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Elbow Dysplasia Explained

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All about ED

Elbow dysplasia (ED) is a general term used to identify inherited polygenic diseases of the elbow in dogs. Affected animals may exhibit intermittent lameness or an abnormal gait which is aggravated by exercise or when the dog first moves following prolonged rest. Watch out for sudden or gradual front leg lameness, morning stiffness or stiffness after a period of rest. In this technical article, vet Peter van Dongen goes through the anatomy of ED.

Elbow Dysplasia (ED) is an abnormal development of the elbow joint and includes several primary specific abnormalities affecting different sites in the joint. These abnormalities involve the cartilage, which makes up the surface of the joint itself, or the other structures of the joint, such as the bones themselves, the synovial membrane and the ligaments and tendons surrounding the joint. The primary abnormalities cause secondary changes such as osteo-arthritis (arthrosis, degenerative joint disease (DJD)) due to excessive wear and tear of the joint. Most primary lesions occur in the young growing animal and are often present in both left and right elbow joint.

The Elbow Joint
The elbow joint works like a hinge and allows movement mainly in one plane only. It is made up of three bones, which normally fit together perfectly (See photo and line drawings).

The single bone of the upper foreleg is called the humerus, the two bones of the lower foreleg are called the radius and the ulna. The ulna is the longer one, which makes up the point of the elbow, called the olecranon. The distal (furthest away from the body) part of the humerus is called the condyle, which has a medial (towards to inside of the body) and lateral (towards the outside) part. The proximal (closest to the body) part of the ulna has a medial and lateral coronoid process and an anconeal process, in between which the trochlear notch articulates with the humerus. The proximal part of the radius is called the radial head. The ends of the bones are all covered by hyaline cartilage (joint cartilage) which is normally very smooth. The joint is surrounded by a synovial sac, called the joint capsule, which contains the synovial fluid (joint fluid) to help lubricate the joint. The bones are held together by means of ligaments (collateral ligaments), one on either side of the joint. In addition several tendons cross the joint on either side.

If there is any change to the anatomical build of any part of the above, the joint will not fit together properly, leading to damage to one or more of the structures involved and an excessive wear and tear of the joint. The elbow joint is particularly prone to these changes as it is the major point of movement of the foreleg. The other joints of the foreleg, shoulder and carpus (wrist) do not move as much during the normal locomotion of the dog.

Causes of Elbow Dysplasia
Elbow dysplasia is a multi-factorial disease, which means that there are several factors which can influence the occurrence of the condition. The genetic make-up of the dog is by far the most important factor. Furthermore there are many factors which influence the chance of developing ED or the severity of the problem, such as nutrition, hormonal status, growth rate and exercise level. The latter factors can not cause or prevent the disease on their own and they can not influence the way that the disease is passed on to a dog’s offspring.

Genetics
As mentioned above, the most important factor in the development of ED is the genetic make-up of a dog. Unfortunately the disease is controlled by a number of genes (it is ‘polygenic’) and this makes for a complicated inheritance. It also means that certain breeds of dog are more prone to the development of ED than others, as many dogs within one particular breed have a large number of genes in common. In general, these are the medium-to-large and giant breeds.

The breeds which are prone to any particular primary condition are mentioned below. Males are affected more often than females, possibly due to their faster rate of growth or heavier build. One of the problems in deciding which dogs to breed from is the fact that many dogs which are affected genetically, or even anatomically, are not necessarily affected clinically. They may not show any clinical symptoms such as lameness. These dogs are called sub-clinical dogs. They can only be detected radiographically at the moment. In the future perhaps there will be DNA tests available to assess the genetic make up of a dog for a particular trait.

