Many foals are born with angular limb deformities (ALDs), which should be treated early to prevent permanent soundness and athleticism complications. Our Leatherstocking Veterinary Services team knows that a crooked-legged foal can be concerning, and we provide information about ALDs in case you have an affected foal.

What is an angular limb deformity in foals?

An ALD refers to conformational deviation of a limb best seen when viewed from the front or back. Terms used to describe these deviations include:

  • Valgus — A valgus ALD occurs when the limb deviates laterally, or away from the body’s midline. 
  • Varus — A varus ALD occurs when the limb deviates medially, or toward the body’s midline. 

ALDs can affect the carpus (i.e., knee), tarsus (i.e., hock), and metacarpophalangeal (i.e., fetlock) joints. The most common ALDs affecting foals include carpus valgus and fetlock varus.

What causes angular limb deformities in foals?

ALDs can be congenital or acquired after birth. Specific causes include:

  • Congenital — When a foal is born with an ALD, causes include:
    • Improper positioning in utero — Malpositioned fetal limbs may lead to uneven long bone growth, defective bone development, and ligament laxity around joints, leading to an ALD.
    • Overweight pregnant mare — If the mare carries excess weight during pregnancy, the increased abdominal pressure may inhibit normal fetal movement, causing improper fetal limb positioning and an ALD.
    • Skeletal immaturity — The carpal and tarsal bones ossify during the last two to three months of gestation, and these bones may not ossify normally if the foal is born prematurely. 
    • Hypothyroidism — The fetus of a mare who is fed a diet containing nitrates or low in iodine can develop hypothyroidism, which causes delayed carpal and tarsal bone ossification.
  • Acquired — When a foal acquires an ALD after birth, causes include:
    • Excessive exercise — Excessive overloading during exercise can damage the foal’s growth plates, resulting in an ALD.
    • Poor conformation — Poor conformation can cause uneven weight distribution across joints and growth plates, potentially leading to an ALD.
    • Overnutrition — Improper nutrition can lead to uneven bone growth and ossification, and result in an ALD.
    • Growth-plate injury — Growth-plate injuries caused by trauma or infection can lead to an ALD.

How are angular limb deformities diagnosed in foals?

ALDs are typically easy to detect by standing at the front of the foal and observing their limbs. Foals should be examined for an ALD early in life, so treatment can be instigated if they are affected. Other diagnostics include:

  • History — Our veterinary team will ask you to provide a thorough history about the foal and mare, including their diet and any birthing complications.
  • Palpation and flexion — We will palpate and flex your foal’s limbs, checking for swelling, heat, and excessive ligament laxity.
  • X-rays — X-rays are necessary to determine the location and degree of deviation, condition of bones in the affected joint, and growth plate appearance.

How are angular limb deformities treated in foals?

ALDs can be treated conservatively or surgically, depending on the foal’s condition. Options include:

  • Conservative treatment — For mild ALDs, conservative treatment may correct the issue. This involves:
    • Controlled exercise — Strict stall confinement can inhibit normal muscular development, but unlimited exercise can exacerbate the deformity. The mare and foal should be confined to a small paddock or a large stall and given periodic access to a small paddock to ensure the foal gets some exercise, but does not overexercise.
    • Splints or casts — In some cases, splints or casts are needed for two to four weeks to keep the limb straight and allow the tissues around the joint to tighten. 
    • Corrective hoof trimming — Frequent hoof trimming is important for ALD management. For valgus cases, the outside hoof wall should be trimmed slightly shorter, and for varus cases, the inside hoof wall should be trimmed slightly shorter. Glue-on shoes or extensions can also be used.
  • Surgical treatment Surgical treatment is recommended for foals affected by severe deviation, those who don’t respond to conservative management, and for older foals whose affected bone has completed the rapid growth phase. Options include:
    • Periosteal stripping — The bony covering over the growth plate is cut and lifted to accelerate growth on the shorter side of the affected joint.
    • Transphyseal bridging — Screws and wires are placed on the longer side of the affected joint to slow growth.
    • Corrective osteotomy — If the growth plate has closed, a wedge of bone can be removed, and the remaining bone stabilized using bone plates and screws.

What is the prognosis for foals affected by angular limb deformities?

Approximately 50% to 80% of foals affected by an ALD perform at their intended level. Forelimb deformities typically have better outcomes than hindlimbs, especially when the hock is involved, and foals treated before 2 months of age usually have a better prognosis.

Early detection and intervention is key if your foal is affected by an ALD. Contact our Leatherstocking Veterinary Services team to evaluate your new foal, so we can ensure crooked limbs won’t inhibit their athletic ability.