Angular limb deformities (ALDs) and flexural deformities (FDs) frequently affect foals’ legs. When severe, they are deemed clinically significant and require conservative management or veterinary intervention to achieve correction. [1]

ALDs are a deviation from the normal patterns of limb alignment, with lateral or medial angulations usually visible at the fetlock, carpal (knee) or tarsal (hock) level.

The causes of ALDs and FDs are multifactorial. Angular limb deformities may develop due to genetics, maternal diseases, premature birth, soft tissue trauma, or nutritional imbalances.

Several treatment options are available once a deformity is recognized, ranging from conservative management by controlled exercise and hoof trimming to more active management such as medical or surgical intervention.

Early detection and intervention are vital to improving the outcome for foals with ALDs and FDs. Mild deformities may be corrected with short-term exercise restriction, and the prognosis for affected horses is generally positive.

Angular Limb Deformities

Angular and flexural deformities in horses can be congenital or acquired.

They are generally classified as congenital when seen in the neonate (newborn foal), having been present from birth. Sometimes the term ‘perinatal’ is used. [2][3]

Acquired ALDs develop over time in response to a primary pathology, which may be developmental or trauma related  or due to an unrecognized congenital ALD affecting another joint. [1]

Flexural deformities are often congenital and identified under the misnomer contracted tendons. In the neonatal foal, it is usually observed bilaterally in the forelimbs and is characterized by the inability of the fetlock and carpal joints to straighten. If this remains unresolved, upright hooves may develop.

Types of ALD

ALDs can be categorized into valgus and varus deformities.

  • Valgus refers to a lateral or outward deviation of the bone below the joint
  • Varus refers to a medial or inward deviation of the bone below the joint. [1][4]

The following deviations are seen in foals:

Carpal valgus

This is a lateral deviation of the third metacarpal (cannon) bone below the knee (carpus), giving a knock-kneed appearance. It is often present in newborn foals, and mild to moderate cases may improve without intervention. [1][4][6]

Carpal varus
This is a medial deviation of the third metacarpal (cannon) bone below the knee, giving a bow legged appearance. It is often associated with lameness on the other forelimb, although it has been seen to develop in weanlings. [1][4][6]

Fetlock valgus
This is a lateral deviation of the phalanges (pastern bones) below the fetlock, giving a toe out appearance. It is common in newborn foals and can be managed conservatively.1,4-6

Fetlock varus

This is a medial deviation of the phalanges (pastern bones) below the fetlock, giving a toe in appearance. It is present in newborn foals and is often more serious than fetlock valgus. [1][4][6]

Tarsal valgus
This lateral deviation of the third metatarsal (cannon) bone below the hock gives a cow-hocked appearance in one or both hinds. [1][4][6]

‘Windswept’

Some foals are born windswept, with two limbs deviating in the same direction. This is a valgus in one leg and a varus in the contralateral limb (i.e. affecting both forelimbs and/or both hindlimbs). [1][2][4][5]

It is important to note that different types of ALD may be present at the same time. For example, it is common for a foal presenting a fetlock varus to have a carpal valgus above it. Carpal valgus is often accompanied by rotation at the distal physis of the radius, although the rotation is usually conformational. [1]

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