*Almost exlusively in small dogs, particularly terriers and poodles
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*Clinical signs appear at age of 4-11 months
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*Grossly:
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**[[Osteosis|Aseptic ischaemic necrosis]] in central parts of femoral head
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***Possibly due to occlusion of blood vessels
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**Fragmentation of [[Bones - Anatomy & Physiology|trabecular bone]]
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**Collapse of femoral head
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**Revascularisation of femoral head
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**Formation of new bone and [[Musculoskeletal Terminology - Pathology|osteophyte]] formation around femoral head and acetabular rim prior to old bone reabsorption