the pastern should be at the same angle, but a club foot will have a hoof that is more upright than normal with a short toe and high heel.

Flexural deformity at the fetlock

If the superficial digital flexor tendon is relatively too short, it causes the fetlocks to be too straight or even knuckle over. The SDFT attaches to the bones of the pastern instead of the coffin bone, so that’s why you’ll see the fetlock knuckled over even though the hoof might be normal.

Flexural deformity at the carpus (knee)

This deformity is usually present at birth and can be a cause of dystocia (difficult birth). The tendons and ligaments around the back of the knee prevent it from extending.  A mildly affected foal should be treatable but unfortunately, if the condition is severe, the foal may be unable to stand and correction may not be possible.

So what can we do to fix hyperflexion?

What exactly my doc will do to straighten your foal’s legs will depend on its age and how severe the deformity is. Once of the most important things my doc will do is balance your foal’s nutrition and perhaps reduce his energy intake, because rapid growth can be one of the main causes of this problem. Exercise should be limited, and pain medications may be recommended. With very young foals, my doc may be able to give a dose of a medication called oxytetracycline that allows the tendons to stretch. Corrective trimming and toe extension shoes might be used. Remember how I told you never to use a heavy bandage or splint for hyperextension because it can make them even looser? Bandages and splints can actually be really useful in hyperflexion because loosening is what we want in this case.

For foals that are either more severely affected or unresponsive to conservative treatment, surgery might be needed. The procedure my doc will choose depends on the type of deformity and how severe it is. For example, a young horse with a milder club foot may respond very well to cutting the accessory ligament of the deep digital flexor tendon and still have a good prognosis for an athletic career. A severe club foot may require cutting the deep digital flexor tendon itself, and would be unlikely to be an athlete. Horses less than a year old respond best to surgery.

If the horse is younger, there are generally more options for treatment, and more likelihood of success, so don’t wait long before giving my doc a call. Are you surprised that advice applies to pretty much any problem your horse could have? If you’ve been reading my blog like you should, you won’t be!

Until next week,

Tony

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