The acetabulum (; : acetabula), also called the cotyloid cavity, is a concave surface of the

pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...

. The head of the femur meets with the pelvis at the acetabulum, forming the

hip joint In vertebrate anatomy, the hip, or coxaLatin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) (: ''coxae'') in medical terminology, refers to either an anatomical region or a joint o ...

Structure

There are three bones of the ''os coxae'' (hip bone) that come together to form the ''acetabulum''. Contributing a little more than two-fifths of the structure is the

ischium The ischium (; : is ...

, which provides lower and side boundaries to the acetabulum. The ilium forms the upper boundary, providing a little less than two-fifths of the structure of the acetabulum. The rest is formed by the pubis, near the midline. It is bounded by a prominent uneven rim, thick and strong on top, which serves as the point of attachment for the

acetabular labrum The acetabular labrum (glenoidal labrum of the hip joint or cotyloid ligament in older texts) is a fibrocartilaginous ring which surrounds the circumference of the acetabulum of the hip, deepening the acetabulum. The labrum is attached onto the bo ...

. The acetabular labrum reduces the size of the opening of the acetabulum and deepens the surface of the hip joint. At the lower part of the acetabulum is the acetabular notch, which is continuous with a circular depression, the acetabular fossa, at the bottom of the cavity of the acetabulum. The rest of the acetabulum is formed by a curved, crescent-moon shaped surface, the

lunate Lunate is a crescent or moon-shaped microlith. In the specialized terminology of lithic reduction, a lunate flake is a small, crescent-shaped lithic flake, flake removed from a stone tool during the process of pressure flaking. In the Natufian cu ...

surface, where the joint is made with the head of the femur. Its counterpart in the pectoral girdle is the glenoid fossa. The acetabulum is also home to the acetabular fossa, an attachment site for the ''ligamentum teres'', a triangular, somewhat flattened band implanted by its apex into the antero-superior part of the fovea capitis femoris. The notch is converted into a foramen by the transverse acetabular ligament; through the foramen nutrient vessels and nerves enter the joint. This is what holds the head of the femur securely in the acetabulum. The well-fitting surfaces of the femoral head and acetabulum, which face each other, are lined with a layer of slippery tissue called

articular cartilage Hyaline cartilage is the glass-like (hyaline) and translucent cartilage found on many joint surfaces. It is also most commonly found in the ribs, nose, larynx, and trachea. Hyaline cartilage is pearl-gray in color, with a firm consistency and has ...

, which is lubricated by a thin film of

synovial fluid Synovial fluid, also called synovia, elp 1/sup> is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its egg white–like consistency, the principal role of synovial fluid is to reduce friction between the articul ...

. Friction inside a normal hip is less than one-tenth that of ice gliding on ice.

Blood supply

The acetabular branch of the obturator artery supplies the ''acetabulum'' through the acetabular notch. The pubic branches supply the pelvic surface of the ''acetabulum''. Deep branches of the superior gluteal artery supply the superior region and the inferior gluteal artery supplies the postero-inferior region.

Reptiles and birds

In reptiles and

birds Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

, the ''acetabula'' are deep sockets. Organisms in the dinosauria clade are defined by a perforate ''acetabulum'', which can be thought of as a "hip-socket". The perforate ''acetabulum'' is a cup-shaped opening on each side of the pelvic girdle formed where the

ischium The ischium (; : is ...

, ilium, and pubis all meet, and into which the head of the femur inserts. The orientation and position of the ''acetabulum'' is one of the main morphological traits that caused dinosaurs to walk in an upright posture with their legs directly underneath their bodies. In a relatively small number of dinosaurs, particularly ankylosaurians (e.g. '' Texasetes pleurohalio''), an imperforate ''acetabulum'' is present, which is not an opening, but instead resembles a shallow concave depression on each side of the pelvic girdle.

Development

In infants and children, a Y-shaped

epiphyseal plate The epiphyseal plate, epiphysial plate, physis, or growth plate is a hyaline cartilage plate in the metaphysis at each end of a long bone. It is the part of a long bone where new bone growth takes place; that is, the whole bone is alive, with ma ...

called the

triradiate cartilage The triradiate cartilage (in Latin cartilago ypsiloformis) is the Y-shaped epiphyseal plate between the ilium, ischium and pubis to form the acetabulum of the os coxae. Human development In children, the triradiate cartilage closes at an appr ...

joins the ilium, ischium, and pubis. This cartilage

ossifies Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by Cell (biology), cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes r ...

as the child grows.

History

The word ''

acetabulum The acetabulum (; : acetabula), also called the cotyloid cavity, is a wikt:concave, concave surface of the pelvis. The femur head, head of the femur meets with the pelvis at the acetabulum, forming the Hip#Articulation, hip joint. Structure The ...

'' literally means "little vinegar cup". It was the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

word for a small vessel for serving

vinegar Vinegar () is an aqueous solution of diluted acetic acid and trace compounds that may include flavorings. Vinegar typically contains from 5% to 18% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting ...

. The word was later also used as a unit of volume.

Additional images

File:Gray235.png, Right hip bone. External surface. File:Gray237.png, Plan of ossification of the hip bone File:Iliopectineal line, ilioischial line, tear drop, acetabular fossa, and anterior and posterior wall of the acetabulumi.jpg, alt=X-ray of the acetabulum, with measurements used in X-ray of hip dysplasia in adults.,

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

of the acetabulum, with measurements used in

X-ray of hip dysplasia X-rays of hip dysplasia are one of the two main methods of medical imaging to diagnose hip dysplasia, the other one being medical ultrasonography. Ultrasound imaging yields better results defining the anatomy until the cartilage is ossified. When th ...

in adults
Attribution 4.0 International (CC BY 4.0)
/ref> File:Gray321.png, Symphysis pubis exposed by a coronal section File:Gray341.png, Left hip-joint, opened by removing the floor of the acetabulum from within the pelvis File:Gray342.png, Hip-joint, front view File:Gray343.png, Capsule of hip-joint (distended). Posterior aspect. File:Gray344.png, Structures surrounding right hip-joint File:Slide9AA.JPG, Acetabulum File:Slide2DAD.JPG, Hip joint. Lateral view. Acetabulum. File:Slide2DADA.JPG, Hip joint. Lateral view. Acetabulum.

References

External links

{{Authority control Bones of the lower limb Bones of the pelvis