Lame puppyThis 8 months old toy poodle was showing lameness on the right pelvic limb for the past few days - physical examination demonstrated pain on palpation of the right hip joint and also muscle atrophy in the right limb.Radiographs were made of the pelvis with the limbs extended - the resulting figures are grainy because of the small size of the patient and the subsequent enlargement of the original study. Radiographic diagnosis Malformation of the capital epiphysis on the right is combined with thickening of the femoral neck - the acetabulum remains only minimally affected with early periarticular spurring that increases the coverage of the femoral head - there is loss of density in the subchondral bone in the acetabulum as a result of lack of weight bearing - the modeling in the head and neck suggests a minimal varus deformity - note the increase in bone density within the femoral neck as the change in weight bearing alters the bone density - change of this type in an immature puppy of a small breed without any history of trauma is diagnostic of aseptic necrosis of the femoral head. Differential diagnosis Early changes of hip dysplasia are joint laxity and minimal bony modeling - changes in the acetabulum are early and modeling changes occur equally on both sides of the joint. Early changes of aseptic necrosis are within the capital epiphysis - modeling changes are seen in the femoral neck - changes in the acetabulum are late and occur after repair of the necrotic bone tissue within the epiphysis. Early changes associated with trauma induced capital epiphyseal separation are limited to the femoral neck - the capital epiphysis remains unchanged because of loss of the blood supply - the acetabulum is slow to change and only reflects the lack of weight bearing. The presentation of the three mentioned diagnoses are all found in young patients, but the frequency is greatly influenced by breed with aseptic necrosis found in smaller breeds. More chronic lesion Aseptic necrosis is a lesion with marked differences seen in the radiographic evaluation depending on the age of the lesion - below is a study made in a 13 month old toy poodle that shows the collapse of the capital epiphysis and the development of the secondary arthrosis that includes enlargement in the acetabulum at this time - the radiolucent zone across the capital epiphysis suggests incomplete bony healing and persistent fibrocartilage - there is a possibility of fragmentation of the capital epiphysis further complicating the resulting arthrosis.
