Stifle joint alterations in dogs with patellar luxation

Patellar luxation results in abnormal positioning of the patella outside the trochlear groove, leading to microscopic and macroscopic alterations within the canine stifle joint. This study evaluated histopathological changes in the articular cartilage and joint capsule of dogs affected by patellar luxation, along with gross intra-operative findings observed during surgical correction. Articular cartilage and joint capsule samples from fourteen affected stifle joints and two control joints were examined histologically. Erosive lesions of articular cartilage were observed across multiple stifle joint subdivisions. Affected joints demonstrated inflammatory and degenerative changes in both articular cartilage and joint capsule. Quantitative analysis revealed significantly greater chondrocyte loss in Group III (Grade 4) cases compared with lower-grade luxation groups, while Safranin–O staining demonstrated significantly reduced proteoglycan content in Group III compared with control samples. Gross intra-operative assessment identified articular cartilage erosions, most frequently involving the distal patella and lateral trochlea, as well as variable degrees of osteophytosis. These findings indicate an association between patellar luxation and structural alterations of stifle joint tissues, with more pronounced changes observed in higher-grade cases.