Demistifying equine limb deformities and how they refer to hoof capsule distortions - 4 hoof types

In part I of this series of articles we have gone through the ways in which horses’ limbs can be deformed and learned how and why hoof capsule distortions occur. In this part we are going to focus on correlations between specific limb deformities and corresponding hoof deformation patterns. 

As stated in the previous article, the amount of variations in which equine limbs can be deformed seems tremendous and overwhelming. On the other hand, some of the possibilities seem to be only hypothetical.

Even though naming all possible configurations of deformities is rather impossible (and pointless!), I’ve been noticing consistent patterns in which hooves of crooked-legged horses deform. Analysing those patterns led me to realising what factors seem to be playing major roles in affecting the load distribution and forces acting on the hoof capsule and thus leading to its permanent or semi-permanent deformations.

What was catching my attention was the fact that some horses with seemingly mildly deformed limbs could have severely deformed hoof capsules (sheared heels, a lot of asymmetry in the sole and walls) whilst some horses with really significantly crooked legs may have almost perfectly symmetrical hooves. 

And those deformations (almost) always occur in specific feature configurations, in repetitive patterns. Very few ones that would break out of the rule were the ones that had undergone some significant human intervention. 

I really like analysing extreme cases of deformations. They are very helpful when it comes to revealing the patterns, as they clearly show the tendencies in exaggeration, like a caricature.

The features I would be looking at were:

• symmetry of the whole hoof capsule

• symmetry of the heels and heelbulbs

• symmetry of the walls thickness, angles and shape

• symmetry of the coronary band and growth rings

• symmetry of the bars, frog and sole

• occurrence of flares, underrun walls and cracks

• continuity of white line tightness

• symmetry of growth rate

              and more.

Those observations led me to some interesting conclusions which ultimately made it possible to clarify the determining factors into 2 categories and (based on that) to classify the ways in which hoof capsules deform into 4 patterns (types).

DETERMINING FACTORS

In short: whether a hoof capsule is going to be symmetrical or not is a result of the distribution of forces acting on it. Those depend on the horse’s conformation and posture.

When comes to the hoof capsule deformities, conformation and posture can be reduced to 2 variables:

DIRECTION OF FETLOCK DESCEND and BASE WIDTH.

 Fig. 1. Illustration showing how fetlock descend direction and base width affect the load distribution over the hoof capsule.

1. BASE WIDTH

Neutral (balanced), base wide (COP shifts medially) or base narrow (COP shifts laterally).

To be assessed on a standing horse from in front as a relationship between the position of the center of the hoof's base of support and the center of the proximal joint surface of the radius (my suggestion of how to assess, to be verified). 

Can be a result of an abnormal posture and/or angular limb deformities. 

(Abnormal posture can consist in placing limbs wide or narrow and/or twisting the whole limb inward or outward. It causes different forces being at play which are included in considering the fetlock descend direction.)

Fig. 2. Sets of drawings showing what components add up to the ultimate position of the limbs and base width.

A horse with carpus valgus or presumed fetlock valgus conformation (most of those seem to have a ‘banana’ shape in P1 and not a fetlock valgus - more on that in part I) present a base wide stance as well as a straight legged horse that would spread its limbs abnormally wide. This is common for young horses with undeveloped chest and narrow-chested horses in general, but can be also present in a properly conformed horse that would compensate for some discomfort or pain.

A horse with fetlock or carpus varus conformation would most likely present as base narrow, as well as a straight legged horse with a wide chest that would stand abnormally narrow to compensate for something.

This factor decides mostly about which side of the hoof capsule exhibits more load and thus grows slower than the opposite one, but does not necessarily cause significant capsular deformations.

2. DIRECTION OF THE FETLOCK DESCEND

Fetlock can descend inline with the hoof capsule sagittal plane (balanced), medially (overload of the medial-caudal part of the hoof capsule) or laterally (overload of the lateral-caudal part of the hoof capsule).

To be assessed from the top, looking down vertically, or from in front.

Fig. 3. When the fetlock descends towards one side of the hoof (not aligned with the hoof axis), it doesn’t smoothly fit between the collateral cartilages but instead it omits one cartilage and gets in the way of the other one. It pushes its axial part up, in time changing its position to more vertical permanently and making it look like the whole cartilage on this side is pushed up - whilst it’s just that it’s unfolded and positioned more vertically which makes it look higher. At the same time, the off-axis descending fetlock is shifting the COP towards the side it descends to, leading to vertical (transversal) shift of the hoof capsule (more on that in Part I).

Fig. 4. Illustrations showing how the difference in the collateral cartillages heights occurs. It’s not really about one of them being pushed up but rather compressed by the hoofwall and descending pastern, which leads it to becoming more vertical. On the bottom photos of the same hoof: the one on the left is after appropriate corrections, the one on the right is before.

