Monday, Feb 8 2010 - Winding up the Hock

Vet Tip of the Day: Oral Joint Supplements
Key words: chondroprotectant, synovial fluid, cartilage, joint capsule

Osteoarthritis is only one of many conditions that affect the hock; in the future we will come back and discuss other disease processes that affect tarsal joints.  But to conclude this introduction to hock anatomy and bone spavin, the most common cause of hock lameness, there will be two final Vet Tips of the Day: today we will look at oral joint supplements, how they work, and IF they work.  Tomorrow we will consider injectables.

It is important to distinguish between oral and injectable agents administered as chondroprotectants.  "Chondro" refers to cartilage, "protectant" is self-explanatory.  Chondroprotectant joint supplements are substances which claim to enhance the health of joints by improving the the quality of joint fluid and joint cartilage.  Cartilage is the spongey substance which lines the surface of bones within joints.  The cartilage is bathed in synovial fluid, or joint fluid, which is contained within the joint space by the joint capsule.  The joint capsule is lined by synovium, the site of joint fluid production.  In the simplest terms, the joint fluid and cartilage act as shock absorbers to diminish the force transmitted to bones when joints are compressed by weight bearing.

You've almost certainly heard of glucosamine and chondroitin.  These are two of the most common ingredients in oral chondroprotective joint supplements.  These substances are two of the primary building blocks the body uses in the construction of cartilage.  Theoretically, by increasing the amount and quality of glucosamine and chondroitin in the diet, the body is better able to produce and maintain healthy cartilage.  There are three major problems with this theory.  First, there are many structural varieties of glucosamine and chondroitin, and their absorption across the gut wall is widely variable.  Second, and perhaps more importantly, there are few government regulations regarding the manufacture of oral joint supplements, which are considered "neutraceuticals".  Therefore, the amount and quality of ingredients listed on the label vary widely from product to product, and there is not even any guarantee that the label claims of a given product are true.  Therefore, when buying an oral joint supplement, you are completely at the mercy of the manufacturer's ethics regarding the actual contents of the product.

Finally, the third problem is, assuming the product you buy is excellent quality and your horse absorbs the ingredients, there is very limited research availabe indicating what an appropriate dosage is for a given combination of chondroprotective ingredients.  In addition to glucosamine and chondroitin, additional additives found in many joint supplements include cetyl myristoleate (an anti-inflammatory) , hyaluronic acid (a major components of joint fluid), as well as various herbal extracts such as devil's claw, boswellia and avocado extract, just to name a few.

Before you throw in the towel, be comforted in knowing that, while limited, there are a few well designed clinical studies indicating that the oral administration of chondroprotective agents can improve lameness in horses with chronic osteoarthritis.  The bottom line is, at this time there is more unknown than known about these products, so if you choose to give one to your horse, buy a recognized brand manufactured by a company with a longstanding reputation.  Be sure the product is clearly labelled with respect to ingredients, amounts of ingredients, and recommended dosage.  It should be easy to calculate the actual amount of each ingredient you will be giving your horse by reading the label.  The product should have a lot number and expiration date easily identifiable, and there should be clearly printed information telling you how to contact the manufacturer.  Finally, if the product claims to cure everything from laminitis to navicular disease to hock pain in 30 days, don't buy it.  Remember, you get what you pay for, and if it sounds too good to be true, it probably is.

Fri & Sat Feb 4,5. More on the hock

Vet tip of Two Days!
Key words: osteoarthritis, hock,chondoprotective, joint therapy, glucosamine, chondroitin

My apologies for this late vet tip. It's actually Sunday morning, but it is snowing again and I've get an hour before I go out to do a couple of calls this morning. One of them is to inject the carpus of an older rope horse with chronic osteoarthritis. Do you remember how many joints there are in the carpus and which joint on your body is similar anatomically to this equine joint? (for review see last Wednesday's blog).

Osteoarthritis of the lower hock joints (bone spavin) is the most common cause of chronic lameness that I see in my practice, with forelimb heel pain a close second. Bone spavin occurs in every type of athletic horse, and unfortunately it is not uncommon to see horses develop sore hocks at a relatively early age. The 3 or 4 year old cutting horse is the extreme example, but jumpers, dressage horses, foxhunters, endurance horses, and other western sport horses may have degenerative changes in their hocks before 10 years of age.

Why are these joints predisposed to arthritis more than other joints of the body? Probably because of their unique position of high stress and low motion. Watch your horse's hocks closely as he trots on the longe line. Most of the flexion that occurs is due to motion of the large tibiotarsal joint, which has a large joint space and round, ball bearing like sliding surface where the tibia sits on the knuckle shaped talus. This joint is an uncommon site for osteoarthritis secondary to athletic activity.

Now look at the radiograph from Thursday's blog (the normal hock), then look at this radiograph which demonstrates osteoarthritis in the distal intertarsal and tarsometarsal joints. These are the joints at the bottom of the hock that are complex and relatively rigid in construction. The joint space is the thin black line between the rows of tarsal bones. Imagine the force that flows through these joints when your jumper throws his thousand plus pound body into the air to clear an obstacle or your barrel horse digs in to accelerate out of the turn around the last barrel or your dressage horse sucks it up to sit back on his hocks and put that tremendous effort into a canter pirouette. There isn't much room for error in these joints, because there is very little room for movement, so over time, the stress of high force through tightly packed bone results in chronic inflammation.

Joint fluid lubricates and cushions the cartilage that lines bone surfaces. The inflammatory process causes this fluid to becomes thin and less able to absorb repeated impact. The cartilage, in turn, looses its flexibility and ultimately the bone is left to take up too much of the load of activity. It's response is to say "Hey, I'm working too hard, maybe if there is more of me this job will be easier." Unfortunately, the production of extra bone simply destroys the smooth architecture of the carefully constructed joint anatomy with the end result: pain.

That's how the process starts, now how do we treat it?

Many of the key words for this vet tip are related to the huge topic of joint therapies. Tomorrow's vet tip will be devoted to the subject of oral and intra-articular therapies, and trying to separate fact from fiction. To close today's entry, here is the bottom line: there is sound, repeatable scientific evidence that certain oral and injectable chondroprotective agents can help to alleviate the inflammation, and therefore the pain, associated with osteoarthritis of the hock. The efficacy of these products is variable, and the products themselves are variable. We will look at them in more detail tomorrow.

I hope you are enjoying these vet tips - we are in the process of updating the practice website - the blog name is probably going to change (high brow internet search engine stuff that is GREEK TO ME). I promise to keep everyone up to date as the High Desert Veterinarian continues to explore cyberspace in order to share the knowledge and wonderful life of a practicing veterinarian with you all.