Hip bone is also known as inominate bone or pelvic bone and is formed by fusion of three bones namely ilium, ischium and pubis bones. Hip bone forms part of pelvis and takes part in hip joint articulation.
The hip bone is made up of the three parts – the ilium, pubis and ischium. Prior to puberty, the triradiate cartilage separates these constituents. At the age of 15-17, the three parts begin to fuse.
Their fusion forms a cup-shaped socket known as the acetabulum, which becomes complete at 20-25 years of age. The head of the femur articulates with the acetabulum to form the hip joint.
Thus the hip bone has three articulations –
- Sacroiliac joint – articulation with sacrum
- Pubic symphysis – articulation with the other hip bone.
- Hip joint – articulation with the head of femur.
Side determination of Hip Bone
- Acetabulum is on lateral side
- Obturator formen lies below the acetabulum, pubis being anterior and ischium posterior
- Flat expanded part, the ilium is above the acetabulum.
Anatomical Position of Hip Bone
- Pubic tubercle and anterior superior iliac spine lie in same coronal plane.
- Pelvic surface of pubis is directed backwards and upwards
- Symphyseal surface of the body of pubis is in the median plane.
Ilium is largest part of the hip bone and forms upper expanded plate in upper part and contributes to acetabulum formation in lower part. Roughly two fifth of acetabulum is contributed by ilium.
Upper end of ilium is called iliac crest. Iliac crest is broad, convex, topmost portion of ilium which can be palpated in the flank area.
Anterior end of iliac crest is called the anterior superior iliac spine which is a very important anatomical landmark.
Iliac crest ends posteriorly in the posterior superior iliac spine [Located about dimple of venus about by a dimple 4 cm lateral to the second sacral spine. ]
Iliac crest is divided in to a ventral segment and a dorsal segment which meet at the tubercle. The ventral segment forms more than the anterior two thirds of the crest. The dorsal segment forms less than the posterior one third of the crest.
Lower end is fused with ischium and pubis at the acetabulum.
Ilium has got three borders [anterior, posterior and medial] and three surfaces [gluteal, iliac, and a sacropelvic surface].
Borders of Ilium
Anterior border of ilium starts at the anterior superior iliac spine and runs downwards to the acetabulum. In upper part , the border has a notch and while its lower part has anterior inferior iliac spine.
Posterior border extends from the posterior superior iliac spine to the upper end of the posterior border of the ischium. It is marked by prominence called posterior inferior iliac spine and lower a large deep notch called the greater sciatic notch.
Medial Border is on the inner surface of the ilium from the iliac crest to the iliopubic eminence and separates the iliac fossa from the sacropelvic surface. Its lower rounder part form the iliac part inlet of pelvis or arcuate line.
Surfaces of Ilium
Gluteal surface is the outer surface of the ilium, which is convex in front and concave behind. Three gluteal lines divide the gluteal surface.
- The posterior gluteal line is the shortest and extends from a point front of the posterior superior spine to a point of the posterior inferior spine.
- The anterior gluteal line is the longest , begins about an inch behind the anterior superior spine, runs backwards and then downwards to end at the middle of the upper border of the greater sciatic notch.
- The inferior gluteal line is not well defined. It begins a little above and behind the anterior inferior spine, runs backwards and downwards to end near the apex of the greater sciatic notch.
Inner surface of ilium is divided by medial border into iliac fossa and sacropelvic surface.
Iliac fossa is the large concave area on the inner surface of the ilium, situated in front of its medial border. It forms the lateral wall of the false pelvis.
Sacropelvic surface is the uneven area on the inner surface of the ilium, behind its medial border. It is subdivided in three parts: the iliac tuberosity, auricular surface and pelvic surface.
Iliac tuberosity is a large rough area below dorsal segment of iliac crest. It is raised in the middle and depressed both above and below. Articular surface is called auricular surface and articulates with corresponding auricular surface on scarum to form sacroiliac joint.
Anteroinferior to auricular surface is smooth pelvic surface which forms lateral wall of true pelvis. Preauricular surface is marked by preauricular sulcus.
Attachments on Ilium
Anterior Superior Iliac Spine
ASIS provides attachment to inguinal ligament. Sartorius muscle originates from ASIS and area below that.
Outer lip of iliac crest gives origin to fascia lata in whole extent and tensor fasica lata in front of the tubercle.
Latissimus dorsi muscle takes origin just behind the highest point of crest. Anterior two thirds of crest provides origin to external oblique muscles.
