Elbow Disorders in the Mastiff and Other Breeds

Fred Lanting is the author of "Canine Hip Dysplasia" and the soon-to-be published "Canine Or- thopedic Problems." The following is Part I of a three part article on elbow dysplasia written for The Mastiff Reporter.

A number of questions were posed in the commission for an article on elbow dysplasia, and still this article will only dent the surface of the subject. For a full treatment of orthopedic disorders of the elbow and other joints in the dog, please contact Alpine Publishing, 225 S. Madison, Loveland CO 80537 (303-667-2017) and urge them to move up publishing date of "Canine Orthopedic Problems" by Fred Lanting. One of the questions asked was "Is it a problem in our breed?" which indicates the need for breeder/fancier education on the subject, for "elbow dysplasia" is not a single disorder but a catch-all term for several abnormalities, with many separate genetic causes and overlapping environmental (nutritional) influences. One type of lesion may be more prevalent in certain breed types, a different disorder in another group of similar breeds, though nearly all breeds are at greater or lesser risk for almost any of them. In some breeds the incidence is of frightening magnitude. One in every 300 dogs seen at more than a dozen veterinary colleges in the USA from 1967 to 1979 had one of the elbow problems collectively and popularly known as elbow dysplasias. Depending partly upon breed susceptibility, these malformations may affect the anconeal or the coronoid portion of the olecranon or the humeral condyle, (the humerus is the upper arm, and its lower knobs are called condyles) with secondary effects on ligaments and synovium (lubricating fluid and membrane). There may also be OCD (osteochondritis dissecans, a loose piece of cartilage or bone irritating the joint), congenital dislocation, or subluxation (joint looseness) brought on by premature growth plate closure (either in the ulna or the radius). Already you can see that a thorough study and background is too large for magazine articles!

The radius of the lower arm supports most of the dog's weight (75-80% of the bearing surface of the joint) while the ulna and its "processes" (the preferred term for the protruding bumps between which the condyle of the upper arm works in a hinge-like action) stabilizes and constrains the movement of the elbow's parts. The annular ligament (annular means ring-like) holds the head of the radius close to the ulna and the rest of the joint. Other ligaments also help maintain stability by means of their position and tautness in the joint. When the dog extends its elbow (straightens its arm), the anconeal process is inserted into the fossa, the deep depression above and between the back part of the humeral condyles, so that the hinge cannot fold sideways in the normal dog. When the arm is flexed (elbow is bent), the coronoid process rides into the groove at the bottom and between the condyles, also ensuring the normal stability of that hinge. Since before birth, the development of these parts is by endochondral ossification (bone replacing cartilage preferrably at a normal rate and manner). "Secondary" (other than the main part) bone or ossification centers are seen by about 10 weeks in most breeds, a little sooner in toys and slightly later in giant breeds. Although there are several of these centers, we'll discuss the ones of major interest here. Ossification of the anconeal process (the upper, beak-like protrusion in front of the olecranon) gradually proceeds until, somewhere in the 16-24 week timeframe, the center not only turns completely to bone, but also fuses with the ulna. The result is a stronger joint with more stability and weight- bearing ability than cartilage could offer. With the normal anconeal process in place (riding or inserting into the notch between the condyles of the humerus), there is stability in motion. Without it, there is a side-to-side action, with the olecranon (topmost point of elbow) rolling around in what is referred to as an "out at the elbows" gait.

Primary and secondary ossification centers in the elbow grow toward each other and eventually fuse. That is, if all goes according to plan. If adverse genetic and environmental factors work together, results could include one of a few elbow dysplasias. For example, dogs fed high-calcium, high-calorie diets can have a delayed development of these centers with concurrent lag or retention of cartilage in the growth plates between centers. At 16 weeks of age, the anconeal process of dogs on higher calcium rations is seen with X-rays as a partially ossified separate center, but in dogs on low-calcium food, it is typically fully ossified. It is about this age that this center begins to fuse with the olecranon, that top part of the ulna often referred to as the "point of the elbow." If it remains ununited, the dog has UAP (ununited anconeal process), and at some point around this age it will be too late for it to "heal" by itself, and the piece should be removed.

The growth rates of the two bones (radius and ulna) in the lower foreleg are not the same nor are they individually constant during maturation of the dog. Growth studies on young dogs of a variety of mostly mid-size and large breeds gave much information. Ossification of these bones occurred after about 16 weeks of age, but in the meantime, the bones not only grow at different and differing rates, but the ends of each bone change in growth rates, too. It may be that osteochondrosis-type defects in the growth plates cause disruptions in the lengthening of one of these two bones, which makes it too long or too short compared to its companion, and in turn puts uneven stresses on parts of the joint.

