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Genetic Welfare Problems of Companion Animals
An information resource for prospective pet owners
German Shepherd Dog (Alsatian)
Elbow Dysplasia (Ununited Anconeal Process)
Related terms: Disunited anconeal process
Outline: In this condition, a protuberance of the ulna bone – the anconeal process - that forms part of the elbow joint, and which should during development fuse to the ulna, fails to do so and develops separately. This results in an ununited anconeal process (UAP), a condition that is most commonly seen in dog breeds of a large body size, including the German Shepherd dog in which the prevalence appears to be in the order of 12-21% (which would suggest about 60,000 dogs of this breed with the disease in the UK). UAP leads to arthritis of the elbow joint which, unless successfully treated (which is difficult) is likely to cause lifelong pain and discomfort, which may be mild or more severe.
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Summary of Information
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1. Brief description
An ununited anconeal process (UAP) is characterised by disease of a part of the ulna bone at the elbow joint. This process (protruberance) of the ulna bone fails to form properly and, because of this, the function of the elbow is affected and osteoarthritis develops.
Dogs with UAP develop osteoarthritis (degenerative joint disease) of the elbow, which causes pain. The disease is often present by 5-9 months of age but can show later. Affected dogs may be treated with rest and pain-killers, and treatment may need to be life-long. Various surgical procedures have been recommended to treat or alleviate the condition but there is no consensus as to which is best. Some procedures require major intervention, eg removal of sections of bone (Burton and Owen 2008a).
2. Intensity of welfare impact
UAP leads to pain and disability associated with the osteoarthritis of the elbow joint. This can be mild to severe.
3. Duration of welfare impact
UAP leads to pain and disability associated with the osteoarthritis of the elbow joint. This can be mild to severe.
4. Number of animals affected
Various reports suggest that the prevalence may be around 12- 21% in GSDs (Wind & Packard 1986, OFA 2006, Kirberger & Stander 2007, Coopman et al 2008). From data on estimates of total dog population in the UK and on the percentage of all micro-chip registered dogs that are GSDs (Lucy Asher 2011, personal communication), we estimate that the UK population size of this breed may be around 400,000. If the prevalence is around 15% (above), then it is possible that there are some 60,000 of this breed of dog with the disease in the UK.
5.Diagnosis
The disease is likely to be suspected in dogs showing signs of forelimb lameness and can be confirmed, and its nature, extent and severity determined by examinations including x-rays (van Ryssen & van Bree 1997), CT and MRI scans and exploratory surgery – often using an arthroscope.
6. Genetics
The genes involved have not been determined.
7. How do you know if an animal is a carrier or likely to become affected?
Affected dogs should not be used for breeding. Affected puppies can be born to unaffected parents (Hazelwinkel & Nap 2009). Determining carriers - those which carry and may pass on the gene(s) but which do not show signs of the disease themselves - is not currently possible.
8. Methods and prospects for elimination of the problem
A voluntary scheme to grade the elbows of dogs susceptible to elbow dysplasia has been in operation in the UK since 1998 although it has been suggested that breeder uptake has been relatively low (Sampson 2006). For this scheme, elbows are scored once for the condition when the dog is over one year old.
As with other complex, multi-gene diseases that are influenced also by environmental factors, efforts to reduce the prevalence of UAP are complicated by the lack of information about the underlying genetics. One approach is to breed from dogs that have a better breeding value (see below) than is average for the breed (Sampson 2006). Breeding values take account of both the individual being evaluated and its relatives (Malm et al 2008). Out-breeding GSDs with breeds known to have much lower prevalences of UAP, and elbow dysplasia (ED) in general, is likely to result in fewer dogs being born with a lifetime of painful joint problems before them.
For further details about this condition, please click on the following:
(these link to items down this page)
- Clinical and pathological effects
- Intensity of welfare impact
- Duration of welfare impact
- Number of animals affected
- Diagnosis
- Genetics
- How do you know if an animal is a carrier or likely to become affected?
