| Hip | |
|---|---|
 Bones of the hip region | |
 Right hip of a female human | |
| Details | |
| Identifiers | |
| Latin | coxa |
| Greek | ισχίο |
| MeSH | D006615 |
| TA98 | A01.2.08.005 A01.1.00.034 |
| TA2 | 316,158 |
| FMA | 24964 |
| Anatomical terminology | |
Invertebrateanatomy, thehip, orcoxa[1] (pl.:coxae) inmedical terminology, refers to either ananatomical region or ajoint on the outer (lateral) side of thepelvis.
Thehip region is locatedlateral andanterior to thegluteal region,inferior to theiliac crest, and lateral to theobturator foramen, withmuscle tendons andsoft tissues overlying thegreater trochanter of thefemur.[2] In adults, the three pelvic bones (ilium,ischium andpubis) have fused into onehip bone, which forms the superomedial/deep wall of the hip region.
Thehip joint, scientifically referred to as theacetabulofemoral joint (art. coxae), is theball-and-socket joint between the pelvicacetabulum and thefemoral head. Its primary function is tosupport the weight of thetorso in both static (e.g.standing) and dynamic (e.g.walking orrunning) postures. The hip joints have very important roles in retaining balance, and for maintaining thepelvic inclination angle.
Pain of the hip may be the result of numerous causes, including nervous, osteoarthritic, infectious, traumatic, and genetic.
The hip joint, also known as a ball and socket joint, is formed by the acetabulum of the pelvis and the femoral head, which is the top portion of the thigh bone (femur). It allows for a wide range of movement and stability in the lower body.[3]
The proximal femur is largely covered by muscles and, as a consequence, thegreater trochanter is often the only palpable bony structure in the hip region.[4]
Thehip joint orcoxofemoral joint[5][6] is a ball and socketsynovial joint formed by the articulation of the roundedhead of the femur and the cup-likeacetabulum of the pelvis.[7] The socket of the acetabulum is pointing downwards and anterolaterally. The socket is also turned such that the outer edge of its roof is more lateral than outer edge of the floor.[7] It forms the primary connection between the bones of the lower limb and theaxial skeleton of the trunk and pelvis. Both joint surfaces are covered with a strong but lubricated layer called articular hyalinecartilage.
The cuplike acetabulum forms at the union of three pelvic bones — theilium,pubis, andischium.[8] The Y-shaped growth plate that separates them, thetriradiate cartilage, is fused definitively at ages 14–16.[9] It is a special type of spheroidal orball and socket joint where the roughly spherical femoral head is largely contained within the acetabulum and has an average radius of curvature of 2.5 cm.[10] The acetabulum grasps almost half the femoral ball, a grip deepened by a ring-shaped fibrocartilaginous lip, theacetabular labrum, which extends the joint beyond the equator.[8] The centre of the acetabulum (fovea) does not articulate to anything. Instead, it is lined with fat pad and attached toligamentum teres. The acetabular labrum is horse-shoe shaped. Its inferior notch is bridged by transverse acetabular ligament.[7] The joint space between the femoral head and the superior acetabulum is normally between 2 and 7 mm.[11]
The head of the femur is attached to the shaft by a thin neck region that is often prone to fracture in the elderly, which is mainly due to the degenerative effects ofosteoporosis.
The acetabulum is oriented inferiorly, laterally and anteriorly, while the femoral neck is directed superiorly, medially, and slightly anteriorly.
