Horse Conformation Conundrums
by: Stacey Oke, DVM, MSc
October 01 2010, Article # 17050
Which limb defects matter and which don't?
Since horses' domestication, humans have been scrutinizing equine legs in an attempt to judge
which horse will perform best in a given situation. Be it for racing, reining, or riding, a horse
needs to be put together properly; but does a horse need to be put together perfectly? Given that
some poorly conformed horses surprise even the most emphatic proponents of perfect
conformation and go on to be champions begs the question: Is conformation really all that
important?
What is Conformation?
According to Mike W. Ross, DVM, Dipl. ACVS, a professor of surgery at the University of
Pennsylvania's school of veterinary medicine and co-editor of Diagnosis and Management of
Lameness in the Horse along with Sue Dyson, MA, VetMB, PhD, DEO, FRCVS, head of
clinical orthopaedics at the Animal Health Trust in Newmarket, England, "Conformation simply
refers to the physical appearance or 'outline' of a horse."
Conformation is more or less defined by the horse's bones, muscles, associated soft tissues, and
how they all fit together. If all horses were created equal and used for the same purpose, then
judging conformation would be easy. Alas, this is not the case. Every classification of horse (i.e.,
draft, light, or pony) has a different "normal" conformation and its own set of conformation traits
defined by the breed and type of work the horse is intended to do. For example, sport, stock,
hunter, pleasure, race, and show horses are all types of light horses, and each has its own
accepted standard of conformation.
Conformation assessment involves a fine eye, patience, and a bit of luck. The horse is usually
examined with four key functional components in mind: the head and neck; the forelimbs; the
trunk (barrel); and the hind limbs. Ideally, the forelimbs are evaluated from the front and sides.
Part I: Forelimb Conformation
A horse's forelimbs should match and bear weight equally. Both toes are expected to point
forward, and when the horse stands square the feet should stand as wide as the limbs are at their
origin (i.e., the chest). If a straight line is drawn from the point of the shoulder, it should course
perfectly down the front of the limb to the middle of the foot. Similarly, a line drawn from the
tuber spinae (the prominent bony protuberance on the shoulder blade) should travel down the
middle of the limb to the fetlock (ankle) then drop down to meet the bulbs of the heel when
assessing the horse from the side.
Assess the bones and musculature from the shoulder all the way down to the hoof systematically.
This includes the humerus, radius, and ulna, the angle of the elbow joint, the carpus (knee),
cannon and pastern bones, and the angle of the pastern and foot. The hoof should be an
appropriate size for the horse, well-shaped, symmetrical, and have a high-quality horn.
There are a large number of conformation faults that commonly occur in the forelimbs, some of
which are described here. It is important to recognize that a horse can have none, one, or several
of these faults and that the presence of a fault does not necessarily mean a horse will develop a
problem.
Base-Narrow This describes horses whose feet are closer together at the ground than the origin
of the limbs at the chest when examining the horse from the front. This is a common fault noted
in large-chested horses such as Quarter Horses. This defect causes a horse to bear weight
unevenly and can lead to the development of osteoarthritis.
Base-Wide These horses' feet stand wider at the ground than the limbs are where they originate
from the chest. This fault places stress on the medial (inner) aspect of the legs and can cause
lameness problems such as ringbone (osteoarthritis of the pastern or coffin joint).
Toeing-In (Pigeon-Toed) The horse's toes point inward toward each other. Affected horses bear
more weight on the outside of their feet, which places abnormal stresses on all of the structures
located on the medial aspect of the limbs from the foot to the shoulder. These horses tend to
"paddle" when moving, or swing their legs to the outside during the flight phase of the stride,
then return back to the middle with the toe in when bearing weight.
Toeing-Out (Splay-Footed) The toes point to the side, away from each other like a ballerina's.
This fault is commonly seen in base-wide horses. Not quite as graceful as a dancer, these horses
"wing" to the inside--swing the foot in toward the midline when they move. The problem with
this conformation defect is that affected horses bear more weight on the medial aspect of the
foot. Horses can be both toe-out and base-narrow and have an abnormal gait called "plaiting."
This means the foot travels in an inward arc and lands in front of the opposite foot. This is a
highly undesirable trait because these horses can stumble when the forefeet hit each other (i.e.,
interference).
Buck and Calf Knees Many horse owners call the buck-knee conformation fault "over at the
knees." Affected horses appear to be standing with their carpi slightly bent. On the opposite end
of the spectrum is the calf-kneed horse that has a backward deviation of the knees (i.e.,
hyperextended).
Knock Knees (Carpal Valgus) Horses with a carpal valgus have an outward deviation (away
from midline) of the lower part of the limb stemming from the knee. Many foals are born with
carpal valgus, and the conformation is often self-correcting.
