The hip is one of the largest weight-bearing joints in the body. When it's working properly, it lets you walk, sit, bend, and turn. To keep it moving smoothly, a complex network of bones, cartilage, muscles, ligaments, and tendons must all work in harmony.
The hip is a very stable ball-and-socket joint: A ball (femoral head) at the top of the thighbone (femur) fits into a rounded socket or cup-like cavity (acetabulum) in your pelvis. Bands of tissues called ligaments form a capsule connecting the ball to the socket and holding the bones in place.
A layer of smooth tissue called cartilage cushions the surface of the bones, helping the ball to rotate easily in the socket. Fluid-filled sacs (bursae) cushion the area where muscles or tendons glide across bone. The capsule surrounding the joint also has a lining (synovium) that secretes a clear liquid called synovial fluid. This fluid lubricates the joint, further reducing friction and making movement easier.
Read about hip replacement surgery