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introductionstatpearls· Introduction· item NBK526019

The articulation of the femoral head with the acetabulum forms the hip joint. This articulation connects the axial skeleton with the lower extremity and functions to transmit forces encountered during daily activities from the axial skeleton through the lower extremities. The hip joint’s ability to balance forces through its full range of motion provides providing the stability required to execute everyday tasks such as standing upright, maintaining a smooth and balanced gait, rising from a chair, and lifting weight from a squatting position.  [1] The hip joint is a spheroidal, or ball-and-socket-type, synovial joint stabilized by bony and ligamentous restraints. The osseous anatomy of the femoroacetabular articulation contributes to the hip’s inherent stability. The pelvis is made up of three parts: the ilium, ischium, and pubis. These innominate bones come together at the triradiate cartilage to form the cup-shaped socket known as the acetabulum. At 15 to 17 years of age, the triradiate cartilage begins to ossify, and it completely fuses by 20 to 25 years of age. Acetabular development is a complex process that involves both endochondral growth from the triradiate cartilage and intramembranous growth from primary and secondary ossification centers of the innominate bones.[2] The acetabulum covers approximately 40% of the femoral head at any position of hip motion. Additional stability is conferred by the labrum, a rim composed of circumferential collagen fibers that surrounds the acetabulum and acts to deepen the hip socket and limit the extreme range of motion. The acetabular labrum contributes approximately 22% of the articulating surface of the hip and increases the volume of the acetabulum by 33%. [1] The hip joint capsule is formed by three major ligaments: the iliofemoral, pubofemoral, and ischiofemoral ligaments. The capsular ligaments run in a spiral fashion preventing hip extension and are surrounded by thick longitudinal fibers that provide additional stability in the lateral plane. The capsule is thicker anterosuperiorly, where the predominant stresses of weight bearing occur, and thinner posteroinferiorly.[1] The ligamentum teres fans out from the fovea of the femoral head and attaches to nearly the full length of the acetabular ligament.