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Radiographic Case Study: The importance of correct positioning

Clinical history

This is a 9 month old cockerpoo. It was deemed fit and well with no physical abnormalities and was admitted to undergo a routine neutering procedure.
The owner's previous dog had severe hip dysplasia and consequently had developed early onset degenerative joint disease. The owner requested that their cockerpoo's hips were radiographed at the time of neutering to check for signs of hip dysplasia. The limitations of the findings were discussed with the owner before proceeding with the radiographs.

Ventro dorsal radiographs were taken of the dog in a frog legged position. See below:



From this x-ray the dog was deemed to have normal hips and the vet was about to wake the dog up and tell the owner that the dog was fine. However the Joint Venture Partner intervened and the dog was re radiographed with the hind legs in the correct position (see radiograph below). The correct patient positioning is described below:

The patient is positioned in dorsal recumbency and the femurs should be fully extended. The femurs should be parallel and can be rotated mildly internally so that the patellas are in the midline of the trochlear groove. A sponge pad between the stifles can be used and then the limbs can be taped into this position. The beam is centred over the hips and collimated to include the entire pelvis and femurs. Care should also be taken to ensure that the pelvis is straight with the hips at the same height above the table. Often it is worth considering full general anaesthesia for pelvis views to make positioning easier as the muscles are fully relaxed and extended views in dogs with hip dysplasia may also be painful with this causing discomfort under sedation making positioning more difficult.



Diagnostic Interpretation

There is bilateral subluxation of the femoral heads with marked widening of the joint space between the femoral head and acetabulum and the coverage of the femoral head by the acetabulum is substantially less than the normal (50%). There is mild muscle atrophy on the left side.




Conclusions

Bilateral hip dysplasia

The interpretation of the two sets of radiographs are very different, and consequently the prognosis for this dog has changed significantly. This case shows how important it is to correctly prepare and position your patient before taking radiographs.