- Methods and prospects for elimination of the problem
- Acknowledgements
- References
1. Clinical and pathological effects
Elbow dysplasia (ED) is a general term that encompasses five distinct anatomical problems that tend to result in malformation of the elbow joint, and that lead to early-onset osteoarthritis.
Ununited anconeal process (UAP) is one of these problems, and is the main focus here, but some of the other four conditions outlined below are referred to in the descriptions (below) about how UAP may develop. These conditions are:
Fragmented medial coronoid process (FMCP): The medial coronoid process is a piece of bone that should form part of the top of the ulna and of the elbow joint. In FMCP this fails, during development, to connect to the ulna.
Osteochondrosis dissecans (OCD): In OCD an area of joint cartilage develops abnormally or becomes damaged leading to thickening, cracking and fragmentation of the cartilage.
Elbow incongruity (IC): Dogs with IC have malformed articular surfaces of the three bones that make up the elbow and because of this they do not fit together normally. It can affect the weight-bearing surfaces between the humerus and the radius and ulna and also the way in which the upper part of the ulna fits inside the lower end of the humerus (Schwarz 2000).
Ununited medial epicondyle (UME): This is an uncommon condition in which the medial epicondyle, a part of the humerus, fails to unite with the humerus during development.
The elbow is a complex joint of three bones; the humerus (upper bone of the foreleg/arm bone), the ulna and the radius (lower foreleg/arm bones). At their upper ends, the radius and part of the ulna form a flattened surface that bears the load imposed by the humerus. The anconeal process (protruberance) is normally part of the end of the ulna. Its main function is not weight bearing, rather it helps to stabilize the elbow joint, particularly when the leg is extended. The anconeal process articulates with the caudal (towards the tail of the dog) surface of the humerus (the back of the elbow joint) and when the leg is extended (straightened) it fits into a hole at the lower end of the humerus called the humeral fossa.
Figure 1. The three bones of the elbow joint separated and in normal alignment. In a healthy canine elbow joint the ulna and radius form a flat surface for articulation with the humerus. (Image property of Phil Witte, to whom we are grateful for permission to reproduce it here).
Figure 2. A diagram of the upper end of the ulna illustrating the locations of the coronoid and anconeal processes. (Image property of Phil Witte, to whom we are grateful for permission to reproduce it here).
In most dogs the anconeal process grows as part of the ulna and as such there is no possibility of it not “uniting”. But in breeds with large body size it is normal for the anconeal process to start as a separate small bone at birth, which, during development, should fuse on to the ulna. This usually occurs by 20 weeks of age. In UAP this fails to happen. The cause of this is unclear but one possibility is that it is a consequence of the radius growing disproportionately longer than the ulna such that the elbow joint is malformed and the anconeal process experiences abnormal pressures that cause it to be pushed away from the ulna, thus preventing it from fusing (uniting). UAP therefore only becomes apparent in dogs aged over 20 weeks (Schwarz 2000).
Figure 3. In larger dog breeds, the anconeal process forms separately. It should fuse with the ulna during development. If this process fails, the result is an Ununited Anconeal Process (UAP).
Dogs with UAP develop osteoarthritis (degenerative joint disease) of the elbow. In osteoarthritis there are progressive changes to the cartilage of the affected joint, varying amounts of inflammation and ongoing damage to other joint structures - the joint capsule, the synovial fluid of the joint and the surrounding bone. These changes are often present by 4-6 months of age and lead to clinical signs later. Typical signs include: stiffness after rest, lameness (which can be worse after exercise) and reduced mobility of the joint, with the leg tending to be held twisted outwards (abducted and suppinated). Such signs are indistinguishable from those shown in other forms of elbow dysplasia and imaging of the joint is usually needed to make a definitive diagnosis (Schwarz 2000).