Primary Lesions

Osteo-Chondritis Dissecans (OCD)
This condition affects the distal aspect of the medial part of the humeral condyle, where it articulates with the ulna. It causes thickening of part of the articular (joint) cartilage, which is then prone to fibrillation, fissuring and separation. If a flap forms, this can become detached and ‘float’ inside the joint (‘joint mouse’) which leads to intra-articular inflammation. Sometimes the thickened cartilage can be seen as a ‘defect’ in the bone contour on radiographs (x-ray films) on some views, but usually this condition is not actually seen itself on radiographs, only the secondary changes which result from the condition. When a loose flap is formed this can sometimes become mineralised, in which case it can be seen.
Fragmented (or un-united) Coronoid Process (FCP)
This condition affects the proximal aspect of the ulna on the medial side. It leads to a fragmentation and/or fracturing of the coronoid process, where the ulna articulates with the humerus. This in turn leads to joint inflammation and secondary changes as above. The primary lesion is very rarely seen on radiographs, even on good quality radiographs. This is the most common primary condition causing elbow dysplasia.
Un-united Anconeal Process (UAP)
This condition affects the proximal aspect of the ulna at the top of the trochlear notch. The anconeal process sometimes has a separate centre of ossification, which means it develops separately as part of the boney ulna from cartilage and joins the shaft of the ulna later. Between the anconeal process and the shaft of the ulna lies a growth plate (physis), made up of cartilage, which contributes in part to the growth in length of the ulna. When the anconeal process does not join the rest of the ulna, we call this a UAP. In about 40% of cases it affects both left and right elbow.
Un-united Medial Humeral Epicondyle
This, much more rare, condition affects a part of the distal humerus, just proximal to the medial aspect of the humeral condyle. Again, this part of the bone has a separate centre of ossification and sometimes fails to joint the rest of the humerus. It generally causes a milder form of lameness than the other primary lesions.
Short Radius Syndrome
This is a condition where the radius has not grown at the same rate as the ulna, leading to an incongruency of the elbow joint, called a subluxation. It is usually caused by a premature closure of one of the growth plates (physes) of the radius. It is quite rare, and often thought to be the result of trauma to the growth plate.
Short Ulna Syndrome:
This is a condition where the ulna has not grown at the same rate as the radius due to premature closure of the distal ulna growth plate. It leads to a similar elbow subluxation as short radius syndrome.
Congenital Dislocation of the Elbow
There are two forms of this condition, where the elbow joint has not been formed properly from birth. It leads to a malformation of the joint, again leading to joint incongruency and subsequent arthrosis. In one form of there is lateral (outwards) rotation of the ulna. In the second form of Congenital Dislocation of the Elbow there is caudo-lateral (backwards and outwards) luxation of the radial head.

Breeds Most Prone to ED

OCD: Labrador Retriever, the Golden Retriever and the Rottweiler. Symptoms usually develop between 4-5 months of age.

FCP: Labrador Retriever, the Golden Retriever, the Rottweiler, the German Shepherd Dog and The Bernese Mountain Dog. Other breeds affected are the St. Bernards, Chows, Rhodesian Ridgebacks and Newfoundlands. Symptoms usually develop between 4-5 months of age. Sometimes FCP and OCD occur in the same joint at the same time.

USP: German Shepherd Dog and the Bassett Hound. More rarely we see it in Wolfhounds, Rottweilers, St. Bernards and Great Danes. Symptoms usually develop between 4-5 months of age.

Un-united Medial Humeral Epicondyle: Labrador Retrievers are prone to this condition.

Short Ulna Syndrome: Great Danes, Irish Wolfhounds and the Bassett Hound or after trauma.

Congenital Dislocation of the Elbow - (lateral (outwards) rotation of the ulna. This is mostly seen in Shelties, Pekingese, Cocker Spaniels, Yorkshire Terriers, Boston Terriers, Miniature Poodles, Pugs, Chihuahuas and Miniature Pinschers. It is usually recognised within the first three months of life.

Congenital Dislocation of the Elbow (caudo-lateral (backwards and outwards) luxation of the radial head. This is mostly seen in Pekingese, Yorkshire Terriers, Pomeranians, Staffordshire Terriers, Boxers, Bulldogs, Bull Mastiffs, Old English Sheepdogs and Rough Collies. Affected animals are often 4-5 months old at presentation.

‘Osteochondrosis’
This term is often used inconsistently or confusingly for one or several of the conditions above. Osteochondrosis is a developmental orthopaedic condition in which a disturbance in the normal process of endochondral ossification results in a thickening or retention of articular or physeal cartilage. The thickened cartilage is then prone to fibrillation, fissuring and separation. If a cartilage flap develops in articular cartilage, intra-articular inflammation and degenerative joint disease may result and the condition is then most appropriately described as osteochondritis dissecans (OCD).

Endochondral ossification is one of the two processes in which bones are formed. In this case bone develops on a preformed cartilagenous matrix, either at the end of the bone or in the physis. It is the main process behind the growth in length of the long bones in the body.

