Introduction
Elbow dysplasia (ED) is the most common cause of forelimb lameness in dogs. ED signifies an abnormal development of the elbow joint coupled with characteristic pathological changes of the medial compartment. ED includes an array of abnormalities including fragmented medial coronoid process (FCP), osteochondritis dissecans (OCD), joint incongruity and ununited anconeal process (UAP). The severity of clinical signs, pathologic change and outcome vary greatly amongst patients. Early diagnosis and prompt treatment gives patients the best chance of avoiding debilitating osteoarthritis.
Investigations
Dogs affected by elbow dysplasia begin to show clinical signs from about 5 months of age. These include intermittent or persistent lameness, elbow swelling, decreased range of motion and joint pain. Radiography including cranio-caudal, medio-lateral, and flexed lateral views should enable the differentiation of ununited anconeal process (UAP), fragmented coronoid process (FCP), and osteochondrosis dissecans (OCD). Additional oblique views have been advocated by some authors and may aid in the diagnosis of FCP. The value of computed tomography (CT) in the diagnosis of FCP has been well documented. CT is unnecessary in the diagnosis of FCP based on a high specificity of plain radiography; however, CT is useful on more confusing and milder arthroscopy patients in order to more accurately define the FCP lesion and assess for incongruity. Step lesions associated with short radius syndrome are clearly seen using CT.
Ununited Anconeal Process
Ununited anconeal process (UAP) occurs most commonly in German Shepherd dogs, but can be seen in many dog breeds. The anconeal process should fuse to the metaphyseal region of the proximal ulna at 4–5 months of age. If the process does not fuse, elbow stability is compromised and osteoarthritis ensues. Most patients having UAP have a short ulna relative to the length of the radius. The hypothesis is that as growth proceeds the anconeal process of affected dogs presses against the humeral trochlea. This creates a shear separating the anconeal process from the ulnar metaphysis. In cases of UAP the site of non-union will be clearly visible as an area of cartilage loss with exposed dense subchondral bone and possibly fibrocartilage. Surgical treatment is recommended. Arthroscopy allows assessment of the integrity of the anconeal fragment, the degree of fragment stability and the extent of osteoarthritis. The medial coronoid process should also be examined as many patients having UAP also have FCP. If the UAP fragment is of good integrity, it is a good candidate for reattachment using a lag screw. UAP fragments that are minimally displaced and partially attached may fare well with proximal dynamic ulnar osteotomy only. This procedure allows lengthening of the ulna as the radius grows and removes the shear stress of the anconeal process, allowing it to unite with the ulnar metaphysis. If the fragment is mobile and displaced, it should be reattached and stabilized using a lag screw (and K-wire), combined with a proximal dynamic ulnar osteotomy. If OA of the fragment and trochlear notch is severe or the problem is chronic, fragment removal is suggested.
Incongruity and Short Radius Syndrome
Elbow dysplasia may be associated with a shortened radius relative to the length of the ulna. Incongruity of the joint surfaces occurs. This results in concentration of weightbearing forces on the medial aspect of the joint, leading to cartilage wear and fragmentation of the medial coronoid process and sclerosis and cartilage wear of the medial humeral condyle. The amount of shortening may vary from severe to subtle. CT evaluation is the best way of documenting short radius syndrome in cases of subtle shortening. When shortening of the radius becomes more marked, radiographic and arthroscopic examination can lead to a diagnosis. The goals of treatment include improved congruity of the elbow, removal of any loose intraarticular fragments and surface treatment of osteoarthritic cartilage. Improved congruity of the elbow is accomplished by dynamic partial ulnar ostectomy. A small portion of the ulna is excised, allowing improved humeroradial contact. The ulna is not rigidly stabilized in order to allow it to shift over time to the "best fit" position. Occasionally a small intramedullary pin is placed to give partial stability to decrease pain and prevent excessive caudal translation of the proximal ulna. The cut can be performed proximally, midshaft or distally. Morbidity is reduced the more distal the osteotomy is performed. It would seem that a more proximal osteotomy above the interosseous ligament would have a better chance of correction of incongruity, however anecdotal reports suggest distal osteotomy can also be effective. Some surgeons feel that distal osteotomy is best in immature dogs because they have a more flexible interosseous ligament. Mature dogs may require a higher osteotomy due to a more rigid interosseous attachment.
Osteochondritis Dissecans
Osteochondritis dissecans (OCD) affects the medial humeral condyle. OCD lesions are more difficult to view than FCP lesions. OCD can occur in combination with FCP. OCD will usually appear on the humeral trochlea as a thickened flap of cartilage overlying a relatively deep (1–2 mm) subchondral bone defect. This is in contrast to subchondral bone exposure found with osteoarthritis (often known as a kissing lesion), which is more polished and follows the regular contours of the joint surface. Osteoarthritic lesions of varying degree may also accompany the OCD on either the adjacent humeral trochlea or on the opposing ulnar surface. Treatment includes OCD flap removal and abrasion arthroplasty or microfracture of the subchondral bone. Recent advances have made it possible to replace the damaged area of the medial humeral condyle with a synthetic graft or an osteochondral graft obtained from the patient's stifle joint.
