6c. The Bones of the Lower Extremity. 1. The Hip Bone

(Ossa Extremitatis Inferioris) & (Os Coxæ; Innominate Bone)

The hip bone is a large, flattened, irregularly shaped bone, constricted in the center and expanded above and below. 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. It consists of three parts, the ilium, 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. 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 foramen. The pubis extends medialward and downward from the acetabulum and articulates in the middle line with the bone of the opposite side: it forms the front of the pelvis and supports the external organs of generation. 1 The Ilium (os ilii).—The ilium is divisible into two parts, the body and the ala; the separation is indicated on the internal surface by a curved line, the arcuate line, and on the external surface by the margin of the acetabulum. 2 The Body (corpus oss. ilii).—The body enters into the formation of the acetabulum, of which it forms rather less than two-fifths. Its external surface is partly articular, partly non-articular; the articular segment forms part of the lunate surface of the acetabulum, the non-articular portion contributes to the acetabular fossa. The internal surface of the body is part of the wall of the lesser pelvis and gives origin to some fibers of the Obturator internus. Below, it is continuous with the pelvic surfaces of the ischium and pubis, only a faint line indicating the place of union. 3

FIG. 235– Right hip bone. External surface. (See enlarged image) The Ala (ala oss. ilii).—The ala is the large expanded portion which bounds the greater pelvis laterally. It presents for examination two surfaces—an external and an internal—a crest, and two borders—an anterior and a posterior. The external surface (Fig. 235), known as the dorsum ilii, is directed backward and lateralward behind, and downward and lateralward in front. It is smooth, convex in front, deeply concave behind; bounded above by the crest, below by the upper border of the acetabulum, in front and behind by the anterior and posterior borders. This surface is crossed in an arched direction by three lines—the posterior, anterior, and inferior gluteal lines. The posterior gluteal line (superior curved line), the shortest of the three, begins at the crest, about 5 cm. in front of its posterior extremity; it is at first distinctly marked, but as it passes downward to the upper part of the greater sciatic notch, where it ends, it becomes less distinct, and is often altogether lost. Behind this line is a narrow semilunar surface, the upper part of which is rough and gives origin to a portion of the Glutæus maximus; the lower part is smooth and has no muscular fibers attached to it. The anterior gluteal line (middle curved line), the longest of the three, begins at the crest, about 4 cm. behind its anterior extremity, and, taking a curved direction downward and backward, ends at the upper part of the greater sciatic notch. The space between the anterior and posterior gluteal lines and the crest is concave, and gives origin to the Glutæus medius. Near the middle of this line a nutrient foramen is often seen. The inferior gluteal line (inferior curved line), the least distinct of the three, begins in front at the notch on the anterior border, and, curving backward and downward, ends near the middle of the greater sciatic notch. The surface of bone included between the anterior and inferior gluteal lines is concave from above downward, convex from before backward, and gives origin to the Glutæus minimus. Between the inferior gluteal line and the upper part of the acetabulum is a rough, shallow groove, from which the reflected tendon of the Rectus femoris arises. 4

