Hip bone
Encyclopedia
The hip bone, innominate bone or coxal bone is a large, flattened, irregularly shaped bone, constricted in the center and expanded above and below. It has one of the few ball and socket synovial joints in the body, the hip joint.
It meets its fellow on the opposite side in the middle line in front, and together they form the sides and anterior wall of the pelvic cavity
.
Together with the sacrum
and coccyx
, the hip bone comprises the skeletal component of the pelvis
.
, ischium, and pubis
, which are distinct from each other in the young subject, but are fused in the adult; the union of the three parts takes place in and around a large cup-shaped articular cavity, the acetabulum
, which is situated near the middle of the outer surface of the bone.
Each os coxa of an adult pelvic girdle is formed by the fusion of the ilium, ischium, and pubis. The pelvic girdle consists of two ossa coxae (os, bone + coxa, hip;singular). At birth, these three component bones are separated by hyaline cartilage. The fusion is usually complete by age 25.***
es and shark
s, but they never attach to the vertebral column.
In the early tetrapod
s, this early hip bone evolved to become the ischium and pubis, while the ilium formed as a new structure, initially somewhat rod-like in form, but soon adding a larger bony blade. The acetabulum is already present at the point where the three bones meet. In these early forms, the connection with the vertebral column is not complete, with a small pair of ribs connecting the two structures; nonetheless the pelvis already forms the complete ring found in most subsequent forms.
In practice, modern amphibian
s and reptile
s have substantially modified this ancestral structure, based on their varied forms and lifestyles. The obturator foramen is generally very small in such animals, although most reptiles do possess a large gap between the pubis and ischium, referred to as the thyroid fenestra, which presents a similar appearance to the obturator foramen in mammals. In bird
s, the pubic symphysis is present only in the ostrich
, and the two hip bones are usually widely separated, making it easier to lay large eggs.
In therapsids, the hip bone came to rotate counter-clockwise, relatives to its position in reptiles, so that the ilium moved forward, and the pubis and ischium moved to the rear. The same pattern is seen in all modern mammals, and the thyroid fenestra and obturator foramen have merged to form a single space. The ilium is typically narrow and triangular in mammals, but is much larger in ungulate
s and human
s, in which it anchors powerful gluteal muscles. Monotremes and marsupials also possess a fourth pair of bones, the prepubes or "marsupial bones", which extend forward from the pubes, and help to support the abdominal muscles and, in marsupials, the pouch. In placentral mammals, the pelvis as a whole is generally wider in females than in males, to allow for the birth of the young.
s, and should not be confused with hip fracture
s, which are actually femoral fracture
that occur in the proximal end of the femur
.
It meets its fellow on the opposite side in the middle line in front, and together they form the sides and anterior wall of the pelvic cavity
Pelvic cavity
-External links:* * *...
.
Together with the sacrum
Sacrum
In vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...
and coccyx
Coccyx
The coccyx , commonly referred to as the tailbone, is the final segment of the vertebral column. Comprising three to five separate or fused vertebrae below the sacrum, it is attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between...
, the hip bone comprises the skeletal component of the pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
.
Components
It consists of three parts, the iliumIlium (bone)
The ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.The name comes from the Latin ,...
, ischium, and pubis
Pubis (bone)
In vertebrates, the pubic bone is the ventral and anterior of the three principal bones composing either half of the pelvis.It is covered by a layer of fat, which is covered by the mons pubis....
, which are distinct from each other in the young subject, but are fused in the adult; the union of the three parts takes place in and around a large cup-shaped articular cavity, the acetabulum
Acetabulum
The acetabulum is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.-Structure:...
, which is situated near the middle of the outer surface of the bone.
- The ilium, so called because it supports the flank, is the superior broad and expanded portion which extends upward from the acetabulum.
