A Brief Overview -
Ann L. Reed, DVM, MS, Dipl. ACVR
|Elbow dysplasia is a general term used
to identify inherited polygenic diseases of the elbow in dogs.
Three specific etiologies make up this disease and they can occur independently or in conjunction with one another.
These etiologies include:
1. Fragmented medial coronoid process of the ulna
2. Osteochondritis of the medial humeral condyle
3. Ununited anconeal process
The clinical signs involve lameness which may remain subtle for long periods of time. No one can predict at what age lameness will occur due to a large number of genetic and environmental factors such as degree of severity of changes, rate of weight gain, degree of exercise, etc. Affected dogs may not show obvious lameness and may only have an abnormal gait. Range of motion in the elbow is also usually decreased. Frequently, there is bilateral disease but unilateral elbow dysplasia is not uncommon.
Once it is diagnosed, conservative therapy can be an option for dogs affected by intermittent and/or mild degrees of lameness. The use of pain relievers/anti-inflammatory agents such as Aspirin, EtoGesic or Rimadyl can be used during bouts of lameness especially an hour or so before known periods of exercise. Various osteoarthritis modifying agents and nutraceuticals now on the market would be another option such as Adequan, Cosequin, SynoviCre, Glycoflex, Arthramine, and MaxFlex Pet. The use of these drugs should be tailored for the individual dogs improvement note. If side-effects occur or there is persistence of obvious lameness, change the therapy to a different drug from the above choices. You may notice obvious improvements this way. With oral nutraceuticals, the dog may have to have taken the medication for an extended period of time before benefits are noted. It is important to keep your dog as lean as possible to reduce concussive mechanical forces across the diseased joints. Also, to maintain the range of joint motion, strengthen surrounding muscles to improve joint stability and improve the health of the joint fluid, non-weight bearing forms of exercise such as swimming or low weight bearing exercise with leash walking should be done on a regular basis.
If the dog is
showing a continuous and severe pattern of lameness, arthroscopic or
surgical exploration of the joint is recommended because usually in
these cases, significant pathology is more likely to be found and there
is also more of a possibility for postoperative improvement.
Arthrotomy where an actual incision is made into the joint capsule is the most common surgery performed however it is more invasive. Studies comparing surgical arthrotomy treatment with non-surgical treatment have repeatedly shown that the incidence of lameness is the same in both groups. Some studies have shown that the severity of lameness is reduced in surgically treated dogs, but radiographic progression of osteoarthritis occurs irrespective of the treatment given. Future studies will most likely show a much more favorable outcome with the use of arthroscopic surgery. A more rapid return to normal joint function has been clinically reported by most owners.
The outcome or
prognosis elbow dysplasia depends on the degree of severity of elbow
dysplasia and the degree of severity of secondary degenerative joint
disease (osteoarthritis). Dogs with severe degenerative joint disease
are more likely to have occasional bouts of lameness even after
surgery. Overall, the outcome for full return to normal is guarded.
Clinically, prognosis has been better in dogs that have had arthroscopic
surgery performed early in the course of the disease. With regular
surgery where the joint is opened with an lygenic variation is
determined by the addition or combination of factors. In additive
heredity, traits become more evident according to the number of genes
present. Non-additive heredity does not depend some much on the number
of genes but rather their combination. The results which have been
obtained through selection against hip dysplasia and elbow dysplasia
point to the important role played by additive gene inheritance.
This equation expresses that the variation in hip and elbow conformation phenotype (represented by excellent to severely dysplastic from the OFA hip scoring method and normal to grade 1, grade 2 or grade 3 elbow dysplasia) comes about from the complex interaction of the animal's own inherited genotype with the environment to which it has been exposed. Quantitative hereditary characteristic traits for hip and elbow dysplasia are influenced in various degrees by environmental factors. Overweight, excess of protein and energy rich food, rapid growth rate, excess exercise or lack of excercise, high calcium intake and other dietary influences have been suggested. Without genetic pre-disposition however, environmental influences alone will not create hip or elbow dysplasia (this goes back to the P=G+E equation).
