Q: Based on the case description of a 2-month-old Great Dane with right thoracic limb lameness, what radiographic sign is indicative of a retained cartilage core, and how is it identified in this patient?
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A: The radiographic sign indicative of a retained cartilage core is the presence of wedge-shaped radiolucencies within the distal metaphysis of the ulna that are continuous with the physis. In this case, it is identified by noting the radiolucent regions within the distal ulnar metaphyses bilaterally that have not undergone normal enchondral ossification and therefore appear less dense (radiolucent) compared to the ossified bone.
Q: What is the underlying pathophysiology of retained cartilage cores in young large breed dogs, and how might this condition potentially lead to angular limb deformities?
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A: The underlying pathophysiology of retained cartilage cores involves a failure in the normal process of enchondral ossification, where the cartilage is normally replaced by bone during growth. In cases of retained cartilage cores, regions of the growth cartilage fail to ossify and remain as cartilaginous tissue within the metaphysis, leading to a disruption in the uniform growth of the bone. This disruption can result in uneven growth rates between the radius and ulna, which in turn can lead to angular limb deformities due to the shortening of the ulna. If one bone grows faster than the other, it can cause an abnormal angle to form at the joint, leading to a limb deformity. However, as in the case presented, retained cartilage cores can also be incidental findings that may resolve with age and may not be the cause of lameness or clinical signs.
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