Flexural limb deformities

The most commonly seen flexural deformities are contracted tendons and joint hyperextension. There are a number of causes, but in all cases, prompt treatment is required for the best possible outcome and future soundness of the horse.

A horse is said to have ‘contracted tendons’ when it is unable to fully extend its limb to the normal position. This is a painful and debilitating condition where the tendons grow at a slower rate to the bones leading to tendons that are functionally shorter than the bones of the affected limb.
Tendons are fused to different joints on the limbs; therefore several joints can be affected at a time. Joints that can be affected include the coffin, fetlock, knee and hock, although this is rare. The forelimbs are most commonly affected.
Hyperextension of the joints is also seen, where the limb or part of limb extends beyond its normal limits due to laxity of the tendons involved. Joints commonly involved include the fetlock and hock.
These conditions can be ‘congenital’, so are commonly seen in foals, but they can also develop later on in life, when they are referred to as ‘acquired’.

Horses affected with contracted tendons will be unable to bear full weight on the affected limb and walk on their toes, with their legs curled up underneath them. Other signs include knuckling over at the fetlock, wearing down of the toe of the hooves, and bruising of the toe.
When the coffin joint is affected the heel does not touch the ground, causing pain in the toe and tension in the deep digital flexor tendon which runs down the back of the cannon bone. Contracted tendons in the fetlock and knee is evident by the buckling of the joints forwards.
Hyperextension of the fetlock joints is commonly seen. In these cases the horse is seen to walk on the back part of the hoof and will tend to rock onto the bulbs of the heels which means the toes do not touch the ground. This causes abnormal foot wear and in severe cases soft tissue damage to the back of the fetlock caused by contact with the ground.

When foals are presented with flexural deformity at birth, the condition is referred to as ‘congenital’ and most likely a genetic problem in the foal’s bloodlines.
‘Acquired’ flexural deformity can be caused by poor positioning within the mare’s womb where the foal is too big relative to the mare’s size, teratogens (drugs or substances that interfere with normal foetal development) such as locoweed and Sudan grass, influenza infection, and goitrogenic diets (substances that suppress normal thyroid gland function) in pregnant mares.
Rapid body growth is also a very common cause of flexural deformity, as bones and tendons grow at different rates causing the flexural deformity.

If you suspect your horse has a flexural deformity, your vet can use radiography on the affected limb which will show a detailed picture of the exact nature of the deformity.
X-rays will determine if the deformity can be treated, and the best treatment method for the deformity involved.

Yes, flexural deformities can be treated, but not necessarily cured. The longer a deformity is left to develop, the harder it becomes to treat effectively, therefore it is essential that early treatment is employed to ensure the best possible outcome. Depending on the severity of the deformity, different approaches might be taken.
In early cases treatments may just consist of conservative management, including:

  • Change in diet – to prevent further accelerated growth
  • Decreased exercise – to prevent repetitive trauma to the hoof
  • Anti-inflammatories – to reduce pain and swelling
  • Bandaging

In severe or late onset flexural deformities, the following treatments may be necessary:

  • Remedial farriery – for example the use of extended heel shoes to prevent overextension of the fetlock, or extending toe shoes to increase weight bearing on sole and ‘stretch’ affected tendon
  • Surgery – to make the horse more comfortable, rather than resolve the deformity
  • Casting, splints and brace – to encourage the animal to stand in a more normal position

In contracted tendon cases, surgery can only be used to make your horse more comfortable, rather than to cure the deformity. In less severe cases, it may be possible for the hoof to be trimmed to a healthy shape to promote healing, or the ligament may need to be cut to release the tendon. In more extreme cases where a joint has been severely affected, more extensive surgical methods may be necessary. A special shoe may be applied to your horse’s hoof which is usually done to elevate the back of the hoof to remove the pressure on the toe, so that the horse can stand in a more normal position.
Hyperextension in normally only seen in young foals and correction usually occurs naturally during the first few weeks of life as muscles and tendons strengthen (during this period a small bandage may be needed to protect the soft tissues of the back of the fetlock from coming into contact with the ground). If this doesn’t happen then it can usually be treated with restricted exercise, conservative management and remedial farriery. Even in more severe cases temporary heel extensions usually resolve the problem. The use of intravenous antibiotics (oxytetracycline) has also been used to treat flexural deformities in foals.

This very much depends on the severity of the deformity and the joints involved, but on the whole, horses with mild deformities that are diagnosed early and managed properly have a fairly good prognosis.
For severe deformities that require more complicated surgery, the outcome is not normally as positive.
In cases of hyperextension the prognosis is usually very good.