Intra-membranous ossification is the second process in which bones are formed. In this case bone forms in bands of connective tissue. This happens in flat bones, such as the skull bones and the pelvis, and it is also the way in which bones grow in width. The primary conditions 1-6 are all thought to be due to osteochondrosis.

Symptoms
The symptoms of elbow dysplasia are dependent on the particular condition present in the patient and the chronicity of the problem. Generally it causes lameness, although this can be very subtle and easily missed by an owner, particularly as the problem often occurs in both legs at the same time. In such cases it often causes a minimal stiffness rather than a true lameness. It can also cause pain, especially on manipulation, such as extension, flexion and rotation on the joint. The lameness is often a ‘starting lameness’, which gets better as the patient ‘warms up’ and sometimes intermittent in nature. This is similar to the type of lameness seen in older patients with degenerative joint disease. The most reliable way to make a diagnosis is radiography (x-raying).

Radiography
Radiography is used to detect either the primary lesion itself or the subsequent degenerative joint disease. Normally three different views are taken of each joint to fully assess the joint structures, two in a lateral plane (with the x-ray beam directed sideways through the joint, whilst extended and flexed) and one in the cranio-caudal plane (beam directed from the front of the joint to the back of the joint). Different areas of the joint are more clearly identifiable on each view. As already mentioned above, not always is it possible to identify the primary condition present in the joint, but it is usually possible to detect the secondary changes. Together with the clinical symptoms, the age of the patient and more importantly the breed, it is often possible to come to a definite diagnosis.

Prevention
Prevention of Elbow Dysplasia is based on sensible breeding, using only dogs not affected or only very mildly affected by the condition. To this purpose it is necessary to radiograph each and every dog, as there are many dogs with radiographic evidence of elbow dysplasia, but without any clinical signs. These ‘sub-clinical’ cases would be missed if they were not radiographed. Only dogs who have no, or only very minor, radiographic evidence of elbow dysplasia should be used for breeding. In the UK the ED scheme has been operational for the last few years to this purpose. This scheme is run by the British Veterinary Association and the Kennel Club together, according to guidelines by the International Elbow Working Group.

Dogs examined under the scheme are radiographed as described above, at an age of at least one year old, and the radiographs are then sent for examination by a select group of scrutinisers who have extensive experience in the assessment of radiographs. A grade for each elbow of each patient is decided upon, based on the presence or absence of primary lesions, as well as the presence or absence of any secondary changes in the joint. The score for each elbow can be: 0 if the joint is normal, 1 when there is mild ED, 2 if there is moderate ED or any primary lesion, and 3 if there is severe ED. The overall grade for each individual patient is the highest of the two scores, not the total, as in the hip scoring system. Only dogs with scores of 0 or 1 should be used for breeding purposes. The results of any dog radiographed under the ED scheme are kept on record by the Kennel Club. The effect of this system will only really be seen after several generations of selective breeding in the affected breeds.

Treatment
Treatment of ED depends on many factors, such as the nature and severity of the primary problem. Conservative treatment, such as weight control and exercise control, are important in each and every case. In a number of cases, drugs, used to reduce pain or inflammation, are needed. Furthermore, in some cases surgical intervention is necessary. In some cases nutritional supplements are useful to reduce the possible future build up of arthritic changes. Other forms of treatment include physiotherapy, homeopathy and acupuncture. Nearly all dogs can be managed successfully, if the symptoms are recognised and the dog is diagnosed early on in the disease process.

About the author...
Peter van Dongen qualified as a vet at the Utrecht Veterinary school, The Netherlands, in March 1990. He worked in a mixed practice in Louth, Lincolnshire, UK, for 3 years, before moving to Borough Green, Kent, UK. At the same time he limited himself to small animals only. Since December 1996 he has run his own branch practice in Allington, Maidstone, UK.

In May 1995 Peter started agility (after years of just thinking about it!) with his Jack Russell Cross 'Basil' (a bitch!), then 5 years old. Since then they have qualified for many finals, including 'Crufts' and 'Olympia'. Basil won the coveted Crufts 2001 title in the individual mini agility.

Peter passed the British Agility Club Instructors' exam in October 1999 and has since done the British Agility Club Judging Workshop.

Peter regularly writes for various agility magazines and web sites and has been the official British Team Vet for the Agility World Championships for the last three years.

Peter and his wife Carry still live in Borough Green with their two dogs and two cats. His little Jack Russell X, Sky, has just started agility training and will hopefully follow in Basil’s footsteps!

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