Computed tomographic localization of the deepest portion of the femoral trochlear groove in healthy dogs

Objective: To validate a computed tomographic (CT) method to measure the femoral trochlear groove depth (FTGD). Study design: Cadaveric study. Sample population: Fifteen dogs, 26 femoral trochleae. Methods: Five points were identified from proximal to distal (proximal point [PP], P25, P50, P75, and distal point [DP]) along the trochlea via three-dimensional volume-rendering function on the sagittal plane and measured on multiplanar reconstruction images. Each rater repeated measurements in duplicate, unaware of the identity of the joint. The FTGD was quantitated on the anatomical specimens and statistically compared with CT measurements. Intrarater and interrater agreements were analyzed by using intraclass coefficients. Accuracy was evaluated by using either adjusted R2 coefficients (R2 > 80% was considered acceptable) or Student's t test. The ratio of the patellar and the trochlear width and the ratio of the patellar craniocaudal thickness inside the trochlear groove were calculated at three different patellar locations. Results: Good to excellent intrarater and interrater agreements were observed in four of five trochlear points (P25, P50, P75, and DP), and accuracy was acceptable for these points (R2 > 80%). Computed tomographic measurements differed from the mean anatomical measurements at three of five points (PP, P50, and P75; P <.01), overestimating the FTGD by an overall mean of 0.18 mm (range, 0.02-0.3). P25 and P50 were the deepest points measured. Conclusion: Computed tomography allowed precise measurements of trochlear groove depth except for the most proximal point. The deepest trochlear points were P25 and P50. P25 was the most precise and accurate point measured, while PP was the least consistent. Clinical significance: The deepest portion of the trochlea groove may be located between P25 and P50. Evaluation of this CT method in dogs with patellar luxation is recommended