Figure 4a Figure 4b
Figures 4a and 4b. Osteoarthritic changes to the shape and structure of the elbow joint. The shaded areas on figure 4a (extended elbow) and 4b (flexed elbow) represent the changes to bone and cartilage as a result of UAP and other forms of elbow dysplasia. (Images property of the British Veterinary Association/ Kennel Club Elbow Dysplasia Scheme. We are grateful to the BVA for permission to reproduce them here).
Meyer-Lindenberg et al (2006) found that at least 13% of GSDs with UAP also had fragmented medial coronoid process (FMCP,see above)..
UAP is seen more commonly in males than females and the problem is often bilateral (Schwarz 2000, Burton & Owen 2008a, Janutta et al 2006). This male bias may be associated with the greater weight of males (Hazelwinkel 2009).
Affected dogs may be treated with rest and pain-killers, and often treatment needs to be lifelong. Various surgical procedures have been recommended but there is no clear consensus as to which is best. Some of these procedures involve major surgery, including removing whole sections of the ulna in order to shorten it (Burton & Owen 2008a).
2. Intensity of welfare impact
UAP causes pain and disability associated with osteoarthritis. This can vary from mild to severe. Welfare may also be affected as a result of the veterinary investigations and treatments of the disease. Restricted activity will often be recommended in order to prevent further joint damage and this reduced activity may constrain the dog’s capacity for normal life and behaviour.
3. Duration of welfare impact
The mild to severe pain and disability that result from the osteoarthritis seen in this disease can be expected to start during the first few months of life and, without successful treatment, to continue for life. Treatment may help but keeping affected dogs free from pain and avoiding disabilities is often challenging.
4. Number of animals affected
The GSD is one of the breeds included in the British Veterinary Association/Kennel Club Elbow Dysplasia Scheme (Kennel Club 2010). GSDs have long been known to suffer from elbow dysplasia (ED) (Corley & Carlson 1965) and are predisposed to UAP (Schwarz 2000, Innes 2006, Meyer-Lindenberg et al 2006, Burton & Owen 2008b, Arthurs 2009). Innes (2006) reported that 18-21% of GSDs have ED, based partially on data from the Orthopedic Foundation for Animals (OFA 2006) in North American and on results from Kirberger & Stander (2007) in South Africa. Wind & Packard (1986) suggested there was an incidence of ED of 19% in GSDs. Coopman et al 2008 found that 12% of GSDs in Belgium were affected.
In contrast, although Remy et al (2004) found that 19% of GSDs examined in France had ED, only about 1% of these were due to UAP: The conditions of FMCP and IC were more common diagnoses. However, they suggested that this population of dogs may have already been prescreened to exclude dogs likely to be affected by UAP.
From data on estimates of total dog population in the UK and on the percentage of all micro-chip registered dogs that are GSDs (Lucy Asher 2011, personal communication), we estimate that the UK population size of this breed may be around 400,000. If the estimates of prevalence of around 15% (above) are correct, then it is possible that there are some 60,000 of these dogs with the disease in the UK.
5. Diagnosis
UAP can only be diagnosed in dogs older than about five months as it is normal for those breeds in which UAP occurs to have an ununited anconeal process prior to this (Schwarz 2000).
UAP may be suspected when a GSD shows forelimb pain. Elbow disease and pain may be apparent. Determining the type of elbow disease, its extent and the degree of secondary osteoarthritis requires further diagnostic procedures, including radiography (x-rays) (Burton & Owen 2008b) or other imaging methods. In cases of UAP it is more difficult to detect other concurrent forms of elbow disease (Meyer-Lindenberg et al 2006).
6. Genetics
UAP is generally a disease of large dogs, as it is only in these that the anconeal process develops separately from the ulna. There is some evidence that ED is heritable in GSDs (Junutta et al 2006). The genes involved in GSD UAP are unknown but there is indirect evidence that in the GSD they are distinct from genes that cause other types of ED.
