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Bilateral
Elbow Dysplasia and Elbow Arthroscopy What is an elbow joint? Three bones meet to form this complex joint. The humerus comes down from the shoulder and has a curved end, which rests on top of the radius. The radius is the main weight-bearing bone. Behind the radius is the ulna, which extends up past the bottom of the humerus, and is what you feel as the point of the elbow. The ulna serves more as a lever arm for the extensor muscles of the elbow joint. There is also a curved notch in the ulna into which the curved end of the humerus fits. Note that your dog carries a majority of its weight on its front legs. If there is any joint that is a recipe for disaster, this is it. The precision with which the bones must fit together, combined with cartilage, ligaments, and tendons, added to the stress on the joint from running and jumping - it's a wonder the joint ever works properly. One 1986 Swedish study of 105 Bernese Mountain Dogs found that over 53% of them had elbow joint problems. Elbows are definitely a problem in the breed, and like other joint problems, there appears to be a genetic factor. In fact, one study found that the heritability factor of elbow problems was even higher than that for hip dysplasia! In a dysplastic elbow, the medial coronoid process and the edge of the ulnar surface lie above the level of the adjoining radius, creating a step between the radius and ulna and causing incongruity of the joint. This incongruity alone is often a source of pain and lameness (as with walking around in a shoe that doesn’t fit). The height of the step may vary from barely noticeable to a distance of 4 mm. When this occurs, the weight-bearing force on the ulna is increased, resulting in excessive pressure on the medial coronoid process. This leads to fragmentation of the coronoid (bone chips). This usually occurs between 5 and 7 months of age. The fragment(s) is(are) often the size of a rice grain, or larger. Incomplete fragmentation, in the form of cracks or fissures, can also occur. A superficial to deeply grooved "kissing lesion" is often present on the humeral articular surface opposite the fragment. A cartilage flap or OCD (osteochondritis dissecans) lesion may also be present. Secondary arthritis becomes evident at 6-7 months. Compensatory adjustments during growth may occur in some dogs, tending to minimize unequal growth rates between the three bones and moving the ulna distally to better conform to the radius. However, excessive force is then placed on the anconeal process at the top of the ulnar articular surface. This force will cause a failure of ossification, leading to an ununited anconeal process. The onset of pain usually occurs between 4 and 6 months of age and corresponds with the fragmentation of the coronoid, the development of OCD, and/or failure of ossification of the anconeal process. Joint fluid entering through fissures and cracks in the cartilage causes marked pain. The fragments are a constant irritant (like having a pebble in your shoe), causing more pain, a more severe lameness, and more rapid progression of arthritis.
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