Inner lip of iliac crest gives rise to transverses abdominis muscle and fascia transversalis in anterior part and quadratus lumborum in posterior part.
In dorsal segment of iliac crest
- Gluteus maximus arises from lateral slope
- Erector spinae arises from medial slope
- Interosseus and dorsal sacroiliac ligaments are attached to medial margin deep to erector spinae
- Anterior inferior iliac spine gives origin to straight head of rectus femoris and iliofemoral ligament.
- Sacrotuberous ligament gives origin to upper fibers of sacrotuberous ligament and few fibers of piriformis.
- Gluteus maximus is a big muscle and its upper fibres take origin from area behind the posterior gluteal lines.
- From area between anterior and posterior gluteal lines, gluteus medius arises.
- Gluteus minimus arises from area between anterior and inferior gluteal lines.
- Rectus femoris, reflected head arises from groove above the acetabulum.
- Capsule of the hip joint is attached to acetabular margin.
- Iliac fossa gives origin to iliacus in upper two thirds where as lower one third is covered by iliac bursa.
- Iliac tuberosity provides attachments to interosseus sacroiliac ligament, dorsal sacroiliac ligament and iliolumbar ligament superiorly.
- Margin of auricular surface gives attachment to ventral sacroiliac ligament.
Preauricular sulcus provides atttachement to lower fibers of ventral sacroiliac ligament, few fibers of piriformis and upper half of obturator internus.
Pubis forms anteroinferior part of hip bone, contributes to anterior one fifth of acetabulum, and forms anterior boundary of obturator foramen.
Pubis consists of body, superior ramus and inferior ramus.
Body of pubis
It is flattened anteroposteriorly and has a border superiorly called pubic crest which ends in a pubic tubercle laterally. In males the tubercle is crossed by the spermatic cord.
It has three surfaces
- Anterior surface is is directed downwards, forward and slightly laterally. It is rough on superomedial aspect.
Posterior surface or pelvic surface is directed upwards and backwards and forms anterior wall of true pelvis.
- Medial surface or symphyseal surface articulates with opposite pubic symphysis.
Superior and inferior rami are extension from body of pubis.
- Superior border [also called pectin pubis or pectineal line] is sharp and extends from pubic tubercle to posterior aspect of iliopubic eminence. It forms part of arcuate line. [pelvic inlet]
- The anterior border is called the obturator crest. This border is rounded ridge, extending form the public tubercle to the acetabular notch.
- The inferior border is sharp and forms the upper margin of the obturator foramen.
- The pectineal surface is a triangular area between the anterior and superior borders, extending from the pubic tubercle to the iliopubic eminence.
- The pelvic surface lies between the superior and inferior borders. It is smooth and is continuous with the pelvic surface of the body of the pubis. Pelvic surface is crossed by ductus deferens in males and round ligament of uterus in females.
- The obturator surface or inner surface lies between the anterior and inferior borders. It present the obturator groove. Obturator groove transmits obturator vessel and nerves.
Inferior ramus extends from the body of the pubis to the ramus of the ischium, medial to the obturator foramen. It unites with the ramus of the ischium to form the conjoined ischiopubic rami. [It is discussed separately below after the ischium]
Attachments on the Pubis
Medial end of the inguinal ligament and ascending loops of the cremaster muscle.
The lateral part of the crest gives origin to the lateral head of the rectus abdominis , and to the pyramidalis. Medial head of the rectus abdominis which takes origin from pubic symphysis crosses the medial part of the pubic crest.
Body of Pubis
- Anterior pubic ligament medially
- Adductor longus – From the angle between the crest and the symphysis
- Gracilis – From margin of the symphysis , and from inferior ramus
- Adductor brevis origniates lateral to the gracilis
- Levator ani from middle part
- Obturator internus laterally
The pectineal line provides attachment to
- Conjoint tendon
- Medial end of lacunar ligament
- Pectinate ligament
- Pectineus muscle and its covering fascia.
- Psoas minor [when present].
- Pectineal surface, in its upper part give rise to pectineus muscle.
Ischium is posteroinferior part of hip bone and forms two fifth of acetabulum and posterior body of obturator foramen.
Ischium has a body and a ramus.
Body of Ischium
Body of the ischium is below and behind acetabbulum and ends in ischial tuberosity. Its anterior border forms post margin of obturator foramen.
Posterior border continues with post border of ilium and takes part in lower border of greater sciatic notch and gives out a projection below that called ischial spine. Below that is lesser sciatic notch. The lesser sciatic notch is occupied by the tendon of the obturator internus and a bursa deep to the tendon. The notch is lined by hyaline cartilage.
