Medicine

HIP BONE AND FEMUR

1. Hip bone and femur. РATELLA

2. Leg and foot bones

3. Classification of Joints. Structure of syNovial joint

Lesson # 5

Theme1. Hip bone and femur. РATELLA

Bones of the lower limb consist of girdle and free limb.

Pelvic girdle contains hip bones.

The hip bone (os coxae) consists of three parts, the pubis, the ilium and the ischium which synostose in the acetabular fossa, which is bordered by the limbus of the acetabulum and is surrounded by the lunate articular surface. The acetabular notch opens the acetabulum inferiorly and thus limits the obturator foramen.

Right hip bone. External surface

The Ilium is divided into the body and the ala. The body forms part of the acetabulum and is delimited internally by the arcuate line. Internally the iliac fossa is visible. Behind the iliac fossa there is the sacropelvic surface with the iliac tuberosity and the auricular surface. The iliac crest starts anteriorly at the superior anterior iliac spine and divides into the outer and inner lips and an intermediate line. The iliac crest ends in the posterior superior iliac spine. Beneath the latter lies the posterior inferioriliac spine, whilst anteriorly beneath the anterior superior iliac spine lies the anterior inferior iliac spine. The inferior gluteal, anterior gluteal and posterior gluteat lines on the gluteal surface.

The pubis consists of a body, a superior ramus and an inferior ramus. The two rami border the obturator foramen anteriorly and inferiorly. Near to the superior end of the medially orientated symphysial surface lies the pubic tubercle, from which the pubic crest extends medially and the pubic pecten runs laterally toward the arcuate line of the ilium. At the transition of the superior ramus of the pubis into the ilium, there is the elevation of the iliopubic eminence. The obturator groove lies inferiorly in the superior ramus.

The Ischium is divided Into the body and the ramus of the ischium, which together with the inferior ramus of the pubis forms the inferior border of the obturator foramen. The ischium bears the ischiat spine, which separates the greater sciatic notch from the lesser sciatic notch. The ischial tuber develops on the ramus of the ischium.

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.

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.

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.

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 , 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.

Right hip bone. Internal surface.

The internal surface 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.

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.

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.

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.

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.

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.

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.

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.

The Pubis (os pubis).—The pubis, the anterior part of the hip bone, is divisible into a body, a superior and an inferior ramus.

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.

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.

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.

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.

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.

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.

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.

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.

Ossification—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.

Articulations.—The hip bone articulates with its fellow of the opposite side, and with the sacrum and femur.

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.

Free portion of the lower limb is divided into thigh, leg and foot.

Thigh contains Femur.

The femur is the largest long bone in the body and is divided into the shaft with the neck, and proximal and distal ends. Dorsally in shaft is the linea aspera. The medial and lateral lips of the linea aspera diverge proximally and distally, and the lateral lip ends in the gluteat tuberosity.

The head of the femur with the fovea of the head, has an irregular border with the neck. The transit from the neck to the shaft of the femur Is marked anteriorly by the intertrochanteric line, and posteriorly by the intertrochanteric crest. Immediately below the greater trochanter lies the trochanteric fossa. The lesser trochanter projects posteriorly and medially.

The distal ends are formed by the medial and lateral condyles. They are joined on the anterior surface by the patellar articular surface and they are separated posteriorly by the intercondylar fossa. The latter is demarcated from the posterior surface of the shaft by the intercondylar line, which forms the base of a triangle popliteal surface, the sides of which are formed by the divergent lips of the linea aspera.

The (Thigh Bone) femur, the longest and strongest bone in the skeleton, is almost perfectly cylindrical in the greater part of its extent. In the erect posture it is not vertical, being separated above from its fellow by a considerable interval, which corresponds to the breadth of the pelvis, but inclining gradually downward and medialward, so as to approach its fellow toward its lower part, for the purpose of bringing the knee-joint near the line of gravity of the body. The degree of this inclination varies in different persons, and is greater in the female than in the male, on account of the greater breadth of the pelvis. The femur, like other long bones, is divisible into a body and two extremities.

The Upper Extremity (proximal extremity).—The upper extremity presents for examination a head, a neck, a greater and a lesser trochanter.

