The hip is a complex joint that provides a large amount of stability while also providing mobility and range of motion for many activities. The hip is a true ball-and-socket joint. This design gives the hip a large amount of motion for everyday activities like walking, squatting and climbing stairs. Strong, powerful muscles attach to and around the hip joint, allowing quick acceleration for actions like running and jumping.
The bones of the hip are the femur (thigh bone) and the pelvis. The top end of the femur, which is shaped like a sphere, is called the femoral head. The femoral head sits in a socket in the pelvis called the acetabulum. The femoral neck is a short segment of bone that attaches the femoral head to the rest of the femur. Next to the femoral neck, a large area of bone juts out to the side called the greater trochanter. It can be felt along the side of your hip and acts as the attachment site for many important muscles in the hip.
Articular cartilage covers the ends of bones of any joint. It is a white, shiny material that is about a quarter of an inch thick in a large, weight-bearing joint like the hip. It allows surfaces to glide over one another without damaging either surface. Articular cartilage functions to absorb shock and provide a slippery smooth surface to facilitate motion. In the hip, articular cartilage covers the femoral head and the socket area of the acetabulum.
Ligaments are strong bands of soft tissue that connect bone to bone. There are several important ligaments in the hip. The joint capsule is a sac that surrounds the hip joint. In the hip, the joint capsule is formed by a group of three strong ligaments that connect the acetabulum to the femoral head. These ligaments are a major source of stability for the hip joint. At the very tip of the femoral head, a small ligament, called the ligamentum teres, connects the femoral head and the socket. This ligament does not play as big a role with hip stability but it can sometimes tear and be a source of pain in the hip joint. The iliotibial band is a long tendon that runs along the side of the thigh from the hip to the knee. A tight iliotibial band can cause both hip and knee problems.
The labrum is fibrous cartilage that attaches almost completely around the edge of the acetabulum. The shape and attachment site of the labrum create a deeper socket for the acetabulum. The labrum helps with the stability of the hip joint. This cartilage rim can tear and cause pain and clicking in the hip.
Many muscles surround the hip. The gluteals are the muscles on the back of the hip. The adductor muscles form the inner thigh. Their main action is to bring the leg inward towards the other leg. The muscles in front of the hip joint help flex the hip: the iliopsoas and rectus femoris muscles. The rectus femoris is one of the quadriceps muscles, the large group of muscles on the front of the thigh. There are also a number of smaller muscles around the pelvis and hip that help stabilize and rotate the hip. Finally, the hamstring muscles start at the bottom of the pelvis and run down the back of the thigh to the knee and help extend the hip and bend the knee.
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