Comparison of computed tomographic and standard radiographic determination of tibial torsion in the dog.

OBJECTIVE

To compare the effect of internal tibial rotation on the computed tomographic (CT) and standard radiographic assessment of tibial torsion (TT) in dogs.

STUDY DESIGN

In vitro study.

SAMPLE POPULATION

Cadaveric canine hind limbs (6 pairs).

METHODS

The cranial cruciate ligament was transected, and caudo-cranial radiographic and transverse CT images were obtained with the femur and tibiae in a neutral position, and after 15 degrees internal tibial rotation. Radiographic TT was determined by measuring the distance (d) between the calcaneus and the sulcus of the talus. CT determination of TT was performed using the proximal transcondylar and the distal cranial tibial axes. The distance (d) in the 2 groups and the difference in the CT determination of TT between groups were compared with a hypothetical mean value of 0 mm and 0 degrees, respectively.

RESULTS

The mean distance (d) for the neutral radiographic group was not significantly different from 0 (P=.473); however, for the 15 degree group it was significantly different (P<.0001). The difference in the CT determination of TT did not differ from 0 (P=.317).

CONCLUSION

The standard radiographic technique does not discriminate between internal TT and internal rotation of the tibia. Thus, dogs with normal tibial conformation can be depicted by radiography as torsed, whereas dogs with TT may be misinterpreted as normal because of arbitrary positioning.

CLINICAL RELEVANCE

Lateral displacement of the medial border of the calcaneus on a caudo-cranial radiograph should not be used as the sole arbiter of TT before surgical correction.