Histological analysis of collagen composition in the stifle joint capsule of dogs with congenital patellar luxation and cranial cruciate ligament rupture.

This study aimed to characterize collagen alterations in the stifle joint capsule of dogs diagnosed with patellar luxation or cranial cruciate ligament rupture. Tissue samples were obtained from affected dogs undergoing surgical correction, while control samples were collected from dogs with distal femoral fractures and unrelated conditions. Histological and immunohistochemical analyses were performed to quantify total collagen content and evaluate specific collagen types across the stratum fibrosum, stratum subsynoviale, and stratum synoviale. Collagen distribution varied significantly among capsule layers, with the stratum subsynoviale exhibiting the highest proportional collagen area, particularly in both proximal and distal regions. Larger breed dogs displayed less dense collagen networks compared to smaller breeds. Chronic joint disease was associated with elevated collagen types V and VI in the stratum synoviale, whereas control samples showed higher collagen type IV in the stratum fibrosum. Additionally, dogs presenting with peracute lameness exhibited markedly lower collagen type VI levels than those with subchronic lameness. These findings demonstrate distinct collagen abnormalities associated with patellar luxation and support the role of structural connective tissue defects in joint instability, strengthening the case for early detection and targeted therapeutic strategies.