This depends on the bones conformation (angular deformities in the joints and rotational deformities in P1, P2 and P3), mediolateral balance of the hoof capsule and horse’s posture.

Usually the fetlock descending towards the medial side is caused by inward rotation of the pastern (P1 and/or P2), and exaggerated by ‘banana’ pastern or a lateral offset in the coffin joint. Can be also caused by placing limbs wide without outward twist of the whole limb.

Descending towards the lateral side is either due to angular (varus) deformity or a medial offset in the coffin joint (so far I have not found a P1 or P2 to be rotated outward, most of them twist inward and those of legs with fetlock varus are just straight, not twisted).

Mediolateral balance of the hoof capsule can reduce or exacerbate the offaxis descend of the fetlock. Usually when just left alone, compression on the side of the fetlock descend will cause compromised blood flow and less growth (meaning more growth on the opposite side) and this shift in mediolateral balance will cause even more offaxis descend of the fetlock, along with the postural adjustments of the horse: like a vicious circle.

Fig. 5. Viscious cycle of uneven load distribution and hoof capsule deformations and how we can get out of it.

Fig. 6. X-ray and venogram of the same hoof. Note the difference in angulation of the side walls (the steeper side is experiencing more load|) and how that corresponds with the length of the solar papillae (they are shorter on the overloaded side due to compression). The load distribution affects the blood flow and blood flow affects the growth rate. That is why an unevenly loaded hoof grows unevenly (the less steep side will grow faster.)

X-rays and venograms performed by Doctor Redden at his farm.

Offaxis pastern descend causes abnormal forces acting on collateral cartilage, pushing the axial part of the cartilage on the side of the fetlock descend to be pulled abaxially and pushed into more vertical position, which leads to a shift in the coronary band shape, more vertical angulation and less thickness of adjacent side wall, sheared heels and quarter cracks (more on that in part I).

This factor decides about how badly the hoof capsule gets deformed, including sheared heels, quarter cracks, shunted walls and more.

Fig. 7. A collage of examples how a change in posture can correlate with a change in hoof capsule morphology.

Fig. 8. Illustrations showing 4 types of front hooves determined by conformation and posture.

Fig. 9. Illustrations showing 4 types of hind hooves determined by conformation and posture.

4 HOOF TYPES - WHY TO LEARN THEM?

Every front and hind hoof deformation is a result of a combination of those 2 factors (base width and direction(A/B) of the fetlock descend (A/B)), which give us 4 variations (4 types: AA, BB, BA, AB). Some are easy and some harder to distinguish (when the deformation is very subtle or when one of those factors is close to neutral).

Recognising the type we are working with gives us a lot of benefits, not only informing about the load distribution over the specific hoof capsule (like the way horse is likely to walk, stand and which side is going to be growing faster), knowledge how to address the imbalance and deformation but also indicating weak points and what kind of problems we may be dealing with in the future.

Except for type III (which presents different sets of problems and needs a different approach for front and hind limbs) characteristics of front and hind hooves’ features overlap.

Fig. 10. Illustrations showing 4 types of front hooves determined by conformation and posture.

Fig. 11. Illustrations showing 4 types of front hooves determined by conformation and posture.

TYPE I (AA)

Base wide stance + fetlock descending medially to the hoof axis

Both factors add up to overloading the medial side. Farriery plays a big role in correcting or preventing from exacerbating of the deformations occurring in this type of hooves. Many of those cases are easy to correct, as the deformation is likely to be exponentiated by postural adjustments.

Fig. 12. Illustration showing main features of front hooves type I.

In hind limbs this type often occurs in one leg, when the horse tends to place it to the side, away from the body.

Fig. 13. Illustration showing main features of hind hooves type I.

Typical features:

• often horses with narrow chest but not only
• the medial side is overloaded due to both rotational and angular deformities
• due to uneven load the medial side is growing slower and the lateral faster. This leads to/excerbates the base wide posture.
• on DP x-rays the joint spaced should not be judged if the horse is standing base wide! 
• they tend to grow more sole on the lateral side
• the coffin bone is often remodeled - part of the medial part can be missing, so balancing to the parallel solar surface can keep the horse in the scheme - they often need more sole thickness/depth on the medial side 
• deeper medial groove, coffin bone tilted laterally (opposite)
• frog can be bent and the apex points to the lateral pillar, the medial part of the frog can have less mass
• frog wider on the lateral side
• thinner/wider medial heel bulb
• bar bent not straight on the medial side 
• medial heel shunted
• medial wall more vertical or even folding under, thinner
• flare on the lateral side up to the heel which is less steep as well
• lateral wall thicker
• sole, wall and white line tubules shifted to the lateral side (they don't grow straight down but towards lateral side)
• more sole surface on the lateral side which excerbates the imbalance on soft ground -> the medial side sinks more into the surface -> even more strain to the medial collateral ligaments
• medial pillar as a fulcrum, the wall bands there at a more steep angle and often white line is infected in that area
• most severe cases of sheered heels
• most cases of medial quarter cracks
• most cases of the crack and infection at the junction of the medial bar 
• lateral cartilages more often ossified
• after balancing the hoof properly, the leg may visually seem more toeing in
• really common cases
• more upright/narrow hooves tend to get sheared heels, with the more flat/wide ones it's not as apparent
• may land flat, lateral first or medial first depending on the severity of the pastern intorsion and rotation upper in the limb

