The hip is one of the body's largest weight-bearing joints.
The hip joint is a ball-and-socket joint consisting of the thigh bone (femur) and a rounded socket (acetabulum). The top of the femur is shaped like a ball and is referred to as the femoral head. The femoral head fits into the acetabulum to form the joint.
The joint space between the femoral head and the acetabulum is filled with fluid, which allows the hip head to slide smoothly inside the socket with every movement. In a healthy hip, articular cartilage covers the bone surfaces of the hip joint. Cartilage is a rubbery tissue that acts as a cushion and gliding surface to allow smooth movement within the joint. Thin, smooth tissue called synovial membrane covers all remaining surfaces of the hip joint. In a healthy hip, synovial membrane produces a small amount of fluid that lubricates the joint to reduce friction.
Ligaments are soft tissue structures that connect bone to bone. A joint capsule is a watertight sac that surrounds a joint. In the hip, the joint capsule is formed by a group of three strong ligaments that connect the femoral head to the acetabulum and provide stability to the joint.