In order to achieve rapid genetic progress with the use of hip and elbow conformation phenotypes, heritability estimates can be calculated. Heritability estimates are statistically determined (usually through mid-parent offspring analysis statistical methods) and express the reliability of the phenotypic value (radiographs) as a guide to the breeding value of the animal. Heritability measures the relative . This also increases the accuracy in predicting the animal's breeding value and identifies carrier animals.
heritability estimate is between 0.4 and 1.0, it is generally considered
high and the animal's phenotype is a good predictor of its genetic
makeup and rapid results are obtained with genetic selection for or
against any trait.
An important question that usually arises with regard to genetics of hip conformation is which mate has the most influence on the offsping's hip conformation the sire or dam? Studies looking at progeny hip scores for both the sire and dam show there is approximately the same equal effect. A worse offspring hip conformation will occur as the hip conformation of the dam and the sire worsen. Overall, the transmission of hip dysplasia to the offspring depends on the dam as well as the sire. This would also apply to elbow dysplasia. On the other hand, sire's with many high awards obviously have a far greater influence on the breed than dams and selection of an appropriate sire is more critical because they have the potential for more offspring, therefore more impact on the phenotypic measurement of hip conformation and frequency of elbow dysplasia than a dam.
With regard to genetics of hip and elbow in a breeding program, dogs without canine hip dysplasia and without elbow dysplasia are more likely to be born to parents without hip or elbow dysplasia. It is generally accepted that if two litter mates with similar genetics from a strong pedigree are used in a breeding program and one is rated excellent and the other rated fair, the parent will commonly produce the majority of offspring with hip conformation's similar to their own hip conformation. A small percentage of the offspring may have less superior hip conformation than the parents and another small percentage will have superior hip conformation than the parents. This is expected with any polygenetic trait whether it be hips, size, speed, movement etc. Likewise, numerous reports show that many offspring from parents with hip or elbow dysplasia also become dysplastic, often several or all siblings in a litter are dysplastic. Research performed by Willis summarized results of a number of breeding programs and concluded that in various dog populations, between 64 to 81% of the progeny of normal dogs (as determined on the basis of standard hip conformation scoring) would also be normal and between 19 and 36% would be dysplastic. On the other hand, between 17 and 37% of the progeny of dysplastic dogs would be normal and between 63 to 93 % would be dysplastic. Even with using a dysplastic dog that has a strong pedigree for normal hips, over the course of a few generations, there are higher percentages of dysplastic dogs. Even if the first generation offspring is phenotypically normal from this type of mating, there is increased frequency of dysplastics in subsequent generations due to an increase in the number of carriers in the litter that when breed, go on and pass undesirable traits for hip dysplasia onto their offspring. This is why the OFA does not recommend the use of dysplastic animals in any breeding program no matter what type of pedigree they come from.
The most important information to answer in any breeding program is what is an animal's predictive breeding value? This value can usually be ascertained by the available information present on hip and elbow status of the individual dog, the dog's parents and the dog's littermates. All three of these questions are important with the heritability of canine hip dysplasia and elbow dysplasia being in the moderate range in most dog populations. Unfortunately, all of this information is usually not available since most animals in a litter are not radiographed for hip or elbow conformation. When looking at the order of importance of hip and elbow information on a pedigree analysis and ranking them with regard to placing a predictive breeding value for an individual dog, the dog's parents hip and elbow information is very important followed by the dogs own individual hip and elbow conformation then followed by litter mate information. With most breeders making their predictive breeding value decisions on individual hip and elbow phenotype scores, a decreased frequency of dysplasia will be substantial but slow. Information on parents and siblings makes it more feasible for the breeder to apply greater selection pressure against dysplastic traits and achieve more rapid reductions in the frequency of canine hip dysplasia and elbow dysplasia in their lines. An example would be looking at two potential new sires from different pedigrees to use in a breeding program. Each sire has similar desirable traits that are above average when compared to other members of the breed. The only difference is one sire has excellent hips but has only one parent with an OFA hip number of good (the other did not have an OFA number) and no siblings with OFA hip numbers and one known dysplastic sibling. The other sire has fair hip conformation out of two OFA good parents and 2 OFA good and 2 OFA excellent littermates. The probability for normal hips would most likely be with the use of the fair sire especially when bred to an excellent or good mate that has a similar strong pedigree for hip conformations. When the breeder has all of the information to work with, a higher success rate for hip and elbow conformation is achieved more rapidly.