FIG. 236– Right hip bone. Internal surface. (See enlarged image) The internal surface (Fig. 236) of the ala is bounded above by the crest, below, by the arcuate line; in front and behind, by the anterior and posterior borders. It presents a large, smooth, concave surface, called the iliac fossa, which gives origin to the Iliacus and is perforated at its inner part by a nutrient canal; and below this a smooth, rounded border, the arcuate line, which runs downward, forward, and medialward. Behind the iliac fossa is a rough surface, divided into two portions, an anterior and a posterior. The anterior surface (auricular surface), so called from its resemblance in shape to the ear, is coated with cartilage in the fresh state, and articulates with a similar surface on the side of the sacrum. The posterior portion, known as the iliac tuberosity, is elevated and rough, for the attachment of the posterior sacroiliac ligaments and for the origins of the Sacrospinalis and Multifidus. Below and in front of the auricular surface is the preauricular sulcus, more commonly present and better marked in the female than in the male; to it is attached the pelvic portion of the anterior sacroiliac ligament. 5 The crest of the ilium is convex in its general outline but is sinuously curved, being concave inward in front, concave outward behind. It is thinner at the center than at the extremities, and ends in the anterior and posterior superior iliac spines. The surface of the crest is broad, and divided into external and internal lips, and an intermediate line. About 5 cm. behind the anterior superior iliac spine there is a prominent tubercle on the outer lip. To the external lip are attached the Tensor fasciæ latæ, Obliquus externus abdominis, and Latissimus dorsi, and along its whole length the fascia lata; to the intermediate line the Obliquus internus abdominis; to the internal lip, the fascia iliaca, the Transversus abdominis, Quadratus lumborum, Sacrospinalis, and Iliacus. 6 The anterior border of the ala is concave. It presents two projections, separated by a notch. Of these, the uppermost, situated at the junction of the crest and anterior border, is called the anterior superior iliac spine; its outer border gives attachment to the fascia lata, and the Tensor fasciæ latæ, its inner border, to the Iliacus; while its extremity affords attachment to the inguinal ligament and gives origin to the Sartorius. Beneath this eminence is a notch from which the Sartorius takes origin and across which the lateral femoral cutaneous nerve passes. Below the notch is the anterior inferior iliac spine, which ends in the upper lip of the acetabulum; it gives attachment to the straight tendon of the Rectus femoris and to the iliofemoral ligament of the hip-joint. Medial to the anterior inferior spine is a broad, shallow groove, over which the Iliacus and Psoas major pass. This groove is bounded medially by an eminence, the iliopectineal eminence, which marks the point of union of the ilium and pubis. 7 The posterior border of the ala, shorter than the anterior, also presents two projections separated by a notch, the posterior superior iliac spine and the posterior inferior iliac spine. The former serves for the attachment of the oblique portion of the posterior sacroiliac ligaments and the Multifidus; the latter corresponds with the posterior extremity of the auricular surface. Below the posterior inferior spine is a deep notch, the greater sciatic notch. 8 The Ischium (os ischii).—The ischium forms the lower and back part of the hip bone. It is divisible into three portions—a body and two rami. 9 The Body (corpus oss. ischii).—The body enters into and constitutes a little more than two-fifths of the acetabulum. Its external surface forms part of the lunate surface of the acetabulum and a portion of the acetabular fossa. Its internal surface is part of the wall of the lesser pelvis; it gives origin to some fibers of the Obturator internus. Its anterior border projects as the posterior obturator tubercle; from its posterior border there extends backward a thin and pointed triangular eminence, the ischial spine, more or less elongated in different subjects. The external surface of the spine gives attachment to the Gemellus superior, its internal surface to the Coccygeus, Levator ani, and the pelvic fascia; while to the pointed extremity the sacrospinous ligament is attached. Above the spine is a large notch, the greater sciatic notch, converted into a foramen by the sacrospinous ligament; it transmits the Piriformis, the superior and inferior gluteal vessels and nerves, the sciatic and posterior femoral cutaneous nerves, the internal pudendal vessels, and nerve, and the nerves to the Obturator internus and Quadratus femoris. Of these, the superior gluteal vessels and nerve pass out above the Piriformis, the other structures below it. Below the spine is a smaller notch, the lesser sciatic notch; it is smooth, coated in the recent state with cartilage, the surface of which presents two or three ridges corresponding to the subdivisions of the tendon of the Obturator internus, which winds over it. It is converted into a foramen by the sacrotuberous and sacrospinous ligaments, and transmits the tendon of the Obturator internus, the nerve which supplies that muscle, and the internal pudendal vessels and nerve. 10