- The ischium is the lowest and strongest portion of the bone; it proceeds downward from the acetabulum, expands into a large tuberosity, and then, curving forward, forms, with the pubis, a large aperture, the obturator foramenObturator foramenThe obturator foramen is the hole created by the ischium and pubis bones of the pelvis through which nerves and muscles pass.- General structure :...
.
- The pubis extends medially and inferiorly from the acetabulum and articulates in the midsagittal plane at the pubic symphysis, with the bone of the opposite side: it forms the front of the pelvis and supports the external organs of reproduction.
Each os coxa of an adult pelvic girdle is formed by the fusion of the ilium, ischium, and pubis. The pelvic girdle consists of two ossa coxae (os, bone + coxa, hip;singular). At birth, these three component bones are separated by hyaline cartilage. The fusion is usually complete by age 25.***
Evolution
The hip bone first appears in fishes, where it consists of a simple, usually triangular bone, to which the pelvic fin articulates. The hip bones on each side usually connect with each other at the forward end, and are even solidly fused in lungfishLungfish
Lungfish are freshwater fish belonging to the Subclass Dipnoi. Lungfish are best known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed...
es and shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s, but they never attach to the vertebral column.
In the early tetrapod
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
s, this early hip bone evolved to become the ischium and pubis, while the ilium formed as a new structure, initially somewhat rod-like in form, but soon adding a larger bony blade. The acetabulum is already present at the point where the three bones meet. In these early forms, the connection with the vertebral column is not complete, with a small pair of ribs connecting the two structures; nonetheless the pelvis already forms the complete ring found in most subsequent forms.
In practice, modern amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s and reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s have substantially modified this ancestral structure, based on their varied forms and lifestyles. The obturator foramen is generally very small in such animals, although most reptiles do possess a large gap between the pubis and ischium, referred to as the thyroid fenestra, which presents a similar appearance to the obturator foramen in mammals. In bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s, the pubic symphysis is present only in the ostrich
Ostrich
The Ostrich is one or two species of large flightless birds native to Africa, the only living member of the genus Struthio. Some analyses indicate that the Somali Ostrich may be better considered a full species apart from the Common Ostrich, but most taxonomists consider it to be a...
, and the two hip bones are usually widely separated, making it easier to lay large eggs.
In therapsids, the hip bone came to rotate counter-clockwise, relatives to its position in reptiles, so that the ilium moved forward, and the pubis and ischium moved to the rear. The same pattern is seen in all modern mammals, and the thyroid fenestra and obturator foramen have merged to form a single space. The ilium is typically narrow and triangular in mammals, but is much larger in ungulate
Ungulate
Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...
s and human
Human
Humans are the only living species in the Homo genus...
s, in which it anchors powerful gluteal muscles. Monotremes and marsupials also possess a fourth pair of bones, the prepubes or "marsupial bones", which extend forward from the pubes, and help to support the abdominal muscles and, in marsupials, the pouch. In placentral mammals, the pelvis as a whole is generally wider in females than in males, to allow for the birth of the young.
Fractures
Fractures of the hip bone are termed pelvic fracturePelvic fracture
Pelvic fracture is a disruption of the bony structure of the pelvis, including the hip bone, sacrum and coccyx. The most common cause in elderly is a fall, but the most significant fractures involve high-energy forces such as a motor vehicle accident, cycling accidents, or a fall from significant...
s, and should not be confused with hip fracture
Hip fracture
A hip fracture is a femoral fracture that occurs in the proximal end of the femur , near the hip.The term "hip fracture" is commonly used to refer to four different fracture patterns and is often due to osteoporosis; in the vast majority of cases, a hip fracture is a fragility fracture due to a...
s, which are actually femoral fracture
Femoral fracture
A femoral fracture is a bone fracture that involves the femur. It includes hip fractures.-Classification:A femoral fracture that involves the femoral head, femoral neck or the shaft of the femur immediately below the lesser trochanter may be classified as a hip fracture, especially when associated...
that occur in the proximal end of the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
.