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Hip
Bones of the hip region
Right hip of a female human
Details
Identifiers
Latincoxa
Greekισχίο
MeSHD006615
TA98A01.2.08.005
A01.1.00.034
TA2316, 158
FMA24964
Anatomical terminology

In vertebrate anatomy, the hip, or coxa[1] (pl.: coxae) in medical terminology, refers to either an anatomical region or a joint on the outer (lateral) side of the pelvis.

The hip region is located lateral and anterior to the gluteal region, inferior to the iliac crest, and lateral to the obturator foramen, with muscle tendons and soft tissues overlying the greater trochanter of the femur.[2] In adults, the three pelvic bones (ilium, ischium and pubis) have fused into one hip bone, which forms the superomedial/deep wall of the hip region.

The hip joint, scientifically referred to as the acetabulofemoral joint (art. coxae), is the ball-and-socket joint between the pelvic acetabulum and the femoral head. Its primary function is to support the weight of the torso in both static (e.g. standing) and dynamic (e.g. walking or running) postures. The hip joints have very important roles in retaining balance, and for maintaining the pelvic inclination angle.

Pain of the hip may be the result of numerous causes, including nervous, osteoarthritic, infectious, traumatic, and genetic.

Structure

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Region

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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, the greater trochanter is often the only palpable bony structure in the hip region.[4]

Articulation

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Radiograph of a healthy human hip joint

The hip joint or coxofemoral joint[5][6] is a ball and socket synovial joint formed by the articulation of the rounded head of the femur and the cup-like acetabulum 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 the axial skeleton of the trunk and pelvis. Both joint surfaces are covered with a strong but lubricated layer called articular hyaline cartilage.

The cuplike acetabulum forms at the union of three pelvic bones — the ilium, pubis, and ischium.[8] The Y-shaped growth plate that separates them, the triradiate cartilage, is fused definitively at ages 14–16.[9] It is a special type of spheroidal or ball 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, the acetabular 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 to ligamentum 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 of osteoporosis.

Transverse and sagittal angles of acetabular inlet plane.

The acetabulum is oriented inferiorly, laterally and anteriorly, while the femoral neck is directed superiorly, medially, and slightly anteriorly.

Articular angles

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Acetabular angle (or Sharp's angle)[12] is the angle between the horizontal line passing through the inferior aspects of triradiate 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]

The sagittal 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's centre-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 an anteroposterior radiograph.[16]

The vertical-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 the false angle, that is, a lateral view rotated 25 degrees towards becoming frontal.[16]

The articular cartilage angle (AC angle, also called acetabular index[17] or Hilgenreiner angle) is an angle formed parallel to the weight bearing dome, that is, the acetabular sourcil 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] Suggested cutoff values to classify the angle as abnormally increased include:

  • 30° up to 4 months of age.[22]
  • 25° up to 2 years of age.[22]

Femoral neck angle

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The angle between the longitudinal axes of the femoral neck and shaft, called the caput-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 as coxa vara and an abnormally large angle as coxa valga. Because changes in shape of the femur naturally affects the knee, coxa valga is often combined with genu varum (bow-leggedness), while coxa vara leads to genu valgum (knock-knees).[24]

Changes in trabecular patterns due to altered CCD angle. Coxa valga leads to more compression trabeculae, coxa vara to more tension trabeculae.[23]

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 the trabecular patterns inside the bones. Two continuous trabecular systems emerging on the auricular surface of the sacroiliac joint meander and criss-cross each other down through the hip bone, the femoral head, neck, and shaft.

  • In the hip bone, one system arises on the upper part of the auricular surface to converge onto the posterior surface of the greater sciatic notch, from where its trabeculae are reflected to the inferior part of the acetabulum. The other system emerges on the lower part of the auricular surface, converges at the level of the superior gluteal line, and is reflected laterally onto the upper part of the acetabulum.
  • In the femur, the first system lines up with a system arising from the lateral part of the femoral shaft to stretch to the inferior portion of the femoral neck and head. The other system lines up with a system in the femur stretching from the medial part of the femoral shaft to the superior part of the femoral head.[25]

On the lateral side of the hip joint the fascia lata is strengthened to form the iliotibial tract which functions as a tension band and reduces the bending loads on the proximal part of the femur.[23]

Capsule

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Main article: Capsule of hip joint

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 the shoulder) and yet support the weight of the body, arms and head.

