Pelvic girdle, hip, gluteal region and thigh

Fascia lata

The fascia lata, the expansive deep fascia that surrounds the thigh, is thicker in the proximal and lateral parts of the thigh where tensor fasciae latae and an expansion from gluteus maximus are attached to it. It is thin posteriorly and over the adductor muscles, but thicker around the knee, where it is strengthened by expansions from the tendon of biceps femoris laterally, sartorius medially and quadriceps femoris anteriorly. The fascia lata is attached superiorly and posteriorly to the back of the sacrum and coccyx, laterally to the outer margin of the iliac crest, anteriorly to the inguinal ligament, the iliac fascia and superior ramus of the pubis, and medially to the inferior ramus of the pubis, the ramus and tuberosity of the ischium, and the lower border of the sacrotuberous ligament. From the iliac crest, it descends as a dense layer over gluteus medius to the upper border of gluteus maximus, where it splits into two layers, one passing superficial and the other deep to the muscle, the layers reuniting at the lower border of the muscle.

Saphenous opening

The saphenous opening is an aperture in the deep fascia, inferolateral to the medial end of the inguinal ligament, which allows passage for the long saphenous vein and other smaller vessels ( Fig. 77.1 ). The cribriform fascia, which is pierced by these structures, fills in the aperture and must be removed to reveal it. Adjacent subsidiary openings may exist to transmit venous tributaries. In the adult, the approximate centre of the saphenous opening is 3 cm lateral to a point just distal to the pubic tubercle. The length and width of the opening vary considerably. The fascia lata in this part of the thigh displays superficial and deep strata (not to be confused with the superficial and deep layers of the subcutaneous tissue described above). They lie, respectively, anterior and posterior to the femoral sheath, with the saphenous opening situated where the two layers are in continuity. This serves to explain the somewhat oblique and spiral configuration of the saphenous opening.

The superficial layer, lateral and superior to the saphenous opening, is attached, in continuity, to the crest and anterior superior spine of the ilium, to the whole length of the inguinal ligament, and to the pecten pubis and lacunar ligament. It is reflected inferolaterally from the pubic tubercle as the arched falciform margin, which forms the superior, lateral and inferior boundaries of the saphenous opening; this margin adheres to the anterior layer of the femoral sheath, and the cribriform fascia is attached to it. The falciform margin is considered to have superior and inferior horns. The inferior horn is well defined, and is continuous behind the long saphenous vein with the deep stratum of the fascia lata.

The deep layer is medial to the saphenous opening and is continuous with the superficial stratum at its lower margin. Traced upwards, it covers pectineus, adductor longus and gracilis, passes behind the femoral sheath, with which it blends, and continues to the pecten pubis.

Femoral sheath

The femoral sheath is a funnel-shaped distal prolongation of extraperitoneal fascia, formed of transversalis fascia anterior to the femoral vessels, and of the iliac fascia posteriorly. It is wider proximally and its tapered distal end fuses with the vascular adventitia 3 or 4 cm distal to the inguinal ligament. At birth the sheath is shorter; it elongates when extension at the hips becomes habitual. The femoral branch of the genitofemoral nerve perforates its lateral wall. The medial wall slopes laterally and is pierced by the long saphenous vein and lymphatic vessels. Like the carotid sheath, the femoral sheath encloses a mass of connective tissue in which the vessels are embedded. Three compartments are described: a lateral compartment containing the femoral artery; an intermediate one for the femoral vein; and a medial compartment, the femoral canal, which contains lymph vessels and an occasional lymph node embedded in areolar tissue. The presence of this canal allows the femoral vein to distend. The canal is conical and approximately 1.25 cm in length. Its proximal (wider) end, termed the femoral ring, is bounded in front by the inguinal ligament, behind by pectineus and its fascia and the pectineal ligament, medially by the crescentic, lateral edge of the lacunar ligament and laterally by the femoral vein. The spermatic cord, or the round ligament of the uterus, is just above its anterior margin, while the inferior epigastric vessels are near its anterolateral rim. It is larger in women than in men: this is due partly to the relatively greater width of the female pelvis and partly to the smaller size of the femoral vessels in women. The ring is filled by condensed extraperitoneal tissue, the femoral septum, which is covered on its proximal aspect by the parietal peritoneum. Numerous lymph vessels that connect the deep inguinal to the external iliac lymph nodes traverse the femoral septum ( Fig. 77.2 ).

