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Your Horse From the Ground Up - The Lower Leg - Part 1
 By mosquito   •   19th Jul 2012   •   12,536 views   •   6 comments
Now that we have the foundations – the hoof – let’s move up our horse and find out a little more about how he moves. In this article we’ll visit the lower leg. For the most part, the front and hind legs (below the knee and hock) are pretty much the same, but after this feature, we’ll have to take the front half and back half of the horse separately.

First, let’s establish some context for the lower leg. Did you know that the horse has no muscles below the knee and hock? That means that everything going on is a complicated system of levers and pulleys built around delicate tendons and ligaments, all controlled by the muscles much further up the leg. It might also help you to visualize what’s going on if we compare the horse’s leg to your body. Remember, the horse’s hoof is his toe – and he walks toe-first, not heel first. Try that yourself and see how different that feels. For the horse though, the bones of the lower leg are similar to the bones of your hands and feet, so that the horse’s knee compares to your wrist, and his hock to your ankle. Imagine if the bones of your hand and feet were much longer, so that your wrist and ankle could be more powerful, and have much more flexibility.

Horse Bones of the Lower LegBut let’s start back at the hoof, and see what kind of structures rise out of the leg in the skeleton. The ‘toe’ is made up of three main bones, ending in the coffin or pedal bone inside the hoof. Moving up through the pastern are a stack of bones, the P2 and P1 (you’d think they’d have catchier names, and the ‘P’ actually stands for phalanx, but that’s hard to say and spell). These bones make up the slope of the pastern, but they are not a joint (like the same bones in your fingers) and have little flexibility. This means that all that impact we have talked about in the hoof is passed through to the fetlock, which is where the P1 meets the cannon bone. The cannon bone is commonly compared to your shin, but it has no real similarity. It’s actually one of the long bones of your hand or your foot.

As horses evolved, lost their toes and floppy, hand-like feet, and got bigger and heavier, the other bones of the toes became smaller, leaving just the very strong cannon bone to take the weight. These old finger bones (metatarsals) still exist on the horse. Two of them, called splint bones, which run down either side of the cannon bone toward the back, but they are small, delicate, and end above the fetlock so they can’t contribute any support. The splint bones and the cannon bones are actually the second, third, and fourth metatarsals, so your index, middle and ring fingers. What happened to the first and fifth, the thumb and the pinky? These remain as the ergot (the rough lump at the back of the fetlock) and the chestnut (similar, but higher up the leg). That’s right, your horse walks on his middle finger!

Horse Splint in an XrayThe cannon bone is integral to your horse’s structure and stability. It’s dense and sturdy, but not unbreakable. Because of its strength, it is very poor at absorbing impact, and so the fetlock and the hoof take most of the abuse of movement and concussion. Fractures to the cannon bone are usually minor, but are not uncommon. Small, hairline fractures occur frequently, and usually heal quickly, often leaving a bony lump or ridge where the bone has laid down extra layers to aid healing. Similar bumps are common near the base of the splint bones. You can sometimes see and feel these lumps, called ‘splints’. Splints have several causes, the most common of which is when concussion or rapid growth has caused the splint bones to pull away from the cannon bone, and new bone to be laid down to repair the damage.

Actual fractures of the splint bones can occur, or if the horse knocks the splint bones with the hoof of the opposite leg. When splints are forming and are fresh, the horse may be sore to the touch or even lame, and the injured site may feel hot. Over time, splints usually go ‘cold’, and the horse is just fine, although big ones can be unsightly. If the split bone is fractured, the pieces may need to be surgically removed, but this is usually a straightforward operation. How can you prevent splints? Avoid riding on hard ground, especially at speed, and don’t overdo your jumping! If you are raising a young horse, high protein feeds that accelerate growth are common culprits for splints, so be careful you don’t overfeed your youngsters!

Horse Splint FractureSome injuries to the cannon bones are caused by impact, usually ‘brushing’ or knocks from the hoof on the opposite leg. ‘Splint’ boots or brushing boots can help if your horse has movement likely to cause brushing. If you are doing a lot of work in circles, or ride tight turns a lot, then splint boots are a wise addition to your horse’s clothing. Even if you aren’t riding, if your horse is a likely to go a bit crazy in the paddock, splint boots may prevent a painful and expensive injury.

Major breaks to the cannon bone are serious – but thankfully rare - and a complete break is frequently irreparable and often horses are put down. In some cases, that isn’t because of the bone, but because of the damage to the surrounding tendons and ligaments, but in any case with a major break the horse won’t be able to put any weight on the injured leg until it has healed – that often means living in a sling. It can be done, but it takes a special – and very patient – horse for that to work! (take a look at a famous horse in a sling - raffles – here : http://www.ponybox.com/news_details.php?title=Biography-of-the-Month-Raffles&id=351).

There are a couple other bones hanging around in the leg just waiting to cause trouble. We talked about the navicular bone when we looked inside the hoof, but resting at the base of the cannon bone, at the back of the fetlock, are two tiny bones called the sesamoids. Like the navicular bone, they don’t do much, but they are a common cause of trouble – they are the most commonly fractured bone in the lower leg. It’s the sesamoids that give the fetlock its shape, and that prominence means they can easily be injured. Horses that overreach, especially when galloping or jumping, can knock their sesamoids with the toe of their hind feet – overreach or bell boots may protect the heel, but they won’t cover the sesamoids. Even fetlock boots are often designed to protect the inside of the fetlock from knocks – not the sesamoid. If you are jumping at speed (like hunting or cross country), jumping big fences, doing sliding stops, or any other athletic movements that might put the sesamoids at risk, then shop for some special sesamoid boots to protect these prominent bones.

So how do all these bones move? That’s down to those ligaments and tendons we mentioned, and there are a lot of them! Notice when you look at your horse, where the bones of the leg are. They are toward the front of the leg – protecting the complicated network of soft tissue structures clustered at the back of the leg. We’ll take a look at those delicate and fascinating cables and pulleys next time!
Your Horse From the Ground Up - The Lower Leg - Part 1
Your Horse From the Ground Up - The Lower Leg - Part 1
Your Horse From the Ground Up - The Lower Leg - Part 1
Your Horse From the Ground Up - The Lower Leg - Part 1
Twisted Rose  
Great article!
  Jul 20, 2012  •  11,859 views
 
Double Spur Ranch  
Very great article! I love what your doing with the ground up topic.
  Jul 20, 2012  •  11,857 views
 
Cowzers  
Great article ! Very informative ! =)
  Jul 21, 2012  •  12,265 views
 
C H O S E N  
wow... i really learned something from that :)
  Jul 21, 2012  •  11,874 views
 
Simple As That  
Awesome article! Learned a lot of new stuff :)
  Jul 28, 2012  •  11,874 views
 
Gone forever BYE  
this was an awesome article
  Aug 1, 2012  •  11,850 views
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