Gross differences in growth rates between ulna and radius can put great pressure on anconeal and coronoid "bumps," leading to UAP and FCP (fragmented coronoid process). In many dogs the lower forelimb is bowed as a result of those differences. If lameness does not develop, there may still be very variable amounts of ulnar growth retardation; many fiddle- fronted dogs are seen in the show rings, including Toys, Shar Pei, and many others. In the development of the normal elbow, there is good congruity (tight fit) between humeral condyles and the trochlear notch running from the ulna's anconeal and coronoid processes, and between humerus and radius. Likewise, there is a tight fit between the radius and the ulna, with the curve of the coronoid process continuing in an unbroken arc forming the articular top surface of the radius. In some elbows, the coronoid process is abnormally situated a bit higher than normal (or you could say the top of the radius isn't high enough because it has lagged in growth). This "step" is often accompanied by a crack in the coronoid process, or even a fragmentation. In some elbows with or without FCP, UAP, or OCD, there can be increased joint space between humerus and radius, humerus and ulna, or both. Studies at University of California-Davis showed that joint incongruity preceded FCP and since it is also seen in conjunction with UAP and OCD, the implication is strong that incongruity precedes these lesions as well.

UAP

We are certainly dealing with genes and how they are expressed, regardless of the type of elbow dysplasia. In UAP, as the dog grows, the anconeal process not being anchored continues to move in relation to the ulna, and the collagen fibers in the growth plate get torn in the constant vibration. This leads to trauma, evidenced by pain, lameness, and swelling. It can be major and sudden as in landing from a jump, or it might be a series of minor "events" such as the repetition of pivoting at the ends of the kennel run or along the driveway or yard fence. In any case, trauma brings on the complete fracture, breaking any partial bony bridge if it existed, but most of the time it's just cartilage that tears apart. The anconeal process breaks loose, floats around in the area, causing irritation and edema, and then may continue in that manner or become loosely attached to another part of the joint such as the humerus or perhaps new bone that has filled in the portion of the ulna where the loosened piece had come from. As time goes on, unless the piece is surgically removed, osteoarthritis sets in with its intensified remodeling and swollen look. The rest of the articular cartilage begins to degenerate, and osteophytes (abnormal bony, calcified growths) develop on the humeral con- dyles and often on the radius as well, but especially on the olecranon. At times, the dog may have episodes of severe pain and swelling until it is treated, euthanized, or dies of old age or other causes. If surgery is not used, synovial fluid volume increases, crepitus (that grinding noise or feeling like sand in the joint) is noticed, and ability to flex and extend the limb is reduced. Eventually, the dog is unable to climb even shallow stairs without swinging its stiff forelegs in wide arcs.

DIAGNOSIS of UAP

It is relatively easy to diagnose UAP through radiograph, with a couple of cautionary provisos. Details will be found in my book (as soon as you and I can persuade the publisher to get it printed). Your vet may also have OFA's directions on positioning. The dog doesn't need any chemical restraint for such a picture. It may not be easy for every veterinarian to distinguish in all cases, so have the film of a four-to-six month old pup looked at by an ortho- pedist/radiologist before rushing to surgery. Not every dog that stands "east-west" ("fre- nched," i.e. with pasterns turned inward and toes out) and stands or moves with elbows out has UAP or another elbow dysplasia, but in certain breeds these and the more obvious signs should be enough to move the owner to take the dog to a veterinarian familiar with these disorders. Relative stride length is a poor substitute for a radiographic diagnosis. Dog owners can find out, through OFA statistics (if enough films have been sent in), what elbow and other-joint disorders their breed is most at risk for, and then test first for that or those disorders before continuing with a sale, purchase, breeding, or training. While there are more shoulder arthroses than elbow problems when all canines are looked at, some breeds are especially susceptible to specific-joint problems. German Shepherd Dogs should be checked in adolescence for UAP and massive breeds such as Rottweilers and Bernese Mountain Dogs should be evaluated for FCP at least once during adolescence or early adulthood.

TREATMENT OF UAP

Even as late as the early 1980s, controversial forms of treatment were being promoted and practiced. Some advised rest, pain killers, and patience; others were experimenting with fixation with wires, screws, and the like; a fourth type of treatment proposed was surgical fusion of the elbow. All these have fallen out of favor as a result of comparisons, and removal of the offending particles is now generally agreed upon as the only reasonable treatment. As soon as UAP is diagnosed, the patient should be scheduled for surgery to remove the "loose" piece and thereby the movement, irritation, and worsening degenerative changes. If not diagnosed until gross changes in appearance and gait have become obvious, there may only be a 50/50 chance of improvement in gait and the rate of osteoarthritis development. Early correction is far better, and routine radiography of your young stock is cost-effective in the long run, as well as beneficial to your breed and your public image.

(Part II will discuss FCP (fragmented or fractured coronoid process) and OCD (osteochondritis dissecans) of the humeral condyle while Part III will focus on control through genetic selection and answers to some often-asked questions about elbow dysplasia).