The capsule has two sets of fibers: longitudinal and circular.

  • The circular fibers form a collar around the femoral neck called the zona orbicularis.
  • The longitudinal retinacular fibers travel along the neck and carry blood vessels.

Ligaments

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Extracapsular ligaments. Anterior (left) and posterior (right) aspects of right hip.
Intracapsular ligament. Left hip joint from within pelvis with the acetabular floor removed (left); right hip joint with capsule removed, anterior aspect (right).

The hip joint is reinforced by four ligaments, of which three are extracapsular and one intracapsular.

The extracapsular ligaments are the iliofemoral, ischiofemoral, and pubofemoral ligaments attached to the bones of the pelvis (the ilium, ischium, and pubis 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 from anterior inferior iliac spine to intertrochanteric 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]

The zona orbicularis, which lies like a collar around the most narrow part of the femoral 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]

The intracapsular ligament, the ligamentum 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, the foveal 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]

Blood supply

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The hip joint is supplied with blood from the medial circumflex femoral and lateral circumflex femoral arteries, which are both usually branches of the deep artery of the thigh (profunda femoris), but there are numerous variations and one or both may also arise directly from the femoral 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 the posterior division of the obturator artery, which becomes important to avoid avascular necrosis of the head 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 important anastomoses, the cruciate and the trochanteric 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]

Muscles and movements

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Main article: Muscles of the hip

The hip muscles act on three mutually perpendicular main axes, all of which pass through the center of the femoral head, resulting in three degrees of freedom and three pair of principal directions: Flexion and extension around a transverse axis (left-right); lateral rotation and medial rotation around a longitudinal axis (along the thigh); and abduction and adduction 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, the inferior and Superior gemelli muscles assist the obturator internus and the three muscles together form the three-headed muscle known as the triceps 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:

Clinical significance

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A hip fracture is a break 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 a prosthesis in a hip replacement operation due to fractures or illnesses such as osteoarthritis. Hip pain can have multiple sources and can also be associated with lower back pain.

At the 2022 Consumer Electronics Show, a company named Safeware announced an airbag 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 in hip dysplasia can lead to hip subluxation (partial dislocation), degeneration of the acetabular labrum. Excessive coverage of femoral head by the acetabulum can lead to pincer-type femoro-acetabular impingement (FAI).[7]

Sexual dimorphism and cultural significance

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Dancers often stand with hands on hips.

In humans, unlike other animals, the hip bones are substantially different in the two sexes. The hips of human females widen during puberty.[35] The femora 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 both fertility and general expression of sexuality. Since broad hips facilitate childbirth 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 the Grande 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.

Additional images

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  • Hip joint. Lateral view.
    Hip joint. Lateral view.
  • Hip joint. Lateral view.
    Hip joint. Lateral view.
  • Muscles of Thigh. Anterior views.
    Muscles of Thigh. Anterior views.
  • Illustration of Hip (Frontal view).
    Illustration of Hip (Frontal view).
  • X-ray of the hip, with measurements used in X-ray of hip dysplasia in adults.[36]
    X-ray of the hip, with measurements used in X-ray of hip dysplasia in adults.[36]

