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
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.
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.
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 d