Angular limb deformities (ALDs) (or bent limbs) are relatively common conditions affecting new born and young foals.

When viewed straight on from in front or behind the legs deviate, at or around a joint, from a straight line down the leg (figure 1). The carpus (knee), hock and fetlock are the most commonly affected joints. More than one joint and more than one limb may be affected.

Most foals will be born with some degree of limb deviation, mostly due to ligament laxity and muscle weakness which will normally correct itself as the foal grows and exercises. Growth plates are areas found near each end of most bones, from which the bone grows and lengthens.

Uneven growth across these growth plates can also contribute to ALDs. This can be caused by trauma, excessive exercise, nutritional factors or weakness of the soft tissues around the joint. In premature foals, twins, or in cases where the mare has been ill, the small bones (cuboidal bones) in the carpus or hock may not form properly and can be crushed or mis-shapen resulting in ALD.

Examination of foal limb conformation should start early in life as a swift diagnosis and resultant decision making of management and treatment is essential. The response is significantly affected by both the presence of open growth plates and the phase of growth of the limb.

Affected limbs will show a deviation from an imaginary plumb line from the top of the limb to the bottom. Where the limb deviated from this vertical plumb line is the location of the abnormality. ALDs outward (laterally) are known as valgus; inward (medial) deviations are called varus. Additionally, affected limbs may show lameness, swelling and abnormal hoof wall wear.

X-rays may be useful to assess the exact location of the deviation and measure the degree of the deviation from normal. X-rays also allow evaluation of the condition of the bones of the affected area and the condition of the growth plates.

Treatment of ALDs varies from case to case. In less severely affected foals confinement may be all that is required. Careful corrective hoof trimming is vital in the treatment of ALD.

Over the last 20 years it has become recognised that if this is undertaken quickly and regularly (usually every 2-3 weeks) then some deformities get better with this treatment alone.

In some cases the application of glue on shoes with extensions also helps the leg straighten. Very occasionally in very young foals ALDs may benefit from bandaging the legs with splints or a cast. Shockwave therapy can be of benefit in older foals.

In cases which do not respond adequately to these conservative treatments and in those with severe ALDs, or in older foals with less growth potential of the bone, surgical treatments may be necessary. Various surgical approaches are available most work by slowing down bone growth (transphyseal screws or wires) or occasionally by speeding up growth on one side of the limb (periosteal stripping)

Each case is individual and the outcome varies based on which limbs and joints are affected, how severely they are affected, the age at onset of treatment, underlying conditions and the use of the horse.

The most important single element in treatment is early identification and assessment of abnormalities by your vet.