Joints, Tendons & Ligaments

Your skeleton gives you shape and protects your organs, but it cannot move on its own. Muscles pull on bones to make movement happen. Where two bones meet is a joint. Most of your moving joints are synovial joints like your knee, elbow, shoulder, and hip. They have a capsule filled with slippery fluid that lets bones glide smoothly. Tendons are tough cords that attach muscle to bone. When a muscle contracts, it pulls the tendon, which pulls the bone. Ligaments are tough bands that attach bone to bone. They hold the joint together and stop it from bending the wrong way. Cartilage covers the ends of bones to cushion them. If you hurt your knee playing sport, you might tear a ligament (like the ACL) or a tendon (like the patellar tendon). A torn ligament makes the joint wobbly. A torn tendon means the muscle cannot pull the bone.

Synovial joints are the most movable joints in your body. They include hinge joints like your elbow and knee that open and close like a door. Ball-and-socket joints like your shoulder and hip let you move in many directions. Pivot joints let you rotate, like your neck turning side to side. Gliding joints let bones slide past each other, like in your wrist. Tendons transmit force from muscle to bone. They are made of dense collagen fibres and are very strong but not stretchy. Ligaments also contain collagen but are arranged to hold bones in place while allowing the right amount of movement. The knee joint has four main ligaments: two cruciate ligaments inside and two collateral ligaments on the sides, plus the patellar tendon connecting the kneecap to the shin bone.