Crooked Legs in Foals
Not all foals are born with straight legs.
By Dr. Susan M. Stover in The American Quarter Horse Journal | November 30, 2011
Crooked legs often worry a breeder or owner.
Many times, these irregularities end up being temporary and correct themselves, but sometimes, therapy must be taken early on to correct a more serious irregularity.
An angular limb deformity is defined as the condition where the bones of the forelimb are not aligned in a straight line, When the forelimbs are viewed from the front of the horse, a line dropped from the point of the shoulder should bisect the forearm (radius), knee (carpus), cannon bone (metacarpus), ankle (fetlock), pastern bones and hoof. If any of these bones are out of line, an angular limb deformity is present.
Deformities can be classified as congenital or acquired, depending on the foal’s age when the deformity is recognized. Congenital deformities are those present at birth. Acquired deformities develop after birth, in the first few weeks to several months of age. Because most angular deformities originate in the carpal (knee) area, this discussion will concentrate on angular deformities centered in the carpal region; however, similar principles apply to angular deformities in the fetlock region and in the hind limb.
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Normal Development of the Bones of the Forelimb
Since deformities are a result of abnormal bone growth and development, a knowledge of the normal growth and development will be useful in understanding the development of deformities. Growth in the carpal area occurs in three locations. First, the radius grows in length at the distal growth plate (physis). After the radius has grown to its adult size, the physis “closes” and no longer contributes to growth. However, rapid growth occurs up through 8 months of age. Second, the distal end of the radius enlarges at its margins. Third, the carpal bones enlarge in all directions during growth. Abnormalities in growth at any one or more of these locations can result in an angular limb deformity.
Causes of Angular Limb Deformities
Balanced and coordinated growth of bones in the limb is necessary for normal conformation. If growth within a bone is not balanced, the bone becomes abnormally shaped. The joint formed by this bone with adjacent bones then becomes abnormally angulated.
Several conditions that may result in angular limb deformities include:
- Laxity of collateral ligaments of the affected joint
- Imbalanced growth across the width of the distal radial growth plate
- Imbalanced growth of the distal radial epiphysis
- Abnormal development of the carpal bones
- Abnormal development of the splint bones
- Traumatic injury
A foal may have more than one abnormality in a limb.
Evaluation of Foals With Angular Limb Deformities
By identifying the cause of the deformity, the best method of treatment can be selected, and a prognosis for correction of deformity and future soundness can be established. Several factors helpful in diagnosing the cause of the deformity include:
- The history of the onset and the development of the deformity
- Physical appearance of the angulated limb
- The identification of radiographic abnormalities
Angular limb deformities caused by collateral ligament laxity and carpal bone or splint bone underdevelopment (hypoplasia) are often present at birth. Angular limb deformities that develop after birth are usually due to imbalanced growth of the physis or epiphysis.
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A physical examination can be helpful in determining the underlying cause of the abnormality. For example,flaring of the metaphyseal region may be associated with imbalanced physeal growth, and joint capsule distention may be associated with carpal bone abnormalities. Radiographs of the limb are evaluated for abnormalities:
- The degree of angulation of the limb
- The location of origin of the angulation
- The size and shape of the bones
Important points to remember regarding angular limb deformities:
- Many foals are born with mild angular limb deformities and, in most foals, the deformities begin to correct spontaneously within days.
- Most foals with acquired angular limb deformities respond to regulation of exercise and corrective hoof trimming when the condition is recognized and treated early in its development.
- Premature and twin foals with angular limb deformities should have their affected limbs radiographed for the detection of carpal and/or splint bone underdevelopment or damage.
- Any foal that has a worsening angular limb deformity, despite regulation of exercise and corrective hoof trimming, should be evaluated for radiographic abnormalities.