It could a fracture, a sprain, or even a break. It could an infection, and so many other things. A vet needs to actually see the horse, get better information and be able to do tests on your horse. Only then could the problem be correctly diagnosed.
The tendon on the ankle is called the Peroneal tendon.
Your ankle could be sprained. Achilles Tendonitis occurs when your tendon has become irritated and inflamed. This may happen for many reasons. If you have tendonitis the area of your Achilles tendon would be tender, be painful to move, and/or swollen.
Achiles Tendon
The most famous tendon is the ACHILLES, it is located at the back of your ankle.
The largest and thickest tendon in the human body is the Achilles tendon. This tendon is located at the back of the ankle and connects the calf muscle to the actual bone of the heel.
A sprained ankle is a tear in a ligament or tendon, not an injury to a bone.
My ankle just stopped swelling 2 days ago witch was 2 months after I sprained it! so it may be swollen for a while
Yes, in some cases, a walking boot will heal a split tendon in your ankle. A doctor will decide if the walking boot is suitable for the patient.
Sounds like an Achilles tendon injury.
That feeling is probably just excess fluid from a mild sprain. Press down the tissue of the swollen ankle with your finger, then do it to your other ankle. If the swollen ankle rebounds slower then the normal ankle, it's just a sprain. Elevate and ice it. If not, seek medical advice.
A hot bath
I am not a doctor, but one swollen ankle is often an injury. Two swollen ankles can mean congestive heart failure. It is serious and you should see your doctor as soon as possible.