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Limb Deformities in the Foal

Written and presented July 2006 by R.F. (Ric) Redden, DVM

Introduction

Limb deformities are commonly found in new foals. They can be congenital or developmental and with varying degrees of deformity ranging from mild to severe. The majority of deformations will fall into one of five basic categories.

    1. Angular - Angular deformities occur when the distal extremities of the limb deviate from the midline of the limb. Valgus deformity is a deviation lateral of the mid line. Varus deformity is a deviation medial of the mid line.

    2. Axial - Axial deformities can be described as a medial or lateral shift at the anterior articulation, e.g. offset knees.

    3. Rotational - Rotational deformities are muscular in origin and most commonly involve the front limbs. The limb itself may have acceptable alignment, but rotates outward due to muscle attachment variation. At first glance, these foals appear to have a valgus fetlock.

    4. Spiral - Spiral deformity involves the metacarpal in the majority of cases but can also involve the metatarsus. At first glance the spiral deformity resembles toed-in conformation. The author refers to this deformity as heeled-out, as the pure spiral does not have a varus fetlock.

    5. Flexor Anomalies - Flexor contraction and weak flexors are often found at birth.

How to Assess Foot Flight and Leg Alignment

Start by watching the foal walk straight away from you, preferably on a smooth surface. Walking the mare along a wall or fence offers a reasonable means of assessing the foal as he travels beside the mare. Focus on foot flight and the landing phase. Watch the hind feet land several times before focusing on the front feet as the foal moves away from you. Foot placement and full load stance appears to occur faster than the eye can detect, but with practice the landing phase can be observed in a slow motion mode. Closely observing the air space under the foot as it lands and loads acts to slow the action and brings out subtle details that might otherwise be overlooked.

Next, observe the foot flight and landing pattern of the front feet as the foal comes back toward you. Watch the lateral wall of each front foot land, then observe the medial wall. Note any differences between the two feet. Turn the foal and watch him go away from you once again. This time observe the hind limbs, one at a time, from the hip to the ground as the limb flexes and extends to full length. Placing an imaginary dot at each major joint creates a reliable means of evaluating the angulation. Once both hind limbs are observed focus on the front limbs, paying particular attention to the carpass and the heel of each front foot. The heeled-out foal (spiral deformity) and bowed knee (varus carpass) becomes readily detectable by the trained eye as the foal moves away from you.

As the foal walks back to you observe only the front limbs, one at a time, from the shoulder to the foot. Once again, place imaginary dots at each joint. Connect the imaginary lines between the dots as the limb flexes and extends, and as the foot lands. Foals that aren't broken to lead well are more difficult to observe, but with practice the eye can be trained to follow the dot system even at a trot.

Once the foal has been evaluated while moving, observe him standing as squarely as possible and in a relaxed position. Assign imaginary dots in the following 7 places:
  • 1st dot: Most proximal point on the forearm. A small swirl of hair is normally located at the top and center line of the radius.
  • 2nd dot: Center of the distal radius at the level of the physeal plate.
  • 3rd dot: Center of the most distal aspect of the carpass.
  • 4th dot: Center of the proximal cannon. Note this dot will be superimposed over dot 3 unless axial deformity (offset knees) is present.
  • 5th dot: Center of fetlock.
  • 6th dot: Center of coronary band.
  • 7th dot: Center of toe.

As the dots are observed, visualize an imaginary line between them and note any deviations of those lines. Next, imagine an imaginary laser or arrow centered on each dot, passing through it on the sagittal plane of the limb at that point. Observing these imaginary lines is a reliable, consistent method for identifying planes of deviation that can and often do occur between major joints. Using the dot system helps train the eye to look for minute details that may otherwise be missed in addition to greatly enhancing communication between those observing the foal.

Each type of deformity can be graded on a scale of 5:
    1. Noticeable to the trained eye.
    2. Noticeable to the experienced horseman.
    3. Noticeable to the inexperienced horseman.
    4. Noticeable to anyone.
    5. Off the scale - catastrophic class deformity.

Any given individual may have several types of deformities in any one limb. Developing this system and using it in a disciplined, methodical fashion offers a reliable means of assessing foot flight and leg alignment. Identifying the real problem is a vital step for an efficient treatment protocol.