The Head (caput femoris).—The head which is globular and forms rather more than a hemisphere, is directed upward, medialward, and a little forward, the greater part of its convexity being above and in front. Its surface is smooth, coated with cartilage in the fresh state, except over an ovoid depression, the fovea capitis femoris, which is situated a little below and behind the center of the head, and gives attachment to the ligamentum teres.

The Neck (collum femoris).—The neck is a flattened pyramidal process of bone, connecting the head with the body, and forming with the latter a wide angle opening medialward. The angle is widest in infancy, and becomes lessened during growth, so that at puberty it forms a gentle curve from the axis of the body of the bone. In the adult, the neck forms an angle of about 125° with the body, but this varies in inverse proportion to the development of the pelvis and the stature. In the female, in consequence of the increased width of the pelvis, the neck of the femur forms more nearly a right angle with the body than it does in the male. The angle decreases during the period of growth, but after full growth has been attained it does not usually undergo any change, even in old age; it varies considerably in different persons of the same age. It is smaller in short than in long bones, and when the pelvis is wide. In addition to projecting upward and medialward from the body of the femur, the neck also projects somewhat forward; the amount of this forward projection is extremely variable, but on an average is from 12° to 14°.

Upper extremity of right femur viewed from behind and above.

The neck is flattened from before backward, contracted in the middle, and broader laterally than medially. The vertical diameter of the lateral half is increased by the obliquity of the lower edge, which slopes downward to join the body at the level of the lesser trochanter, so that it measures one-third more than the antero-posterior diameter. The medial half is smaller and of a more circular shape. The anterior surface of the neck is perforated by numerous vascular foramina. Along the upper part of the line of junction of the anterior surface with the head is a shallow groove, best marked in elderly subjects; this groove lodges the orbicular fibers of the capsule of the hip-joint. The posterior surface is smooth, and is broader and more concave than the anterior: the posterior part of the capsule of the hip-joint is attached to it about 1 cm. above the intertrochanteric crest. The superior border is short and thick, and ends laterally at the greater trochanter; its surface is perforated by large foramina. The inferior border, long and narrow, curves a little backward, to end at the lesser trochanter.

The Trochanters.—The trochanters are prominent processes which afford leverage to the muscles that rotate the thigh on its axis. They are two in number, the greater and the lesser.

The Greater Trochanter (trochanter major; great trochanter) is a large, irregular, quadrilateral eminence, situated at the junction of the neck with the upper part of the body. It is directed a little lateralward and backward, and, in the adult, is about 1 cm. lower than the head. It has two surfaces and four borders. The lateral surface, quadrilateral in form, is broad, rough, convex, and marked by a diagonal impression, which extends from the postero-superior to the antero-inferior angle, and serves for the insertion of the tendon of the Glutæus medius. Above the impression is a triangular surface, sometimes rough for part of the tendon of the same muscle, sometimes smooth for the interposition of a bursa between the tendon and the bone. Below and behind the diagonal impression is a smooth, triangular surface, over which the tendon of the Glutæus maximus plays, a bursa being interposed. The medial surface, of much less extent than the lateral, presents at its base a deep depression, the trochanteric fossa (digital fossa), for the insertion of the tendon of the Obturator externus, and above and in front of this an impression for the insertion of the Obsturator internus and Gemelli. The superior border is free; it is thick and irregular, and marked near the center by an impression for the insertion of the Piriformis. The inferior border corresponds to the line of junction of the base of the trochanter with the lateral surface of the body; it is marked by a rough, prominent, slightly curved ridge, which gives origin to the upper part of the Vastus lateralis. The anterior border is prominent and somewhat irregular; it affords insertion at its lateral part to the Glutæus minimus. The posterior border is very prominent and appears as a free, rounded edge, which bounds the back part of the trochanteric fossa.

The Lesser Trochanter (trochanter minor; small trochanter) is a conical eminence, which varies in size in different subjects; it projects from the lower and back part of the base of the neck. From its apex three well-marked borders extend; two of these are above—a medial continuous with the lower border of the neck, a lateral with the intertrochanteric crest; the inferior border is continuous with the middle division of the linea aspera. The summit of the trochanter is rough, and gives insertion to the tendon of the Psoas major.