The Superior Ramus (ramus superior oss. ischii; descending ramus).—The superior ramus projects downward and backward from the body and presents for examination three surfaces: external, internal, and posterior. The external surface is quadrilateral in shape. It is bounded above by a groove which lodges the tendon of the Obturator externus; below, it is continuous with the inferior ramus; in front it is limited by the posterior margin of the obturator foramen; behind, a prominent margin separates it from the posterior surface. In front of this margin the surface gives origin to the Quadratus femoris, and anterior to this to some of the fibers of origin of the Obturator externus; the lower part of the surface gives origin to part of the Adductor magnus. The internal surface forms part of the bony wall of the lesser pelvis. In front it is limited by the posterior margin of the obturator foramen. Below, it is bounded by a sharp ridge which gives attachment to a falciform prolongation of the sacrotuberous ligament, and, more anteriorly, gives origin to the Transversus perinæi and Ischiocavernosus. Posteriorly the ramus forms a large swelling, the tuberosity of the ischium, which is divided into two portions: a lower, rough, somewhat triangular part, and an upper, smooth, quadrilateral portion. The lower portion is subdivided by a prominent longitudinal ridge, passing from base to apex, into two parts; the outer gives attachment to the Adductor magnus, the inner to the sacrotuberous ligament. The upper portion is subdivided into two areas by an oblique ridge, which runs downward and outward; from the upper and outer area the Semimembranosus arises; from the lower and inner, the long head of the Biceps femoris and the Semitendinosus. 11 The Inferior Ramus (ramus inferior oss. ischii; ascending ramus).—The inferior ramus is the thin, flattened part of the ischium, which ascends from the superior ramus, and joins the inferior ramus of the pubis—the junction being indicated in the adult by a raised line. The outer surface is uneven for the origin of the Obturator externus and some of the fibers of the Adductor magnus; its inner surface forms part of the anterior wall of the pelvis. Its medial border is thick, rough, slightly everted, forms part of the outlet of the pelvis, and presents two ridges and an intervening space. The ridges are continuous with similar ones on the inferior ramus of the pubis: to the outer is attached the deep layer of the superficial perineal fascia (fascia of Colles), and to the inner the inferior fascia of the urogenital diaphragm. If these two ridges be traced downward, they will be found to join with each other just behind the point of origin of the Transversus perinæi; here the two layers of fascia are continuous behind the posterior border of the muscle. To the intervening space, just in front of the point of junction of the ridges, the Transversus perinæi is attached, and in front of this a portion of the crus penis vel clitoridis and the Ischiocavernosus. Its lateral border is thin and sharp, and forms part of the medial margin of the obturator foramen. 12 The Pubis (os pubis).—The pubis, the anterior part of the hip bone, is divisible into a body, a superior and an inferior ramus. 13 The Body (corpus oss. pubis).—The body forms one-fifth of the acetabulum, contributing by its external surface both to the lunate surface and the acetabular fossa. Its internal surface enters into the formation of the wall of the lesser pelvis and gives origin to a portion of the Obturator internus. 14 The Superior Ramus (ramus superior oss. pubis; ascending ramus).—The superior ramus extends from the body to the median plane where it articulates with its fellow of the opposite side. It is conveniently described in two portions, viz., a medial flattened part and a narrow lateral prismoid portion. 15 The Medial Portion of the superior ramus, formerly described as the body of the pubis, is somewhat quadrilateral in shape, and presents for examination two surfaces and three borders. The anterior surface is rough, directed downward and outward, and serves for the origin of various muscles. The Adductor longus arises from the upper and medial angle, immediately below the crest; lower down, the Obturator externus, the Adductor brevis, and the upper part of the Gracilis take origin. The posterior surface, convex from above downward, concave from side to side, is smooth, and forms part of the anterior wall of the pelvis. It gives origin to the Levator ani and Obturator internus, and attachment to the puboprostatic ligaments and to a few muscular fibers prolonged from the bladder. The upper border presents a prominent tubercle, the pubic tubercle (pubic spine), which projects forward; the inferior crus of the subcutaneous inguinal ring (external abdominal ring), and the inguinal ligament (Poupart’s ligament) are attached to it. Passing upward and lateralward from the pubic tubercle is a well-defined ridge, forming a part of the pectineal line which marks the brim of the lesser pelvis: to it are attached a portion of the inguinal falx (conjoined tendon of Obliquus internus and Transversus), the lacunar ligament (Gimbernat’s ligament), and the reflected inguinal ligament (triangular fascia). Medial to the pubic tubercle is the crest, which extends from this process to the medial end of the bone. It affords attachment to the inguinal falx, and to the Rectus abdominis and Pyramidalis. The point of junction of the crest with the medial border of the bone is called the angle; to it, as well as to the symphysis, the superior crus of the subcutaneous inguinal ring is attached. The medial border is articular; it is oval, and is marked by eight or nine transverse ridges, or a series of nipple-like processes arranged in rows, separated by grooves; they serve for the attachment of a thin layer of cartilage, which intervenes between it and the interpubic fibrocartilaginous lamina. The lateral border presents a sharp margin, the obturator crest, which forms part of the circumference of the obturator foramen and affords attachment to the obturator membrane. 