Valgus Deformities

Treatment Options

    1. Stall Rest - Newborns with less than 15 degrees of deviation often respond in a favorable fashion with a few days of stall rest. Various degrees of valgus conformation appear to be a natural finding with most all species that have a long front limb relative to neck length.

    2. Medial Extensions - Those that fail to respond sufficiently with confinement can be improved by applying a medial extension to the foot of the affected limb. Several products can be found on today's market that offer quick, easy temporary medial extensions.

    3. Self Correction - Valgus deformity appears to be self-correcting, as the large majority of valgus foals will steadily improve until they reach full growth. Unfortunately, today's market for young performance stock and a lack of patience has changed the scope of raising young horses, routinely speeding up the corrective mechanics as a result. Low grade valgus deformities can be seen in mature, very successful race horses and may simply be a variation of normal.

    4. Surgical Correction - Periosteal elevation and physeal bridging are also means of surgically aiding correction with non-responsive or greater than 15 degree deviations.

    5. Therapeutic Trimming - Therapeutic trimming requires caution. Lowering the lateral side of the hoof in young foals in an effort to bring the toe to center can be detrimental, as it can cause permanent deformation of the fetlock joint and hoof capsule.


Varus Deformity

Varus deformation most often occurs at the fetlock. When it occurs at the carpass it is referred to as bowed knees. Thirty years ago valgus deformities far outnumbered varus deformities, but the opposite is true today. A correlation may exist between incidence and growth rate. Early muscle development and heavy body mass may play a role in the increased incidences found in most breeds today.

Treatment Options for Varus Fetlock

    1. Surgery - Periosteal elevation over the medial and distal MCIII physis can be an effective treatment when performed within the first three weeks of age. Caution: Surgery at one week of age can result in overcorrection. Overcorrection creates a valgus fetlock, which is an extremely rare deformity. The lateral anterior surface of this fetlock joint is proximal to the medial side. Thoroughbred foals that are born with linear long bone alignment are often referred to as straight-legged foals and may be perceived as normal. Unfortunately, in absence of the natural valgus stance, many will develop varus fetlocks within weeks. To prevent this unsightly and costly deformity, periosteal elevation is performed at 1 week of age. The results can offer cosmetic approval on sale yearlings as they appear acceptable when standing, but have a very strange foot flight pattern as the fetlock flexes in an abnormal plane. Further studies need to be conducted to fully evaluate how the valgus fetlock affects racing soundness.

    2. Therapeutic Shoeing - Applying a lateral extension with slight lift can be very effective. The developmental stage of the distal MCIII physis closes very early. Although physiologically closed in 90 days, the most effective window of response is during the first 30 days. Trying to correct varus fetlocks once the foal has reached 3-4 months of age is futile. Unlike a valgus carpass, which remains responsive for many months, the fetlocks mature very quickly. Therefore when observing a foal with a valgus carpass and varus fetlock, the initial focus should be on the fetlock. Once past the stage of responsiveness, focus on the carpass. Note that overzealous trimming (lowering the medial wall) does not appear to have the detrimental side effects found with overcorrective trimming in valgus foals.

    3. Therapeutic Trimming - Lowering the medial side of the foot can offer desirable results with low grade varus deformities. Deciding whether to lower the toe, heel or both is the decision of the farrier based on his experience with corrective trimming. Correction should be put on the untrimmed foot. Trimming the foot on a young foal, then applying correction can be detrimental to the development of the foot and often causes post trim lameness. Note that the varus foal will often have a medial sheared heel with a similar appearance to the valgus foal. More studies are needed to better understand the etiology of the sheared heel.


Axial Deformity

When the cannon bone (MCIII) is displaced lateral to the carpass the deformity is referred to as offset knees. This deformity is not desirable for speed horses and should be distinguished from the canted knee that is often described as offset. The canted knee sits squarely on the proximal cannon. Using the imaginary dot system, the dot at the center of the base of the carpass will be superimposed over the dot at the top of the cannon. The dot at the top of the carpass (center physis), however, will not be in a linear line with the lower dots (see diagram). This line down the radius will be perpendicular to the ground surface but medial to the peripheral lines along the cannon bone. Axial deformity is often referred to as offset, and therefore not considered undesirable. Use of the dot system will clearly distinguish it from the offset knee. Many top race horses have canted knees that apparently cause no threat to soundness. Therefore the deformity may simply be a variation of normal.