A prominence, of variable size, occurs at the junction of the upper part of the neck with the greater trochanter, and is called the tubercle of the femur; it is the point of meeting of five muscles: the Glutæus minimus laterally, the Vastus lateralis below, and the tendon of the Obturator internus and two Gemelli above. Running obliquely downward and medialward from the tubercle is the intertrochanteric line (spiral line of the femur); it winds around the medial side of the body of the bone, below the lesser trochanter, and ends about 5 cm. below this eminence in the linea aspera. Its upper half is rough, and affords attachment to the iliofemoral ligament of the hip-joint; its lower half is less prominent, and gives origin to the upper part of the Vastus medialis. Running obliquely downward and medialward from the summit of the greater trochanter on the posterior surface of the neck is a prominent ridge, the intertrochanteric crest. Its upper half forms the posterior border of the greater trochanter, and its lower half runs downward and medialward to the lesser trochanter. A slight ridge is sometimes seen commencing about the middle of the intertrochanteric’ crest, and reaching vertically downward for about 5 cm. along the back part of the body: it is called the linea quadrata, and gives attachment to the Quadratus femoris and a few fibers of the Adductor magnus. Generally there is merely a slight thickening about the middle of the intertrochanteric crest, marking the attachment of the upper part of the Quadratus femoris.

Right femur. Posterior surface.

The Body or Shaft (corpus femoris).—The body, almost cylindrical in form, is a little broader above than in the center, broadest and somewhat flattened from before backward below. It is slightly arched, so as to be convex in front, and concave behind, where it is strengthened by a prominent longitudinal ridge, the linea aspera. It presents for examination three borders, separating three surfaces. Of the borders, one, the linea aspera, is posterior, one is medial, and the other, lateral.

The linea aspera is a prominent longitudinal ridge or crest, on the middle third of the bone, presenting a medial and a lateral lip, and a narrow rough, intermediate line. Above, the linea aspera is prolonged by three ridges. The lateral ridge is very rough, and runs almost vertically upward to the base of the greater trochanter. It is termed the gluteal tuberosity, and gives attachment to part of the Glutæus maximus: its upper part is often elongated into a roughened crest, on which a more or less well-marked, rounded tubercle, the third trochanter, is occasionally developed. The intermediate ridge or pectineal line is continued to the base of the lesser trochanter and gives attachment to the Pectineus; the medial ridge is lost in the intertrochanteric line; between these two a portion of the Iliacus is inserted. Below, the linea aspera is prolonged into two ridges, enclosing between them a triangular area, the popliteal surface, upon which the popliteal artery rests. Of these two ridges, the lateral is the more prominent, and descends to the summit of the lateral condyle. The medial is less marked, especially at its upper part, where it is crossed by the femoral artery. It ends below at the summit of the medial condyle, in a small tubercle, the adductor tubercle, which affords insertion to the tendon of the Adductor magnus.

From the medial lip of the linea aspera and its prolongations above and below, the Vastus medialis arises; and from the lateral lip and its upward prolongation, the Vastus lateralis takes origin. The Adductor magnus is inserted into the linea aspera, and to its lateral prolongation above, and its medial prolongation below. Between the Vastus lateralis and the Adductor magnus two muscles are attached—viz., the Glutæus maximus inserted above, and the short head of the Biceps femoris arising below. Between the Adductor magnus and the Vastus medialis four muscles are inserted: the Iliacus and Pectineus above; the Adductor brevis and Adductor longus below. The linea aspera is perforated a little below its center by the nutrient canal, which is directed obliquely upward.

The other two borders of the femur are only slightly marked: the lateral border extends from the antero-inferior angle of the greater trochanter to the anterior extremity of the lateral condyle; the medial border from the intertrochanteric line, at a point opposite the lesser trochanter, to the anterior extremity of the medial condyle.

The anterior surface includes that portion of the shaft which is situated between the lateral and medial borders. It is smooth, convex, broader above and below than in the center. From the upper three-fourths of this surface the Vastus intermedius arises; the lower fourth is separated from the muscle by the intervention of the synovial membrane of the knee-joint and a bursa; from the upper part of it the Articularis genu takes origin. The lateral surface includes the portion between the lateral border and the linea aspera; it is continuous above with the corresponding surface of the greater trochanter, below with that of the lateral condyle: from its upper three-fourths the Vastus intermedius takes origin. The medial surface includes the portion between the medial border and the linea aspera; it is continuous above with the lower border of the neck, below with the medial side of the medial condyle: it is covered by the Vastus medialis.

