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.
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.