See also

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Notes

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Hip

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from Grokipedia
The hip joint is a ball-and-socket that connects the head of the (thigh bone) to the (socket) of the , forming one of the largest weight-bearing joints in the . This structure allows for a wide range of movements, including flexion, extension, abduction, adduction, and , while enabling the transmission of forces from the lower limbs to the trunk during activities such as walking, running, and standing. The joint is encased in a fibrous capsule lined with a that produces lubricating fluid, and it is covered by articular cartilage on the and to reduce friction and absorb shock. The hip's stability is primarily provided by a network of strong ligaments, including the (the strongest in the body, preventing hyperextension), pubofemoral ligament, and ischiofemoral ligament, which collectively form a dense reinforcement around the . Surrounding muscles, such as the gluteals (for extension and abduction), iliopsoas (for flexion), adductors (for adduction), and hamstrings (for extension), work in coordination with tendons to generate movement and maintain balance. Blood supply to the hip primarily arises from branches of the medial and lateral circumflex femoral arteries, with the receiving crucial perfusion via the retinacular vessels to prevent . Innervation is provided by branches of the femoral, obturator, and sciatic nerves, contributing to and pain sensation. Clinically, the hip joint is prone to conditions such as , which degenerates the and leads to pain and stiffness; fractures, often in the among the elderly; and , a congenital malformation where the does not fully cover the . These issues can significantly impair mobility, highlighting the hip's critical role in daily function and overall skeletal health.

Anatomy

Skeletal structure

The serves as the deep, cup-shaped socket of the , formed by the fusion of three bones of the : the ilium superiorly and anteriorly, the posteriorly and inferiorly, and the pubis anteroinferiorly. These bones contribute to the acetabular cavity through their respective acetabular portions, which unite at the acetabular triradiate during childhood and fuse by early , creating a structure that is roughly hemispherical with an inverted horseshoe shape due to the deficient superior aspect, known as the acetabular notch. The acetabulum's depth and orientation provide foundational stability, with normal bony coverage encompassing approximately 170 degrees of the circumference, though this varies slightly with age and sex. The proximal femur articulates with the acetabulum via its rounded , a smooth, ovoid structure covered by that occupies about two-thirds of a and is connected to the femoral shaft by the narrower . The measures approximately 3-4 cm in length in adults and is oriented at an angle to the shaft, forming the neck-shaft angle (or colodiaphyseal angle) that averages 126 degrees, with a normal range of 120 to 135 degrees. This angle facilitates efficient load transmission during by positioning the centrally over the lower limb's mechanical axis, reducing shear forces and optimizing compressive stress distribution across the joint. Distal to the neck lie the trochanters: the , a large quadrangular prominence on the lateral aspect serving as an attachment site for abductor muscles, and the smaller lesser trochanter on the medial posteromedial surface for insertion. Articular angles further define the hip's bony morphology and influence joint congruence. Femoral anteversion, the forward angulation of the relative to the femoral condyles, measures an average of 10 to 15 degrees in adults, decreasing from 30 to 40 degrees at birth through torsional remodeling during growth. Acetabular anteversion, the anterior tilt of the acetabular opening relative to the , typically ranges from 12 to 18 degrees in adults, contributing to balanced anterior-posterior coverage. The acetabular index, assessed on anteroposterior radiographs as the angle between the acetabular roof and the horizontal inter-teardrop line, normally falls between 0 and 10 degrees in adults, with values exceeding this indicating increased inclination and potential instability. Bony variations in acetabular and femoral morphology are common and can affect stability. Acetabular depth, measured as the vertical distance from the acetabular to the inferior rim along the acetabular , averages 20 to 25 mm in adults, with shallower depths (less than 15 mm) associated with reduced containment in dysplastic conditions. Femoral head coverage by the varies by direction but averages 50 to 60 percent superiorly in normal adults, quantified radiographically by the lateral -edge of greater than 25 degrees, ensuring adequate load distribution while allowing multiaxial motion. These parameters exhibit , with females often showing slightly greater anteversion and shallower acetabula relative to body size.

