Definitions

• Lateral or medial deviation to the long axis of the bone in the frontal plane

• Valgus: lateral deviation distal to the point of angulation (pivot point)

• Rotational deformity usually accompanies ALD

o Outward or inward rotation

Risk factors

• Age: foals of all ages, usually young foals

• Breed: occurs in all breeds and particularly rapidly growing foals

• Sex: occurs in both sexes, slightly higher incidence in colts

• Limb: most often in front limbs, unilateral or bilateral

• Site: affects carpus, fetlock, and tarsus

• Frequency: carpal valgus is most common fetlock varus is second most common.

Multifactorial and complex pathogenesis

• Asynchronous longitudinal growth of physis

• Ligamentous joint laxity

• Defects in endochondral ossification of the cuboidal bones and/or small metacarpal/metatarsal bones

• Traumatic luxation or fracture of the physis, epiphysis, or carpal/tarsal bones

Alterations of endochondral ossification

• Rapid growth

• Genetic capacity

• High energy intake

• Stunting early in life followed by increase feeding leading to growth spurt

• Trauma to endochondral ossification centers

• Axial compression beyond physiologic limits

• Physeal fracture luxation/infection

• Genetic predisposition

• Nutritional imbalance

o Excess energy

o Protein (excess or deficiency)

o Calcium:phosphorus ratio (excess or deficiency of ratio:1.6)

• Trace minerals

o copper deficiency

o zinc excess

o manganese deficiency

Congenital angular limb deformities

• Intrauterine malpositioning

• Over-nutrition of mare

• Joint laxity

• Incomplete ossification of cuboidal bones

• Premature/dysmature

• Hypothyroidism

• Osteochondrosis

• Incomplete development of MT/MC II and IV

Acquired angular limb deformities

• Excessive exercise

• Growth plate injury or infection

• Excessive weight bearing secondary to contralateral limb lameness

• Over-nutrition

• Improper trimming or poor foot care

• Poor conformation

• Congenital ALD that become worse

Diagnosis

• Visual exam

o Standing and walking

o Is it rotational or angular limb deformity?

• Rotational