Patellar Shape Variation in Cats and Dogs: Implications for Orthopedic Surgical Planning

The patella plays a vital role in stifle joint function by contributing to limb extension and joint stabilization. While its clinical significance in small animal orthopedic surgery is well established, detailed comparative data on patellar morphology in domestic cats and dogs remain limited. This study aimed to investigate interspecific and intraspecific variation in patellar shape and size using three-dimensional geometric morphometric techniques. Computed tomography images of 18 cats and 55 dogs were used to construct 3D models, and a total of 14 anatomical landmarks were manually placed on each patella. Generalized Procrustes Analysis was applied, followed by principal component analysis to explore patterns of shape variation. The results revealed a significant difference in shape between cats and dogs, with dogs exhibiting broader variation and larger centroid sizes. Regression analysis indicated that 12.2% of the observed shape variation could be attributed to centroid size, reflecting the influence of patellar size. This strong link suggests that size has a significant influence on how the patella's shape varies, especially in dogs. These findings highlight the importance of individual variation in patellar morphology, particularly in dogs. A single standardized implant or surgical technique may not be appropriate for all cases. Integrating shape and size evaluations into preoperative imaging can help improve implant fit, joint stability, and overall surgical success. In the absence of breed-specific data, individualized planning remains the most reliable approach.