Iliac fascia

The iliac fascia covers psoas and iliacus. It is thin above but thickens progressively towards the inguinal ligament. The part covering psoas is thickened above as the medial arcuate ligament. Medially the fascia over psoas is attached by a series of fibrous arches to the intervertebral discs, the margins of vertebral bodies and the upper part of the sacrum. Laterally, it blends with the fascia anterior to quadratus lumborum above the iliac crest, and with the fascia covering iliacus below the crest. The iliac part is connected laterally to the whole of the inner lip of the iliac crest and medially to the pelvic brim, where it blends with the periosteum. At approximately the height of the anterior superior iliac spine, the iliac fascia forms an open, curved superior edge, known as the iliopectineal arch (see Fig. 77.1 ). This arch passes directly over the femoral nerve, and iliacus and psoas major. The medial extent of the arch is attached to the iliopubic ramus, where it receives a slip from the tendon of psoas minor, when this muscle is present ( ). The external iliac vessels are anterior to the fascia but the branches of the lumbar plexus are posterior to it. The fascia is separated from the peritoneum by loose extraperitoneal tissue. Lateral to the femoral vessels the iliac fascia is continuous with the posterior margin of the inguinal ligament and the transversalis fascia. Medially, it passes behind the femoral vessels to become the pectineal ligament, attached to the pecten pubis. At the junction of its lateral and medial parts, it is attached to the iliopubic ramus and the capsule of the hip joint. It thus forms a septum between the inguinal ligament and the hip bone, dividing the space here into a lateral part, the muscular space, containing psoas major, iliacus and the femoral nerve, and a medial part, the vascular space, transmitting the femoral vessels (see Fig. 77.2 ). The iliac fascia continues downwards to form the posterior wall of the femoral sheath.

Obturator membrane

The obturator membrane ( Fig. 77.3 ; see Fig. 77.2A ) is a thin aponeurosis that closes (obturates) most of the obturator foramen, leaving a superolateral aperture, the obturator canal, through which the obturator vessels and nerve leave the pelvis and enter the thigh. The membrane is attached to the sharp margin of the obturator foramen except at its inferolateral angle, where it is fixed to the pelvic surface of the ischial ramus, i.e. internal to the foramen. Its fibres are arranged mainly transversely in interlacing bundles; the uppermost bundle, which is attached to the obturator tubercles, completes the obturator canal. The outer and inner surfaces of the obturator membrane provide attachment for the obturator externus and internus, respectively. Some fibres of the pubofemoral ligament of the hip joint are attached to the outer surface.

Acetabulum

The acetabulum (see Fig. 77.4A ) is an approximately hemispherical cavity situated about the centre of the lateral aspect of the hip bone. It faces anteroinferiorly and is circumscribed by an irregular margin deficient inferiorly at the acetabular notch. The acetabular fossa forms the central floor and is rough and non-articular. The articular lunate surface is widest above (the ‘dome’), where weight is transmitted to the femur. Consequently, fractures through this region tend to be associated with unsatisfactory outcomes. All three components of the hip bone contribute to the acetabulum, although unequally. The pubis forms the anterosuperior fifth of the articular surface, the ischium forms the floor of the fossa and rather more than the posteroinferior two-fifths of the articular surface, and the ilium forms the remainder.

