Establishment and Evaluation of the Reliability of Computed Tomography-Based Femoral Joint Reference Angles in Normal French Bulldog Limbs

Objective: This study aimed to determine the femoral conformation of non-lame French Bulldogs using computed tomography and to evaluate the reliability of these measurements and the effect of observer experience. Study Design: Computed tomographic images of normal French Bulldogs were retrospectively reviewed using open-access three-dimensional Digital Imaging and Communications in Medicine reconstruction software to measure femoral varus angle (FVA), anatomical lateral distal femoral angle (aLDFA), anatomical lateral proximal femoral angle, the mechanical caudal distal femoral angle (mCdDFA), the angle of inclination of the femoral neck (AFI) and the femoral torsion angle (FTA). Measurements were made on three occasions by three observers of varying experience using published methodology. Intraclass Correlation Coefficient (ICC) was used to assess the reliability. Results: Thirty-five femurs were included. Mean FVA was 6.7 ± 30, aLDFA was 96.7 ± 3.0 degrees, anatomical lateral proximal femoral angle was 106.2 ± 5.6 degrees, mechanical caudal distal femoral angle was 114.5 ± 1.5 degrees, AFI was 133.2 ± 4.1 degrees and FTA was 20.4 ± 3.5 degrees. Intraobserver agreement was moderate to excellent for all measurements (ICC > 0.5). Interobserver agreement was poor for the AFI and FTA (ICC < 0.5), moderate for the FVA, aLDFA and mechanical caudal distal femoral angle (ICC 0.5-0.75), and good for anatomical lateral proximal femoral angle (ICC 0.75-0.9). Conclusion: Our results provide a breed-specific reference range for the French Bulldogs' femurs using a previously published methodology. Measurements showed moderate-to-good intraobserver agreement using open-access software. The described method is appropriate for assessment of aLDFA/FVA; however, interobserver reliability varied, particularly for AFI and FTA, which were the least reproducible.