ELBOW DYSPLASIA

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Osteochondrosis

of the Humeral Condyle

North American dogs with osteochondrosis/osteochondritis dissecans of the humeral condyle are recognized relatively infrequently in comparison to dogs with fragmented coronoid process and ununited anconeal process. Reports from Europe would suggest that osteochondrosis/osteochondritis dissecans of the humeral condyle occurs much more frequently than in dogs in North America. This may reflect genetic differences in the populations or possibly dietary practices. While osteochondrosis/osteochondritis dissecans of the humeral condyle occurs in many large and giant breeds of dogs, Golden and Labrador retrievers seem particularly prone to develop this condition.

INCIDENCE OF CONFIRMED LESIONS
        BREED

           OCD

            FCP

CONCURRENT OCD & FCP
Labradors

31

45

24
Rottweilers

8

40

2
Others  

21

3
Total

53

129

34

Gutherie S. J Small Anim Pract 1989

Osteochondrosis is a developmental orthopedic condition characterized by a disturbance in the normal process of endochondral ossification. Endochondral ossification is the process responsible for long bone growth and involves the orderly formation of bone from cartilage. In the pathogenesis of osteochondrosis the normal process of cartilage resorption and subsequent calcification process is disrupted and affected articular or physeal cartilage becomes grossly thickened. Cartilage, which is avascular, is dependent on diffusion of synovial fluid for its metabolic needs. Chondrocytes in the deeper zones of abnormally thickened cartilage are deprived of nutritional support because of the increased distance synovial fluid must diffuse. The result is abnormal chondrocyte metabolism and dysfunction. Cartilage in these deeper layers may become necrotic and develop cracks and fissures. If a crack or fissure extends to the surface of the cartilage, synovial fluid dissects beneath the cartilage flap and debris and inflammatory mediators are released from the necrotic cartilage resulting in inflammation of the synovial tissues. When a cartilage flap or osteochondral fragment are present the condition is more appropriately described as osteochondritis dissecans.

The presence of an articular cartilage flap is the classic lesion of osteochondritis dissecans. The inflammation associated with osteochondritis dissecans lesions produces observable clinical signs such as pain and lameness. As the cartilage flap or osteochondral fragment continues to separate from the subchondral bone a number of different sequelae can develop. Cartilage flaps may remain attached and calcify causing lameness and osteoarthrosis. Cartilage flaps and osteochondral fragments often give rise to a superficial erosive ("kissing") lesion of the apposing articular surface. Cartilage flaps may detach and be resorbed or develop into an attached or free floating "joint mice". The remaining articular cartilage defect will eventually fill in with a fibrous repair tissue resembling fibrocartilage.

WP16.jpg (95189 bytes) Osteochondrosis/osteochondritis dissecans lesions of the humeral condyle can be observed on the craniocaudal view radiograph of the elbow as a subchondral bone defect that affects the trochlea (the medial portion) of the humeral condyle. These lesions can be subtle and may not be identified unless the radiographs are of good quality and evaluated carefully. The pronated oblique, craniocaudal view is often of value in identifying lesions that may not be apparent on nonoblique craniocaudal view radiographs. If the lesion is large, an irregular subchondral bone defect or flattening of the articular surface of the medial condyle may be visible on the lateral view radiograph.
Secondary, degenerative changes are usually present in dogs seven months of age and older. As previously stated osteochondrosis/osteochondritis dissecans of the humeral condyle can and often occurs concurrently with fragmented coronoid process. True osteochondrosis/osteochondritis dissecans lesions of the humeral condyle can sometimes be difficult to distinguish radiographically from erosive lesions of the trochlea of the humeral condyle induced by fragmented coronoid process particularly in older dogs. WP17a.jpg (5986 bytes)

Radiographs of a dog's elbow affected with osteochondritis dissecans. These are mild degenerative changes along the medial aspect of the elbow. The lesion (circle) can only be readily visualized on the oblique view.
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Approach to the elbow using an osteotomy of the medial epicondyle to excise and debride an ostochondritis disecans lesion.

 Treatment involves excision of the cartilage flap and curettage of the subjacent subchondral bed.  Some veterinary surgeons are now treating these lesions with arthroscopy. Arthroscopy allows a greater extent of the joint to be evaluated with the advantage of magnification. While the immediate postoperative morbidity is probably less with arthroscopy than arthrotomy, the long-term functional results are probably similar.
Several surgical approaches have been described for approaching the medial compartment of the elbow. A recent study performed using cadaver limbs evaluated articular cartilage exposure and immediate postoperative stability afforded by three described approaches to the medial compartment of the elbow, an osteotomy of the medial epicondyle, a longitudinal myotomy of the flexor carpi radialis muscle, and a desmotomy of the medial collateral ligament which included a tenotomy of the pronator teres muscle. The approach using an osteotomy of the medial epicondyle provided significantly greater exposures of the humeral articular cartilage (22%) than either of the other two approaches and the approach using a desmotomy of the medial collateral ligament provided significantly greater exposure of the humeral articular cartilage (16.5%) than the approach using a longitudinal myotomy of the flexor carpi radialis muscle (6.6%). The immediate postoperative stability of the approach using an osteotomy of the medial epicondyle and the approach using a longitudinal myotomy of the flexor carpi radialis muscle were significantly greater than that of the approach using a desmotomy of the medial collateral ligament. It must be noted, however, that testing of the limb was performed with both the elbow and carpus in 90 of flexion to accentuate the soft tissue contributions to valgus stability of the elbow. At lesser angles of elbow flexion, interlocking of the anconeal process in the trochlea and olecranon fossa provided the valgus stability of the elbow. This locking mechanism of the anconeal process in the trochlea and olecranon fossa probably negates much of the morbidity of any surgical approach to the medial compartment of the elbow and accounts for the lack of reported complications associated with the use of the medial desmotomies in clinical cases.
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Approach to the medial aspect of the elbow using a muscle separating approach.