Lower extremity of right femur viewed from below.

The Lower Extremity (distal extremity),—The lower extremity, larger than the upper, is somewhat cuboid in form, but its transverse diameter is greater than its antero-posterior; it consists of two oblong eminences known as the condyles. In front, the condyles are but slightly prominent, and are separated from one another by a smooth shallow articular depression called the patellar surface; behind, they project considerably, and the interval between them forms a deep notch, the intercondyloid fossa. The lateral condyle is the more prominent and is the broader both in its antero-posterior and transverse diameters, the medial condyle is the longer and, when the femur is held with its body perpendicular, projects to a lower level. When, however, the femur is in its natural oblique position the lower surfaces of the two condyles lie practically in the same horizontal plane. The condyles are not quite parallel with one another; the long axis of the lateral is almost directly antero-posterior, but that of the medial runs backward and medialward. Their opposed surfaces are small, rough, and concave, and form the walls of the intercondyloid fossa. This fossa is limited above by a ridge, the intercondyloid line, and below by the central part of the posterior margin of the patellar surface. The posterior cruciate ligament of the knee-joint is attached to the lower and front part of the medial wall of the fossa and the anterior cruciate ligament to an impression on the upper and back part of its lateral wall. Each condyle is surmounted by an elevation, the epicondyle. The medial epicondyle is a large convex eminence to which the tibial collateral ligament of the knee-joint is attached. At its upper part is the adductor tubercle, already referred to, and behind it is a rough impression which gives origin to the medial head of the Gastrocnemius. The lateral epicondyle, smaller and less prominent than the medial, gives attachment to the fibular collateral ligament of the knee-joint. Directly below it is a small depression from which a smooth well-marked groove curves obliquely upward and backward to the posterior extremity of the condyle. This groove is separated from the articular surface of the condyle by a prominent lip across which a second, shallower groove runs vertically downward from the depression. In the fresh state these grooves are covered with cartilage. The Popliteus arises from the depression; its tendon lies in the oblique groove when the knee is flexed and in the vertical groove when the knee is extended. Above and behind the lateral epicondyle is an area for the origin of the lateral head of the Gastrocnemius, above and to the medial side of which the Plantaris arises.

The articular surface of the lower end of the femur occupies the anterior, inferior, and posterior surfaces of the condyles. Its front part is named the patellar surface and articulates with the patella; it presents a median groove which extends downward to the intercondyloid fossa and two convexities, the lateral of which is broader, more prominent, and extends farther upward than the medial. The lower and posterior parts of the articular surface constitute the tibial surfaces for articulation with the corresponding condyles of the tibia and menisci. These surfaces are separated from one another by the intercondyloid fossa and from the patellar surface by faint grooves which extend obliquely across the condyles. The lateral groove is the better marked; it runs lateralward and forward from the front part of the intercondyloid fossa, and expands to form a triangular depression. When the knee-joint is fully extended, the triangular depression rests upon the anterior portion of the lateral meniscus, and the medial part of the groove comes into contact with the medial margin of the lateral articular surface of the tibia in front of the lateral tubercle of the tibial intercondyloid eminence. The medial groove is less distinct than the lateral. It does not reach as far as the intercondyloid fossa and therefore exists only on the medial part of the condyle; it receives the anterior edge of the medial meniscus when the knee-joint is extended. Where the groove ceases laterally the patellar surface is seen to be continued backward as a semilunar area close to the anterior part of the intercondyloid fossa; this semilunar area articulates with the medial vertical facet of the patella in forced flexion of the knee-joint. The tibial surfaces of the condyles are convex from side to side and from before backward. Each presents a double curve, its posterior segment being an arc of a circle, its anterior, part of a cycloid.

