Flexor tendons play a significant role in equine locomotion by supporting the limb and providing an important store of energy. Considering the large forces (500kg horse) applied to these structures when a horse gallops, it is not surprising that they occasionally fail. There are many factors that contribute to a tendon injury, including conformation, weight, hoof balance, shoeing, track conditions, competing distance and training regime. Initial signs of tendon injury include heat, swelling and pain of the flexor tendons (which run down the back of the cannon bone). Injuries to the superficial or deep digital flexor tendons can occur anywhere from the top of cannon to the pastern region. You may see a subtle or obvious change in shape, resulting in the classical ‘bowed tendon’.
Early diagnosis of tendon injuries is essential as working a horse once it has an existing tendon problem can result in career ending or possibly catastrophic tendon damage. It is important to remember that horses with tendon injuries often show little signs of lameness, even with extensive damage. In cases of acute tendon injury you should apply ice to the tendons and a lower limb pressure wrap or stable bandage. Contact your vet as soon as possible so that the extent of damage can be assessed and appropriate treatment implemented. Examination will include an ultrasound scan of the tendons. It is often best to wait a few days before performing the scan so that the full extent of the injury can be seen. During this time icing, pressure wraps and anti-inflammatories (phenylbutazone and corticosteroids) are recommended.
The above ultrasound image shows a severely enlarged SDFT (right) compared with the unaffected (left) leg. Below is the same tendon with the core lesion outlined.
Healing of tendon injuries is slow, with the defect being replaced by scar tissue rather than being replaced by elastic tissue which makes up a normal tendon. A prolonged period of rest (usually between 6 and 12 months depending on the severity of the injury) is essential. An initial period of stall confinement should be followed by a progressive exercise rehabilitation program to optimize healing. Additional treatment options include injecting stem cells or platelet rich plasma (collected from a spun down sample of the horses blood) directly into the damaged part of the tendon. These treatments are best performed in the first month after injury. Although they do not shorten the rest period required, they have produced encouraging results with respect to the quality of tendon healing.