Joint capsule and ligaments

The hip joint is enclosed by a strong fibrous capsule that attaches proximally to the acetabular rim, excluding the acetabular notch, and distally to the intertrochanteric line anteriorly and along the intertrochanteric crest posteriorly, about 1 cm medial to its crest. This capsule is lined internally by a synovial membrane that secretes synovial fluid to lubricate the joint and nourish the articular cartilage. The capsule thickens selectively into three distinct zones to enhance stability: the anterior iliocapsularis zone, the anteroinferior pubocapsularis zone, and the posterior ischiocapsularis zone, each corresponding to and forming the primary intrinsic ligaments. The intrinsic ligaments are integral thickenings of the capsule that provide primary restraint to excessive motion. The , located in the iliocapsularis zone, is the strongest of the hip and has a Y-shaped configuration with superior and inferior bands; it originates from the and the acetabular rim, inserting onto the intertrochanteric line of the , and primarily resists hyperextension while also limiting external . The pubofemoral ligament, in the pubocapsularis zone, arises from the and superior pubic ramus, blending with the capsule to attach to the intertrochanteric line and distal , functioning to limit abduction and external . The ischiofemoral ligament, forming the ischiocapsularis zone, originates from the acetabular margin of the and posterior capsule, passing posteriorly and laterally to insert on the via a spiral course, where it restricts internal and adduction. The extrinsic ligaments are independent structures that supplement capsular integrity. The ligamentum teres femoris is a flat, triangular intracapsular band that attaches from the transverse acetabular ligament and acetabular notch to the fovea capitis of the , serving to carry the acetabular branch of the obturator artery as an auxiliary blood supply to the . The transverse acetabular ligament is a continuation of the inferior that spans the acetabular notch, completing the bony acetabular rim and providing a site of attachment for the and pubofemoral . These structures collectively ensure hip joint stability by resisting dislocation, particularly in the extended position, where the iliofemoral ligament tightens to enforce the screw-home mechanism—an external rotation of the femur that locks the joint for weight-bearing efficiency.

Vascular and neural supply

The arterial supply to the hip joint primarily derives from the medial circumflex femoral artery and the lateral circumflex femoral artery, both branches of the profunda femoris artery (deep femoral artery), which itself arises from the femoral artery. Additional contributions come from the obturator artery, particularly its posterior division giving rise to the foveal (acetabular) artery that enters the femoral head via the ligamentum teres. Acetabular branches from the obturator, medial circumflex femoral, and superior gluteal arteries form a peri-acetabular anastomotic ring around the joint capsule, ensuring robust circumferential supply. Retinacular branches arising from the medial circumflex femoral artery travel along the femoral neck to penetrate the capsule and supply the majority of the femoral head, particularly its weight-bearing posterior-superior region. Venous drainage of the hip joint follows the arterial pathways through accompanying venae comitantes, with blood from the femoral head and capsule draining via the circumflex femoral veins into the profunda femoris vein, ultimately converging into the external iliac vein system, while medial aspects contribute to the internal iliac vein. Neural innervation of the hip joint capsule and surrounding structures arises from multiple branches of the lumbosacral plexus (L1–S2), providing both sensory and motor components. The femoral nerve (L2–L4) supplies motor innervation to the anterior hip muscles, such as the iliopsoas and rectus femoris, and contributes sensory branches to the anterior joint capsule. The obturator nerve (L2–L4) innervates the medial hip muscles, including the adductor group, and provides articular branches to the inferomedial capsule. Posteriorly, the sciatic nerve (L4–S3) supplies the hamstring muscles and sends branches to the posterior capsule, while the nerve to the quadratus femoris and superior gluteal nerve (L4–S1) contribute additional innervation to the posterosuperior regions. A notable anatomical feature is the watershed zone in the anterior-superior aspect of the , located between the territories of the retinacular branches and the foveal artery, which renders this area particularly susceptible to ischemia due to its marginal .

