Taking the Mystery out of Equine Anatomy – Part 3: The Bones, Tendons & Ligaments of the Lower Leg

We're on a mission to make equine anatomy easy to understand and highlight the importance to your horse's health and well-being that you have a knowledge of equine anatomy.

The world of equine anatomy is full of misconceptions and in this series of articles we are clearing up any confusion. In part 3 of anatomical misconceptions we look at the bones, tendons and ligaments of the lower limb.

There are very few bones in the horse’s lower limb and this often comes as a bit of surprise when people see this painted on a horse at one the Horses Inside Out live painted horse lecture demonstrations. When it comes to learning more about equine anatomy it can help to compare the structures to humans, so let’s have a look at the bony structures in the lower limb and compare it to us.

The horse has very few bones in the lower leg

Humans have lots of bones in their hands and feet – compare this to the horse and in the hoof they only have two and half bones – the pedal bone, the navicular and half of the short pastern.

These bones are equivalent to the bones in the lower part of our middle finger. Still thinking about your own middle finger, the knuckle is equivalent to the horse's fetlock joint.

From the fetlock or hock down the horse has three main bones – the long pastern, the short pastern, and the pedal bone (plus the navicular at the back). These three bones are equivalent to the three bones in our middle finger.

Moving up the leg to between fetlock and either the carpus in the forelimb or the hock (tarsus) in the hindlimb there's one main bone - the cannon bone.

There are splint bones on either side of the cannon bone and these are thought of as the anatomical remains of our second and fourth finger and our second and fourth toe in the hind leg. There are also the sesamoid bones at the back of the fetlock joint.

The Carpus (knee) is equivalent to our wrist

The carpus is often called the knee, but this is anatomically incorrect, because when we talk about the horse’s knee what we're actually referring to is equivalent to our wrist.

Looking at the horse's hind leg, the human knee is equivalent to the horse’s stifle and the hock joint is equivalent to our ankle.

Having discussed the bones of the horse's lower leg and compared them to humans, you can see why it causes a lot of misconceptions.

Why does the horse have so few bones in the lower leg?

To answer this, we need to consider the evolution of the horse – essentially the horse is designed to run very fast in a straight line to get away from predators. To do this effectively, the lower limb needs to be as light as possible to help him run. However, it’s not just about the number of bones that have helped the horse achieve this speed and efficiency, it’s also the muscles. This is where it gets really interesting. The horse doesn’t have any muscles below the knee (carpus) or the hock (tarsus). This would be equivalent to us having no muscles in our hands or feet – now that would be odd!

Understanding Tendons and Ligaments

The musculoskeletal system is supported by fascia, tendons and ligament, which are key to maintaining posture and allow efficient movement.

Tendons and ligaments are both connective tissue

Tendons connect muscle to bone and has the ability to contract. When the muscle contracts tension will pull through the tendon, to the bone and help to create movement. Essentially, tendons are about transferring force from muscles through to the bone.

Ligaments connect bone to bone. They're often quite short, and they span across one or sometimes more than one joint but basically their role isn't about creating movement but limiting movement. Ligaments are often in locations to stop or help prevent undesired movement in a direction that’s out of the normal range of movement of a joint. They're there to protect the joint and provide stability.

Visitors to Horses Inside Out HQ are surprised when they see the tendon and ligament model of the lower limb, in particular at the strap-like nature of the them. These structures are relatively inelastic. Most of the tendons in the lower limb have about 4% elasticity, which isn’t very much.

The function to stretch also gives an ability to recoil. Think about a thick, wide elastic band - it takes quite a lot of energy to pull, but when you let go, it will ping across the room at some speed.

The tendons and ligaments in the lower limb aren't just about the transfer of movement, or about lightening the lower limb their function is about creating movement in a way that reduces the amount of muscular effort required to create the movement.

Tendons and Ligaments of the lower leg

• Superficial digital flexor tendon -Flexes the joints of the lower leg, supporting them during the weight-bearing phase, and also limits fetlock hyperextension

• Deep digital flexor tendon – Flexes the joints of the lower leg – particularly the coffin joint and support them during weight-bearing.

• Common digital extensor tendon – lifts the toe, extends the fetlock, pastern and coffin joints.

• Lateral digital extensor tendon – this assists the common digital extensor tendon.

• Check ligament – these prevent undue strain to the flexor tendons and connect some tendons to bones. They also form part of the horse’s stay apparatus.

• Suspensory ligament – supports and holds the fetlock joint in its correct position and stop it from extending too far.

