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Structure of the elbow joint

  Elbow joint seen from behind
Fig. 1. Elbow joint seen from behind.
  1. Humerus
  2. Olecranon
  3. Radius
  4. Ulna
The elbow joint is a hinge-joint between the humerus on one side and the radius and ulna on the other side. In a number of species the joint is a bit more complex since the radius and ulna can rotate around each other along their length axis. In dogs this kind of movement is not possible. The areas of the bone which form the actual joint are covered with cartilage. The space between the joint surfaces is filled with a lubricant (Synovia), which also plays a role in feeding the cartilage.

The end of the ulna (the hard point of the elbow) is called Olecranon.

Fig. 2. Elbow.
a. Humerus
b. Processus anconeus
c. Processus coronoideus
d. growth disc  
e. cartilage  
f. Olecranon  
g. joint cartilage
h. Ulna
j. Radius

Elbow dysplasia

Elbow dysplasia is a general term that actually describes four diseases:
  1. Osteochondrosis Dissecans (OCD)
  2. Loose Processus Coronoideus (LPC)
  3. Loose Processus Anconeus
  4. Degenerative Joint Disease

Osteochondrosis Dissecans

This type occurs mainly in bigger, fast growing breeds with pups between four and twelve months of age. In most cases the shoulder and elbow joints are affected. OCD is disease of the cartilage of the joint. Climbing stairs (especially downstairs) can facilitate the damage to the cartilage. The susceptibility for these lesions is probably hereditary. The symptoms include slowly increasing limping, shortening of the forward step length, excessive filling of the joint and turning the leg outward.

Joint affected by OCD (macroscopic view)   Cartilage damaged by OCD (microscopic view)
Fig. 3. The cartilage layer on the joint surface is affected (macroscopic view).
(Photo reproduced from "Atlas of veterinary pathology" with the permission of the author2).
Fig. 4. Under the microscope the damage is even clearer. The loose piece of cartilage (blue colour) can easily break and can cause a lot of pain in the joint.
(Photo reproduced from "Atlas of veterinary pathology" with the permission of the author2).

Loose Processus Coronoideus

During the ossification of the processus coronoideus at the age of 4 to 5 months the process can be detached by a development disorder, overloading and/or overweight. This is possibly worsened by too much calcium in the diet.

After the detachment three scenarios can follow:

  • the whole process stays inside the joint
  • the process is broken into pieces by movement
  • the process stays between the radius and the ulna.
  Radius and Ulna (after a fracture of the olecranon)
Fig. 5. Radius and Ulna after fracture of the Olecranon.
  1. plate
  2. screws
  3. Ulna
  4. Olecranon
  5. Processus anconeus
  6. Processus coronoideus
  7. Radius
This occurs more often in larger breeds. Especially dogs appear to be more sensitive than bitches. A combination with Osteochondritis Dissecans is not unusual. The joint is thick and painful and the joint is often turned outward with each step.

Loose Processus Anconeus

Occurs more often in the larger breeds, although it is also seen in the Dachshund and the Basset. The cause is different for the various breeds:

Large breeds: during ossification the cartilage degenerates, which causes the processus anconeus to break.

Small breeds: the growth disc in the ulna closes earlier than the one in the radius. The difference in growth results in abnormal forces on the process, which cause it to break off. Just like the Loose Processus Coronoideus, there are three forms. The symptoms that occur between the age of 6 to 9 months are limping, swelling of the elbow and pain during movement.

The disease ends with arthritis, resulting in the need for (surgical) treatment. In the United States testing for this disorder is done at a small scale. It's curious that in all tested breeds the disorder occurs more often in dogs than in bitches (data from the OFA). The difference is even significant (25-50% more dysplastic elbows in dogs than in bitches) in breeds with a high number (>1000 per breed) of tests.

Degenerative Joint Disease

Degenerative Joint Disease is a degeneration of cartilage without inflammation. This disorder is also visible in x-rays.


Padgett1) finds OCD and LPC to be hereditary in the Labrador Retriever. It is likely that this is also true for other breeds. Test breeding shows that selection influences the likeliness of OCD and LPC; this suggests a genetic background. The fact that healthy pups also occurred in these litters suggests that it is not caused by a simple, recessive gene, but that the disease is more likely polygenic (like CHD).

Testing for elbow dysplasia is not common, nor obligatory. Considering the moderate frequency of occurrence it is not likely to become obligatory in the near future. It is however sensible to withdraw affected dogs and directly related animals from reproduction.

1) PADGETT, G.A., U.V. Mostosky, C.W. Probst, M.W. Thomas, C.F. Krecke; The Inheritance of Osteochondritis Dissecans and Fragmented Coronoid Process of the Elbow Joint in Labrador Retrievers; Journal of the American Animal Hospital Association, Vol. 31, p. 327-330.

2) MOUWEN, J.M.V.M., E.C.B.M. de Groot; Atlas of veterinary pathology; Utrecht; 1982; Wetenschappelijke Uitgeverij Bunge; ISBN 9063483325, p. 124.

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This page last modified: Wednesday, 30-Jul-2008 16:44:16 CEST
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