The Radiographic Development of Severe Hip and Shoulder Dysplasia in a Juvenile Koala (Phascolarctos cinereus)
Hip dysplasia is a prevalent problem in the San Diego Zoo koala colony. In order to better understand the development of hip dysplasia, a longitudinal radiographic study of the hips was performed monthly on a juvenile koala from approximately 7 months old (within 1 month post pouch emergence) to 2 years old. During the study, it was discovered that shoulder dysplasia was also prevalent in the San Diego Zoo colony and so a longitudinal radiographic study of the shoulders was performed monthly on the same koala from 21 months old to 2 years old. Single views of the shoulders were fortuitously obtained at 7 months and 12 months of age. Evidence of femur changes associated with hip dysplasia and humerus changes associated with shoulder dysplasia were radiographically evident as early as 7 months of age in this case. Ossification of the greater trochanter started at 8 months of age and was complete by 15 months of age. Timing of ossification of the femoral head and neck was difficult to determine in this case because neither formed properly, but a review of historic radiographs at San Diego Zoo revealed that ossification should have begun prior to 12 months and mostly completed by 17 months of age. Closure of the acetabular growth plate occurred at 19–20 months of age.
Hip and shoulder dysplasia can be radiographically evident as early as 7 months of age. Survey radiographs would be recommended at 12 months of age.