Comparison of the Tibial Anatomical-Mechanical Axis Angle and Patellar Positions between Labrador Retrievers and Golden Retrievers with and without Cranial Cruciate Ligament Rupture

This study investigated proximodistal and craniocaudal patellar positions and assessed these positions with the tibial anatomical-mechanical axis angle (AMA-angle), tibial plateau angle (TPA), relative tibial tuberosity width (rTTW), and Z-angle in Labrador Retrievers (LR) and Golden Retrievers (GR) with and without cranial cruciate ligament rupture (CCLR). Mediolateral radiographs were obtained from 2 groups. The affected group had a normal contralateral stifle measured at the time of unilateral surgically confirmed CCLR, which developed a subsequent contralateral CCLR (SC-CCLR; 40 dogs), and the control group (60 dogs aged >11 years) had normal stifles. In the SC-CCLR group, 95% of the tibial anatomical axes (AAs) were cranial (CR) to the patella, with a median (range) AMA-angle of 2.92° (1.65°-4.92°), while in the control group, 93% of the stifles had AAs caudal (CA) to or in the middle (M) of the patella, with a median (range) AMA-angle of 1.03° (0°-3.52°). The craniocaudal position of the patella was correlated statistically with the AMA-angles (median (range), 0.86° (0-1.61°), 1.87° (1.22-2.7°), and 2.97° (1.72-4.92°) in the CA, M, and CR positions, respectively, but not with other tibial measurements (p<0.0001). The patellar height did not differ between the groups (p<0.0001). The highly significant difference found in the AMA-angle and the craniocaudal patellar position between LR and GR with or without CCL injury suggest that craniocaudal angulation of the proximal tibia could influence the development of canine CCLR.