Obturator foramen

The obturator foramen lies below and slightly anterior to the acetabulum, between the pubis and ischium. It is bordered above by the grooved obturator surface of the superior pubic ramus, medially by the pubic body and its inferior ramus, below by the ischial ramus, and laterally by the anterior border of the ischial body, including the margin of the acetabulum. It is almost closed by the obturator membrane, which is attached to its margins, except superolaterally, where a communication remains between the pelvis and thigh. This free edge of the membrane is attached to an anterior obturator tubercle at the anterior end of the inferior border of the superior pubic ramus, and a posterior obturator tubercle on the anterior border of the acetabular notch; these tubercles are sometimes indistinct. The foramen is large and oval in males, but smaller and nearly triangular in females.

Structure

The thicker parts of the hip bone are trabecular, encased by two layers of compact bone, while the thinner parts, as in the acetabulum and central iliac fossa, are often translucent and consist of a single lamina of compact bone. In the upper acetabulum and along the arcuate line, i.e. the route of weight transmission from the sacrum to the femur, the amount of compact bone is increased and the subjacent trabecular bone displays two sets of pressure lamellae. These start together near the upper auricular surface and diverge to meet two strong buttresses of compact bone, from which two similar sets of lamellar arches start and converge on the acetabulum. The anterior part of the iliac crest has been much studied with regard to distribution of cortical and trabecular bone. described the cortical bone as very porous, being only 75% bone, decreasing to 35% near the anterior superior iliac spine.

Studies of the internal stresses within the hip bone have revealed a pattern of trabeculae that corresponds well with the theoretically expected patterns of stress trajectories ( ). These patterns are considerably more complex than in any other major bone. Stresses are higher in the acetabular than in the iliac region. In the ilium, the pelvic surface is subjected to considerably less stress than is the gluteal surface.

Muscle attachments

See individual bones.

Vascular supply

In the infant, nutrient arteries are clearly demonstrable for each component of the hip bone. Each nutrient artery branches in a fan-like fashion within its bone of supply ( ). Later, a periosteal arterial network develops, with contributions from numerous local arteries (see under individual bones).

Innervation

Periosteal innervation is by a network of nerves derived from branches of local nerves. These nerves also supply muscles attaching to the periosteum and the joints involving the hip bone. Autonomic nerves accompany nutrient arteries and branch within the bone.

Ossification

Ossification ( Figs 77.6 – 77.7 ) is by three primary centres: one each for the ilium, ischium and pubis. The iliac centre appears above the greater sciatic notch prenatally at about postmenstrual weeks 9–10; the ischial centre in its body during postmenstrual weeks 13–16; and the pubic centre in its superior ramus during postmenstrual weeks 13–20. The pubis is often not recovered from prenatal remains due to its size and fragility and because it is the last of the hip bones to begin ossification ( ). At birth the whole iliac crest, the acetabular floor and the inferior margin are cartilaginous. Gradual ossification of the three components of the acetabulum results in a triradiate cartilaginous stem extending medially to the pelvic surface as a Y-shaped epiphysial plate between the ilium, ischium and pubis, and including the anterior inferior iliac spine. Cartilage along the inferior margin also covers the ischial tuberosity, forms conjoined ischial and pubic rami, and continues to the pubic symphysial surface and along the pubic crest to the pubic tubercle.

FLOAT NOT FOUND

The ossifying ischium and pubis fuse to form a continuous ischiopubic ramus at the seventh or eighth year. Secondary centres, other than for the acetabulum, appear at about puberty and fuse between the fifteenth and twenty-fifth years. There are usually two for the iliac crest (which fuse early), and single centres for the ischial tuberosity (in cartilage close to the inferior acetabular margin and spreading forwards), anterior inferior iliac spine (although it may ossify from the triradiate cartilage) and symphysial surface of the pubis (the pubic tubercle and crest may have separate centres). Progression of ossification of the iliac crest in girls is an index of skeletal maturity and is useful in determining the optimal timing of surgery for spinal deformity.

