Immunolocalization of types I, II, and X collagen in the tibial insertion sites of the medial meniscus

The medial meniscus of the rabbit knee joint attaches to the tibial plateau via anterior and posterior insertions. Intact meniscal tibial insertions a re essential for meniscal function. In the present study the distributions of types I, II, and X collagen in meniscal tibial insertions were investiga ted by indirect immunohistochemistry in a rabbit model. Four tissue zones w ere histologically identified in the anterior insertion site, including the ligamentous zone, uncalcified and calcified fibrocartilaginous zones and b one; the ligamentous zone was not observed in the posterior insertion site. Labeling for type I collagen was found to be strong in the ligament tissue and bone, and weak in the fibrocartilages which were also labeled for type II collagen. Tissues positive for different types of collagen overlapped a nd formed an irregular interface with various angles and depths, especially at the interface between the calcified fibrocartilage and bone. Positive l abeling for type X collagen was identified only in the calcified fibrocarti lage zone. The coexistence of types I and II collagen in the meniscal tibia l insertions may indicate that this structural unit is subjected to both co mpressive and tensile loads. Type X collagen may play a role in maintaining the calcifying status of this tissue zone, so that its mechanical stiffnes s is kept between that of uncalcified fibrocartilage and hard bone. Restora tion of the insertional structure including the distinct collagen distribut ion should be considered for a functional meniscal substitution.