Acetabulum is the deep, cup-shaped pelvic socket that articulates with the femoral head.
The acetabulum is a deep, cup-shaped cavity located on the lateral aspect of the pelvis, formed at the junction of three pelvic bones: the ilium, ischium, and pubis. It serves as the socket for the head of the femur, forming the hip joint or acetabulofemoral joint. The acetabulum plays a vital role in weight transmission from the axial skeleton to the lower limb and allows for a wide range of motion while maintaining joint stability.
The acetabulum has a distinctive hemispherical shape with a central non-articular depression and a peripheral articular surface. It opens laterally, slightly inferiorly, and anteriorly. Its architecture ensures a snug fit for the femoral head, allowing for a stable ball-and-socket articulation.
The acetabulum is formed by the convergence of three bones:
Bone | Contribution |
---|---|
Ilium | Forms the superior portion |
Ischium | Forms the posterior and inferior part |
Pubis | Forms the anterior part |
These bones are separated during development by a Y-shaped triradiate cartilage, which later ossifies by the end of adolescence, typically between ages 16 to 20 years.
The acetabulum is located on the lateral surface of the pelvis, inferior to the iliac wing and superior to the obturator foramen. It faces laterally, slightly anteriorly and inferiorly, providing the socket portion of the hip joint. Its positioning enables efficient load transfer from the vertebral column through the pelvis to the femur during upright posture and locomotion.
The acetabular labrum is a fibrocartilaginous ring attached to the rim of the acetabulum, deepening the socket and enhancing joint stability. It increases the surface area of contact with the femoral head and helps maintain intra-articular pressure, contributing to joint congruence and load absorption.
The acetabulum articulates with the head of the femur to form the hip joint, a synovial ball-and-socket joint. The articulation allows flexion, extension, abduction, adduction, internal and external rotation, and circumduction of the thigh.
Articulating Surface | Joint Type | Movements Allowed |
---|---|---|
Head of femur | Synovial (ball-and-socket) | Flexion, extension, abduction, adduction, rotation, circumduction |
The acetabulum is supplied primarily by branches of the obturator artery (especially via the acetabular branch that travels within the ligament of the head of femur), superior gluteal artery, and medial circumflex femoral artery. These vessels ensure adequate perfusion for the acetabular bone and labrum.
The innervation of the acetabulum and its labrum comes from the obturator nerve, femoral nerve, and branches from the sacral plexus. These nerves carry both nociceptive (pain) and proprioceptive (position) fibers.
During development, the acetabulum begins to form in the fetal period with the establishment of the triradiate cartilage. As growth continues, ossification centers in the ilium, ischium, and pubis contribute to forming the acetabular cavity.
The acetabulum itself is not directly palpable due to its deep location. However, surrounding bony landmarks such as the anterior superior iliac spine (ASIS), pubic tubercle, and ischial tuberosity help estimate its position during physical examination and surgical planning.