Surrounding muscles

The muscles surrounding the hip joint are organized into anterior, medial, posterior, and lateral compartments, along with a group of deep external rotators, each contributing to the and stability of the joint through their attachments to the and . These muscles originate primarily from the , including the ilium, pubis, and , and insert onto the proximal , notably the greater and lesser trochanters, , and intertrochanteric regions. Innervation arises from branches of the lumbar and sacral plexuses, such as the femoral, obturator, and sciatic nerves, facilitating coordinated support. In the anterior compartment, the complex, comprising the psoas major and iliacus, provides key support for hip flexion; the psoas major originates from the transverse processes and lateral aspects of the vertebral bodies of T12 to L5 and the lateral arcuate , while the iliacus arises from the superior two-thirds of the , concave surface of the , and anterior sacroiliac , with both fusing to insert via a common onto the lesser of the . The rectus femoris, part of the group, originates from the and the anterior acetabular margin (supra-acetabular groove), inserting distally into the base of the via the , thereby supporting hip flexion alongside its role in extension. These anterior muscles attach proximally to the at the and vertebral column, enhancing anterior joint stability. The medial compartment includes the adductor muscles, which originate from the pubic bone and insert along the medial femur to support adduction. The adductor longus arises from the anterior body of the pubis and the inferior pubic ramus, inserting onto the middle third of the linea aspera of the femur; the adductor brevis originates from the superior pubic ramus and body of the pubis, attaching to the upper portion of the linea aspera; the adductor magnus has dual origins from the inferior pubic ramus and the ischial tuberosity, with its adductor portion inserting on the medial margin of the gluteal tuberosity and linea aspera, and its hamstring portion on the adductor tubercle; the gracilis originates from the inferior pubic ramus and the body of the pubis, inserting onto the superior medial tibia via the pes anserinus. These muscles anchor to the pelvic brim at the pubic symphysis and rami, providing medial reinforcement. Posteriorly, the , the largest hip muscle, originates from the posterior ilium (gluteal surface below the posterior gluteal line), dorsal surface of the and , and the , inserting primarily into the and the of the to support extension. The hamstrings—semitendinosus, semimembranosus, and femoris—originate from the of the ; the semitendinosus and semimembranosus insert onto the medial (pes anserinus), while the femoris (long head) inserts onto the fibular head, collectively supporting hip extension and knee flexion. These posterior muscles connect to the via the , bolstering posterior stability. The lateral compartment features the gluteus medius and minimus, which abduct the hip for lateral support; the gluteus medius originates from the external surface of the ilium between the anterior and posterior gluteal lines, inserting into the lateral surface of the greater trochanter, while the gluteus minimus arises from the ilium between the anterior and inferior gluteal lines, attaching to the anterior border of the greater trochanter. The tensor fasciae latae originates from the anterior superior iliac spine and the anterior part of the iliac crest, inserting into the iliotibial tract, which extends to the lateral condyle of the tibia. These muscles attach to the iliac portion of the pelvic brim and the greater trochanter, aiding in lateral joint integrity. Deep to the superficial layers, the external rotator group includes the piriformis, obturator internus and externus, superior and inferior gemelli, and quadratus femoris, which support rotational stability through attachments around the . The piriformis originates from the anterior surface of the (between the pelvic sacral foramina) and the gluteal surface of the ilium, inserting onto the medial surface of the . The obturator internus arises from the internal surface of the obturator membrane and surrounding bones, inserting via a onto the medial surface of the ; the obturator externus originates from the external surface of the obturator membrane and adjacent bone, attaching to the trochanteric fossa of the . The superior gemellus originates from the , and the inferior gemellus from the , both inserting onto the medial surface of the in conjunction with the obturator internus ; the quadratus femoris arises from the upper lateral border of the , inserting into the quadrate and intertrochanteric crest of the . These deep rotators originate near the at the , , and obturator regions, with insertions concentrated on the and adjacent femoral structures for rotational support.

