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The term elbow dysplasia has come to describe a group of developmental disorders of the canine elbow joint including:
• Fragmentation of the medial coronoid process (FCP)
• Osteochondritis dissecans (OCD) of the medial portion of the humeral condyle
• Ununited anconeal process (UAP)
• Elbow incongruity
Whilst the pathologies of FCP, OCD and UAP are relatively clearly defined and distinguishable, the term “incongruity” is poorly defined and there is a lack of understanding regarding what constitutes normal congruity of the elbow. All of these conditions start in early life, typically between three and six months old, although clinical signs may not become apparent in some cases until some time later.
Elbow dysplasia is common, particularly in certain breeds. FCP is particularly common and occurs in breeds such as the Labrador and Golden Retriever, Rottweiler, Bernese Mountain Dog, and Newfoundland1. OCD is much less common but also occurs in these breeds. UAP has a somewhat different breed prevalence with the German Shepherd Dog commonly reported in published papers along with the Bassett Hound and other miscellaneous large breed dogs2,3. Both OCD and UAP can occur concurrently with FCP4.
Elbow dysplasia is a multifactorial disorder but is known to be a complex genetic trait with heritability figures in the range 0.10 – 0.775-8 depending on the breed and population studied. Thus, in some populations, the majority of the phenotypic variance can be explained by genetics, whereas in others, there appears to be more environental influence on variance. Radiographic screening programmes have been in place in many countries to identify dogs with elbow dysplasia phenotypically. The insensitivity of radiography to elbow dysplasia is an issue in these programmes, as is the complex, polygenic nature of the conditions.
The pathogenesis of FCP is unclear. The early lesion appears to be consistent with a fracture in the lateral part of the medial coronoid process of the ulna9. Recent studies suggest that microdamage within the bone of the medial coronoid process is the earliest identifiable pathology10 and that cartilage pathology is a later event.
The classic fragmentation lesion is not seen in all dogs. Approximately 30% of dogs presenting for signs of elbow pain will not show a separate fragment but may have fibrillation and erosion of the cartilage of the medial coronoid process and sometimes partial fissuring of the underlying bone1. This is logical since one would expect a continuum of pathological change. However, it does highlight the fact that fragmentation is not necessary for pain and lameness to occur.
The pathology of OCD of the medial humeral condyle of the dog is not well studied. Studies in other species again suggest that the early lesion starts deep within the articular-epiphyseal cartilage complex with necrosis around cartilage canals11, leading to dissecting lesions which propagate towards the articular surface12.
UAP appears to be related to a relatively short ulna compared to the radius3. This presumably creates tension within the elbow joint which leads to separation of the anconeal apophysis.
DIAGNOSIS OF ELBOW DYSPLASIA
History and Clinical Signs...
Diagnosis of elbow dysplasia can be challenging. The signalment can be helpful in that the breeds commonly affected by FCP include Labrador and Golden Retrievers, Rottweiler, Bernese Mountain Dog, Mastiff and Newfoundland. Ununited anconeal process occurs most commonly in the German Shepherd Dog and Bassett Hound, although it can occur in other medium-large breed dogs. A typical age for presentation is 5-9 months but some dogs are older (9-18 months) and, occasionally, much older (e.g. 4-6 years).
Clinical signs include mild-moderate thoracic limb lameness and inactivity stiffness. Affected dogs may also typically stand with the distal thoracic limbs externally rotated. Because the disease is usually bilateral, there may be symmetry to the clinical signs and lameness may not be obvious, with merely a bilaterally shortened stance phase to the thoracic limb gait cycle. There is pain on elbow joint manipulation, particularly full extension, external rotation, and full flexion combined with internal rotation. A minority of affected joints have a palpable effusion caudolaterally.
Radiography is the traditional method of evaluating elbow joints. Of course, this does not make it the best method. Mediolateral (flexed, neutral and extended) and craniocaudal views of the joint can provide information on secondary osteophytosis, sclerosis in the ulnar notch, or whether there is OCD of the medial humeral condyle, or ununited anconeal process; in the majority of joints that have FCP, osteophytosis is the only change noted. One major problem with relying on osteophytosis as a marker of FCP is that it can take weeks or months for this secondary change to occur. The clinician should also be aware that the evaluation of sclerosis may be prone to significant error13. Oblique radiographs have been investigated as an alternative method to detect fragmentation14 but since the position of the fragment is usually on the lateral aspect of the medial coronoid process, adjacent to the radial head, it is unlikely that oblique views will add significantly useful information. The degree of osteophytosis can be graded but the relationship between osteophyte grade and FCP is poorly documented. One study did suggest a correlation between osteophyte grade and degree of cartilage erosion15.
Distal humeroradial subluxation may be an early change in elbow dysplasia16,17. However, the radiographic assessment of elbow joint incongruity is not easy unless it is severe. One study showed that for subjective assessment of incongruity the greatest agreement between observers is with a 90º flexed mediolateral radiograph centred on the elbow joint18. Measurement of joint spaces can be achieved with image processing software and this was reliable as a technique for most joint spaces evaluated. However, the position of the elbow joint can significantly alter the measured joint space18. Further information is required to validate the radiographic assessment of joint spaces and incongruity.
Advanced Imaging Modalities...
Advanced imaging techniques can also be used to evaluate elbow joints but the limited availability if these is an issue at present. Computed tomography (CT) has been shown to be sensitive to detection of FCP19 but the author's experience is that false-negative results are still a problem when compared to arthroscopic findings. Nevertheless, CT is undoubtable a useful imaging modality for elbow dysplasia, although limited availability and cost are issues. There is limited informatuon on the use of MRI to assess the canine elbow joint20-22.
