Signalment: 9-month-old male German shepherd
History: Patient presented for lameness of the right forelimb and pain on palpation of the humerus and midantebrachium.
1. What are the primary findings?
2. What do you think is the primary reason for the clinical signs?
Radiographic Findings: Increased medullary opacity is noted in the proximal diaphysis of the ulna as well as the mid to distal diaphysis of the radius. The elbow is normal. The line of the medial coronoid process is normal on the lateral view. The humerus is normal. There is no evidence of elbow dysplasia or united anconeal process in this patient.
Interpretation: The proximal ulna shows signs of panosteitis. This is likely the cause of the lameness, particularly given the clinical exam findings. The lack of radiographic change in the humerus does not rule out this diagnosis, as the radiographic signs can lag behind the clinical signs.
Discussion: When evaluating radiographs of the skeleton of the immature animal, it is necessary to have knowledge of the normal anatomy, in particular, the sites of physes and the normal closure times. The most common reason that the axial skeleton of an immature animal is radiographed is for evaluation of lameness. There are many causes of lameness, from trauma to diseases of unknown etiology. The following is a short list of the most common.
Panosteitis: This is a disease of unknown etiology and is often seen in young dogs but can be seen in adults as well. There are three radiographic phases of panosteitis:
Phase 1: endosteal and medullary opacity
Phase 2: opacities coalesce and become mottled
Phase 3: medullary canal becomes normal opacity and cortices remain thick
A history of shifting leg lameness is often suggestive of panosteitis. There are instances when the radiographic signs lag behind the clinical presentation. If there is a history of lameness in another limb at a previous time, radiographs of this area may confirm the diagnosis. Bone scintigraphy is the most sensitive for detecting panosteitis and will show areas of uptake well before they are radiographically evident.
Osteochondrosis/osteochondritis dessicans: This disease is often seen in young, rapidly growing large-breed dogs and is the result of failure of endochondral ossification. This causes an area of osteomalacia, which may lead to the formation of a cartilage flap or defect.
Osteochondritis dessicans is when the flap of cartilage separates from origin. Osteochondrosis is a general term, as determination of a cartilage flap is often difficult on survey radiographs. Common areas affected by this problem include the caudal humeral head, the distomedial aspect of the humerus, distal femoral condyles and trochlear ridges of the talus.
Radiographically, OC and OCD are seen as areas of subchondral bony flattening, which may also be accompanied by adjacent sclerosis. In some instances, a discrete mineralized flap is identified adjacent to the defect. In other instances, the flap may dislodge and be found in other aspects of the joint space (these sometimes are called "joint mice").
Elbow Dysplasia: Elbow dysplasia is commonly seen in large, rapidly growing dogs. It encompasses a variety of problems but the most common include fragmented medial coronoid process, ununited anconeal process or OC of the medial humeral condyle. The cause of the first two problems is thought to be due to asynchronous growth with subsequent joint incongruity. However, there are other theories regarding the abnormal formation of the joint due to abnormal weight bearing forces.
Fragmented medial coronoid processes are often difficult to identify on survey radiographs due to superimposition of structures. Often, the only abnormality identified is degenerative changes. Computed tomography is considered the best non-invasive imaging technique for evaluation.
Ununited anconeal processes are easily identified on the flexed lateral view of the elbow. German shepherd dogs are often affected. The cranial caudal view is best for identifying OC of the humerus and can affect any large breed dog.
Hypertrophic osteodystrophy: This disease is also of unknown etiology. Nutritional causes have been implicated as have bacterial etiologies. This disease is commonly seen in young, large-breed dogs and can affect more than one puppy in a litter. The following are common findings:
- "Double physeal lines" seen on initial radiographic presentation
- Transverse radiolucent bands on the metaphyseal side
- May involve all long bones
- As the disease progress, will see periosteal "cuffing" of the metaphyses
- Periosteal "cuffing" can result in angular limb deformities
- Some dogs may become septic and die
- In many dogs, signs resolve with age.
Dr. Bahr, Dipl. ACVR, is a consulting radiologist for PetRays Veterinary Radiology Consultants in Spring,
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