Bowlegs (Carpal Varus) This condition is essentially the opposite of valgus. The outer aspect of
the knee grows faster than the inner aspect, causing an outward deviation of the knee. Knock
knees and bowlegs are both angular limb deformities that occur in foals and, if left uncorrected
or if they don't resolve on their own, can place a great deal of stress on the ligaments and small
bones of the carpus.
Short or Long Pasterns In some horses the pastern is short or "too upright." This conformation
is often noted in concert with a base-narrow, toe-in conformation. Horses with short pasterns
often also have short limbs, powerful bodies, and straight shoulders. These horses tend to be
predisposed to traumatic arthritis of the fetlock and phalangeal (cannon bone, pastern bones, and
coffin bone) joints and navicular syndrome due to the increased concussion on all of the bones
and joints below the fetlock. On the other end of the spectrum is a long, sloping pastern that
places increased stress on the structures located on the palmar (rear) surface of the limb, such as
the flexor tendons, suspensory ligament, and sesamoid bones.
The Feet Not to be ignored, the forefeet are also common sites of conformation defects. Feet can
be flat or contracted, bull-nosed (having a dubbed toe, where the front of the toe is ground/rasped
off), or the horse could be coon- or club-footed. A club foot has a foot axis--the angle between
the hoof and the pastern--of more than 60°, whereas a coon foot has a steeper foot axis as
compared to the pastern angle with the ground (i.e., the opposite of a club foot). Like any of the
conformation faults described above, foot abnormalities can occur in one or both feet. Usually, a
unilateral defect is indicative of injury while a bilateral deficit indicates a genetic (heritable) or
developmental problem.
Blemished or Unsound?
An owner or prospective owner should consider whether a certain forelimb conformation defect
is important relative to the job the horse will perform. Is a scar over the carpus (knee) important?
Is that divot on the point of the shoulder an issue?
Ross says, "Conformation is one piece of the complex puzzle of a lame horse. Although poor
conformation does not necessarily condemn a horse to lameness, the relationship of
conformation, especially of the distal extremities, and lameness is well-recognized."
Conformation faults such as base-wide or base-narrow, whether in the forelimbs or hind limbs,
have less severe conse-quences. Weight bearing with these defects is simply not optimal; the feet
wear unevenly, which could lead to undue and abnormal stress on the bones and supporting soft
tissue structures. But what about the other faults?
Ross suggests, "Despite foot problems contributing to a large number of equine lamenesses,
particularly in racehorses, con-formation faults involving the carpus appear to be most important
in the forelimbs."
For example, a severe case of buck knees is problematic because it places stress on the extensor
tendons on the front of the limb as well as the suspensory ligament. But calf knees are widely
thought of as worse.
Kenneth E. Sullins, DVM, MS, Dipl. ACVS, a professor of equine surgery at Virginia Tech's
Marion DuPont Scott Equine Medical Center, notes, "Being back at the knees (calf-kneed) is bad
for athletes because it stresses the dorsal (forward) aspect of both the fetlocks and carpi. Horses
with this conformation tend to suffer 'chip' fractures in the knees and ankles (fetlocks)."
As discussed by Eric Parente, DVM, Dipl. ACVS, an associate professor at the University of
Pennsylvania's New Bolton Center, in his chapter on angular limb deformities in Diagnosis and
Management of Lameness in the Horse, many foals are born with a slight carpal valgus and a
toed-out appearance. In fact, Parente suggested that many clinicians view this conformation as
normal for a foal and that as the foal grows and the chest widens the limbs will progressively
straighten on their own.
"In more severe cases of angular limb deformities, treatment is indicated," says Ross. "Leaving a
foal with severe carpus valgus can lead to osteoarthritis of the carpal joints and lameness
problems in the proximal metacarpal region (upper cannon bone). Often, toed-out conformation
accompanies carpus valgus limb deformity, predisposing horses to lameness issues in the lower
forelimb and to problems with interference (winging in)."
Treatment Options
As Confucius said, "The real fault is to have faults and not to amend them."
Most veterinary surgeons agree; conformation defects such as severe angular limb deformities
will not correct themselves, and intervention is required.
"Many foals can be corrected right before your eyes with hoof balancing and dubbing the toe
(making a bull-nosed foot)," ex-plains Sullins. "Surgery is generally indicated if the angulation is
too much for hoof balancing and shoeing to work."
In foals with angular limb deformities, time is of the essence. Correcting the angulation requires
some form of intervention, be it surgery or shoeing, before the affected growth plate closes.
Growth plates (physes) are a specialized region of cartilage located near the ends of long bones.
Once the periods of rapid growth are over, usually between the third and sixth month of life, the
growth plates are considered "closed" and correction is essentially impossible. Closure occurs in
the fetlock around 60 days of age and in the carpus around six months.
