Arthritis and the Long Bone
ARTHRITIS AND THE LONG BONE
The true definition of arthritis is inflammation of the joint. We have discussed arthritis due to trauma of the joint. This week we would like to discuss the effect injuries have on the long bones, and to explain any discomfort they cause the horse.
We are frequently asked to evaluate knots on the long bones. These are usually on the cannon bones below the knee or hock. These bones are easily injured because there is little padding over them. They are also in close proximity to the feet, which can cause considerable damage when they make contact. Add a shoe to the foot and envision the results of that coming in contact with the hard bone!
When we examine a knot on the long bone, we feel to see if it is warmer than the surrounding bone:
If it is warmer, then there is still healing activity and we can expect some improvement from our treatment.If the bone is the same temperature, then the injury occurred some time ago and healing is complete; any attempts to treat it will produce little results.If there is heat, we check for any break in the skin over the bone. Frequently with bone injuries, a piece of bone will break free:
It stays in place, but with no blood supply the bone tissue starts deteriorating.This deterioration causes changes in the bone, and the body recognizes it as "foreign tissue."Consequently, the body’s white cells will accumulate around it, forming the inflammatory substance we know as 'pus.'As this 'pus' builds up, it looks for an escape by the path of least resistance, which is out through the soft overlying tissue.The 'pus' will drain until most of the volume is gone.The tissue will then heal over and it appears everything is OK.
At some point in the future, however, there will be another buildup, and the process will be repeated:
The piece of bone is still locked in place, but it does not reheal.As long as it is there, this periodic 'pus' buildup will occasionally reoccur, and the knot around it will continue to grow bigger.Most of this knot is scar tissue, but it will feel almost as hard as bone.X rays are the only way to evaluate the bone. It will show up well because, by now, its density has changed from the surrounding bone. Once it is located, we can surgically remove it and the surrounding tissue build-up. The wound usually heals nicely and without complications.
If there is no wound to the skin over the bony knot, we evaluate its location:
If the knot is located under a tendon, it may be the source of some discomfort. As the tendons move in response to the horse’s movement, the knot can feel like a large rock in our shoe.If this is the situation (and that would have to be confirmed while infiltrating the area with a local anaesthesia), the knot may have to be removed.While the removal can be accomplished, the after care is critical to prevent a regrowth.Once bone has been traumatized by injury or by surgery, the body immediately starts trying to heal it by pouring more bone tissue into the area. If this is not treated properly, there will be a larger knot after surgery than before!We must be certain that the knot is a real problem before we recommend removal.
If the knot is on the side of the cannon bone, it will not be under any tendons. Its location here is not causing any problem other than cosmetic. If the knot is warm to the touch, the healing process is still active. We treat it topically to help remove the heat and to slow the build-up of bone tissue. We also administer phenyalbutazone for the same reason. These treatments will help prevent the knots from growing any larger.
If the knots are treated quickly and aggressively, they will not grow to be unsightly. If you notice a small wound on the cannon bone, front of the knee, or any other bony area, it should be treated: both to prevent infection and to slow bony growth. While at first there is not usually a knot at the location, if untreated one may develop. Treated as we discussed above, the wound will heal and only a slightly roughened area will result.
This is a lot of time to spend on a knot, but they can be unsightly and are very common. They can be due to an impact from another horse, or just from doing something stupid (but of course this is rare in our horses!). Almost all those knots on the inside of the cannon bone are due to interference from the opposite foot. If there are multiple knots--or if the same knot is repeatedly injured--the shoes or shoeing should be evaluated. If the knots are treated quickly and aggressively, they will not result in large knots.
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