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Approach to the medial aspect of the elbow using a tenotomy of the pronator teres muscle.
We and others have experienced implant complications in clinical cases in which we used an osteotomy of the medial epicondyle to approach the medial compartment of the elbow and feel exposure of the trochlea of the humeral condyle is sufficient to excise cartilage flaps and curette the lesion's bed using a muscle separating approach between the flexor carpi radialis muscle and the pronator teres muscle. In some instances exposure is sufficient by retracting the medial collateral ligament but in many instances a medial desmotomy is required. A myotenotomy of the pronator teres muscle can be performed if additional exposure is required; however, this is seldom necessary and should be avoided in performance dogs.

Osteochondritis dessicans lesions of the humeral condyle may not always be obvious at surgery. If a lesion is suspected based on the pre-operative radiographs and is not readily apparent at arthrotomy, the articular surface of the trochlea of the humeral condyle should be probed with a Freer periosteal elevator. In these instances the malacic cartilage will readily separate from the adjacent unaffected cartilage. All diseased cartilage should be excised and the subchondral bed curettaged. Osteochondritis dissecans lesions of the humeral condyle should be differentiated from erosive or "kissing" lesions of the trochlea of the humeral condyle which frequently occur in response to fragmented coronoid process.
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Removal of osteochondritis lesion of the humeral condyle during arthrotomy

 
Postoperatively the limb is placed in a soft padded bandage for 2 to 4 days following surgery to limit swelling and exercise is restricted for 3-4 weeks. The prognosis for return to function is again somewhat guarded for dogs with osteochondrosis of the humeral condyle. The prognosis seems to be somewhat dependent on the size of the lesion and the extent of degenerative joint disease present at the time of surgery.  Young dogs with small lesions and minimal degenerative joint disease are stated to have a more favorable prognosis than older dogs with larger lesions and more advanced degenerative joint disease. Although degenerative joint disease progresses irrespective of surgical intervention, most dogs regain reasonable limb function following surgery. Medical management of degenerative joint disease may be necessary. Some dogs may have acceptable limb function to return to hunting and other working activities.




 

  
wp1.jpg (85757 bytes) The term "elbow dysplasia" has been coined to describe three developmental conditions, osteochondrosis/ osteochondritis dissecans (OC/OCD) of the humeral condyle, ununited anconeal process (UAP), and fragmented coronoid process (FCP), that commonly affect the elbow of many large and giant breeds of dogs. All three conditions share many clinical similarities. Lesions are often bilateral and multiple disease processes can occur concurrently in the same dogs as well as in the same joint. Most commonly osteochondrosis/osteochondritis dissecans and fragmented coronoid process are recognized concurrently.
The history, signalment, and clinical signs are similar with all three conditions. Clinical abnormalities result from acute joint inflammation and progressive degenerative joint disease of the elbow. Affected animals may exhibit lameness as early as four months of age. The lameness is intermittent and may be exacerbated by exercise or when the dog first ambulates following prolonged rest. Affected dogs may stand or sit with the carpus and paw held in an externally rotational position and with the elbow abducted. The dog may circumduct the antebrachium during the swing phase of the stride. Full flexion and particularly extension of the elbow may elicit a pain response. In dogs with ununited anconeal process it has been stated that a pain response also can be elicited by applying direct pressure to the anconeal process through the anconeus muscle as the dog's elbow is held in flexion. Crepitus, joint capsule thickening, and decreased range of motion are present in advanced cases. Although synovial effusion is considered a classic sign of ununited anconeal process, synovial effusion can also be present with osteochondrosis of the humeral condyle and fragmented coronoid process.
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Obvious synovial effusion of the elbow. There is a fluctuant swelling below the lateral epicondyle of the humerus (circle).

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Aspiration of synovial effusion of the elbow
These conditions can be differentiated by high quality craniocaudal and lateral radiographic views of the elbow joint. Additional oblique and flexed lateral views of the elbow may also be warranted. In all three conditions the prognosis for return to working or athletic performance, irrespective of whether or not surgical intervention has been done, is guarded. This guarded prognosis is based on the progression of degenerative joint disease with all three of these conditions irrespective of whether or not surgery is performed. In addition, an exploratory arthrotomy is not a benign procedure, especially if the collateral ligaments are incised, or an osteotomy of the medial epicondyle is performed. Although the apparent recovery following surgery is rapid, some morbidity is expected. Also, elbow function is dependent on a normal anatomic relationship of the radioulnar, humeroulnar and radiohumeral articulations and abnormal elbow conformation is believed to be an integral component in the pathogenesis of these diseases.

The heritability of fragmented coronoid process and osteochondrosis of the humeral condyle are well established and a heritable basis is also suspected in ununited anconeal process. Thus, consideration should be given to neutering affected dogs thus eliminating them from breeding programs.