The Architecture of the Femur.—Koch by mathematical analysis has “shown that in every part of the femur there is a remarkable adaptation of the inner structure of the bone to the machanical requirements due to the load on the femur-head. The various parts of the femur taken together form a single mechanical structure wonderfully well-adapted for the efficient, economical transmission of the loads from the acetabulum to the tibia; a structure in which every element contributes its modicum of strength in the manner required by theoretical mechanics for maximum efficiency.” “The internal structure is everywhere so formed as to provide in an efficient manner for all the internal stresses which occur due to the load on the femur-head. Throughout the femur, with the load on the femur-head, the bony material is arranged in the paths of the maximum internal stresses, which are thereby resisted with the greatest efficiency, and hence with maximum economy of material.” “The conclusion is inevitable that the inner structure and outer form of the femur are governed by the conditions of maximum stress to which the bone is subjected normally by the preponderant load on the femur-head; that is, by the body weight transmitted to the femur-head through the acetabulum.” “The femur obeys the mechanical laws that govern other elastic bodies under stress; the relation between the computed internal stresses due to the load on the femur-head, and the internal structure of the different portions of the femur is in very close agreement with the theoretical relations that should exist between stress and structure for maximum economy and efficiency; and, therefore, it is believed that the following laws of bone structure have been demonstrated for the femur:

“1. The inner structure and external form of human bone are closely adapted to the mechanical conditions existing at every point in the bone.

“2. The inner architecture of normal bone is determined by definite and exact requirements of mathematical and mechanical laws to produce a maximum of strength with a minimum of material.”

The Inner Architecture of the Upper Femur.—“The spongy bone of the upper femur (to the lower limit of the lesser trochanter) is composed of two distinct systems of trabeculæ arranged in curved paths: one, which has its origin in the medial (inner) side of the shaft and curving upward in a fan-like radiation to the opposite side of the bone; the other, having origin in the lateral (outer) portion of the shaft and arching upward and medially to end in the upper surface of the greater trochanter, neck and head. These two systems intersect each other at right angles.

“A. Medial (Compressive) System of Trabeculæ.—As the compact bone of the medial (inner) part of the shaft nears the head of the femur it gradually becomes thinner and finally reaches the articular surface of the head as a very thin layer. From a point at about the lower level of the lesser trochanter, 2 1/2 to 3 inches from the lower limit of the articular surface of the head, the trabeculæ branch off from the shaft in smooth curves, spreading radially to cross to the opposite side in two well-defined groups: a lower, or secondary group, and an upper, or principal group.

Frontal longitudinal midsection of upper femur.

“a. The Secondary Compressive Group.—This group of trabeculæ leaves the inner border of the shaft beginning at about the level of the lesser trochanter, and for a distance of almost 2 inches along the curving shaft, with which the separate trabeculæ make an angle of about 45 degrees. They curve outwardly and upwardly to cross in radiating smooth curves to the opposite side. The lower filaments end in the region of the greater trochanter: the adjacent filaments above these pursue a more nearly vertical course and end in the upper portion of the neck of the femur. The trabeculæ of this group are thin and with wide spaces between them. As they traverse the space between the medial and lateral surfaces of the bone they cross at right angles the system of curved trabeculæ which arise from the lateral (outer) portion of the shaft.

“b. The Principal Compressive Group.—This group of trabeculæ springs from the medial portion of the shaft just above the group above-described, and spreads upward and in slightly radial smooth curved lines to reach the upper portion of the articular surface of the head of the femur. These trabeculæ are placed very closely together and are the thickest ones seen in the upper femur. They are a prolongation of the shaft from which they spring in straight lines which gradually curve to meet at right-angles the articular surface. There is no change as they cross the epiphyseal line. They also intersect at right-angles the system of lines which rise from the lateral side of the femur.

Diagram of the lines of stress in the upper femur, based upon the mathematical analysis of the right femur. These result from the combination of the different kinds of stresses at each point in the femur. (After Koch.)

“This system of principal and secondary compressive trabeculæ corresponds in position and in curvature with the lines of maximum compressive stress, which were traced out in the mathematical analysis of this portion of the femur.

“B. Lateral (Tensile) System of Trabeculæ.—As the compact bone of the outer portion of the shaft approaches the greater trochanter it gradually decreases in thickness. Beginning at a point about 1 inch below the level of the lower border of the greater trochanter, numerous thin trabeculæ are given off from the outer portion of the shaft. These trabeculæ lie in three distinct groups.

“c. The Greater Trochanter Group.—These trabeculæ rise from the outer part of the shaft just below the greater trochanter and rise in thin, curving lines to cross the region of the greater trochanter and end in its upper surface. Some of these filaments are poorly defined. This group intersects the trabeculæ of group (a) which rise from the opposite side. The trabeculæ of this group evidently carry small stresses, as is shown by their slenderness.

