A quantitative study of the microstructure and biochemistry of the medial meniscal horn attachments.

Little quantitative data is available on the structure of meniscal attachments. Therefore, as an aid to designing meniscal replacements as well as a possible explanation for mechanical behavior, this study was designed to further the knowledge of the microstructure and biochemistry of native meniscal attachments. Bovine medial meniscal attachments (the external ligamentous portion as well as the transition zones at the bony insertion) were removed and prepared for microstructural evaluation. After embedding in paraffin, the samples were sliced on a microtome and stained for quantitative analysis. The anterior and posterior insertion sites are known to contain three zones: subchondral bone, calcified fibrocartilage, and uncalcified fibrocartilage. Additionally, others have shown that the anterior insertion site contains a ligamentous zone. The insertion zones were further divided into proximal, middle, and distal zones. The posterior attachment's insertion site had a significantly greater thickness of interdigitations, subchondral bone, uncalcified fibrocartilage, and calcified fibrocartilage zone thickness compared to the anterior attachment insertion. The anterior attachment's insertion had the greatest GAG fraction in each zone when compared to the posterior attachment's insertion. GAG fraction decreased from the meniscus to the subchondral bone. Both GAG fraction and normalized thickness varied within a given zone, decreasing from the distal to proximal regions in both the anterior and posterior attachments' insertion zones. Crimp frequency of the collagen fibrils in the external ligamentous portion of the tissue was homogeneous along the length. The findings from this study agree with previously published material property data on the medial meniscal attachments, and could be used in the future to design methods of attachment for tissue engineered replacement menisci.