Elbow Dysplasia or Ununited Anconeal Process

29 05 2011

Elbow Dysplasia or Ununited Anconeal Process

 

 

If you have a large breed, rapidly growing dog that is limping on a front leg you may be dealing with elbow dysplasia.  Three different development problems can lead to the development of elbow dysplasia.  The three defects are separately identified as fragmented medial coronoid process, ununited anconeal process or osteochondritis (OC) of the medial humeral condyle, all of which are more commonly seen in the German shepherd breed of dog.

 

Clinical signs of elbow dysplasia include signs of pain during palpation of the elbow joint, swelling of the elbow joint, a decreased range of motion with the elbow joint, or outward rotation of the joint.

 

Elbow Dysplasia is believed to be caused by an asynchronous growth (uneven growth) of two possible bony prominences of the ulna and the parts of the humerus to which they normally attach.  The resulting skeletal abnormalities result in a subsequent joint incongruity (the three bones involved in the elbow joint do not fit together in a normal fashion) thereby resulting in instability of the entire elbow joint. Although ununited anconeal process is the most well known abnormality of the elbow joint, the fragmented medial coronoid process is more common.  Fragmented medial coronoid process is a commonly seen defect in German shepherds, Golden and Labrador Retrievers as well as Rottweilers, Bernese Mountain Dogs and Giant Schnauzers..

 

These conditions are believed to have several contributing factors including a genetic component which is influenced by abnormal weight bearing forces the leg may be subjected to.

 

OC of the medial humeral condyle is a problem with continuity of the developing cartilage surface of the ventral medial condyle of the humerus or joint surface of the lower humerus that articulates with the radius.  The cartilage surface of the medial humeral condyle does not develop normally causing it to be pitted or the surface may become loose, both of which result in secondary instability of the joint.  The etiologies of these cartilage lesions are suspected to be multifactorial including genetics, hormonal or nutritional imbalances and trauma. The end result of OC is vascular disruption resulting in ischemic damage (lack of oxygen) to the growing cartilage causing abnormalities in the cartilage.

 

At the elbow joint three bones come together to create movement.  The ulna and the humerus interlock by what is termed a trochlear notch.  The upper portion of the notch on the ulna is called the anconeal process, while the ventral or lower portion is called the coronoid process.  The humerus or the bone located above the elbow has a deep excavation or hole in the back portion of the bone ventrally to which the anconeal process will move in and out of during movement of the elbow.  While a young dog is growing the anconeal process is attached by cartilage to allow for growth. A complete bony union normally occurs between the anconeal process and the ulna at 4 to 5 months of age.  A similar situation develops with the medial coronoid process were by the growing bony prominence on the ventral part of the trochlear notch does not adequately fuse during growth resulting in the fragmentation of the coronoid process.

 

OCD of the medial humeral condyle is where the distal portion of the humerus nearest the side of the body develops a cartilage defect were the bone articulates with the radius.

 

The ossification center of the anconeal process develops at about 11-13 weeks and expands for about 6 weeks until osseous (permanent bony) union with the ulna is achieved by 4-5 months.  If extensive fissures develop in the bipolar growth cartilage between the anconeal process and the ulna, the normal plate closure will not occur and a fibrocartilaginous or fibrous union results.

 

Lameness typically develops between 4 to 8 months of age on the affected legs.  The elbow joints range of motion may be restricted.  In advanced cases osteoarthritis, crepitus (crackling sound) and effusion (swelling of the joint) will be apparent.  The condition may be unilateral (one-sided) or bilateral with varying degrees of severity being apparent.

 

Ununited anconeal processes are easily identified on the flexed lateral radiographic view of the elbow. With a united anconeal process a cleavage line is radiographically apparent or the process appears as an additional unattached bone free-floating within the joint.  A cranial-caudal radiographic view is best for diagnosing OC of the humerus and may affect any large breed of dog.  Both elbows should be radiographed regardless of the presence of clinical signs since the condition is often bilateral and varying degrees of severity may exist.

 

Radiographic diagnosis of fragmentation of the medial coronoid process can often be difficult.  Reasons for the difficulty in diagnosis includes:  partial fragmentation of the medial coronoid process, minimal fragment displacement, the presence of a small fragment or the fragment may be located between the radial head and the intact portion of the medial coronoid process obscuring it from view radiographically.  In some clinical cases the process may be on fissured and not displaced or mineralized.  Additionally the process may just be abnormally shaped which may further complicate the radiographic diagnosis.  The overall accuracy of radiographic diagnosis with an ununited coronoid process is a mere 57%.  When a special radiographic view called a craniolateral-caudomedial oblique is obtained the sensitivity of radiography to confirm a diagnosis may reach 67%.

 

Due to the difficulty in confirming elbow dysplasia resulting from an ununited anconeal process, radiographs should be taken of the shoulder, humerus, radius and ulna to rule out possible shoulder dysplasia or OD of the shoulder joint and panosteitis.
 

 

 

 

 

 

 

 

References:

 

Bahr, Anne.  “Reasons for Lameness.”  Veterinary Practice News.”  September 2008. P16.

 

Evans, Howard and George Christensen.  Miller’s Anatomy of the Dog.  W.B. Saunders Co. 1979.  Pp. 182-190.

 

Maxie, M Grant Editor.  Pathology of Domestic Animals.  Vol. l. 5th Edition.  Saunders. 2007. Pp. 136-142.

 

Morgan, Joe.  Radiology in Veterinary Orthopedics.  Lea and Febiger.  1972. Pp. 351-353.

 

Seyrek-Intas, Deniz and Ursula Michele et al.  “Accuracy of Ultrasonography in detecting Fragmentation of the Medial Coronoid Process in Dogs.”  JAVMA, Vol 234, No. 4, February 15, 2009. Pp. 480-485.

 

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