Differentiating forelimb lameness in dogs: shoulder or elbow? (Proceedings)


Differentiating forelimb lameness in dogs: shoulder or elbow? (Proceedings)

Aug 01, 2011

Forelimb lameness can often be a diagnostic challenge in sporting breeds and active family pets. Commonly the owner reports the presence of a long standing lameness which has not resolved with the application conservative treatment modalities such as physical therapy (rest, therapeutic ultrasound, aquatic therapy), NSAIDs, nutraceuticals, and other traditional modalities. Frequently physical examination is unrewarding other than the finding of an obvious forelimb lameness. Although it is beyond the scope of this presentation to discuss all pathologic conditions of the forelimb, more common problems and application of imaging modalities to facilitate the achievement of an accurate diagnosis will be addressed.

Forelimb lameness

Forelimb lameness can be a diagnostic challenge in the athletic dog; often the lameness has been treated for months with no improvement. The only abnormal physical finding may be the observation of Grade 2 or Grade 3 lameness. The source of lameness may be attributed to soft tissue injury, bony injury or a combination of both. In the active adult dog the most common cause of latent forelimb lameness can be attributed to pathology in the elbow and to injury of the active and passive shoulder restraints. In the author's experience, pathology in the elbow is regularly caused by occult microfracture/fragmentation of the medial coronoid process. There is no joint effusion, loss of motion, pain, or crepitus on physical examination. Radiographs are reported as normal or may show minimal subtrochlear sclerosis of the ulna.

Modalities to facilitate an accurate diagnosis in these cases are CT, nuclear scan, and arthroscopy. Recommendations for performing CT include scanning from the point of the olecranon to 2cm distal to the radial head. Scan thickness should be 1-2mm with .5mm overlapping slice index. Transverse slices using 1500 to 3500 HU are ideal for imaging subchondral bone and fragments of the medial coronoid; transverse images at 3500HU are considered ideal for identifying ostomalacic lesions of the medial coronoid.

Nuclear scintigraphy can be used to localize the origin of the lameness and can be used to facilitate detection of subtle pathologic changes before changes are evident of radiographs. Technetium phosphonates are typically used for scintigraphy of joint tissues. Scintigraphy has high sensitivity for detection of presence of elbow pathology but is not specific for definitive diagnosis. Regulatory issues often limit the use of scintigraphy to academic institutions or large referral practices. Nevertheless it is invaluable facilitating lesion localization in dogs with forelimb lameness. Most commonly, it is used to rule in or rule out elbow pathology. Note in the cases shown below the uptake in technetium in the involved elbow compared to the normal elbow. Each of the below cases had a long standing undiagnosed forelimb lameness. Radiographs of these cases were considered within normal limits. The use of scintigraphy localized the lesion to the elbow which then allowed application of more specific diagnostic modalities such as CT or arthroscopy.

Arthroscopy is more invasive than imaging modalities but is very specific for identification of pathology in the medial compartment of the elbow. A comparison of CT with arthroscopy showed that these procedures were complimentary for medial coronoid assessment. Care must be exercised when assessing the medial coronoid on CT and arthroscopically. Fragmentation of the articular cartilage, micro fissures and nondisplaced fragments may not be detected on CT. Likewise, with arthroscopy, thorough probing and or curettage adjacent to the radial head often will reveal abnormal bone or fragments beneath the cartilage surface not visualized on with casual observation.

Passive and active restraints of the shoulder joint may present as subtle injuries difficult which are difficult to identify. Medial restraint (cranial arm of the medial collateral ligament) injury may occur resulting in subluxation of the glenohumeral joint. The hall mark of diagnosis on physical exam is the abduction test. Comparing abduction of the involved limb with the normal limb will show a side to side difference in abduction laxity. Caution must be exercised when performing the exam that internal rotation of the shoulder does not accompany abduction. If the latter is the case, a false positive test will result; as such, the shoulder must be kept in neutral position when abducting the limb. Additionally, a dog with a long standing lameness will have cuff muscle atrophy which will give a false positive abduction test. MRI has been used to identify normal restraints in the shoulder as well as identify abnormal mild lesions in the shoulder. Although early evidence shows this to be a viable modality, it is not widely available.

Bicipital tenosynovitis is an inflammation of the biceps brachii tendon and its surrounding synovial sheath. The etiology of bicipital tenosynovitis is either direct or indirect trauma to the bicipital tendon or tendon sheath. Direct trauma due to repetitive injury may be an inciting factor and result in partial or complete tearing of the tendon. Indirect trauma secondary to proliferative fibrous connective tissue, osteophytes or adhesions between the tendon and sheath limit motion and cause pain. It has been hypothesized that thickening or mineralization of the supraspinatus tendon causes a secondary mechanical bicipital tenosynovitis. Radiographically, bone resorption at the supraglenoid tuberosity is characteristic of chronic strain at the origin of the biceps tendon. Ultrasound of the cuff muscles is also a useful modality for diagnosing cuff muscle injury and differentiating which muscle(s) is involved.