Equine tendons and ligaments
These deformities may be either congenital or acquired and are blamed on “tight tendons”. Contracture of the deep digital flexor tendon pulls on the coffin bone (club foot), while contracture of the superficial flexor tendon pulls on the fetlock (fetlock contracture). Joint capsules may also be tight, leading to all three forms. The pathogenesis of congenital forms is discussed in the next chapter. Acquired deformities are believed to occur secondary to fast growth and high nutrition plane. Most acquired forms occur in older foals and weanlings but can occur in 1-2 year olds. Fetlock contracture is most commonly seen as an acquired form and is the most common acquired form.
Club feet (contracture of deep digital flexor tendon; DIP joint flexion)
- The feet look like clubs because the heels grow toward the ground; this causes long heels and relatively short toes.
- DDFT (deep digital flexor) is the only tendon involved in most cases
Fetlock flexural deformity
- Either the SDF (superficial digital flexor) or both the SDF and DDF may be involved
- Likely tight joint capsule
*Many cases will also develop rupture of the common digital extensor tendon. This results in a nonpainful soft tissue swelling below the carpus. The rupture does not worsen the prognosis.
Medical therapy – congenital forms
Limb bandage or splint
These relax the tendons through the myotactic reflex. The firmer the bandage, the more relaxation achieved. The same response is seen when young animals require a cast. Casted limbs are very relaxed or noodly when the cast is removed. The effect decreases with age.
The heel should be rasped or trimmed to allow the heel to drop when the tendons relax.
The tetracycline drugs bind calcium and can relax the muscular part of the tendon. This therapy works in the very young and is typically combined with limb bandaging as the response is time limited. If left unbandaged, the limb will return to its contracted state when the drug wears off. Tetracycline causes relaxation only in very young animals, rapidly losing efficacy as animals age. Most will respond well at day 1-3 of age and minimally by 14 days of age.
Exercise and physical therapy may be enough to stretch structures in mildly affected foals. The exercise encourages normal function. Exercise should be controlled and not overdone. Painful animals will contract the limb, preventing the relaxation needed.
Foals have to walk on these limbs to improve the conformation; if uncomfortable, they won’t walk enough and further tendon contracture may occur due to the withdrawal reflex (aka hot stove reflex)
Medical therapy – acquired forms
Often these foals are on a high plane of nutrition for rapid growth. This results in a mismatch between tendon length and bone length. It is imperative to slow growth rate but without starvation. Starvation results in a compensatory growth spurt once food is reintroduced.
Pain may be a cause of contracture (withdrawal reflex). Check for hoof abscesses and fractures of P3 if the contracture is acquired. If you don’t eliminate the source of pain, no therapy will help
Oxytetracycline and bandaging are usually ineffective in this age group.
Cut the inferior (distal) check ligament to allow more stretch of the DDF tendon. This is not a tiny ligament (see image below). Cutting it makes a difference.
- Excellent prognosis if not >90 degrees joint flexion.
- This procedure does not impair performance and can be performed in any age horse to improve hoof-pastern angle
- Bandaging and hoof trimming are also required peri-operatively.
- If the contracture is >90 degrees of joint flexion, the deep flexor tendon must be cut. This is a salvage procedure.
- Iodine deficiency in the mare can lead to growth abnormalities in the foal. If the foal has contracted joints, check for an undershot jaw. Those foals have a much more guarded prognosis due to overall lack of response to treatment for the joint contracture.
Fetlock flexural deformity
- Cut the proximal and distal check ligaments
- Poorer prognosis than club feet but should gain some improvement, especially in young foals
- Older horses can have the surgery but get less release and have more scarring (unsightly)
- No good surgical options although cutting the ulnaris lateralis and flexor carpi ulnaris muscles has been used occasionally
Prognosis depends on which joint is flexed and how much contracture is present. In general, the more distal the contracture in older horses, the better the prognosis : foot >fetlock > carpus. However, if the foot is flexed so that the angle between P2 and P3 is > 90 degrees, these can be hard to fix.
Contracted tendons are generally more readily fixable in babies. After that it gets harder. Not all babies can be fixed.
Club feet are easier to treat than fetlock contracture. Treating carpal contracture in older animals is really hard. There is no good surgery for carpal contracture.
Oxytetracycline and bandaging have magical powers but just in babies.
Foals with contracted tendons and undershot jaws may have dams with iodine deficiency. These foals have a poor prognosis.
Fast growing weanlings and young horses can develop fetlock contracture.