Biomechanics and function

Range of motion

The hip , as a ball-and-socket articulation, exhibits a wide in multiple planes, quantified through standardized goniometric assessments in healthy adults. Normal active includes flexion of 110° to 135°, extension of 15° to 30°, abduction of 40° to 50°, adduction of 20° to 30°, internal of 35° to 45°, and external of 45° to 60°. These values represent the enabling triplanar movement, with flexion and abduction facilitating forward and lateral reach, while extension and adduction support posterior and medial positioning. Several factors influence individual variations in hip , including age, sex, tautness, and capsular constraints. generally decreases with advancing age, particularly in extension, where differences exceeding 20% have been observed between younger (20-29 years) and older (70-79 years) adults due to progressive stiffening. Females typically demonstrate greater flexion, adduction, and internal rotation compared to males, attributed to differences in pelvic structure and laxity. The and associated ligaments, such as the iliofemoral and ischiofemoral, impose passive limits by tightening at end ranges, preventing excessive translation and maintaining stability across movements like extension and rotation. Measurement of hip relies primarily on goniometry, a technique using a handheld protractor-like device aligned with bony landmarks such as the and , performed in standardized positions like for flexion or prone for rotation. Normative data from large-scale anatomical studies, including those by the American Academy of Orthopaedic Surgeons, provide baselines for clinical evaluation, with exceeding 0.90 for most motions when protocols are followed. These assessments distinguish passive (ligament-determined) from active (muscle-influenced) limits, offering a foundational metric for function.

Muscle actions and movements

The hip joint's movements are primarily driven by coordinated actions of surrounding muscles, enabling flexion, extension, abduction, adduction, and rotation. Flexion of the hip is chiefly accomplished by the muscle, comprising the psoas major and iliacus, which contract to lift the toward the trunk. Extension is powered mainly by the and the muscles, pulling the posteriorly to propel the body forward during locomotion. Abduction, the movement of the away from the midline, is primarily facilitated by the and minimus muscles, which stabilize and elevate the . In contrast, adduction draws the toward the midline, predominantly through the actions of the adductor longus, brevis, and magnus muscles. Rotational movements at the hip involve specific muscular contributions for internal and external torsion. Internal rotation is driven primarily by the anterior fibers of the and minimus, along with assistance from the tensor fasciae latae, rotating the medially. External rotation is achieved mainly by the piriformis, obturator internus and externus, gemelli, and quadratus femoris muscles, turning the laterally to adjust limb orientation. Muscles around the hip often function synergistically or as antagonists to ensure stability and efficient motion, particularly during dynamic activities like . Co-contraction between agonists and antagonists, such as the and , increases to enhance stability and control perturbations during phases. For instance, during the stance phase of walking, the contracts eccentrically with synergistic hip flexors to maintain pelvic level and facilitate smooth weight transfer from one leg to the other, preventing contralateral pelvic drop. Antagonistic pairs, like the and , alternate dominance to produce reciprocal movements while providing baseline tension for integrity. Certain hip movements are inherently coupled due to the ball-and-socket joint's geometry and muscular leverage, optimizing force transmission. Flexion is frequently coupled with external rotation, as the femoral head's orientation and synergistic activation of external rotators like the piriformis allow concurrent lift and lateral twist, aiding in activities requiring multiplanar control. This coupling supports efficient weight transfer in by aligning the limb for optimal ground reaction force absorption and propulsion.