Between the ages of 8 and 9 years, three major centres of secondary ossification appear in the acetabular cartilage. The largest appears in the anterior wall of the acetabulum and fuses with the pubis, the second in the iliac acetabular cartilage superiorly, fusing with the ilium, and the third in the ischial acetabular cartilage posteriorly, fusing with the ischium. At puberty, these epiphyses expand towards the periphery of the acetabulum and contribute to its depth ( ). Fusion between the three bones within the acetabulum occurs between the sixteenth and eighteenth years. have suggested that ossification of the ilium is similar to that of a long bone, possessing three cartilaginous epiphyses and one cartilaginous process, although it tends to undergo osteoclastic resorption comparable with that of cranial bones. During development the acetabulum increases in breadth at a faster rate than it does in depth.

Avulsion fractures of pelvic apophyses may occur from excessive pull on tendons, usually in athletic adolescents. The most frequent examples of such injuries are those to the ischial tuberosity (hamstrings) and anterior inferior iliac spine (rectus femoris).

Body

The body, anteroposteriorly compressed, has anterior, posterior and symphysial (medial) surfaces and an upper border, the pubic crest. The anterior surface also faces inferolaterally; it is rough superomedially and smooth elsewhere, giving attachment to medial thigh muscles. The smooth posterior surface faces upwards and backwards as the oblique anterior wall of the lesser pelvis and is related to the urinary bladder. The symphysial surface is elongated and oval, united by cartilage to its fellow at the pubic symphysis. Denuded of cartilage, it has an irregular surface of small ridges and furrows or nodular elevations, varying considerably with age, features that are of forensic interest. The pubic crest is the rounded upper border of the body and overhangs the anterior surface; the pubic tubercle is a small rounded eminence on its lateral end. Both crest and tubercle are palpable; the latter partly is obscured in males by the spermatic cord that crosses above it from the scrotum to the anterior abdominal wall. The pubic rami diverge posterolaterally from the superolateral corners of the body.

The anterior surface of the pubic body faces the adductor region. The anterior pubic ligament attaches to its medial part along a rough strip, which is wider in females. The posterior surface is separated from the urinary bladder by retropubic fat. The puboprostatic ligaments are attached to this surface medial to levator ani.

Superior pubic ramus

The superior pubic ramus passes upwards, backwards and laterally from the body, superolateral to the obturator foramen, to reach the acetabulum. It is triangular in section and has three surfaces and borders. Its anterior, pectineal surface, tilted slightly up, is triangular in outline and extends from the pubic tubercle to the iliopubic ramus. It is bounded in front by the rounded obturator crest and behind by the sharp pecten pubis (pectineal line), which, with the crest, is the pubic part of the linea terminalis (i.e. anterior part of the pelvic brim). The posterosuperior, pelvic surface, medially inclined, is smooth and narrows into the posterior surface of the body, which is bounded above by the pecten pubis and below by a sharp inferior border. The obturator surface, directed down and back, is crossed by the obturator groove sloping down and forwards. Its anterior limit is the obturator crest and its posterior limit is the inferior border.

Inferior pubic ramus

The inferior pubic ramus, an inferolateral process of the body, descends inferolaterally to join the ischial ramus medial to, and below, the obturator foramen. The union may be locally thickened, but not obviously so in adults. The ramus has two surfaces and borders. The anterolateral surface, continuous above with that of the pubic body, faces the thigh and is marked by muscles. It is limited laterally by the margin of the obturator foramen, and medially by the rough anterior border. The posteromedial surface is continuous above with that of the body and is transversely convex; its medial part is often everted in males and gives attachment to the crus of the penis. This surface faces the perineum medially, its smooth lateral part tilted up towards the pelvic cavity.

The internal surface is indistinctly divided into medial, intermediate and lateral areas. The medial area faces inferomedially in direct contact with the crus of the penis or clitoris and is limited above and behind by an indistinct ridge for attachment of the fascia overlying the superficial perineal muscles. The medial margin of the ramus, strongly everted in males, provides attachment for the fascia lata and the stratum membranosum perinei.

Pubic tubercle

The pubic tubercle provides attachment to the medial end of the inguinal ligament. It forms part of the floor of the superficial inguinal ring and is crossed by the spermatic cord.