The dot at the top of the cannon will be lateral to the dot at the bottom of the carpass. When both offset and canted, the cumulative effect of the deformity is very noticeable and undesirable as it leads to unsoundness.

Treatment Options

No treatment exists at this time.

Spiral Deformity

Spiral deformities appear to toe in. In pure spirals the fetlock has normal alignment, therefore it is not a varus or toed-in deformity, and is best referred to as heeled-out. This deformity creates a twist or inward spiral involving the metacarpass (MCIII), which may be located from just below the carpass to the fetlock. Looking closely at the foot, you will find it is quite symmetrical relative to the degree of deformity, which indicates that the foot is loaded in a natural fashion. Varus and valgus defects will shift hoof mass medially or laterally depending on the area of excessive load, and will most often have a medial sheared heel.

Defining the Deformity

Holding the cannon bone in your hand and flexing the foot via a finger centered on the pastern can help distinguish a spiral from a varus fetlock. A center point between the bulbs of the heel will remain flexed in line with the pastern as the fetlock is flexed. The foot and pastern flex medial to the cannon bone when the fetlock is varus. Watching the spiral horse walking away clearly reveals the lateral heel. Normally the heel of the front foot cannot be easily observed as the foal walks straight away from you. Identifying the spiral at an early age is difficult, as the fetlock is a very smooth, round joint with no center point of reference. The finger test is a reliable means of distinguishing the young foal spiral from the varus fetlock.

Observing the arrows through the dots helps distinguish the spiral from the varus fetlock. An arrow through the center of the top of the cannon will be in a plane lateral to the plane of arrows through the center of the fetlock. The pure varus fetlock will produce arrows in the same plane.

Treatment Options

There is no known effective means of correcting the spiral in the long bone. A surgical osteotomy would be an effective treatment if the outcome outweighed the disadvantages. Failure to identify the spiral and trimming the foot as though it were a varus deformity will quickly create an imbalanced foot that becomes a permanent disfigurement and leads to unwarranted foot problems. Cosmetic shoeing can camouflage this deformity and is a common practice with sale yearlings. However, artificially moving the center of the toe more lateral improves the front conformation view, but does not alter the heeled out aspect of the deformity.

Rotational Deformity

Rotational deformities are often called toe-out as the toe deviates lateral to the mid line. With pure rotational deformities the limb alignment will fall within acceptable conformation standards but the entire limb, including the scapula, is attached to the thoracic cavity in a plane that deviates lateral to the sagittal plane of the animal. Due to the plane at which the limb is attached to the body, the lateral side of the foot is closer to the ground as the limb approaches the landing phase. The more severe the deformity, the longer the time frame from touch down of the lateral side of the foot to full stance phase as the medial side lands and loads. It is the medial side of the foot that incurs a large majority of load once the foot is fully loaded instead of the lateral that lands first, thus setting the stage for excessive internal trauma that often results in sheared medial heels, crushed digital cushion and quarter cracks involving the medial heel. Quarter cracks are rarely found involving the lateral quarter of breeds with a tendency to have some degree of rotational deformity. When present they are the result of direct trauma to the lateral side of the foot or coronary band and usually connected to an injury when found.

Standing off to one side of the foal's center line, look at the face of the knee, fetlock and toe and use the imaginary arrows passed through each dot. Pure rotational deformity exists when the arrows are on the same plane but lateral to the sagittal plane of the foal's spine. This system helps rule out the often misdiagnosed valgus fetlock, a very rare deformity that only occurs as the result of injury or periosteal elevation of the medial distal physis of MCIII at a very young age.

To convince others who have trouble seeing the deformity, sedate the foal, stand him up as squarely as possible and slowly pull the elbow away from the chest. Pulling the elbow away from the chest will align the limb along the saggital plane of the animal. This is an easy way to evaluate the degree of self-correction that can occur with the same amount of chest development.

Treatment Options

Correction is self-adjusting in most breeds other than the quarter horse. As the chest develops the increased thoracic mass pushes the elbows outward, rotating the limb toward the mid line. Colts develop their chest muscles at an earlier date than fillies, and often correct this deformity by 12-18 months of age. Discretion should occur with corrective trimming. Lowering the lateral wall to achieve flat or uniform landing should not be attempted with this deformity, as it grossly distorts the hoof capsule, adversely alters the physeal plates of the fetlock joint and has no influence on the developing chest and limb attachment.

