Histological and biological comparisons between complete and incomplete discoid lateral meniscus

The discoid lateral meniscus (DLM) is an anatomically abnormal meniscus that covers a greater area of the tibial plateau than the normal meniscus. The DLM is classified into two types: complete (CDLM) and incomplete (ICDLM) types. In this study, we investigated the histological and cell biological characteristics of CDLM and ICDLM. The number of blood vessels, proteoglycan deposition, and collagen distribution were assessed using meniscal tissues. Collagen production was also investigated in CDLM and ICDLM cells. The intercondylar region of the CDLM had a higher number of blood vessels than the inner region of the ICDLM. Safranin O staining density and type II collagen deposition in ICDLM were higher than those in CDLM. Type II collagen-positive cells were higher in ICLDM than in CDLM. CDLM cells showed slender fibroblastic morphology, while ICDLM cells were triangular chondrocytic in shape. This study demonstrated that the intercondylar region of the CDLM showed similar properties to the outer region of the meniscus. The inner region of the ICDLM, on the other hand, differed from the intercondylar region of the CDLM. Our results suggest that the intercondylar region of the CDLM may have a high healing potential like the outer meniscus.