"Foals are like molding plastic," notes Parente. "Because the greatest impact on conformation is
made during periods of rapid growth, early recognition and regular reevaluations are extremely
important to achieve a positive outcome."
Sullins adds, "A very common error among horse owners is refusal to confine a foal to a stall
with an angular limb deformity when treating with trimming and/or shoeing. Too much exercise
in a foal with angular limb deformities will worsen the result."
In mature horses corrective trimming and shoeing can alter a horse's stance, stride, or breakover,
as described in Adams' Lameness in Horses, 5th Edition. These methods can be used in horses
with conformation defects to achieve a more normal limb movement. For example, balancing the
hoof to avoid unequal shoe wear in horses that "interfere" is advocated when poor conformation
is an underlying cause of the interference. However, keep in mind that once a horse is an adult,
more damage can often be done by trying to "correct" faults than by managing them
appropriately. See www.TheHorse.com/13622 for more information on cor-rective trimming and
shoeing.
Part II: Hind Limb Conformation
Bog Spavin
Bog spavin is a collection of fluid
in the tibiotarsal joint on the
medial or inside aspect of the hock.
Kenneth E. Sullins, DVM, MSc,
Dipl. ACVS, a professor of equine
surgery at Virginia Tech's Marion
duPont Scott Equine Medical
Center, explains, "It is true that a
bog spavin is commonly
overlooked by owners and
veterinarians when the horse is not
obviously lame. The fact is that a
bog spavin is a synovitis
(inflammation of the synovial
lining inside the joint) that more
often than not has an underlying
cause detectable by X rays or
arthroscopy. Over the career of a
horse, this seemingly minor
synovitis could lead to overt
osteoarthritis in later years."
Each hind limb carries only 20% of a horse's body
weight, but that doesn't mean that limb's conformation is
any less important than forelimb conformation. "Hind
limb conformation can be more forgiving compared to
the forelimbs, but it is not possible to directly compare
the knees to the hocks or the front ankles to the back
ankles," explains Sullins.
Just like with the forelimbs, you should assess specific
and important conformation traits. "In addition, the
importance of each conformation deficit must be
considered relative to the type of work the horse will
perform," adds Sullins.
The Standard
Like the front end, the hind end of the horse is evaluated
from two directions: the side and from behind. From the
side, if one were to drop a straight line from the point of
the buttocks, the tuber ischii, it should course down to
the hock, follow the con-tour of the back of the cannon
bone (the plantar surface) to the level of the fetlock, then
drop to the ground. Unlike the line to assess the
forelimbs from the side, the line for the hind limb does
not travel down the center of the limb to the heel bulbs. When assessing the horse from behind, it
should be possible to imagine a straight line dropping from the point of the buttocks that bisects
the limbs along the length of the leg, all the way to the bulbs of the heels where they meet the
ground. Again, unlike the forelimbs, the hind limbs of a horse naturally point outward to some
degree. Specifically, the stifles point outward in order to clear the abdomen while in motion. As
a result, the points of the hocks are pointed slightly inward, and the toes are pointed slightly
outward. The hind limbs should appear symmetrical (i.e., equally muscled, of equal length, and
bearing equal weight).
The hind feet are usually more pointed at the toe than the forefeet, and the frog divides the foot
into two equal halves. Both the medial and lateral walls should show the same level of wear. The
sole is usually more concave in hind limbs than it is in the forelimbs. A normal hind limb
pastern-foot axis is approximately 55��.
Where the Fault Lies
Hind limb conformation faults are numerous. Some of the most common are described here:
Base-Wide Horses with a base-wide conformation stand with the the center of their feet wider
apart than the center of the thighs. A "perfectly" conformed horse would have a vertical line pass
through the center of both the thigh muscles and feet before reaching the ground.
Base-Narrow Opposite to being base-wide, base-narrow horses have their hind feet closer
together compared to the -center of the thighs when viewing the horse from behind. Many basenarrow horses also are bowlegged or have a tarsal varus. This occurs when the lateral aspect of
the bones in the hock grow more quickly than the medial aspect. Both base-narrow and basewide horses are prone to osteoarthritis due to the abnormal loading on their feet and lower legs.
Base-Narrow from the Fetlock Some horses can have desirable conformation through the upper
and middle regions of the limb but then deviate from the level of the fetlock down. Similar to
bowleggedness, base-narrow from the fetlock means the lateral (outer) aspect of the bones of the
fetlock grew more quickly compared to those located on the medial (inner) aspect of the limb.
Sickle Hocks The angle of the hock is assessed based on the angle of the femur and the tibial
bones when viewed from the side. The normal hock angle is approximately 50��; any hock
angle less than 53�� is considered sickle. This defect tends to stress the structures at the
back of the hock and cannon bone, particularly in horses that are in heavy training.