Pecten pubis

The pecten pubis is the sharp, superior edge of the pectineal surface. The conjoint tendon (inguinal falx) and lacunar ligament are attached at its medial end and a strong, fibrous pectineal ligament is attached along the rest of its surface. The smooth pelvic surface is separated from parietal peritoneum only by areolar tissue, in which the lateral umbilical ligament descends forwards across the ramus and, laterally, the vas ductus deferens (vas deferens) passes backwards. The obturator groove, which is converted to a canal by the upper borders of the obturator membrane and obturator muscles, transmits the obturator vessels and nerve from the pelvis to the thigh. Some fibres of the pubofemoral ligament are attached to the lateral end of the obturator crest.

Muscle attachments

The tendon of adductor longus is attached on the anterior (external) surface of the body, below the pubic crest. Below adductor longus, gracilis is attached to a line near the lower margin extending down on to the inferior ramus. Above gracilis, adductor brevis is attached to the body and inferior ramus. Above again, obturator externus is attached to the anterior surface, spreading on to the inferior pubic and ischial rami. Adductor magnus usually extends from the ischial ramus on to the lower part of the inferior pubic ramus between adductor brevis and obturator externus. Pectineus is attached to the pectineal surface of the superior ramus along its upper part. Ascending loops of cremaster are attached to the pubic tubercle. The lateral part of rectus abdominis and, inferiorly, pyramidalis, are attached lateral to the tubercle, on the pubic crest. Medially, the crest is crossed by the medial part of rectus abdominis, ascending from ligamentous fibres that interlace in front of the pubic symphysis. Anterior fibres of levator ani are attached on the posterior (internal) surface of the body near its centre. More laterally, obturator internus is attached on this surface, extending on to both rami. Psoas minor, when present, is attached near the centre of the pecten pubis ( ).

Vascular supply

The pubis is supplied by a periosteal anastomosis of branches from the obturator, inferior epigastric and medial circumflex femoral arteries. The superficial and deep external pudendal arteries may also contribute. Multiple vascular foramina are present, mainly at the lateral (acetabular) end of the bone, but there is no consistently placed nutrient foramen.

Innervation

The pubic periosteum is innervated by branches of the nerves that supply muscles attached to the bone, the hip joint and the symphysis pubis.

Ossification

Ossification of the pubis is described on page 1355 .

Iliac crest

The iliac crest is the superior border of the ilium. It is convex upwards but sinuous from side to side, being internally concave in front and convex behind. Its ends project as anterior and posterior superior iliac spines. The anterior superior iliac spine is palpable at the lateral end of the inguinal fold; the lateral end of the inguinal ligament is attached to the anterior superior iliac spine. The posterior superior iliac spine is not easily palpable but is often indicated by a dimple, approximately 4 cm lateral to the second sacral spinous process, above the medial gluteal region.

The iliac crest has ventral and dorsal segments. The ventral segment occupies slightly more than the anterior two-thirds of the iliac crest and its prominence is associated with changes in iliac form as a result of the emergence of the upright posture. It has internal and external lips and a rough intermediate zone that is narrowest centrally. The dorsal segment, which occupies approximately the posterior one-third in humans, is a feature of all land vertebrates. It has two sloping surfaces separated by a longitudinal ridge ending at the posterior superior spine. The interosseous and posterior sacroiliac ligaments arise from the medial margin of the dorsal segment. The tubercle of the iliac crest projects outwards from the outer lip approximately 5 cm posterosuperior to the anterior superior spine. The summit of the iliac crest, a little behind its midpoint, is level with the fourth lumbar vertebral body in adults and with the fifth lumbar vertebral body in children aged 10 years or less ( ).

Anterior border

The anterior border descends to the acetabulum from the anterior superior spine. Superiorly, it is concave forwards. Inferiorly, immediately above the acetabulum, is a rough anterior inferior iliac spine, which is divided indistinctly into an upper area for the straight head of rectus femoris and a lower area extending laterally along the upper acetabular margin to form a triangular impression for the proximal end of the iliofemoral ligament.