Acetabular angle (or Sharp's angle)[12] is the angle between the horizontal line passing through the inferior aspects oftriradiate cartilages (Hilgenreiner's line) and another line passing through the inferior angle of triradiate cartilage to superior acetabular rim. The angle measures 35 degrees at birth, 25 degrees at one year of age, and less than 10 degrees by 15 years of age.[13] In adults the angle can vary from 33 to 38 degrees.[14]
Thesagittal angle of the acetabular inlet is an angle between a line passing from the anterior to the posterior acetabular rim and the sagittal plane. It measures 7° at birth and increases to 17° in adults.[13]
Wiberg'scentre-edge angle (CE angle) is an angle between a vertical line and a line from the centre of the femoral head to the most lateral part of the acetabulum,[15] as seen on ananteroposteriorradiograph.[16]
Thevertical-centre-anterior margin angle (VCA) is an angle formed from a vertical line (V) and a line from the centre of the femoral head (C) and the anterior (A) edge of the dense shadow of the subchondral bone slightly posterior to the anterior edge of the acetabulum, with the radiograph being taken from thefalse angle, that is, a lateral view rotated 25 degrees towards becoming frontal.[16]
Thearticular cartilage angle (AC angle, also calledacetabular index[17] or Hilgenreiner angle) is an angle formed parallel to the weight bearing dome, that is, the acetabularsourcil or "roof",[18] and the horizontal plane,[15] or a line connecting the corner of the triangular cartilage and the lateral acetabular rim.[19] In normal hips in children aged between 11 and 24 months, it has been estimated to be on average 20°, ranging between 18° and 25°.[20] It becomes progressively lower with age.[21] Suggestedcutoff values to classify the angle as abnormally increased include:
The angle between the longitudinal axes of the femoral neck and shaft, called thecaput-collum-diaphyseal angle or CCD angle, normally measures approximately 150° in newborn and 126° in adults (coxa norma).[23][dubious –discuss]
An abnormally small angle is known ascoxa vara and an abnormally large angle ascoxa valga. Because changes in shape of the femur naturally affects the knee,coxa valga is often combined withgenu varum (bow-leggedness), whilecoxa vara leads togenu valgum (knock-knees).[24]
Changes in the CCD angle is the result of changes in the stress patterns applied to the hip joint. Such changes, caused for example by a dislocation, change thetrabecular patterns inside the bones. Two continuous trabecular systems emerging on the auricular surface of thesacroiliac joint meander and criss-cross each other down through the hip bone, the femoral head, neck, and shaft.
On the lateral side of the hip joint thefascia lata is strengthened to form theiliotibial tract which functions as a tension band and reduces the bending loads on the proximal part of the femur.[23]
Proximally, capsule of the hip joint is attached to the edge of the acetabulum, acetabular labrum, and transverse acetabular ligament. Distally, it is attached to the trochanters of the femur and intertrochanteric line anteriorly. Posteriorly, it is attached to a junction between medial two-thirds and lateral one-third of the femoral neck,[7] one finger breadth away from the intertrochanteric crest.[24] From its attachment at the femoral neck, the fibres of the capsule reflected backwards towards the acetabulum, carrying retinacula vessels supplying the femoral head.[7] The part of femoral neck outside the capsule is shorter in front than posteriorly.[24]
The strong but loose fibrous capsule of the hip joint permits the hip joint to have the second largest range of movement (second only to theshoulder) and yet support the weight of the body, arms and head.
The capsule has two sets of fibers: longitudinal and circular.
The hip joint is reinforced by four ligaments, of which three are extracapsular and one intracapsular.
Theextracapsular ligaments are theiliofemoral,ischiofemoral, andpubofemoral ligaments attached to the bones of the pelvis (theilium,ischium, andpubis respectively). All three strengthen the capsule and prevent an excessive range of movement in the joint. Of these, the Y-shaped and twisted iliofemoral ligament is the strongest ligament in the human body. It has a tensile strength of 350 kg.[24] Iliofemoral ligament is a thickening of the anterior capsule extending fromanterior inferior iliac spine tointertrochanteric line.[7] Ischiofemoral ligament is the thickening of posterior capsule of the hip and pubofemoral ligament is the thickening of the inferior capsule.[7] In the upright position, iliofemoral ligament prevents the trunk from falling backward without the need for muscular activity, thus preventing excessive hyperextension. In the sitting position, it becomes relaxed, thus permitting the pelvis to tilt backward into its sitting position. Ischiofemoral prevents excessive extension and the pubofemoral ligament prevents excess abduction and extension.[26]