Fragmented Medial Coronoid Process
Changes associated with FCP are extremely varied. The area of fragmentation is most commonly on the craniolateral aspect of the medial coronoid adjacent to the radial head. The fragments will most often be dead and yellow in appearance in contrast to well-vascularized red coloured bone. Additional changes associated with FCP will include varying degrees of osteoarthritic lesions on the remainder of the coronoid, trochlear notch and humeral trochlea. Changes seen in the radial head may include rounding off of the cranial and medial borders.
Pathologic changes are associated with the coronoid process and humeral condyle. Pathology of the medial coronoid is typified by subchondral bone micro-cracks and fragmentation as well as cartilage erosion secondary to incongruence. Many hypotheses have been formulated about the etiopathogenesis of the pathologic changes including radio-ulnar incongruence. The prevailing belief is that radio-ulnar incongruence is secondary to improper growth of the radius/ulna during maturation. The result is malalignment of the articular surfaces where the medial coronoid is subject to high mechanical loads and microfracture or fragmentation. Arthroscopy confirms fragmentation of the medial coronoid adjacent to the radial head without the presence of visible cartilage erosion. In these cases, fragmentation/microfracture of the medial coronoid may be secondary to mechanical overload associated with contraction of the biceps brachii/brachialis muscle complex. The histologic and ultrastructural appearance of FCP is consistent with mechanical failure and subsequent unsuccessful fibrous repair.
Treatment Options
Some dogs with mild signs of elbow dysplasia may be treated successfully with medical management including weight loss, antiinflammatory medication and adjunctive therapies such as hydrotherapy and physiotherapy. Osteoarthritis is likely to progress to a greater or lesser degree in all dogs with ED and this may cause lameness and pain in later life.
Surgical management involves one or a combination of the following options.
Arthroscopic Debridement
The FCP fragment and underlying necrotic bone should be removed arthroscopically or through a minimally-invasive arthrotomy. The underlying subchondral bone can be treated with abrasion arthroplasty or microfracture to encourage fibrocartilaginous repair. Osteoarthritis can still progress after debridement.
Subtotal Coronoidectomy
Traditionally removal of identifiable FCPs has been performed in dogs with ED. However some dogs have disease affecting the deeper regions of the coronoid, or they have diseased medial coronoid bone without fragmentation. These dogs may benefit from removal of a more significant piece of the medial coronoid, this is usually performed through a small arthrotomy incision.
Biceps Release
The biceps/brachialis muscles constitute a large muscular complex. The origin and insertion of the biceps and brachialis muscles are such that the muscular complex exerts considerable force on the medial compartment of the elbow. The force of the muscle rotates and compresses the craniolateral segment of the medial coronoid against the radial head. Interestingly, microfracture/fragmentation of the coronoid seen clinically is in the craniolateral segment of the medial coronoid adjacent to the radial head. Biceps tendon release from its insertion on the ulna can be performed as a means of reducing pressure on the medial aspect of the elbow joint.
Ulna Osteotomy
Dogs with elbow incongruity may benefit from an ulna osteotomy to restore joint congruity and relieve abnormal forces on the bones. The procedure can be performed in isolation as either an osteotomy or partial ulna ostectomy or the bone can be stabilized after cutting with a customized bone plate and screws such as the PAUL (proximal abducting ulna osteotomy plate, Kyon).
Osteoarthritis
The severity of osteoarthritis in ED is best evaluated using an arthroscope. The goal of the treatment is debridement of necrotic cartilage, removal of sclerotic bone, neovascularization, and recruitment of pluripotential mesenchymal cells. Cartilage debridement is accomplished using a hand burr, hand curette or motorized shaver. The exposed subchondral bone can be treated using abrasion arthroplasty or micropick technique.
Sliding Humeral Osteotomy (SHO)
The medial compartment of the humerus is usually the area of bone most affected in dogs with elbow dysplasia. Severely affected dogs will have lost all their cartilage on this aspect of the joint (often termed medial compartment disease). The sliding humeral osteotomy aims to transfer weight bearing from the medial aspect of the joint to the lateral. In dogs a mid diaphyseal humeral osteotomy is performed and a specific SHO plate applied to translate the distal bone medially which results in the desired transfer of weight to the lateral side. Complications with the procedure were quite high in early cases, and included humeral fracture and implant breakage. Improvements in the implants and procedure have resulting in a decrease in complications and initial results are promising with many dogs showing significant improvement in weight bearing.
Elbow Replacement
Elbow replacement has now become a valid and viable possibility in dogs. The joint can be totally replaced or partially replaced. Implantation of some of the earlier prostheses was associated with a very poor outcome and high complication rate. Dogs with complications after elbow replacement often require further surgery - often eventually requiring arthrodesis, amputation, or euthanasia. Newer implants or versions are available and the complication rate associated with their implantation is lower.
Elbow Arthrodesis
This is the final salvage procedure (prior to amputation) and should only be offered for an end stage painful joint in a small dog with unilateral lameness. The procedure will result in pain relief but the gait abnormality will be marked. Not ideal for dogs with bilateral disease.
Conclusion
To conclude ED is a common problem, especially in large breed dogs. Early treatment such as fragment removal or procedures to improve joint congruity can resolve lameness and decrease osteoarthritis formation. Osteoarthritis will however progress to a lesser or greater extent in all dogs, which can cause continual and recurrent lameness and these dogs may later benefit from salvage procedures or weight shifting procedures to decrease pain.