Flexor Contraction

New born foals with deep digital flexor contraction involving only the last digit are the most common and fortunately the easiest to treat. These foals will be on their toes at birth. The palmar surface of the foot may form a 30 degree to 45 degree angle with the ground surface.

Treatment Options

    1. Tetraglycine given at a dose of 2-3 grams IV, preferably diluted in saline can be very effective with results evident within hours of administration. Two to 3 grams of tetraglycine can be repeated every other day if indicated. Very young foals seem to be more responsive to this treatment than older, more mature ones. Caution is due with tetraglycine. Adverse effects can cause sudden death while administering tetraglycine to foals. Despite very low risk, the client should be informed and consent to treat the foal prior to administering the drug.

    Time is of the essence to obtain best results. The stronger the foal becomes, the more difficult flexor contraction is to correct.

    2. Bandaging the lower limb with a firm combine cotton bandage from the carpus to the ground can produce favorable results for foals with mild flexor contractions.

    3. Passive extension stretching in conjunction with bandages is also very helpful with milder cases.

    4. Air splints have been advocated as a means to relax the flexor group.

    5. PVC Splints can offer favorable results with most flexor contractions.

      The author prefers to use custom molded, thin wall PVC down the posterior side of the limb as a means to quickly weaken the flexor group. The foal is sedated and bandaged from the elbow to the ground surface with firm-fitted combine cotton. Use an amount adequate to protect the sensitive skin.

      Cut a 36 inch piece of thin wall PVC pipe down each side. Fit one half of the pipe down the back of the limb, 2-3 inches below the elbow and an inch above the ground surface. Using a heat gun, warm the top until the PVC becomes soft. Wear gloves, as it will be very hot. Quickly trim the corners with a pair of scissors and fit the top of the half pipe to the back of the forearm. Hold in place until it has cooled. Heat the area of the pipe that will fit over the back of the carpass in the same fashion, allowing it to cool in place. This step is very important. The custom fit over the forearm and carpass prevents unwarranted pressure sores and tell-tale white hairs. Heat a small area at the fetlock and cut a small pie-shaped wedge out of each side. This allows the lower pieces to flex, fitting closer to the shape of the pastern.

      Vet wrap the pipe to the bandaged limb, then secure it with a roll of 4 inch Elasticon. Foals only a few hours old will normally respond quite favorably within 4-6 hours. One or two week old foals will require 12-24 hours in the splinting. Two to three days may be required for foals 2-3 weeks of age.

      Often, foals born contracted develop a mid to high grade club foot later in life. This bandaging technique can offer favorable results to club-footed foals of 3-4 months of age, as well as grade 3 club feet in weanlings. When treating club feet and older foals that may require a few days in the splint, it is best to apply a glue-on Dalric® raised heel shoe or a full rocker aluminum attached with Equilox® before splinting. The shoe will protect the toe - as foals will drag the toe while the splint is on - and releases tension on the DDF. Note: the author finds best results are achieved by leaving the splint on the leg long enough to create hyperextension of the carpass. Caution is due. Hand walk or restrict the foal to stall rest until the carpass is once again in its normal position. Do not turn foals out with hyper extension of the carpass.

      Often foals respond quite well with one treatment, but occasionally the robust, fast growing individuals will go upright and show mild signs of contraction as a result of sporadic growth spurts. Repeat the process as often as needed to control the affects of contraction.


    6. Toe extensor shoes have been advocated and used to stretch the DDF network. Caution is needed, as the hoof capsule, coffin bone and laminae are very immature and are easily damaged by excessive pressure. It is quite easy to permanently damage the apex of PIII, create a dished hoof, or in extreme cases, slough the entire capsule due to excessive tearing of the laminae.

Conclusion

Accurately assessing angular deformities requires keen observation. Using the imaginary dot system offers a reliable means of training the eye for the minute, characteristic differences that make each limb on each individual a unique study. This methodical approach also offers a means to become more familiar with the range of norm that is influenced by breed, age, use and environment. Many foals have multi-facet deformities, some being compatible with future soundness, others not. Undesirable characteristics need to be distinguished from potential soundness risk deformities, and when attempting to correct foals we must keep first and foremost in mind what is best for the future of the animal.