Posterior border

The posterior border is irregularly curved and descends from the posterior superior spine, at first forwards, with a posterior concavity forming a small notch. At the lower end of the notch is a wide, low projection: the posterior inferior iliac spine. Here the border turns almost horizontally forwards for approximately 3 cm, then down and back to join the posterior ischial border. Together these borders form a deep notch, the greater sciatic notch, which is bounded above by the ilium and below by the ilium and ischium. The upper fibres of the sacrotuberous ligament are attached to the upper part of the posterior border. The superior rim of the notch is related to the superior gluteal vessels and nerve. The lower margin of the greater sciatic notch is covered by piriformis and is related to the exiting sciatic nerve.

Medial border

The medial border separates the iliac fossa and the sacropelvic surface. It is indistinct near the crest, rough in its upper part, then sharp where it bounds an articular surface for the sacrum, and finally rounded. The latter part is the arcuate line, which inferiorly reaches the posterior part of the iliopubic ramus, marking the union of the ilium and pubis.

Gluteal surface

The gluteal surface, facing inferiorly in its posterior part and laterally and slightly downwards in front, is bounded above by the iliac crest, and below by the upper acetabular border and by the anterior and posterior borders. It is rough and curved, convex in front, concave behind and marked by three gluteal lines. The posterior gluteal line is shortest, descending from the external lip of the crest approximately 5 cm in front of its posterior limit and ending in front of the posterior inferior iliac spine. Above, it is usually distinct, but inferiorly it is poorly defined and frequently absent. The anterior gluteal line, the longest, begins near the midpoint of the superior margin of the greater sciatic notch and ascends forwards into the outer lip of the crest, a little anterior to its tubercle. The inferior gluteal line, seldom well marked, begins posterosuperior to the anterior inferior iliac spine, curving posteroinferiorly to end near the apex of the greater sciatic notch. Between the inferior gluteal line and the acetabular margin is a rough, shallow groove. Behind the acetabulum, the lower gluteal surface is continuous with the posterior ischial surface, the conjunction marked by a low elevation.

The articular capsule is attached to an area adjoining the acetabular margin, most of which is covered by gluteus minimus. Posteroinferiorly, near the union of the ilium and ischium, the bone is related to piriformis.

Iliac fossa

The iliac fossa, the internal concavity of the ilium, faces anterosuperiorly. It is limited above by the iliac crest, in front by the anterior border and behind by the medial border, separating it from the sacropelvic surface. It forms the smooth and gently concave posterolateral wall of the greater pelvis. Below it is continuous with a wide shallow groove, bounded laterally by the anterior inferior iliac spine and medially by the iliopubic ramus.

The converging fibres of iliacus occupy the wide groove between the anterior inferior iliac spine and the iliopubic ramus laterally and the tendon of psoas major medially; the tendon is separated from the underlying bone by a bursa. The right iliac fossa contains the caecum, and often the vermiform appendix and terminal ileum. The left iliac fossa houses the terminal part of the descending colon and the proximal sigmoid colon.

Sacropelvic surface

The sacropelvic surface, the posteroinferior part of the medial iliac surface, is bounded posteroinferiorly by the posterior border, anterosuperiorly by the medial border, posterosuperiorly by the iliac crest and anteroinferiorly by the line of fusion of the ilium and ischium. It is divided into iliac tuberosity and auricular and pelvic surfaces. The iliac tuberosity, a large, rough area below the dorsal segment of the iliac crest, shows cranial and caudal areas separated by an oblique ridge and connected to the sacrum by the interosseous sacroiliac ligament. The sacropelvic surface gives attachment to the posterior sacroiliac ligaments and, behind the auricular surface, to the interosseous sacroiliac ligament. The iliolumbar ligament is attached to its anterior part. The auricular surface, immediately anteroinferior to the tuberosity, articulates with the lateral sacral mass. Shaped like an ear, its widest part is anterosuperior, and its ‘lobule’ posteroinferior and on the medial aspect of the posterior inferior spine. Its edges are well defined but the surface, though articular, is rough and irregular. It articulates with the sacrum and is reciprocally shaped. The anterior sacroiliac ligament is attached to its sharp anterior and inferior borders. The narrow part of the pelvic surface, between the auricular surface and the upper rim of the greater sciatic notch, often shows a rough pre-auricular sulcus (that is usually better defined in females) for the lower fibres of the anterior sacroiliac ligament. For the reliability of this feature as a sex discriminant, refer to and . The pelvic surface is anteroinferior to the acutely curved part of the auricular surface, and contributes to the lateral wall of the lesser pelvis. Its upper part, facing down, is between the auricular surface and the upper limb of the greater sciatic notch; the lower part faces medially and is separated from the iliac fossa by the arcuate line. Anteroinferiorly, the pelvic surface extends to the line of union between the ilium and ischium.

