Menisci present in the KNEE joint located on the upper end of TIBIA are the avascular structures,then during meniscal injuries why does swelling...

This is a good question, and the answer is still the
subject of research. In some instances swelling comes on immediately after a knee
injury, in which case it is probably caused by trauma to other nearby tissues, rather
than to the knee cartilage itself. However, in many cases a person with a damaged
meniscus can actually walk on it immediately following the injury, with the swelling
only occurring hours or even days later. In this case, the culprit appears to be
proteoglycans, which are large molecules that are part of the cartilage tissue. When the
cells and intercellular matrix of the cartilage are disrupted by an injury, the
proteoglycans can leak into nearby tissues, causing the release of immune system
molecules know as interleukins. The interleukins cause the swelling by increasing the
permeability of the surrounding tissues, which is a common part of the immune
response.