Clinical significance

Common pathologies

Hip is a degenerative characterized by progressive loss of articular in the hip , leading to bone-on-bone contact and space narrowing. Its is often primary (idiopathic) or secondary to factors like congenital deformities, with key risk factors including advanced age and , which increase mechanical stress on the . Symptoms typically manifest as or pain that radiates to the or , intensifying with vigorous activity, accompanied by morning lasting less than 30 minutes. Anatomically, it results in subchondral bone sclerosis, formation, and synovial , altering stability and function while contributing to around the hip. Avascular necrosis of the hip, or osteonecrosis, arises from ischemia of the due to vascular disruption, often from trauma, use, or alcohol excess. This leads to and structural weakening. Initial symptoms include a dull, throbbing pain in the or buttock that develops gradually and worsens with activities. The disease progresses in stages: stage I shows no radiographic changes but marrow ; stage II involves sclerosis and cysts; stage III features subchondral collapse with the ; and stage IV entails flattening and secondary . Anatomically, it causes and , compromising the hip's load-bearing capacity and potentially accelerating degeneration. Femoral neck fractures represent a major hip injury, typically resulting from low-energy falls in osteoporotic elderly patients or high-energy trauma in younger individuals. These are classified as intracapsular (within the joint capsule, prone to disrupted blood supply) or extracapsular (below the capsule, with better vascularity). Symptoms include acute, severe groin or thigh pain, inability to ambulate, and deformity such as leg shortening or external rotation. Anatomically, intracapsular fractures interrupt retinacular vessels, heightening risk of femoral head avascular necrosis, while disrupting the hip's structural integrity and stability. Pelvic fractures, often from vehicular accidents or falls, impact the acetabulum or pubic rami, causing localized pain, instability, and potential neurovascular compromise in the hip region. Femoroacetabular impingement (FAI) involves abnormal abutment of the -neck junction against the , stemming from bony overgrowth or that alters normal mechanics. It manifests in two primary types: cam (abnormal sphericity) and pincer (excessive acetabular coverage), with mixed forms common. Prevalence is elevated among athletes engaging in repetitive hip flexion, such as soccer players, affecting up to 92.5% in some cohorts. Symptoms comprise insidious , hip stiffness, and mechanical issues like catching or locking during motion. FAI frequently precipitates acetabular labral tears through shear forces, with labral tears occurring in 22-55% of patients presenting with hip . Labral tears arise from acute trauma or chronic overload, producing anterior , clicking, and instability. Anatomically, FAI and associated tears damage the labrum's sealing function, leading to chondral wear, increased pressure, and early . Trochanteric bursitis, inflammation of the subgluteus maximus bursa overlying the , often results from repetitive friction, direct trauma, or compensatory patterns. It commonly coexists with gluteal tendinopathies within . Symptoms feature sharp lateral hip pain radiating to the , exacerbated by side-lying, , or prolonged standing. Gluteal tendinopathies involve degenerative tears or thickening of the and minimus tendons due to microtrauma and overload, predominantly affecting women aged 40-60 with higher BMI. These present with chronic lateral or buttock pain, tenderness over the , and pain during hip abduction or . Anatomically, both conditions impair the abductor mechanism, causing trochanteric prominence , bursal , and potential from weakened hip stabilization.

Diagnostic and treatment approaches

Diagnosis of hip conditions begins with a thorough and to identify symptoms such as pain, stiffness, or instability, often linked to underlying joint . Key physical tests include the , which evaluates gluteal medius strength by having the patient stand on one leg; a positive result occurs if the contralateral drops more than 2 cm, indicating abductor weakness. The FABER (flexion, abduction, external rotation) test, also known as the , assesses for intra-articular hip versus issues by flexing, abducting, and externally rotating the hip while applying pressure to the ; it demonstrates high specificity (up to 90%) for hip-related pain when positive. These maneuvers help differentiate hip-specific issues from sources. Imaging modalities complement physical exams to visualize structural abnormalities. Plain X-rays serve as the initial imaging tool, evaluating acetabular and femoral angles, joint space narrowing, and signs of impingement or , such as cam or pincer morphology. (MRI) is preferred for assessing soft tissues, including the labrum, , and ligaments, due to its superior contrast resolution and multiplanar capabilities in detecting tears or . Computed (CT) provides detailed three-dimensional reconstruction, useful for measuring femoral version, identifying subtle fractures, or planning surgical corrections, though it involves . Conservative management focuses on symptom relief and functional restoration without invasive procedures. emphasizes strengthening exercises for hip stabilizers, range-of-motion activities, and retraining to reduce and improve mobility in conditions like . Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly prescribed to alleviate and , serving as a first-line pharmacologic option. Intra-articular injections offer targeted relief for inflammatory hip disorders, providing short-term reduction and functional gains, particularly in , with effects lasting several weeks to months. When conservative measures fail, surgical interventions address structural defects or advanced degeneration. Total hip arthroplasty replaces the damaged joint with prosthetic components, commonly using a metal-on-polyethylene bearing surface for its durability and lower wear rates compared to earlier alternatives. Hip enables minimally invasive repair of the , suturing tears to restore joint stability and alleviate impingement-related discomfort. For (FAI), periacetabular or femoral realigns bony abnormalities, such as excessive femoral version, to improve joint mechanics and delay progression. Post-injury or postoperative rehabilitation follows structured protocols to optimize recovery and prevent complications. Early phases prioritize protected and gentle , progressing to strengthening and proprioceptive ; , often with assistive devices, aims to normalize stride and reduce compensatory patterns. Programs typically span 3-6 months, incorporating phase-based goals like restoring full and muscle endurance, with evidence showing improved balance and function after total . These approaches target anatomical structures affected by the condition, such as the or abductors, to support long-term joint health.