TYPE II (BB)

Base narrow stance + fetlock descending laterally to the hoof axis

Both factors add up to overloading the lateral side. Farriery is less likely to correct the deformations, as usually they tend to be caused by conformation, not postural adjustments. 

Fig. 14. Illustration showing main features of front hooves type II.

In hind limbs it may predispose to instability and pronounced supination of the hocks, so proper managing those hooves is really important. The more out of balance they get, the bigger the instability leading to more uneven wear creating more imbalance. The other way round: the better the balance, the more stable they get and the less they wear on the lateral side.

Fig. 15. Illustration showing main features of hind hooves type II.

Typical features:

• often wide chest and in draft horses

• lateral side overloaded due to both rotational and angular deformities

• due to uneven load the lateral side is growing slower and the medial faster; this leads to/exacerbates the base narrow posture

• on DP x-rays the joint spaces should not be judged if the horse is standing excessively base narrow

• they tend to grow more sole on the medial side

• the coffin bone is often remodeled - part of the lateral part can be missing, so balancing to the parallel solar surface can keep the horse in the scheme - they often need more sole thickness/depth on the lateral side 

• deeper lateral groove, coffin bone often tilted medially (opposite)

• lateral heel shunted - but rarely this is as severe as sheared heels in type 1

• lateral wall more vertical or even folding under

• lateral heel more underrun

• medial wall thicker

• frog can be bent and the apex points to the medial pillar, the lateral part of the frog can have less mass

• thinner/wider lateral heel bulb

• bar bent not straight on the lateral side 

• flare on the medial side up to the heel which is more open as well

• sole, wall and white line tubules shifted to the medial side (they don't grow straight down but towards medial side)

• more sole surface on the medial side which excerbates the imbalance on soft ground -> the lateral side sinks more into the surface -> even more strain to the lateral collateral ligaments

• lateral pillar as a fulcrum, the wall bends there at a more steep angle and often white line is infected in that area

• quarter cracks may occur on the lateral side

• in hind limbs they tend to cause instability and pronounced supination of the hocks, leading to excessive wear on the lateral side

• most of those cases will land (sometimes significantly) lateral first, regardless of the hoof balance

TYPE III (BA)

Base narrow stance + fetlock descending medially to the hoof axis

‘Spiral’ type of bones deformity. Unlike type I and II, features of front and hind limbs differ significantly. 

Front limbs

Less common than the previous 2. This is the type where you may see a really crooked leg and a fairly symmetrical hoof capsule.

Unlike Type I and II, forces created by factors 1 and 2 balance each other out to some degree. Base narrow posture makes up for medial fetlock descend (thus those cases have no severe hoof deformations, like sheared heels) and medial fetlock descend partially makes up for base narrow posture, reducing the lateral overload. As a result, those hooves usually just grow faster medially, without significant deformations

Correct farriery should be focused on preventing the problem from exacerbating - typically the medial side will grow faster and exacerbate the imbalance - the horse will tend to stand more and more base narrow.

Fig. 16. Illustration showing main features of front hooves type III.

Typical features:

• lateral side overloaded due to base narrow posture, which is partially canceled out by caudomedial overload due to medial fetlock descend

• due to uneven load the lateral side is growing slower and the medial faster; this leads to/exacerbates the base narrow posture

• they tend have quite symmetrical coffin bones and soles and to grow quite equal thickness or a little bit more medially

• uneven growth mostly in the walls

• medial walls tend to flare mildly

• very common lateral toe wear is exacerbating the imbalance

• heels, frog, collateral grooves and bars quite symmetrical

• like type AA, they may land flat, lateral first or medial first, depending on the severity of the medial twist and rotation upper in the limb

Hind limbs

Often found in horses with anterior pelvic tilt and compensatory posture - this type of base narrow stance seems to occur mostly in horses with some kind of hind end problems. Those horses usually don’t respond to change in hoof balance by adjusting their posture.

This type was the hardest for me to understand and seems to be the most misunderstood when it comes to being addressed by farriery. These hooves tend to have pronounced horizontal bend with the lateral heel bulb displaced caudally, making it harder to assess the balance looking from behind: as the heel bulbs are not aligned with the hoof capsule axis! Judging from the heel bulbs axis will create an impression of the medial side being much higher than the lateral, which is misleading. Very often those hooves need lowering of the lateral/craniolateral side, which will be apparent when looking a bit laterally to the heelbulbs axis.