Frontal longitudinal midsection of left femur. Taken from the same subject as the one that was analyzed. 4/9 of natural size. (After Koch.)

The Distal Portion of the Femur.—In frontal section in the distal 6 inches of the femur “there are to be seen two main systems of trabeculæ, a longitudinal and a transverse system. The trabeculæ of the former rise from the inner wall of the shaft and continue in perfectly straight lines parallel to the axis of the shaft and proceed to the epiphyseal line, whence they continue in more or less curved lines to meet the articular surface of the knee-joint at right angles at every point. Near the center there are a few thin, delicate, longitudinal trabeculæ which spring from the longitudinal trabeculæ just described, to which they are joined by fine transverse filaments that lie in planes parallel to the sagittal plane.

“The trabeculæ of the transverse system are somewhat lighter in structure than those of the longitudinal system, and consist of numerous trabeculæ at right angles to the latter.

“As the distal end of the femur is approached the shaft gradually becomes thinner until the articular surface is reached, where there remains only a thin shell of compact bone. With the gradual thinning of the compact bone of the shaft, there is a simultaneous increase in the amount of the spongy bone, and a gradual flaring of the femur which gives this portion of the bone a gradually increasing gross area of cross-section.

“There is a marked thickening of the shell of bone in the region of the intercondyloid fossa where the anterior and posterior crucial ligaments are attached. This thickened area is about 0.4 inch in diameter and consists of compact bone from which a number of thick trabeculæ pass at right angles to the main longitudinal system. The inner structure of the bone is here evidently adapted to the efficient distribution of the stresses arising from this ligamentary attachment.

Plan of ossification of the femur. From five centers.

“Near the distal end of the femur the longitudinal trabeculæ gradually assume curved paths and end perpendicularly to the articular surface at every point. Such a structure is in accordance with the principles of mechanics, as stresses can be communicated through a frictionless joint only in a direction perpendicular to the joint surface at every point.

“With practically no increase in the amount of bony material used, there is a greatly increased stability produced by the expansion of the lower femur from a hollow shaft of compact bone to a structure of much larger cross-section almost entirely composed of spongy bone.

Epiphysial lines of femur in a young adult. Anterior aspect. The lines of attachment of the articular capsules are in blue.

Ossification.—The femur is ossified from five centers: one for the body, one for the head, one for each trochanter, and one for the lower extremity. Of all the long bones, except the clavicle, it is the first to show traces of ossification; this commences in the middle of the body, at about the seventh week of fetal life, and rapidly extends upward and downward. The centers in the epiphyses appear in the following order: in the lower end of the bone, at the ninth month of fetal life (from this center the condyles and epicondyles are formed); in the head, at the end of the first year after birth; in the greater trochanter, during the fourth year; and in the lesser trochanter, between the thirteenth and fourteenth years. The order in which the epiphyses are joined to the body is the reverse of that of their appearance; they are not united until after puberty, the lesser trochanter being first joined, then the greater, then the head, and, lastly, the inferior extremity, which is not united until the twentieth year.

The Patella is the largest sesamoid bone of the human body. It is triangular in shape with its base facing proximally and its top, the apex patellae facing distally.

Right patella. Posterior surface.

Theme 2 Leg and foot bones

Tibia is positioned medially in leg and fibula - laterally.

The tibia has a somewhat triangular shaft and proximal and distal ends. At the proximal end lie the medial and lateral condyles. The proximal surface, the superior articular facet is interrupted by the intercondytar eminence. This elevation is subdivided into a medial and a lateral intercondylar tubercle. In front of and behind the eminence lie the anterior and posterior intercondylar area. The three-sided shaft of the tibia has a medial, lateral margins and sharp anterior margin, which proximally becomes the tibial tuberosity and is flattened distally. Margins separate the medial, lateral and posterior surfaces. Proximally on the posterior surface of the shaft of the tibia is a slightly roughened area, the musclu solei line.

The distal end is prolonged medially to form the medial malleolus with its malleolar articular surface. The malleolar groove runs along its posterior surface. The inferior articular surface of the tibia, which lies on the lower surface of the distal end of the tibia, articulates with the talus. On the lateral side, in the fibular notch, there is a syndesmotic connection, i. e., a fibrous joint, with the fibula.