Thezona orbicularis, which lies like a collar around the most narrow part of thefemoral neck, is covered by the other ligaments which partly radiate into it. The zona orbicularis acts like a buttonhole on the femoral head and assists in maintaining the contact in the joint.[24]All three ligaments become taut when the joint is extended - this stabilises the joint, and reduces the energy demand of muscles when standing.[27]
Theintracapsular ligament, theligamentum teres, is attached to a depression in the acetabulum (the acetabular notch) and a depression on the femoral head (the fovea of the head). It is only stretched when the hip is dislocated, and may then prevent further displacement.[24]It is not that important as a ligament but can often be vitally important as a conduit of a small artery to the head of the femur, that is, thefoveal artery.[28] This artery is not present in everyone but can become the only blood supply to the bone in the head of the femur when the neck of the femur is fractured or disrupted by injury in childhood.[29]
The hip joint is supplied with blood from themedial circumflex femoral andlateral circumflex femoral arteries, which are both usually branches of thedeep artery of the thigh (profunda femoris), but there are numerous variations and one or both may also arise directly from thefemoral artery. There is also a small contribution from the foveal artery, a small vessel in the ligament of the head of the femur which is a branch of theposterior division of the obturator artery, which becomes important to avoidavascular necrosis of thehead of the femur when the blood supply from the medial and lateral circumflex arteries are disrupted (e.g. through fracture of the neck of the femur along their course).[29]
The hip has two anatomically importantanastomoses, thecruciate and thetrochanteric anastomoses, the latter of which provides most of the blood to the head of the femur. These anastomoses exist between the femoral artery or profunda femoris and the gluteal vessels.[30]
The hip muscles act on three mutually perpendicular main axes, all of which pass through the center of thefemoral head, resulting in threedegrees of freedom and three pair of principal directions:Flexion andextension around a transverse axis (left-right);lateral rotation andmedial rotation around a longitudinal axis (along the thigh); andabduction andadduction around a sagittal axis (forward-backward);[31] and a combination of these movements (i.e.circumduction, a compound movement in which the leg describes the surface of an irregular cone).[24]Some of the hip muscles also act on either the vertebral joints or the knee joint, that with their extensive areas of origin and/or insertion, different part of individual muscles participate in very different movements, and that the range of movement varies with the position of the hip joint.[24]Additionally, theinferior andSuperior gemelli muscles assist theobturator internus and the three muscles together form the three-headed muscle known as thetriceps coxae.[32][24]
The movements of the hip joint is thus performed by a series of muscles which are here presented in order of importance[24] with the range of motion from the neutral zero-degree position[31] indicated:
Ahip fracture is abreak that occurs in the upper part of the femur.[33] Symptoms may include pain around the hip particularly with movement and shortening of the leg.[33] The hip joint can be replaced by aprosthesis in ahip replacement operation due to fractures or illnesses such asosteoarthritis.Hip pain can have multiple sources and can also be associated withlower back pain.
At the2022 Consumer Electronics Show, a company named Safeware announced anairbag belt that is designed to prevent hip fractures among such uses as the elderly and hospital patients.[34]
Abnormal orientation of the acetabular socket as seen inhip dysplasia can lead to hip subluxation (partial dislocation), degeneration of theacetabular labrum. Excessive coverage of femoral head by the acetabulum can lead to pincer-type femoro-acetabular impingement (FAI).[7]
In humans, unlike other animals, the hip bones are substantially different in the two sexes. The hips of human females widen duringpuberty.[35] Thefemora are also more widely spaced in females, so as to widen the opening in the hip bone and thus facilitate childbirth. Finally, the ilium and its muscle attachment are shaped so as to situate the buttocks away from the birth canal, where contraction of the buttocks could otherwise damage the baby.
The female hips have long been associated with bothfertility and general expression ofsexuality. Since broad hips facilitatechildbirth and also serve as an anatomical cue of sexual maturity, they have been seen as an attractive trait for women for thousands of years. Many of the classical poses women take when sculpted, painted or photographed, such as theGrande Odalisque, serve to emphasize the prominence of their hips. Similarly,women's fashion through the ages has often drawn attention to the girth of the wearer's hips.
![X-ray of the hip, with measurements used in X-ray of hip dysplasia in adults.[36]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aIliopectineal_line%2c_ilioischial_line%2c_tear_drop%2c_acetabular_fossa%2c_and_anterior_and_posterior_wall_of_the_acetabulumi.jpg)
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