16 The Lateral Portion of the ascending ramus has three surfaces: superior, inferior, andposterior. The superior surface presents a continuation of the pectineal line, already mentioned as commencing at the pubic tubercle. In front of this line, the surface of bone is triangular in form, wider laterally than medially, and is covered by the Pectineus. The surface is bounded, laterally, by a rough eminence, the iliopectineal eminence, which serves to indicate the point of junction of the ilium and pubis, and below by a prominent ridge which extends from the acetabular notch to the pubic tubercle. The inferior surface forms the upper boundary of the obturator foramen, and presents, laterally, a broad and deep, oblique groove, for the passage of the obturator vessels and nerve; and medially, a sharp margin, the obturator crest, forming part of the circumference of the obturator foramen, and giving attachment to the obturator membrane. The posterior surface constitutes part of the anterior boundary of the lesser pelvis. It is smooth, convex from above downward, and affords origin to some fibers of the Obturator internus. 17 The Inferior Ramus (ramus inferior oss. pubis; descending ramus).—The inferior ramus is thin and flattened. It passes lateralward and downward from the medial end of the superior ramus; it becomes narrower as it descends and joins with the inferior ramus of the ischium below the obturator foramen. Its anterior surface is rough, for the origin of muscles—the Gracilis along its medial border, a portion of the Obturator externus where it enters into the formation of the obturator foramen, and between these two, the Adductores brevis and magnus, the former being the more medial. The posterior surface is smooth, and gives origin to the Obturator internus, and, close to the medial margin, to the Constrictor urethræ. The medial border is thick, rough, and everted, especially in females. It presents two ridges, separated by an intervening space. The ridges extend downward, and are continuous with similar ridges on the inferior ramus of the ischium; to the external is attached the fascia of Colles, and to the internal the inferior fascia of the urogenital diaphragm. The lateral border is thin and sharp, forms part of the circumference of the obturator foramen, and gives attachment to the obturator membrane. 18 The Acetabulum (cotyloid cavity).—The acetabulum is a deep, cup-shaped, hemispherical depression, directed downward, lateralward, and forward. It is formed medially by the pubis, above by the ilium, laterally and below by the ischium; a little less than two-fifths is contributed by the ilium, a little more than two-fifths by the ischium, and the remaining fifth by the pubis. It is bounded by a prominent uneven rim, which is thick and strong above, and serves for the attachment of the glenoidal labrum (cotyloid ligament), which contracts its orifice, and deepens the surface for articulation. It presents below a deep notch, the acetabular notch, which is continuous with a circular non-articular depression, the acetabular fossa, at the bottom of the cavity: this depression is perforated by numerous apertures, and lodges a mass of fat. The notch is converted into a foramen by the transverse ligament; through the foramen nutrient vessels and nerves enter the joint; the margins of the notch serve for the attachment of the ligamentum teres. The rest of the acetabulum is formed by a curved articular surface, the lunate surface, for articulation with the head of the femur. 19 The Obturator Foramen (foramen obturatum; thyroid foramen).—The obturator foramen is a large aperture, situated between the ischium and pubis. In the male it is large and of an oval form, its longest diameter slanting obliquely from before backward; in the female it is smaller, and more triangular. It is bounded by a thin, uneven margin, to which a strong membrane is attached, and presents, superiorly, a deep groove, the obturator groove, which runs from the pelvis obliquely medialward and downward. This groove is converted into a canal by a ligamentous band, a specialized part of the obturator membrane, attached to two tubercles: one, the posterior obturator tubercle, on the medial border of the ischium, just in front of the acetabular notch; the other, the anterior obturator tubercle, on the obturator crest of the superior ramus of the pubis. Through the canal the obturator vessels and nerve pass out of the pelvis. 20 Structure.—The thicker parts of the bone consist of cancellous tissue, enclosed between two layers of compact tissue; the thinner parts, as at the bottom of the acetabulum and center of the iliac fossa, are usually semitransparent, and composed entirely of compact tissue. 21 Ossification (Fig. 237).—The hip bone is ossified from eight centers: three primary—one each for the ilium, ischium, and pubis; and five secondary—one each for the crest of the ilium, the anterior inferior spine (said to occur more frequently in the male than in the female), the tuberosity of the ischium, the pubic symphysis (more frequent in the female than in the male), and one or more for the Y-shaped piece at the bottom of the acetabulum. The centers appear in the following order: in the lower part of the ilium, immediately above the greater sciatic notch, about the eighth or ninth week of fetal life; in the superior ramus of the ischium, about the third month; in the superior ramus of the pubis, between the fourth and fifth months. At birth, the three primary centers are quite separate, the crest, the bottom of the acetabulum, the ischial tuberosity, and the inferior rami of the ischium and pubis being still cartilaginous. By the seventh or eighth year, the inferior rami of the pubis and ischium are almost completely united by bone. About the thirteenth or fourteenth year, the three primary centers have extended their growth into the bottom of the acetabulum, and are there separated from each other by a Y-shaped portion of cartilage, which now presents traces of ossification, often by two or more centers. One of these, the os acetabuli, appears about the age of twelve, between the ilium and pubis, and fuses with them about the age of eighteen; it forms the pubic part of the acetabulum. The ilium and ischium then become joined, and lastly the pubis and ischium, through the intervention of this Y-shaped portion. At about the age of puberty, ossification takes place in each of the remaining portions, and they join with the rest of the bone between the twentieth and twenty-fifth years. Separate centers are frequently found for the pubic tubercle and the ischial spine, and for the crest and angle of the pubis. 22 Articulations.—The hip bone articulates with its fellow of the opposite side, and with the sacrum and femur. 23

FIG. 237– Plan of ossification of the hip bone. The three primary centers unite through a Y-shaped piece about puberty. Epiphyses appear about puberty, and unite about twenty-fifth year. (See enlarged image)

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