Management of degenerative joint disease (Proceedings)

Degenerative joint disease (DJD), aka osteoarthritis (OA), is a diarthrodial joint's non-specific response to insults such as instability (e.g. CCL, patella luxation, hip dysplasia), incongruity (FCP, OCD, UAP), or trauma.

Pathophysiology of DJD

The best treatment for degenerative joint disease is prevention, by removing the inciting cause before DJD is established if at all possible (TPO, JPS, cruciate stabilization, patella stabilization, etc.) Irreversible changes of DJD (visible in the form or periarticular osteophytes) are present by 28 days after the cause is present. If eliminating DJD before it becomes established is not possible, then understanding the multi-tissue involvement of DJD is very helpful in explaining the problem (and why a pill won't cure it) to clients.

Synovitis is the first response to joint insult, and occurs within minutes to hours. This change is reversible if the inciting cause is no longer present. Joint taps will verify excessive joint fluid, as will radiographs for some joints, especially the stifle, if the fluid is excessive.

Cartilage fibrillation, erosion, and ulceration are the most irreversible components of DJD. Damaged cartilage has very poor healing potential, primarily due to its poor blood supply. Currently, medications and/or surgical techniques to reliably replace articular cartilage in situ are not available. Damaged cartilage is forever. With substantial cartilage loss the joint space is more narrow radiographically.

Osteophytes full name is periarticular osteophytes. Osteophytes begin histologically 3 days after joint instability is present, and are radiographically visibly by 28 days. Although they may not seem like it, osteophytes occur where the joint capsule inserts to bone, and are a response primarily to joint instability. Periarticular osteophytes have been speculated as the body's way to increase the joint size to increase stability; CCL tears typically have much greater response in osteophyte size and number early in the disease process than there is for cartilage erosion. Mineralization in a tendon or ligament is called an enthesiophyte, and is a response to excessive tension. Osteophytes are a symptom of DJD, not a cause; their surgical removal does not lessen the DJD and they typically return in a few weeks, especially if the inciting cause is not or cannot be corrected.

Periarticular fibrosis of fascia and enlargement of ligaments and tendons is also a response to DJD, especially if the cause is joint instability. Again, this appears to be the body's attempt to stabilize the joint.

Loss of cartilage, which among other things acts like a shock absorber, results in greater than normal forces being transferred to the subchondral bone. The subchondral bone, in response to these increased forces, thickens and becomes more mineralized which is radiographically seen as subchondral bone sclerosis.

Muscle atrophy is the remaining major tissue effected by DJD. Pain and dysfunction of the joint(s) cause the dog to use the leg less via inactivity, transferring weight bearing to other legs, or both. Decreased use of muscle results in loss of muscle, which for many joint pathologies also results in increased instability of the pathologic joint (e.g. hip dysplasia).

Conservative management of DJD

     1. Build muscle

     2. Correct any obesity or overweight

     3. Medications

Building muscle and correcting weight issues are of equal importance, and much more important than medications. This concept may be difficult for some clients to understand / accept. Wouldn't it be nice to just take a pill and the problem go away? An analogy I routinely use to educate clients (and students) is to have them imagine two people with exactly the same severity of degenerative arthritis in the same joint (hip, knee, whatever). Now picture one of those people is a slim, well muscles athlete; the other is a 400 lb couch potato. It does not take a medical degree to intuitively know which person is going to deal with the arthritis better.

Muscle building cannot be achieved with a pill. The only way to build muscle is to exercise. Exercise may seem counter-intuitive to some clients because exercise often exacerbates the lameness; however, that is the short view. Long term, not exercising produces the couch potato. If surgery is not in the dog's near future, then exercise over a course of 4-8 weeks is almost always indicated to improve the lameness proportional to the muscle generated. The frequency of exercise and the amount of exercise are paramount. No one (or dog) ever got in shape exercising just on the weekends. Although low impact exercise is better than high impact exercise (e.g. swimming vs. running), almost any exercise on a daily basis is better than holding out for low impact exercise that occurs a few days a week or less. If the owner realistically is not walking the dog daily (for whatever reason), I would prefer the higher impact exercise of chasing a ball daily that the owner will do daily, than walks or swimming on a less than daily basis. Similarly, length of exercise is more important than speed. Walking a mile a day is more beneficial than sprinting 100 yards a day. Walking multiple times a day is more beneficial than a single walk of a lesser distance.

Weight is not a "by the way" issue, and if not dealt with seriously by the veterinarian and client, medical therapy will not be successful. A greyhound running at full speed has been estimated to put 7X their body weight in force through their back legs. 7 x 100 lbs is 700 lbs force vs. 7 x 80 lbs is 560 lbs force; that is a significant difference. Having an arthritic joint support more weight than necessary is obviously harmful.

Managing weight is a matter of the number of calories taken in versus the number of calories burned. The number of calories taken in means all calories, from dog food, cat food or human food. The number of calories of many dog foods and treats can be found at www.petobesityprevention.com/category/food-and-calories/. Burning calories is the second issue. Exercise burns more calories. Do not assume normal metabolism in an overweight dog. Thyroid function test (especially free T4) and evaluation for Cushings disease should be performed in overweight dogs. Hypothyroidism can begin at any time of life, and is safely and economically treatable. If both thyroid test and Cushing's test are normal, then weight issues are most likely due to calories eaten versus exercise.

Medications are the least important (but most desired by clients) aspect of conservative management of DJD. NSAID's of the veterinarian's choice can be used. Because DJD (and therefore it's treatment) is for life, I recommend using NSAID's on a less than daily basis, e.g. 4 days a week, or every other day. NSAID's should not be used concurrently with corticosteriods due to the risk of colonic perforation. NSAID's do not grow cartilage, reduce bone sclerosis, etc. NSAID's decrease inflammation and the pain associated with inflammation, period. The purpose of NSAID's, in my opinion, is to make the dog less painful so they can exercise to build muscle.

Adequan is a medication I typically recommend for management of DJD. I use it a label dose on Monday, Wednesday and Friday for two weeks, then q 3-4 weeks thereafter. It should be used for at least two months before evaluating effectiveness. If a monthly dose is missed the loading dose needs to be repeated. Adequan rarely has side effects, and can be used concurrently with NSAID's or other medication.Periodic evaluation of a dog being conservatively managed for DJD is very beneficial. How the dog is doing clinically is more important than radiographic changes (especially for hips). Muscle atrophy and loss of joint range of motion (evaluated by cloth tape measure and goniometer and compared to prior recordings) are indications of failure of conservative therapy. Any orthopedic surgery has a better outcome if significant muscle atrophy is not present (the goal is to make the leg function, not just the joint). Likewise, excessive discomfort (primarily historical and subjective) indicate conservative therapy failure. If corticosteroids and or narcotics are required to reasonably manage pain, then surgery should be considered instead.