How and Why?
Horses are prone to tendon/ligament injuries, especially when being worked hard. Their legs were not designed to cope with the stresses of everyday hard work. In nature the horse spends most of its time grazing which does little to the tendons/ligaments of the legs. This is why it is very important to ensure the horse is strong enough to do the required work. The horse has to be warmed up properly before staring the work. Working sessions should be started slow and then built up over a period of time so that the muscles, tendons and ligaments can become strong enough to cope.
Tendons/ligament injuries result from severe strain or direct trauma. Other factors can contribute to a tendon/ligament injury: muscle fatigue, uneven/deep ground, poor conformation, ill-fitting bandages/boots and sudden turns.
Different types of injury
Overuse or overstress causes damage to the tendons. Damage will range from minor inflammation to the actual tearing on the tendon. The area will be painful and swollen.
This injury is better known as a bowed tendon. It refers to strains of the SDF tendon. It often occurs when the muscles becomes fatigued and can't compensate for the rapid loading and overstretching of the tendon. This type of injury is not as common in the hindlegs as it is in the frontlegs. The leg will be swollen, warm and painful. The injury is usually described by its location and will either be a low, middle or high bow. Injury to the DDF tendon will cause swelling in the back and below the fetlock joint, and is referred to as a low low bow.
Tendons are surrounded by a sheath, the synovial membrane, that secretes fluid to lubricate the tendon. Inflammation of this sheath causes a build up of fluid in the sheath, resulting in obvious swelling. There are several types of tenosynovitis:
1.Acute Tenosynovitis- there is a sudden build up of fluid within the sheath. It is followed by pain, heat and lameness. This can progress to chronic tenosynovitis.
2.Septic Tenosynovitis- this involves a bacterial infection. The synovial fluid (lubricating fluid) will contain pus and inflammatory enzymes which can digest the tendon. Pain and lameness are severe.
3.Idiopathic Tenosynovitis- these are mild injuries that result in swelling with no pain or lameness. This includes thoroughpin, bog spavin and wind puffs.
This can be caused by a deep cut to the leg or overextension/overflexion of a fatigued joint during work.
How the injury heals
When the tendon/ligament is injured the tendon fibers and blood vessels tear. The process worsens when blood and fluid leaks into the tendon.
Inflammatory cells migrate to the damaged area. The inflammatory cells secrete enzymes that will break down the damaged tissue so that the body can remove it. Inflammation is a very important part of the healing process, but if it goes unchecked, it can cause damage to the good tendon tissue too.
One to six months after injury new blood vessels and immature tissue are formed. The immature tendon tissue aren't as strong as the old ones. These fibers are made of a weaker collagen called Type III collagen. This type of collagen is less mature, weaker and arranged haphazardly (instead of parallel).
Six months (and onwards) after injury the Type III collagen is slowly replaced by stronger Type I collagen, but not completely. The fibers are slowly rearranged in a more parallel fashion. The fibers has to be strengthened with controlled exercise. Controlled exercise will also help reduce scar tissue. However, the tendon will never be as strong as it was before.
The entire healing process takes anything from 9 to 12 months. Additional healing may occur years after.