Development and variations

Embryonic development

The embryonic development of the commences with the appearance of lower limb buds during the fourth week of , as mesenchymal cells within the aggregate to initiate limb outgrowth and form the foundational structures of the lower extremity. These early condensations outline the future and pelvic bones, setting the stage for subsequent differentiation into cartilaginous precursors. By the sixth week, chondrification begins in the femoral and the pelvic components (, , and pubis), establishing models for the proximal and through the process of mesenchymal condensation, where undifferentiated cells cluster and secrete rich in . This phase is critical, as it defines the initial morphology of the ball-and-socket configuration, with the forming as a deepening indentation in the pelvic around the same time. Between the seventh and eighth weeks, the differentiates further through the formation of an —a flattened layer of cells between the opposing cartilaginous surfaces of the and —which undergoes to create the . This process involves enzymatic degradation and mechanical forces from embryonic movements, leading to the separation of the joint surfaces and the development of and articular cartilage. Concurrently, formation emerges from the intermediate layer of the interzone, with precursors to the and ligamentum teres vascularizing by the eighth week, providing early stability to the nascent articulation. Primary initiates in the at approximately seven weeks via endochondral mechanisms, where hypertrophic chondrocytes are replaced by , but the and acetabular regions remain cartilaginous until later stages. The secondary ossification center of the typically emerges between two and eight months postnatally, while the acetabulum's Y-shaped triradiate cartilage, which unites the ilium, , and pubis, undergoes starting in and completes fusion during . Disruptions during these embryonic phases, such as abnormal mesenchymal patterning or delayed cavitation, can result in congenital anomalies like developmental dysplasia of the hip (DDH), characterized by shallow acetabular development and or . A key prenatal risk factor is breech presentation, which elevates DDH incidence by approximately sixfold due to mechanical constraints on hip positioning in utero. At birth, clinical detection relies on the Barlow test (provoking ) and Ortolani maneuver (reducing a dislocated hip), which assess stability in the immediate neonatal period.

Anatomical variations and dimorphism

Sexual dimorphism in hip anatomy primarily manifests in the pelvis, where females exhibit a wider structure to accommodate , including a broader , longer pubic bones, and a wider . This configuration results in a larger angle (Q-angle), typically ranging from 15° to 20° in females compared to 10° to 15° in males, influencing patterns by increasing lateral pull on the during movement. Additionally, the female tends to be shallower with reduced coverage of the , contributing to differences in stability and load distribution. Racial and ethnic variations in hip include differences in anteversion angle and acetabular depth. Populations of African descent often display a higher average anteversion angle compared to other groups, which can affect hip rotation and alignment. Acetabular depth is generally greater in than in Caucasians, potentially influencing the prevalence of certain joint conditions and prosthetic fit in surgical interventions. These variations highlight the importance of population-specific anatomical data in clinical and biomechanical applications. Age-related changes in hip involve shifts in joint laxity and degenerative processes. In youth, the hip joint exhibits greater laxity due to more elastic connective tissues, allowing wider ranges of motion that stabilize with maturation. In older adults, progressive degeneration leads to narrowing of the joint space, thinning, and subchondral bone changes, increasing susceptibility to .

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