The joints of your body refer to where two bones meet. While some joints, such as those connecting your skull bones, do not move, others, like the ball-and-socket joint in the hips, are very movable. Very movable joints feature a complicated network of muscles, tendons and bursa sacs that make the joint susceptible to injury.
Anatomy
Your hip joint is a connection of the cup-like acetabulum of your pelvis and the dome-shaped top of your femur, or thighbone. The joint is called a ball-and-socket joint because of the way the thighbone, which serves as the ball, fits into the socket, which is at the pelvis. The thigh rotates around the fixed point of your pelvis. Another ball-and-socket joint is the shoulder. Because the shoulder fits together slightly more loosely than the hip, it is more movable, but the hip joint is considered one of the more movable joints in the body.
Range of Motion
The ball-and-socket joint of your hip can perform a number of movements, including hip flexion and extension, or kicking the leg backward and forward, respectively. The hip joint also can adduct and abduct the leg, or lift the leg to the side and lower it. The final movement the joint allows is rotation. Your hip joint can be activated to turn the leg out, then turn the leg in. Muscles and tendons in the hip joint limit your movement, but can be stretched to increase flexibility.
Muscles Acting on the Joint
Because the hip joint has significant range of motion, it requires a number of muscles to move it. Many large muscle groups attach to the hip joint, including your gluteal muscles -- also known as your buttocks muscles -- that stabilize the pelvis and allow your hip to rotate. Your four quadriceps muscles on the front of the thigh connect to the hip to lift your knee. The hamstrings are the three muscles that allow you to lift your leg backward. The groin muscles lift the leg to the side, and the iliopsoas muscles, including the iliopsoas muscles, flex the hips, helping you lift your thigh.
Hip Replacement
Injury, arthritis or a congenital disorder can cause your hip joint to deteriorate, which causes extreme pain and difficulty moving. When the pain becomes too great, your physician might recommend replacing your joint. An artificial hip joint consists of four pieces, according to Medline Plus: a hip socket, a liner for the inside of the socket, a metal ball to replace the thighbone and a stem that connects to the thigh bone, stabilizing your leg. Innovations in joint replacement have improved the materials, strength and durability of the hip joint. Hip joint replacements typically last between 15 and 20 years, after which the artificial joint might loosen.
