Early changes in lapine menisci during osteoarthritis development: Part I: cellular and matrix alterations.

Osteoarthritis (OA) is the most common form of arthritis and patients with meniscal and ligament injuries of the knee are at high risk to develop the disease. The purpose of this study was to evaluate changes occurring in both medial and lateral menisci from the knees of anterior cruciate ligament (ACL) transected rabbits during the early stages of OA development. Meniscal tissues from control and experimental rabbits were processed for histology and immunohistochemistry for assessment of matrix organization and composition. At 3 and 8 weeks following ACL transection, histological examination demonstrated extensive extracellular matrix deterioration. Altered cell distribution, areas depleted of cells, and areas of cell clusters were found within the medial but not in the lateral meniscus. Immunohistochemistry of both medial and lateral menisci demonstrated significant changes in collagen distribution. Type I and III collagen staining was increased in both medial and lateral menisci. In contrast, type II collagen staining was overtly increased only in the medial meniscus. These results demonstrate that after ACL transection, extracellular matrix deposition as well as altered matrix organization and altered cell distribution occur early in the medial meniscus.