SYNOVIAL FLUID
A tissue called the synovial membrane lines the joint and secretes synovial fluid. Normally a clear, colourless thick and stringy liquid like eggwhite, synovial fluid is the main source of nourishment for cartilage. It also lubricates cartilage and provides a cushion for synovial lining by filling the crevices which synovial tissue cannot reach.

LIGAMENTS AND TENDONS
Ligament is a dense, fibrous material that connects bone-to-bone. It needs to be very strong and, in order to maintain stability, it needs to resist stretching. Tendon is also a strong and dense fibrous material, but less so than ligament. Muscles do not directly attach to bones, but instead, merge into tendons and it is the tendon that attaches to bone. Usage helps keep tendons strong and functioning efficiently. This is particularly important in hinge joints such as the knee where the cartilage may not be able to bear extra weight.

MUSCLES
Muscles are crucial for movement: they're the tough, elastic tissues that pull our bones when we move. Working together, bones, joints, and muscles enable us to do all the physical activities we do every day. Muscles move body parts by contracting and then relaxing. Your muscles can pull bones, but they can't push them back to their original position. So they work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint and bring it closer to your body. Then, when you've completed the movement, the flexor relaxes and the extensor contracts to extend or straighten the limb at the same joint.