Sex-associated differences in patellotrochlear morphology in small-breed dogs

The purpose of this study was to make a between-sex comparison of trochlear groove and patellar metrics in healthy dogs on tangential radiographs. A total of 38 stifle joints from 19 healthy dogs (9 males; 10 females) from three small breeds (Pomeranian, Pinscher, Chihuahua) were evaluated. The following morphometric parameters of patella and trochlear groove were measured: trochlear sulcus angle (SA), lateral and medial trochlear inclination angles (LTI; MTI), trochlear groove depth (TD), retropatellar angle of Wiberg (WA), lateral and medial patellar facet angles (LFA, MFA), lateral and medial facet lengths (LF, MF), horizontal and vertical patellar diameters. In the studied joints, both patellar diameters, LF, MF, MF/LF ratio, MTI, LFA and MFA were found to be statistically significantly lower in females. The Wiberg angle and sulcus angle tended to be higher in females yet the differences were not consistent. The results suggest that the smaller patellar thickness, respectively the reduced communication time between the patella and the trochlear groove together with the shorter medial femoral condyle letting the kneecap to escape from the trochlear groove, are anatomical features that may explain the greater predisposition of small-breed female dogs to medial patellar luxation.