Fibula consists of two extremities and a shaft. The proximal end is the head of the fibula with its articular facet and a small protuberance, the apex of the flbula head. The shaft of the fibula is approximately triangular in its middle part and has three margins and three surfaces. On the lateral surface of the distal end, which expands distalward, there is the large, flat lateral malleolus with a facet for articulation with the talus on its inner surface. Behind it there is a deep groove, the lateral malleolar fossa, to which the posterior talofibular ligament is attached.

Bones of the foot are divided into tarsal, metatarsal and phalanx bones.

Tarsal bones are positioned in 2 groups: proximal and distal. Proximal group includes talus, calcaneus. Distal group contains navicular, cuboid, lateral, intermedial and medial cuneiform bones.

Metatarsal bones (five) each have a head, a body and a base. On all of the there are articular facets at one end (base) for articulation with the tarsal and at the other (head) for the phalanges.

The bones of the digits: Each digit consists of more than one bone. namely a proximal, a medial and a distal phalanx. The sole exception is the halux, which has only two phalanges. At the distal end of the distal phalanx there is a the tuberosity of the distal phalanx.

VIDEO

Theme 3. Classification of joints. Structure of syNovial joints

Classification of Joints

The articulations are divided into three classes: synarthroses or immovable, amphiarthroses or slightly movable, and diarthroses or freely movable, joints.

types of the joints

synarthrosis

amphiarthrosis

diarthrosis

(synovial joints)

f u n c t i o n

syn-desmosis

fibrous joints

syn-

ostosis

bony

joints

syn-chondro

sis

cartilaginous joints

axis

axises

S h a p e

Liga-ments:

Fibrous

and

elastic

Suturae:

plane

dentate

squamous

homphosis

Mем-

branes:

interossei and

fontanels

1.Hyaline and fibrous cartilage

2.Temporary and permanent

cylindrical

trochlear (block)

hinge

ellipse

condyloid

saddle

plane

ball

cup

Synarthroses (immovable articulations).—Synarthroses include all those articulations in which the surfaces of the bones are in almost direct contact, fastened together by intervening connective tissue or hyaline cartilage, and in which there is no appreciable motion, as in the joints between the bones of the skull, excepting those of the mandible. There are four varieties of synarthrosis: sutura, schindylesis, gomphosis, and synchondrosis.

Sutura.—Sutura is that form of articulation where the contiguous margins of the bones are united by a thin layer of fibrous tissue; it is met with only in the skull. When the margins of the bones are connected by a series of processes, and indentations interlocked together, the articulation is termed a true suture (sutura vera); and of this there are three varieties: sutura dentata, serrata, and limbosa. The margins of the bones are not in direct contact, being separated by a thin layer of fibrous tissue, continuous externally with the pericranium, internally with the dura mater. The sutura dentata is so called from the tooth-like form of the projecting processes, as in the suture between the parietal bones. In the sutura serrata the edges of the bones are serrated like the teeth of a fine saw, as between the two portions of the frontal bone. In the sutura limbosa, there is besides the interlocking, a certain degree of bevelling of the articular surfaces, so that the bones overlap one another, as in the suture between the parietal and frontal bones. When the articulation is formed by roughened surfaces placed in apposition with one another, it is termed a false suture (sutura notha), of which there are two kinds: the sutura squamosa, formed by the overlapping of contiguous bones by broad bevelled margins, as in the squamosal suture between the temporal and parietal, and the sutura harmonia, where there is simple apposition of contiguous rough surfaces, as in the articulation between the maxillæ, or between the horizontal parts of the palatine bones.

Section across the sagittal suture.

Section through occipitosphenoid synchondrosis of an infant.

Schindylesis.—Schindylesis is that form of articulation in which a thin plate of bone is received into a cleft or fissure formed by the separation of two laminæ in another bone, as in the articulation of the rostrum of the sphenoid and perpendicular plate of the ethmoid with the vomer, or in the reception of the latter in the fissure between the maxillæ and between the palatine bones.

Gomphosis.—Gomphosis is articulation by the insertion of a conical process into a socket; this is not illustrated by any articulation between bones, properly so called, but is seen in the articulations of the roots of the teeth with the alveoli of the mandible and maxillæ.