Getting Hands On

Why is it so important to understand and appreciate the anatomy and action of the lower limb. As part of your daily routine get into the habit of feeling your horse’s lower legs. This practice will give you an understanding of what is normal for your horse and any changes in heat, swelling or tenderness will be spotted quickly and you can take necessary action.

Secondly, it's important to understand what structures you are palpating and can learn to recognise what's normal from an anatomical perspective.

To boost your knowledge in this area, take a look at our on-demand recorded seminar Understanding Tendons and Ligaments of the Lower Limb. Gillian goes into a lot of detail on the anatomy of tendons and ligaments. She also demonstrates how to palpate the tendons and the ligaments.

Using this knowledge to improve your riding and training

From a riding and training perspective, appreciating the biomechanics of the tendons and ligaments is important to understand because just like any other structure in the horse’s body, it responds to some degree of training. In other words, it will respond to force and will adapt and get a little bit stronger in response to force. Now, when we talk about forces, these are generated through different movements, and exercises and always needs to be progressive.

This is particularly important when you are bringing a horse back into work. Starting off with walk, building up the variety of surfaces that you're working with. Gradually introducing trot and if you are rehabbing following a tendon injury and you're at that stage when you are about to start trot, a common question is how much trot should you be doing? It can be helpful to think in strides saying, I’ll do a few strides of trot initially. For example – start with five strides of trot and then walk, then increase it to 10 and so on.  This way it helps to keep the trot small and therefore don't get the same amount of force compared to trotting for a few minutes where you will find the trot gets bigger and bigger and the forces get greater and greater.

If you have a healthy horse and you're wanting to strengthen the tendons and ligaments in preparation for training, incremental increases in force are important.

Increasing Forces

At the other end of the scale when you’re looking at which exercises put the greatest force through the horse’s tendons and ligaments - a series of bounces.

limb when the horse lands from a fence

Think about jumping gymnastic exercises and it's really important to consider how the horse lands. The surface is massively important but how the horse lands is crucial and we’re talking in terms of straightness here.

As a rider, you ideally want horse to take off and land with the limbs upright. This refers to when you look at the horse from the front.

If you take off and land while turning that this going to put more torsional force or twist through the tendons and ligaments compared to if the horse is taking off and landing straight and upright through his body.

We also need to think about which leg the horse is landing on. When the horse lands from a fence, for example, in left canter, it’s actually the right forelimb that will land first and will have to absorb most of the forces quite quickly.

Learn more about the biomechanics of jumping with the on-demand lecture demonstration Jumping from the Anatomical Approach

A horse jumping a fence of about one metre will absorb two and a half times his body weight through that trailing forelimb and that's without a rider. Make the fence big, add a rider - also the landing is on sloping ground – plus there’s a turn and this will make the forces even greater.

It's really important in your jump training to practice landing equally on both the left and right forelimb. Also to incrementally build in slopes and turns but always with the focus being on balance. This a fundamental part of your training to make sure the horse has the best possible posture and balance to help the forces be evenly distributed through his body. If the horse has poor posture, or poor balance it can increase forces through certain structures. This of course, puts those structures at greater risk of injury and in particular, repetitive strain injury.

Keen to Discover More?

If you have you enjoyed reading about these common anatomical misconceptions about the horse's lower leg and are keen to learn more, take a look at our on-demand online seminar Understanding Tendons and Ligaments presented by Gillian Higgins and Dr Seth O'Neill.

It studies the anatomy and biomechanics of the lower leg in detail and focuses on tendon injury and its prevention, early detection, management and rehabilitation.​

This seminar gives you a better understanding of

• Your horse's lower leg

• The tendons and ligaments of the lower limb

• Reducing the risk of injury

• Improving performance

• Designing appropriate training regimes

• Managing your horse's tendons and ligaments effectively

Live Painted Horse Lecture Demonstration

These fun, educational and interactive lecture demos are the perfect opportunity to discover more about equine anatomy. Watching anatomically painted horses performing dressage or jumping in real time is an amazing way to bring equine anatomy to life and see for real how your horse moves and functions.

Our next live painted horse lecture demonstration is at Moulton College, Northants on Saturday 21 September. Tickets are on sale now - you don't want to miss it!

Horses Inside Out Evening Extravaganza - Moulton College

21 September 2024, 17:30–20:30|Moulton College Equestrian Centre

Register Now

Coming up.....In the next part of our Anatomical Misconceptions series, we will take a look at the horse's back.

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