Difficulties in assessing the balance and misunderstanding of the distortions are probably the cause of those hooves very often being extremely distorted due to improper trimming. 

When addressed properly, they don’t tend to flare and grow quite balanced. However, the displacement of the lateral heel bulb due to horizontal bend is difficult to correct, especially in severe cases, where there is complete loss of suspension in the caudolateral area of the hoof capsule.

Those horses are unlikely to adjust posture due to change in hoof balance.

Fig. 17. Illustration showing main features of hind hooves type III.

Typical features:

• caudal displacement of the lateral heel bulb

• a very characteristic flare starting at the lateral heel and ending at the lateral pillar

• the sole tubules are not pulled towards the flare but rather grow straight, creating a pronounced cavity at the lateral white line

• this flare is usually created by improper balancing of the foot, often coupled with rasping the lateral flare (which always comes back with each cycle unless the balance of the sole plane is addressed properly)

• medial heel bulb higher and steeper but without significant shearing of the heels

• lateral heel often looks extremely underrun from the side with the tubules growing almost horizontally; in fact, this is caused more by the heel bulb being pushed back rather than the heel base being too far forward

• camped under posture exacerbates the distortions, especially the lateral heel displacement

• crushing and complete loss of suspension to the caudolateral area of the hoof capsule: very little depth at the lateral collateral groove

• unlikely to achieve change in horse's posture due to change in hoof balance

• unlike type I, sole tubules grow straight down and the wall flares away from the sole tubules on the lateral side, stretching/tearing the white line and the medial wall/heel does not tend to fold under

• they may land flat, lateral first or medial first, depending on the severity of the medial twist and rotation upper in the limb

TYPE IV (AB)

Base wide stance + fetlock descending laterally to the hoof axis

Fetlock varus combined with significant outward rotation of the whole limbs, resulting in base wide posture despite the varus deformity. The base wide posture with outward rotation is not overweighing the lateral fetlock descend: these hooves are quite symmetrical but grow faster medially and show some signs of lateral compression. Still the deformations are pretty mild, especially in reference to the look of the limbs.

Fig. 18. Illustration showing main features of front hooves type IV.

Fig. 19. Illustration showing main features of hind hooves type IV.

Typical features:

• caudolateral side overloaded due to lateral fetlock descend, which is partially canceled out by medial overload due to base wide posture

• due to uneven load the lateral side is growing slower and the medial faster; still those horses keep the base wide posture 

• medial side walls tend to flare more significantly than in type BA, due to persisting base wide posture even when medial sides are too high

• like type BB, they tend to grow more sole medially

• heelbulbs and heels shifted slightly medially which creates and impression of the hoof capsule twisting out in reference to the pastern

• heels, frog, collateral grooves and bars quite symmetrical

• they usually land significantly laterally first, due to both fetlock varus and outward rotation of the whole limb

TYPE IV’ - super rare!

Base wide stance + fetlock descending laterally to the hoof axis (outward twist in the phalange)

Very rare, seems to only occur in horses that had some kind of surgical intervention at the young age.

Fig. 20. Illustration showing main features of hind hooves type IV.

Despite a significantly crooked leg and significant base wide posture, the hoof capsule is almost symmetrical. The lateral side grows faster, suggesting that the medial side is slightly more loaded. The horse is landing severely laterally first, due to outward rotation of the whole limb and the pastern and I don't think this pattern can be changed.

'OVERCORRECTED' TYPES

The deformations occuring in the hooves can be corrected or exacerbated by farriery. There are also situations, where the deformity can be 'overcorrected', which may lead to different scheme of deformity to the ones presented in this article. 'Overcorrecting' usually leads to flares occuring on the opposite sides than before and/or a flare at the toe quarter which is a 'fulcrum'. This can and should also be corrected by farriery: the goal is to get the hoof to not be be deformed further than the horse's conformation forces it to be - more on that in the following materials.

SUMMARY

Recognising the repetitive patterns is really helpful when it comes to understanding the reasons and mechanisms of hoof deformations occurring. Using the classification of the deformation patterns into 4 hoof types allows for easy communication and more precise ways to explain, discuss and teach about mediolateral balance.

It also helped me develop a method and protocols for addressing each type of deformity with trimming/shoeing, as it gave me the understanding of why and how those deformations occur: partially in a process of reverse engineering. I am going to explain it in the next article or webinar.

There are still many unanswered questions and probably many more still to be asked. I am going to further develop this research.

Working with hooves is really rewarding as it gives you almost direct feedback on whether what has been done was beneficial or not. 

Here are some examples of this kind of feedback! :)