It is known that the father and mother contribute equally to the likelihood of the development of elbow dysplasia (Maki et al 2002). There are genetic influences both on the presence or absence of UAP and on whether, and to what degree, osteoarthritis occurs in an individual with UAP (Clements et al 2006). Environmental factors also play a part in the development of the disease and its severity (Hazelwinkel & Nap 2009).
7. How do you know if an animal is a carrier or likely to become affected?
Affected dogs should not be used for breeding. Affected puppies can be produced from normal parents (Hazelwinkel & Nap 2009). Determining carriers - those which carry and may pass on the gene(s) but which do not show signs of the disease themselves - is not currently possible.
8. Methods and prospects for elimination of the problem
A voluntary scheme to grade the elbows of dogs susceptible to elbow dysplasia (all forms) has been in operation in the UK since 1998 although it has been suggested that breeder uptake has been relatively low (Sampson 2006). Details of the scheme can be found at: http://www.thekennelclub.org.uk/item/309.
In this scheme, the elbows are scored once when the dog is over one year old. Radiographs taken by a local veterinary surgeon are forwarded to veterinary radiologists on the scheme panel for assessment. Each elbow is graded 0-3, with zero meaning that no evidence of elbow dysplasia was seen. If the two elbows have different grades, the higher of the grades is the one used to characterise the dog. The scheme recommends that dogs used for breeding should have grades of zero or one and that those with higher scores should not be used for breeding.
No evidence has yet been published as to whether this scheme has been effective in reducing the prevalence of elbow dysplasia in the GSD. A comparable scheme run in New Zealand since 1991 seems to have significantly reduced the severity of ED in GSDs being screened for the disease prior to breeding (Worth et al 2010) and one run in Sweden since 1990, appears to have reduced the prevalence of elbow dysplasia in Swedish Bernese Mountain dogs and Rottweilers (Swenson et al 1997, Malm et al 2008).In common with other complex, multi-gene diseases that are influenced also by environmental factors, efforts to reduce the prevalence of UAP are complicated by the lack of information about the underlying genetics. One approach is to breed from dogs that have a better estimated breeding values (EBV) than average for the breed for this condition (Sampson 2006). The EBV is a numerical prediction of the relative genetic value of a particular dog in relation to one or more genetic problems and to degree of inbreeding. EBVs are calculated using all available information on the dog including pedigree, health status and physical characteristics. For this type of health programme to work many breeders and owners need to submit their animals for monitoring and analysis.
EBVs are also useful because they enable selection against several hereditary diseases simultaneously and this is relevant in the case of the GSD which is predisposed to a number of hereditary disorders eg hip dysplasia, degenerative myelopathy, exocrine pancreatic insufficiency, anal furunculosis.
Out-breeding GSDs with breeds known to have much lower prevalences of UAP and elbow dysplasia (ED) is likely to result in fewer dogs being born with a lifetime of painful joint problems before them.
9. Acknowledgements
UFAW is grateful to Rosie Godfrey BVetMed MRCVS and David Godfrey BVetMed FRCVS for their work in compiling this section and to Stephanie Kaufman for assistance in illustrating it.