Muscle attachments

The attachment of sartorius extends down the anterior border below the anterior superior iliac spine. The iliac crest gives attachment to the anterolateral and dorsal abdominal muscles, and to the fasciae and muscles of the lower limb. The fascia lata and iliotibial tract are attached to the outer lip and tubercle of its ventral segment. Tensor fasciae latae is attached anterior to the tubercle. The lower fibres of external oblique and, just behind the summit of the crest, the lowest fibres of latissimus dorsi are attached to its anterior two-thirds. A variable interval exists between the most posterior attachment of external oblique and the most anterior attachment of latissimus dorsi, and here the crest forms the base of the lumbar triangle through which herniation of abdominal contents may rarely occur. Internal oblique is attached to the intermediate area of the crest. Transversus abdominis is attached to the anterior two-thirds of the inner lip of the crest, and behind this to the thoracolumbar fascia and quadratus lumborum. The most superior fibres of gluteus maximus are attached to the dorsal segment of the crest on its lateral slope. Erector spinae arises from the medial slope of the dorsal segment. The straight head of rectus femoris is attached to the upper area of the anterior inferior spine. Some fibres of piriformis are attached in front of the posterior inferior spine on the upper border of the greater sciatic foramen.

The gluteal surface is divided by three gluteal lines into four areas. Behind the posterior line, the upper rough part gives attachment to the upper fibres of gluteus maximus and the lower, smooth region to part of the sacrotuberous ligament and iliac head of piriformis. Gluteus medius is attached between the posterior and anterior lines, below the iliac crest, and gluteus minimus is attached between the anterior and inferior lines. The fourth area, below the inferior line, contains vascular foramina.

The reflected head of rectus femoris attaches to a curved groove above the acetabulum. Iliacus is attached to the upper two-thirds of the iliac fossa and is related to its lower one-third. The medial part of quadratus lumborum is attached to the anterior part of the sacropelvic surface, above the iliolumbar ligament. Piriformis is sometimes partly attached lateral to the pre-auricular sulcus, and part of obturator internus is attached to the more extensive remainder of the pelvic surface.

Vascular supply

Branches of the iliolumbar artery run between iliacus and the ilium; one or more enter large nutrient foramina lying posteroinferiorly in the iliac fossa. The superior gluteal, obturator and superficial circumflex iliac arteries contribute to the periosteal supply. The obturator artery may supply a nutrient branch. Vascular foramina on the ilium underlying the gluteal muscles may lead into large vascular canals in the bone.

Innervation

The periosteum is innervated by branches of nerves that supply muscles attached to the bone, the hip joint and the sacroiliac joint.

Ossification

Ossification of the ilium is described on page 1355 .

Ischial ramus

The ischial ramus has anteroinferior and posterior surfaces continuous with the corresponding surfaces of the inferior pubic ramus. The anteroinferior surface is roughened by the attachment of the medial thigh muscles. The smooth posterior surface is partly divided into perineal and pelvic areas, like the inferior pubic ramus. The upper border completes the obturator foramen; the rough lower border, together with the medial border of the inferior pubic ramus, contributes to the pubic arch. The fascia overlying the superficial muscles of the perineum is attached below the ridge between the perineal and pelvic areas of the posterior surface of the ischial ramus. Above the ridge, areas give attachment to the crus of the penis or clitoris and the external urethral sphincter. The lower border of the ramus provides an attachment for the fascia lata and the stratum membranosum perinei.

