Knee menisci. Correlation between microstructure and biomechanics.

Light and scanning electron microscopy techniques were used to define the microstructure of human knee menisci. Two structurally different regions were shown: a mesial part that included the innermost two thirds and a peripheral part formed by the remaining outer one third. The organization of collagen bundles of the mesial part demonstrated a radial pattern. Those of the peripheral part were larger and circumferential. The articular surfaces of the mesial part were lined by thinner bundles parallel to the surface, while the outer portion was covered by synovium. This structural organization suggested specific biomechanical functions: mainly compression mesially with tension peripherally and a direct translation of forces from the inner wedge-shaped part to the outermost region. The covering layer is well suited for surface to surface motion. Outward displacement of the menisci by the femoral condyles is resisted by solid anchorage of the peripheral circumferential fibers to the intercondylar bone. The resistance to such displacement would force the femoral condyles inwards. Such an organization of menisci has implications in knee joint stability and in the pathology of meniscal injuries.