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10. References
Arthurs G (2009) Canine Elbow Disease. In: Proceeding of British Small Animal Veterinary Congress 2009
Burton N and Owen M (2008a) Canine elbow dysplasia 2. Treatment and prognosis. In Practice 30: 552-557
Burton N and Owen M (2008b) Canine elbow dysplasia 1. Aetiopathogenesis and diagnosis. In Practice 30: 508-512
Corley EA and Carlson WD (1965) Radiographic, genetic and pathologic aspects of elbow dysplasia. Journal of the American Veterinary Medical Association 147: 1651
Clements DN, Carter SD, Innes JF and Ollier WER (2006) Genetic basis of secondary osteoarthritis in dogs with joint dysplasia. American Journal of Veterinary Research 67: 909-19
Coopman F, Verhoeven G, Saunders J, Duchateau L and van Bree H (2008) Prevalence of hip dysplasia, elbow dysplasia and humeral head osteochondrosis in dog breeds in Belgium. Veterinary Record 163: 654-658
Hazelwinkel HAW (2009) Preamble. Proceedings of 24th Annual Meeting of International Elbow Working Group. pp 2
Hazelwinkel HAW and Nap RC (2009) Elbow dysplasia, definition and known aetiologies. Proceedings of 24th Annual Meeting of International Elbow Working Group. pp 5-10
Innes JF (2006) Is elbow dysplasia a syndrome? Proceedings of the British Veterinary Orthopaedics Association Autumn Meeting 2006. 10-11
Janutta V, Hamann H, Klein S, Tellhelm B and Distl O (2006) Genetic analysis of three different classification protocols for the evaluation of elbow dysplasia in German shepherd dogs. Journal of Small Animal Practice 47: 75–82
Kennel Club (2010) The BVA /KC Elbow Dysplasia Scheme http://www.thekennelclub.org.uk/item/309 accessed 17th December 2010
Kirberger RM and Stander N (2007) Incidence of canine elbow dysplasia in South Africa.Journal of the South African Veterinary Association 78: 59-62
Mäki K, Groen AF, Liinamo-E and Ojala M (2002) Genetic variances, trends and mode of inheritance for hip and elbow dysplasia in Finnish dog populations. Animal Science 75: 197-207
Mäki K, Janss LLG, Groen AF.Liinamo A-E and Ojala M (2004) An indication of major genes affecting hip and elbow dysplasia in four Finnish dog populations. Heredity 92: 402–408
Malm S, Fikse WF, Danell B and Stanberg E (2008) Genetic variation and genetic trends in hip and elbow dysplasia in Swedish Rottweiler and Bernese Mountain dogs. Journal of Animal Breeding and Genetics 125: 403-12
Meyer-Lindenberg A, Fehr M and Nolte I (2006) Co-existence of ununited anconeal process and fragmented coronoid process of the ulna in the dog. Journal of Small Animal Medicine 47: 61-5
OFA (2006) Statistics and data, elbow dysplasia statistics. www.offa.org/elbowstatbreed.html. Accessed 25.5.11
Remy D, Neuhart L, Fau D and Genevois JP (2004) Canine elbow dysplasia and primary lesions in German shepherd dogs in France. Journal of Small Animal Practice 45: 244–248
Sampson J (2006) What is required for breeding programmes or Molecular technologies to make impact on the prevalence and incidence of elbow dysplasia in dogs? Proceedings of the British Veterinary Orthopaedics Association Autumn Meeting 2006. 4-5
Schwarz PD (2000) Canine elbow dysplasia. In; Kirks Current Veterinary Therapy XIII editor J.D. Bonagura. W.B. Saunders, Philadelphia. pp 1004
Shell L and Harasen G (2007) Ununited anconeal process. VIN Associate. (on-line) http://www.vin.com/Members/Associate/Associate.plx?DiseaseId=447. accessed 17.12.2010
Swenson L, Audell L and Hedhammar A (1997) Prevalence and heritance of and selection for elbow dysplasia in Bernese mountain dogs in Sweden and benefit: cost analysis of a screening and control programme. Journal of the American Veterinary Medical Association 210: 215-221
van Ryssen B and van Bree H (1997) Arthroscopic findings in 100 dogs with elbow lameness. Veterinary Record 140: 360-362
Wind AP and Packard ME (1986) Elbow incongruity and developmental elbow diseases in the dog: Part II. Journal of the American Animal Hospital Association 22: 725-730
Worth AJ, Bridges JP and Jones G (2010) Reduction in the incidence of elbow dysplasia in four breeds of dog as measured by the New Zealand Veterinary Association scoring scheme New Zealand Veterinary Journal 58: 190- 5
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