The hip, one of the body’s largest weight-bearing joints, supports the body both when it is still and when it is moving. It is designed to provide stability during standing and other weight-bearing activities, mobility for movement, and shock absorption for the torso and upper body.
The hip is a ball and socket joint. This type of joint allows movement and rotation in a variety of directions, including front-to-back, side-to-side, and left to right.
The hip is comprised of bones, cartilage, synovial membrane, ligaments, tendons and muscles that work together to keep the joint functioning correctly. A problem with any one of these parts can cause pain or hip function problems.
The hip joint consists of two primary bones: the thighbone, or femur, and the pelvis. The top or head of the thighbone is shaped like a ball. It fits tightly into a socket on the side of the pelvis. This cup-shaped depression in the pelvis is called the acetabulum.
The hip socket and the ball of the thighbone are covered in a layer of hard, smooth articular cartilage. The cartilage cushions the bones during weight-bearing activities and helps them move smoothly with little friction.
The remaining surfaces of the hip joint are lined with a synovial membrane, a connective tissue that makes a small amount of synovial fluid to lubricate and eliminate almost all friction in the hip joint.
A complex system of connective tissue called ligaments attaches the thighbone to the pelvis. The ligaments provide stability to the joint during rest and movement.
There are three main ligaments in the hip joint.
- At the front of the joint is the iliofemoral ligament, a Y-shaped ligament that attaches the pelvis to the thighbone. It is often considered the strongest ligament in the body.
- The ligament that attaches across the front of the joint from the pubis bone of the pelvis to the thighbone is the pubofemoral ligament.
- The back of the hip joint is reinforced by the ischiofemoral ligament that attaches from the back of the hip socket to the thighbone.
Muscles and Tendons
The muscles in the hip area both support and stabilize the joint and provide the power for the hip to move in multiple directions. Tendons connect muscles to bones. All muscles have tendons at the end where they meet the bone.
Flexing from the hip joint is made possible primarily by a muscle called iliopsoas. Extending from the hip joint is made possible by the gluteus maximus and the hamstrings muscles. There are quite a few other muscles in the hip area, also. They all work together to produce movement and reinforce the joint.