In order to determine where your horse is lame, and what is causing it, a systematic approach must be taken. Anything short of this is guesswork.
We will palpate the structures of your horse's legs such as the joints and tendons to see if there is any heat or swelling. Sometimes your horse will resent pressure being applied to the soft tissue and this can give us information about where the pain is coming from. But, many times there is nothing abnormal to be found on the physical exam.
Next we will see how your horse moves either on a lunge line, in a round pen, or simply trotting in hand. This will help us determine which leg is hurting, and if the pain can be exacerbated when traveling in one direction vs. the other.
Flexion testing is another way to try to discern where your horse is hurting. We will pick up your horse's leg and hold it in a bent position for about a minute. When you trot the horse off sometimes the horse's lameness will be temporarily worse after the flexion test. This gives us further information regarding the location of the lameness.
The next step of the process is performing diagnostic nerve blocks. The idea behind this is simple- if we take away the pain your lame horse will go sound. A small amount of a numbing agent similar to novocaine is injected into the leg at very specific locations. If the pain goes away, and your horse goes sound, then the location that is numb is usually where the pain is coming from.
This is a time consuming process. In order to be certain where the pain is coming from we typically need to start with the foot and then carefully work up the leg. Each nerve block will take several minutes to take effect. Then the horse is checked to see if the lameness is still there. If it is, we move a little further up the leg and block the nerves there. We repeat this process until the horse goes sound. Once he goes sound we can get a good idea what structures are causing the pain based on where we injected the numbing agent. Sometimes we can skip right to a region where we suspect the pain is coming from based on the physical exam, or flexion tests.
Once we determine a region where the lameness is coming from, then we usually need more information to form a diagnosis. If the soft tissue structures such as tendons or ligaments are suspected, then we will use an ultrasound machine to look for the problem. If we suspect the problem is with a bone we will take digital x-rays to look for arthritis, bone chips, or other abnormalities.
Once we have a diagnosis we will come up with a treatment plan that is appropriate for your horse, and your budget.