Dorsal surface of body of ischium is continuous with gluteal surface of ilium. Piriformis, the sciatic nerve, and the nerve to the quadratus femoris are closely related to this surface. The groove transmits the tendon of the obturator internus .
The surface between anterior and lateral borders is called femoral surface.
Pelvic surface is smooth and takes part in lateral wall of true pelvis [the lateral wall of the ischiorectal fossa.]
Ischial tuberosity has upper and lower areas demarcated by transverse ridge. An oblique ridge further divides upper area into superolateral and inferomedial area. The inferomedial area is covered with fibrofatty tissue which supports body weight in the sitting position.
Lower area of ischial tuberosity is divided into inner and outer areas by a longitudinal ridge.
Ramus of Ischium
Ramus of ischium combines with inferior pubic ramus to form conjoined ischiopubic rami which is discussed below.
Conjoined Ischiopubic Rami
The inferior ramus of the pubis unites with the ramus of the ischium on the medial side of the obturator foramen . The site of the union may be marked by a localized thickening. The conjoined rami have two borders- upper and lower, and two surfaces – outer and inner.
The upper border forms part of the inferior margin of the obturator foramen and lower border forms the pubic arch along with the corresponding border of the bone of the opposite side.
The inner surface is convex and smooth . It is divided upper middle and lower areas by two ridges.
Attachments on the Ischium
- Sacrospinous ligament along its margins
- origin for the coccygeus and posterior fibers of levator ani from its pelvic surface.
Lesser Sciatic Notch
The upper and lower margins of the notch give origin to the superior and inferior gemelli.
Femoral Surface of the Ischium
- Origin to obturator externus along the margin of the obturator foramen
- Quadratus femoris along the lateral border of the upper part of the ischial tuberosity.
- Surperolateral part – origin to the semimembranosus
- Inferomedial area v-vsemitendinosus and the long head of the biceps femoris
- Inferolateral area – adductor magnus. .
- Sacrotuberous ligament on medial margin
- Ischiofemoral ligament on lateral border, just below the acetabulum.
- obturator internus.
Conjoined ischiopubic rami
- Upper border – obturator membrane
- Lower border – Fascia latae, membranouns layer of superficial fascia of the perineum, also known as Colle’s fascia.
- Outer surface
- Obturator externus [ near the obturator margin of both rami]
- the adductor brevis and gracilis [mainly from the pubis ramus]
- the adductor magnus [mainly from the ischial ramus]
- Inner surface
- Upper ridge – upper layer of the urogenital diaphragm.
- Lower ridge – perineal membrane
- Upper area – obturator internus.
- Middle area – Sphincter urethrae and to the deep transverse perinei
- Lower area – crus penis, ischiocavernosus and superficial trasverse perinei
Acetabulum is a deep cup-shaped hemispherical cavity on the lateral aspect of the hip bone roughly about its centre. Acetabulum is directed laterally, downwards and forwards. Margin of the acetabulum is deficient inferiorly. This deficiency is called the acetabular notch and is bridged by the transverse ligament.
The acetabulum is formed by
- Ilium – Upper 2/5
- Pubis – anterior 1/5
- Ischium the posterior 2/5.
Acetabular fossa is nonarticular roughened floor of the acetabulum. It contains of fat and is lined by synovial membrane.
Articular surface is horseshoe shaped articular surface and is called lunate. It occupies anterior, superior , and posterior part of the acetabulum. It articulates with the head of the femur to form the hip joint. Acetbular labrum is fibrocartilaginous rim on the margins of the acetabulum which functions to deepen the acetabular cavity.
Obturator foramen is a large gap in the hip bone anteroinferior to acetabulum, between pubis and ischium. It is large and oval in males; and small and triangular in females. Obturator membrane is attached to its margins, except at the obturator groove, where the obuterior vessels and nerve pass out of the pelvis.
The anterior superior iliac spine (ASIS) is an important landmark. Its comparative level with opposite side is important in spine, pelvis and hip examination. Midway along the inguinal ligament [midway between ASIS and pubic tubercle], the femoral artery can be palpated.
ASIS also serves a s a point for measuring leg lengths.
Hip bone can be injured and trauma and its its treatment is dictated by fracture site, pattern and patient age.
Following video sums up hip bone anatomy quite well
Get more stuff on Musculoskeltal Health
Subscribe to our Newsletter and get latest publications on Musculoskeletal Health your email inbox.
Thank you for subscribing.