Synchondrosis.—Where the connecting medium is cartilage the joint is termed a synchondrosis. This is a temporary form of joint, for the cartilage is converted into bone before adult life. Such joints are found between the epiphyses and bodies of long bones, between the occipital and the sphenoid at, and for some years after, birth, and between the petrous portion of the temporal and the jugular process of the occipital.

Amphiarthroses (slightly movable articulations).

—In these articulations the contiguous bony surfaces are either connected by broad flattened disks of fibrocartilage, of a more or less complex structure, as in the articulations between the bodies of the vertebræ; or are united by an interosseous ligament, as in the inferior tibiofibular articulation. The first form is termed a symphysis, the second a syndesmosis.

Diagrammatic section of a symphysis.

Diarthroses (freely movable articulations).—This class includes the greater number of the joints in the body. In a diarthrodial joint the contiguous bony surfaces are covered with articular cartilage, and connected by ligaments lined by synovial membrane (Fig. 299). The joint may be divided, completely or incompletely, by an articular disk or meniscus, the periphery of which is continuous with the fibrous capsule while its free surfaces are covered by synovial membrane.

Diagrammatic section of a diarthrodial joint.

Diagrammatic section of a diarthrodial joint, with an articular disk.

The varieties of joints in this class have been determined by the kind of motion permitted in each. There are two varieties in which the movement is uniaxial, that is to say, all movements take place around one axis. In one form, the ginglymus, this axis is, practically speaking, transverse; in the other, the trochoid or pivot-joint, it is longitudinal. There are two varieties where the movement is biaxial, or around two horizontal axes at right angles to each other, or at any intervening axis between the two. These are the condyloid and the saddle-joint. There is one form where the movement is polyaxial, the enarthrosis or ball-and-socket joint; and finally there are the arthrodia or gliding joints.

Ginglymus or Hinge-joint.—In this form the articular surfaces are moulded to each other in such a manner as to permit motion only in one plane, forward and backward, the extent of motion at the same time being considerable. The direction which the distal bone takes in this motion is seldom in the same plane as that of the axis of the proximal bone; there is usually a certain amount of deviation from the straight line during flexion. The articular surfaces are connected together by strong collateral ligaments, which form their chief bond of union. The best examples of ginglymus are the interphalangeal joints and the joint between the humerus and ulna; the knee- and ankle-joints are less typical, as they allow a slight degree of rotation or of side-to-side movement in certain positions of the limb.

Trochoid or Pivot-joint (articulatio trochoidea; rotary joint).—Where the movement is limited to rotation, the joint is formed by a pivot-like process turning within a ring, or a ring on a pivot, the ring being formed partly of bone, partly of ligament. In the proximal radioulnar articulation, the ring is formed by the radial notch of the ulna and the annular ligament; here, the head of the radius rotates within the ring. In the articulation of the odontoid process of the axis with the atlas the ring is formed in front by the anterior arch, and behind by the transverse ligament of the atlas; here, the ring rotates around the odontoid process.

Condyloid Articulation (articulatio ellipsoidea).—In this form of joint, an ovoid articular surface, or condyle, is received into an elliptical cavity in such a manner as to permit of flexion, extension, adduction, abduction, and circumduction, but no axial rotation. The wrist-joint is an example of this form of articulation.

Articulation by Reciprocal Reception (articulatio sellaris; saddle-joint).—In this variety the opposing surfaces are reciprocally concavo-convex. The movements are the same as in the preceding form; that is to say, flexion, extension, adduction, abduction, and circumduction are allowed; but no axial rotation. The best example of this form is the carpometacarpal joint of the thumb.

Enarthrosis (ball-and-socket joints).—Enarthrosis is a joint in which the distal bone is capable of motion around an indefinite number of axes, which have one common center. It is formed by the reception of a globular head into a cup-like cavity, hence the name “ball-and-socket.” Examples of this form of articulation are found in the hip and shoulder.

Arthrodia (gliding joints) is a joint which admits of only gliding movement; it is formed by the apposition of plane surfaces, or one slightly concave, the other slightly convex, the amount of motion between them being limited by the ligaments or osseous processes surrounding the articulation. It is the form present in the joints between the articular processes of the vertebræ, the carpal joints, except that of the capitate with the navicular and lunate, and the tarsal joints with the exception of that between the talus and the navicular.

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