Straight Behind Unlike horses with sickle hocks, horses that are straight behind do not have
enough of an angle between the femur and tibia. Horses that are straight behind generally are not
as unsightly or perceived as negatively as horses with sickle hocks; however, this defect can still
lead to osteoarthritis of the hock, problems with the patella within the stifle joint, and suspensory
disease.
Cow Hocks This is a very common conformation flaw, particularly in Western performance
horses. Cow-hocked horses are base-narrow at the point of the hocks, but base-wide from the
hocks to the feet. The defect is also called a tarsal valgus and is a result of the medial part of the
bones of the tarsus growing more quickly than the lateral part of the bones. Cow-hocked horses
also can have sickle hocks, which highlights the importance of carefully and completely
assessing a horse's conformation so as not to miss multiple faults at each anatomically distinct
region.
The Feet Despite the hind feet having a slightly different appearance and angulation than the
forefeet, conformation defects in the hind feet are essentially the same as the forefeet. As
described in the forelimbs, the most common conformation defects of the hind limb feet are flat
feet, contracted feet and heels, a bull-nosed, coon or club foot, and thin walls/soles.
Decisions, Decisions
Now is the time to ponder which of the above-described conformation faults are important and
which aren't.
"In the forelimbs, deficits in the carpus tend to be the most important," says Sullins. "Similarly,
(hind limb) conformation faults involving the hock are typically of most interest to owners and
veterinarians."
According to Sullins, the most common hind limb issue in all breeds is an overly straight hind
limb. "The angles of the hocks and stifles absorb compressive forces so horses with straight hind
limbs have joints that routinely undergo more wear," he says. "Overly straight hind limbs tend to
overstress the hock joint and surrounding soft tissues over time in athletic horses, particularly
those that work at speed. Collapse of the third tarsal bone (part of the hock joint) due to
dysmaturity at birth predisposes the horse to osteoarthritis and fracture. Radiographs are usually
necessary to see this conformation."
Excessively straight limbs are also thought to predispose horses to bog spavin (see sidebar) and
upward fixation of the patella. Nonetheless, some horse people believe horses that are straight
behind have a good gait quality attributable to increased action in the hock joints.
According to Adams' Lameness in Horses, cow hocks are one of the worst possible hind limb
defects.
"This is because the points of the hocks are too close together and there is excessive stress on the
hocks," explains Sullins. "Affected horses are prone to bone spavin, which is an osteoarthritis or
osteitis (inflammation of the bone) of the hock, particu-larly the lower hock joints. Bone spavin,
also referred to as distal tarsal osteoarthritis, is one of the most common causes of tarsal
lameness."
According to Sullins, "(Radiographic) changes in the distal tarsus, meaning the tarsometatarsal
joint or proximal intertarsal joint, must always be viewed with a grain of salt."
When noted in the distal hock joints, these changes do not necessarily mean the horse is or will
become lame. On the other hand, a horse with "clean" radiographs (X rays) of the hock is not
always in the clear.
The changes that Sullins refers to include "bone spurs," or small bony growths commonly noted
along the margins of the joints that might cause lameness and narrowing of the joint spaces due
to loss of the cartilage that normally lines the bones in the joints.
"Diagnostic local anesthesia (a joint block) or scintigraphy (a bone scan) is advisable to confirm
the significance of suspected hock lesions because the management of a horse with hock
problems will be for the rest of the horse's life," says Sullins. "Rare-ly, we do see horses with no
changes on X rays of the distal hock joints, but these horses may still have hock lameness."
Responsible Breeding
Conformation faults can be congenital (something a foal is born with) or
developmental/acquired. According to Ross, "Certain conformation defects appear to be highly
heritable and the dam seems to contribute more to faulty conformation than the sire." Examples
of hind limb conformation faults believed to be genetic include:



Toeing in and toeing out;
Sickle hocks; and
Straight behind.
Despite there being wide suspicion among practitioners that these faults have a genetic
component, so far researchers haven't identified any specific genes responsible for any particular
defect.
Take-Home Message
"Good conformation is not synonymous with success," cautions Ross. "In addition to
conformation, natural athleticism, intelligence, aggression, 'will to win,' and other intangible
factors are important considerations."
Breeding is also an important consideration with regards to conformation. Ross notes, "Many
conformation faults are believed to be inherited, such as angular limb deformities. Based on my
experience, a well-bred horse from a successful family can endure faulty conformation much
better than a less well-bred horse."
The ability to recognize desirable conformation traits and to learn when to overlook one or more
faults that are not likely to be clinically relevant is also an important part of evaluating horses,
according to Ross. Albeit correct, some things are easier said than done, and there always seems
to be an anomaly lurking in every sector of the equine industry to prove even the most veteran
conformation expert wrong.