The CT dorsolateral subluxation index is a feasible method for quantifying laxity in the feline hip joint

The dorsolateral subluxation index of the femoral head is a good proxy of hip dysplasia in dogs. An exploratory, prospective, descriptive study was carried out in order to assess whether the dorsolateral subluxation index may also be useful to improve diagnosis of hip dysplasia in cats. The dorsolateral subluxation index was determined by CT scans simulating the loading position, and compared with measurements of the Norberg-Olsson angle. A total of 82 cats were subjected to radiographic examination of the pelvis, in the standard ventro-dorsal projection, and to CT scans of the pelvis and hips. The Norberg-Olsson angle of each hip was calculated radiographically, while the dorsolateral subluxation index of the femur was calculated on CT images according to a technique recently developed for evaluation of hip dysplasia in dogs. Using the Norberg-Olsson angle a total of 52 hips (31,7%) were diagnosed as dysplastic, 74 (45,1%) as non-dysplastic, and 38 (23,1%) as borderline. Using the dorsolateral subluxation index, values ranged from a minimum of 34.6% to a maximum of 66.6% and four distribution classes were proposed. Findings indicated that the dorsolateral subluxation index previously described as method for quantifying hip dysplasia in dogs is also a feasible method for quantifying hip dysplasia in cats. Future studies are needed to more definitively determine the diagnostic sensitivity of this method.