The acetabulum (), also called the cotyloid cavity, is a

concave Concave or concavity may refer to: Science and technology * Concave lens * Concave mirror Mathematics * Concave function, the negative of a convex function * Concave polygon, a polygon which is not convex * Concave set In geometry, a subset o ...

surface of the

pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

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

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

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 () form ...

, 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, which is thick and strong above, and serves for the attachment of the

acetabular labrum The acetabular labrum (glenoidal labrum of the hip joint or cotyloid ligament in older texts) is a ring of cartilage that surrounds the acetabulum of the hip. The anterior portion is most vulnerable when the labrum tears. It provides an articulat ...

, which reduces its opening, and deepens the surface for formation of the hip joint. At the lower part of the ''acetabulum'' is the

acetabular notch The acetabular notch is a deep notch in the acetabulum of the hip bone. The acetabular notch is continuous with a circular non-articular depression, the acetabular fossa, at the bottom of the cavity: this depression is perforated by numerous aper ...

, 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 flake removed from a stone tool during the process of pressure flaking. In the Natufian period, a lu ...

surface, where the joint is made with the head of the femur. Its counterpart in the pectoral girdle is the

glenoid fossa The glenoid fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word ''glenoid'' is pronounced or (both are common) and is from el, gléne, "socket", reflecting the shoulder joint's ball-and-socket form. It is a sha ...

. 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 femoral head (femur head or head of the femur) is the highest part of the thigh bone (femur). It is supported by the femoral neck. Structure The head is globular and forms rather more than a hemisphere, is directed upward, medialward, and a l ...

. 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

reptiles Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates ( lizards and snakes) and rhynchoceph ...

and

birds Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

, 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 () form ...

, 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

ankylosaurian Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...

s (e.g. ''

Texasetes ''Texasetes'' (meaning " Texas resident") is a genus of ankylosaurian dinosaurs from the late Lower Cretaceous of North America. This poorly known genus has been recovered from the Paw Paw Formation (late Albian) near Haslet, Tarrant Count ...

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 (or 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, wit ...

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 ...

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 cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in th ...

as the child grows.

History

The word ''

acetabulum The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint. Structure There are three bones of the ''os coxae'' (hip bone) that c ...

'' 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 a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

word for a small vessel for serving

vinegar Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings. Vinegar typically contains 5–8% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting simple sugars to eth ...

. The word was later also used as a

unit of volume A unit of volume is a unit of measurement for measuring volume or capacity, the extent of an object or space in three dimensions. Units of capacity may be used to specify the volume of fluids or bulk goods, for example water, rice, sugar, grain or ...

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,

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

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

* – "Major Joints of the Lower Extremity: Hip joint" * – "The Female Pelvis: Articulated bones of pelvis" {{Authority control Bones of the lower limb Bones of the pelvis