Elbow dysplasia is a common developmental disorder of the elbow joint of dogs. The common causes that will lead to this are fragmented medial coronoid process (FMCP), ununited anconeal process (UAP), osteochondrosis (OC) and incongruity of the elbow joint. Concurrent presence of 2 of more causes in a single joins is not uncommon. Clinically, we are not able to differentiate the cause based on clinical signs. It does not matter what is the primary cause of the elbow dysplasia, they will eventually leads to secondary degenerative joint disease.

Diagnostic imaging plays a very important role in evaluation of elbow dysplasia. There are two important aspect of diagnostic imaging: To diagnose the disorder with the identification of the cause and to screen and identify dogs with and without this disorder. Radiography evaluation of the elbow joints is acceptable as the initial step for diagnosing and screening purposes as radiography is readily available and it is not too technical to be performed.

As a rule of thumb, a minimum of 2 orthogonal views (mediolateral and craniocaudal) are needed to diagnose elbow disorders with manifestation of clinical signs. Additional craniolateral-15°-caudomedial oblique may be needed.¹ As for the purpose of screening, the international elbow working group recommended at least a flexed lateral view of dogs with a minimum age of one year. The objective of performing only one flexed lateral view is to evaluate the secondary arthrosis. However, many countries required additional views such as mediolateral and craniocaudal and sometimes a craniolateral-15°-caudomedial oblique view to identify the primary cause in addition to the secondary arthrosis.

Anconeal process is a separate ossification center of the proximal ulna. It is normally fused at the age of 5 months. It is thus only possible to make a diagnosis of ununited anconeal process in dogs older than 5 months old. A mediolateral view demonstrating separation of the anconeal process from the proximal ulna with irregularly marginated lucent gap is the hallmark of united anconeal process.

Osteochondrosis occurs mostly on the weight-bearing surface of the distal medial humeral condyle. The radiographic features are present of a subchondral flattening or defect with sclerotic margins. Depending on the size and severity of the lesion, most of the time OC can be identified on all views.

The primary lesion of FMCP is not easy to be detected on radiography. Absent of the sharply marginated triangular-shaped MCP, suggest FMCP. In severe cases, flattening, rounding, proliferation and distinct fragmentation of the MCP could be observed on multiple radiographic views. Due to its low sensitivity of radiography to visualize the primary lesion of FMCP, secondary osteoarthrosis seen without other primary cause seen such as UAP, OC or elbow incongruity is considered as having FMCP.

Sensitivity of radiographic detection of elbow incongruity depends on the severity of the incongruity. The sensitivity is higher for detection of incongruity of > 2 mm.² Flexed mediolateral view at 90° with the radiographic beam centered at medial epicondyle is recommended. The radiographic signs of incongruity are a step defect between the radial head and the ulnar lateral coronoid process and an increased in the humero-ulnar joint width.

The purpose of screening is to identify dogs with radiographic elbow dysplasia but without any clinical signs. Thus, the identification of the primary cause is not really important since no treatment plan is needed most of the time. Only a flexed mediolateral radiograph is needed to assess the secondary arthrosis (presence of osteophytes dorsal to the anconeal process) of the elbow neglecting the primary cause. However, some owner/veterinarians elected to perform more radiograph to identify the primary cause if there is present of the secondary arthrosis. This is to prevent repetition of the elbow radiographs in case the dog develops clinical sign in the future.

Computed tomography (CT) evaluation of elbow dysplasia is particularly target to the evaluation of MCP as OC and UAP are readily identified with radiography. This is performed mainly after radiographic examination and diagnosis of the primary cause of elbow disorder could not be made or the radiographic changes of the elbow are subtle and a definitive diagnosis is difficult to achieve. Information that could be obtained from CT is changes of the subchondral bone (sclerosis, fissures, necrosis, cysts and fragmentation).

In addition to this, CT can detect abnormalities of the MCP such as abnormal shape, sclerosis, present of osteophytes, fragmentation, and changes of the bone attenuation. Computed tomography has been used widely for the evaluation of the joint congruence due to the advantage and capability of performing multiplanar reconstruction of the joint with CT study. Diagnostic certainty of joint congruency was higher with sagittal plane. Higher diagnostic certainty of MCP and subchondral abnormalities was transverse plane and dorsal plane respectively. It is suggested that CT has a higher sensitivity for diagnosing elbow dysplasia.³ A different window display is needed for the evaluation of different lesion in the elbow.⁴

In conclusion, the objective of the diagnostic imaging investigation of elbow should be established before the procedure as this may help in deciding the views needed and also the imaging modality used.

References

1.  Voorhout G, Hazewinkel AW. Radiographic evaluation of the canine elbow joint with special reference to the medial humeral condyle and the medial coronoid process. Vet Radiol Ultrasound. 1987;28:158–165.

2.  Blond L, Dupuis J, Beauregard G, Breton L, Moreau M. Sensitivity and specificity of radiographic detection of canine elbow incongruence in an in vitro model. Vet Radiol Ultrasound. 2005;46:210–216.

3.  Kunst CM, Pease AP, Nelson NC, Habing G, Ballegeer EA. Computed tomographic identification of dysplasia and progression of osteoarthritis in dog elbows previously assigned OFA grades 0 and 1. Vet Radiol Ultrasound. 2014;55:511–520.

4.  Tromblee TC, Jones JC, Bahr AM, Shires PK, Aref S. Effect of computed tomography display window and image plane on diagnostic certainty for characteristics of dysplastic elbow joints in dogs. Am J Vet Res. 2007;68:858–871.