Arthroscopy is probably the gold standard for diagnosis and staging of FCP, OCD and UAP. A medial portal with a 1.9mm or 2.4mm arthroscope is the standard approach. Arthroscopy allows for the detection of nondisplaced FCPs as well as cartilage fissures and chondromalacia.
Arthroscopy is also useful for diagnosis of OCD, investigation of UAP lesions, and evaluation of the remainder of the elbow joint; it should be noted that UAP and FCP occur together with a frequency in the region of 15-20%4. Training and practice in this technique are important to develop an appropriate level of expertise. Arthroscopic studies have demonstrated that the classic fragmentation lesion is not seen in all dogs. Approximately 30% of dogs presenting for signs of elbow pain do not have the classic fragmention lesion but may just have erosion of the cartilage of the medial coronoid process and possibly fissuring of the underlying bone1. This does support the hypothesis that fragmentation is not necessary for pain and lameness to occur.
Arthroscopy also facilitates operative management of FCP and OCD (see below) should surgical management be selected.
TREATMENT OF ELBOW DYSPLASIA
Treatment of FCP...
Treatment of FCP is controversial because the benefits of surgical treatment over conservative management have not been demonstrated clearly23. Conservative management might typically involve 4-8 weeks of reduced lead exercise and tactical use of NSAIDs; obviously, an NSAID licensed for long-term use such as firocoxib, carprofen, meloxicam or tepoxalin should be chosen. One might also consider the use of a functional food or nutraceuticals although there is no published evidence to support their use in this scenario. One should ensure that affected animals are not obese; dogs carry 60% of their bodyweight on their thoracic limbs, so obesity can compound the discomfort of elbow pain. It is also likely that long-term obesity will hasten the progression of secondary osteoarthritis24.
Conservative management may result in 65% of dogs improving over 1-3 months.
Key components of conservative management are:
• Analgesia in the form of long-term NSAIDs
• Controlled exercise
• Avoidance of obesity
Surgical management most often involves removal of loose fragments, preferably under arthroscopic guidance. Medial arthrotomy is an alternative means to achieve fragment removal but is not recommended because arthroscopy provides more accuracy and reduced post-operative morbidity.
There is also evidence to suggest that the clinical outcome is better following arthroscopic removal compared to medial arthrotomy25.
Some other reported techniques have attempted to address the underlying incongruity by performing an ulna osteotomy26 with or without medial arthrotomy, although there are at present no data to say whether this results in a better outcome in the long or medium term. This procedure does cause considerable morbidity and the recovery time is 6-12 weeks. Perhaps because of these issues, the procedure has not gained widespread popularity.
In the long term, all dogs with this condition will develop osteoarthritis that may or may not cause clinical problems in later life. In fact, it is likely that many more dogs present in later life with elbow osteoarthritis, than present as young dogs. This suggests that many cases of elbow dysplasia are clinically silent until the secondary osteoarthritis starts to cause stiffness, pain and lameness in later life. Management of elbow osteoarthritis is discussed later in this article.
Treatment of OCD...
Treatment of OCD of the medial humeral condyle can also be conservative, although perhaps there is a greater consensus towards surgical management. Conservative management would be as for FCP. If surgery is to be considered, arthroscopy is the recommended approach. The loose cartilage flap is removed using arthroscopic grasping forceps and the underlying subchondral defect is subjected to light curettage to encourage bleeding and migration of mesenchymal cells to invade the defect to facilitate fibrocartilage repair tissue.
Treatment of Ununited Anconeal Process...
Treatment of UAP has progressed significantly over the past 10-15 years. Traditional treatment for UAP was removal of the ununited anconeus. However, this destabilizes the joint and tends to result in rogressive osteoarthritis27 and poor function. Fixation of the anconeal process is also reported using lag screws28 or screw plus pin29. Results seem satisfactory but fixation alone can result in implant failure.
Ulna osteotomy has also been advocated as a logical extrapolation of the data on aetiopathogenesis3. Ulna osteotomy alone can result in spontaneous fusion of the anconeus2,3, although it appears that the technique is more successful in younger dogs. Ulna osteotomy combined with fixation appears to give the most predictable results29,30 and this is the author’s preferred technique. If attempted fusion is unsuccessful, or if the case presents late with severe secondary osteoarthritis, removal of the anconeal process may be the preferred option.
Treatment of Elbow Osteoarthritis...
For many dogs, elbow dysplasia goes unnoticed until the secondary osteoarthritis has progressed sufficiently to cause stiffness, pain and lameness in later life. For the vast majority of such cases, conservative and medical management of the osteoarthritis is the logical option.
Improving function in these patients is the aim, and pain relief is central to this mission.
For severely affected patients, there is also now the option of total elbow joint replacement. Whilst this procedure can produce major benefits for such patients34 when the procedure is successful, there is a 20% complication rate and clients need to assess carefully the risk:benefit ratio of the procedure.
Elbow dysplasia and osteoarthritis affect large numbers of pedigree dogs of popular medium-large breeds such as the Labrador Retriever and Rottweiler. Patients should be carefully assessed at every stage of the natural history of this disease. Young dogs may be treated medically or surgically. For the majority of older dogs with pain from chronic elbow osteoarthritis, multimodal therapy including long-term use of NSAIDs is the preferred treatment option.
This article was kindly provided by Merial, makers of Previcox:
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