Conventional vs Three-Dimensional Computed Tomography for Measurement of Tibial Tuberosity to Trochlear Groove Distance in Small Breed Dogs With and Without Medial Patellar Luxation

The operative technique for medial patellar luxation (MPL) is dependent on the degree of accompanying bone deformities. The most frequent abnormalities: the shallow trochlear groove and tibial tuberosity medialisation are corrected surgically with trochleoplasty and tibial tuberosity transposition, respectively. The aim of the present study was to determine the distance between the tibial tuberosity and the trochlear groove (TT-TG) on two-dimensional axial computed tomography (CT) scans and three-dimensional multiplanar reconstruction images from 21 stifles from healthy dogs and 15 stifles from dogs with grade 2 MPL and to compare the performance of both methods. Two axial CT scans of the tibial tuberosity and the entire femoral trochlea were selected to measure the TT-TG. The median TT-TG of healthy stifles was statistically significantly (P<0.001) shorter (1.4 mm on 2D and 1.3 mm on 3D images) compared to that of MPL stifles (2.1 mm on 2D and 2.3 mm on 3D images). 2D and 3D measurements showed good and excellent intra-rater agreement, respectively. TT-TG measured on 2D scans was compatible to that on 3D images. The measurement on single 3D images is easier and faster, permitting a more accurate identification of osseous landmarks. The preoperative measurement of the TT-TG distance would allow for more precise tibial tuberosity transposition surgery when indicated.