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Elbow dysplasia in small animals (Proceedings)
Elbow dysplasia is a group of diseases made up of several conditions including ununited anconeal process, osteochondritis dissecans humerus, fragmented coronoid process, and incomplete humeral ossification.
Elbow dysplasia is a group of diseases made up of several conditions including ununited anconeal process, osteochondritis dissecans humerus, fragmented coronoid process, and incomplete humeral ossification.1 Osteoarthritis can develop following these diseases and after fracture or infection. The diagnosis of an elbow problem may seem straight forward, especially if there is joint swelling in the caudal proximal joint, however in some cases the forelimb lameness is inconsistent and the animal does not exhibit pain on routine palpation. On exam of the elbow in these difficult cases, I try to determine the range of motion of the joint, which commonly will be decreased in flexion if there is a problem. I also will supinate and pronate the forelimb while holding the carpus or distal radius/ulna (to exclude the carpus as the cause of pain) and determine if there is pain there. In many instances the patient will have a pain response only in extensive supination or pronation. This is often the case with dogs affected with fragmented medial coronoid process early in the course of the disease.
Other diagnostics that can be used to diagnose elbow disease include radiographs, of course, but this will in most instances, give only indirect evidence of disease and only if the disease is subacute to chronic. Nuclear scintigraphy can be much more rewarding especially if the patient is lame at the time of the scan. The scan will identify increased uptake of radioactive element in soft tissues with an early scan after intravenous injection and bone uptake in areas of chronic inflammation 2 hours after injection of the element. Computed tomography is useful for bone lesions involving the coronoid process and does not require 24 to 48 hours of isolation following the scan, as does nuclear scintigraphy. Finally, arthroscopy can be used as a minimally invasive method of not only diagnosing the disease process, but also treating the process such as removing a coronoid fragment. Often, if the lameness is severe enough the owners will choose to proceed directly to arthroscopy (following radiographs) of both elbows in the same anesthetic procedure, knowing that a normal elbow may be found in one or both joints. If the lameness is nebulous and intermittent, a nuclear scintigraphy scan, when the patient is lame, will be the most helpful, although false negative scans can and do occur. 1
Most often elbow dysplasia is diagnosed in young adults and puppies. Development of the elbow joint in growing puppies is still under much investigation but we do know the elbow undergoes some periods of incongruity that resolve once the dog has reached skeletal maturity. In the adult dog the radial head transmits 75 to 80% of body weight through the joint but the medial coronoid still transmits the rest (20-25%). The anconeal process engages the humerus in extension and prevents lateral and rotary instability during weight bearing.
There are several theories as to the cause of elbow dysplasia. One such theory is of ulnar humeral incongruity in which the humerus pushes on the anconeal process caudally and proximally preventing the growth plate there from uniting or closing. In addition, the medial coronoid then receives more weight than it normally would and is fractured over time. Another theory describes radio-ulnar incongruence in which there is a discrepancy between rate of growth of radius and ulna. If ulna is growing more quickly, the medial coronoid process (MCP) is forced to bear all the weight of the animal transmitted through the elbow since the radial head is no longer in contact with the humerus resulting in microfractures and fragmentation of the coronoid over time. In addition, by applying concentrated forces to the medial portion of the humeral condyle, the theory describes a resulting osteochondritis lesion of the medial portion of the humeral condyle.
With ununited anconeal processes, the anconeus has failed to fuse to the olecranon by 20 to 24 weeks of age in a large to giant breed puppy. Some researchers believe that the lack of fusion is due to radio-ulnar incongruity and the longer radius forces the humerus proximally along with the anconeal process. Others believe there is a malformation of the trochlear notch of the ulna that is not congruent with the humerus. Whatever the cause, excision of the process is not recommended if at all possible. Instead, fixation of the process to the ulna with a lag screw and/or pins and ulnar ostectomy has the best long term prognosis. (JANACH AJVR 06) Unfortunately, fixation of the process is small breeds may not be possible. Long term diet restriction, especially during the first 6 weeks to 8 months of life may decrease the incidence of ununited anconeal process in dogs and should be discussed with puppy owners of high-risk breeds at the time of initial examination.2,3
Fragmented medial coronoid process is a common cause of elbow disease in the dog and many dogs are not diagnosed until they are adults with degenerative joint disease. Because the coronoid is difficult to visualize on radiographs, many clinicians look for signs of early degeneration, including osteophytes on the caudal anconeal process, sclerosis of the ulnar notch and osteophytes on the radial head.4,5 Treatment of fragmented coronoid process involves removing the fragment either arthroscopically or through an arthrotomy and microfracture of the exposed bone of the coronoid to try to induce fibrocartilage formation over the exposed bone. The prognosis long term is poor and only 60% are considered to have a good outcome.1 The specific cause of fragmentation remains unknown, but we do know that the bone fractures first before any abnormalities in the overlying articular cartilage.6 No known genetic defects in collagen synthesis have been found, but no incongruity in the radius and ulna except at the very base of the coronoid process has been identified either.7,8 Whatever the cause complete remove of the coronoid in dogs affected with fragmentation does resolve the lameness but most dogs (70%) have significant progression of degenerative joint disease over time.9 Unfortunately, once osteoarthritis in the joint has developed it cannot be stopped and the elbow is a very unforgiving joint, with most dogs showing signs of lameness at least intermittently with the osteoarthritis.
Osteochondritis dissecans of the distal humeral condyle can be diagnosed on radiographs, however an oblique view highlighting the medial compartment of the joint is usually needed. Treatment involves removing the cartilage flap and microfracture of the underlying bone but the prognosis longterm is poor.1
Once osteoarthritis has become progressed, chronic unrelenting lameness develops that can significantly affect the quality of life of the patient. Only three options exist at that point. Either the limb is amputated, the elbow is arthrodesed, or the elbow joint is replaced.10 Amputation may not be an option since many dogs have bilateral elbow disease and the remaining contralateral limb, while currently functional, can have significant progression of degenerative joint disease without the other limb very quickly. Arthrodesis can remove the pain from the elbow joint itself but places increased stress on the contralateral elbow as well as the more proximal and distal joints in the arthrodesed limb. Again, following arthrodesis as with amputation, progression of more joint disease, either in the same limb or others commonly occurs.11 The only other option is to replace the joint. In humans, elbow joint replacement is a salvage end-stage procedure in which the radial head is resected and never replaced. The patient can never lift more than 5 pounds of weight with the arm ever again. Clearly, this much decreased function on a weight bearing limb is not an acceptable option for dogs. Two elbow implants are currently available to veterinarians. One has been produced that uses cement for implantation.12 While it functions extremely well, the surgery is technically demanding and complications can be severe including fracture, luxation and chronic infection.13,14 Recently, a more constrained implant system has been developed that does not require the use of bone cement and is less technically demanding to implant.15 No severe complications have yet occurred but the clinical cases in which it has been used are only 1 year postoperative, (personal communication, Randy Acker, DVM). This implant is very constrained as well, which may make the contact surfaces of the implants wear faster than a less constrained system such as the more established cemented model. Only time will tell if the new implant has longevity.
Clearly, current and future research would be best employed toward developing an understanding of the pathology causing elbow disease in order to avoid the very painful debilitating osteoarthritis that develops long term in dogs. If an implant system is developed that can last 8 years in dogs, this would be ideal for those cases in which degenerative joint disease is no longer manageable. For the general practitioner, identifying puppies at greatest risk of developing elbow problems and treating the problem as early as possible gives the individual the best prognosis, because if osteoarthritis can be prevented, the prognosis improves long term.
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