Ischial tuberosity

The ischial tuberosity is divided nearly transversely into upper and lower areas. The upper area is subdivided by an oblique line into superolateral and inferomedial parts. The lower area, narrowing as it curves on to the inferior ischial aspect, is subdivided by an irregular vertical ridge into lateral and medial areas. The medial area is covered by fibroadipose tissue that usually contains the sciatic bursa of gluteus maximus, which supports the body in sitting. Medially the tuberosity is limited by a curved ridge that passes on to the ramus and which gives attachment to the sacrotuberous ligament and its falciform process.

Ischial spine

The ischial spine projects downwards and a little medially (see Fig. 77.4B ). The sacrospinous ligament is attached to its margins, separating the greater from the lesser sciatic foramen. The ligament is crossed posteriorly by the internal pudendal vessels, pudendal nerve and the nerve to obturator internus.

Muscle attachments

Part of obturator externus is attached to the lower femoral surface of the ischial body. Part of obturator externus, the anterior fibres of adductor magnus and, near the lower border, gracilis are all attached to the anterior surface of the ischial ramus. Between adductor magnus and gracilis, the attachment of adductor brevis may descend from the inferior pubic ramus. The posterior surface is divided into pelvic and perineal areas. The pelvic area, facing back, has part of obturator internus attached to it. The perineal area faces medially; its upper part is related to the crus of the penis or clitoris, and its lower part gives attachment to sphincter urethrae, ischiocavernosus and the superficial transverse perineal muscle.

The ischial tuberosity gives attachment to the posterior thigh muscles. Quadratus femoris is attached along the upper part of its lateral border. The upper area of the tuberosity is subdivided by an oblique line into a superolateral part for semimembranosus and an inferomedial part for the long head of biceps femoris and semitendinosus. The lower area is subdivided by an irregular vertical ridge into lateral and medial areas. The larger lateral area is for part of adductor magnus. Superomedial to the tuberosity, the posterior surface has a wide, shallow groove, usually covered by hyaline cartilage, with a bursa between it and the tendon of obturator internus. Gemellus inferior is attached to the lower margin of the groove, near the tuberosity. Gemellus superior is attached to the upper margin, near the ischial spine. Forceful activation and/or severe stretch of the hamstrings can result in an avulsion fracture of the ischial tuberosity.

The pelvic surface of the ischial spine gives attachment to coccygeus and to the most posterior fibres of levator ani. Obturator internus is attached to the upper part of the smooth pelvic ischial surface and converges on the bony part of the lesser sciatic foramen, covering the rest of this surface other than the pelvic aspect of the ischial spine; the muscle and its fascia separate the bone from the ischio-anal fossa.

Vascular supply

There are multiple vascular foramina at the acetabular margins and a few are usually present on the pelvic surface. Branches of the obturator, medial circumflex femoral and inferior gluteal arteries supply the ischium.

Innervation

The periosteum is innervated by branches of nerves that supply the hip joint and muscles attached to the bone.

Ossification

Ossification of the ischium is described on page 1355 .

Greater pelvis

The greater pelvis consists of the ilium and pubis above the lineae terminales and the base of the sacrum. This junctional zone is structurally massive and forms powerful arches from the acetabular fossae to the vertebral column around the visceral cavity, which is part of the abdomen. It has little anterior wall because of the pelvic inclination.

Pelvic inlet (superior pelvic aperture)

The pelvic inlet or brim may be round or oval in shape, and is indented posteriorly by the sacral promontory. The pelvic brim is obstetrically important and has also long been measured for anthropological reasons, as has the pelvic cavity.

By convention, the pelvic inlet is described in three dimensions. The anteroposterior diameter (true conjugate) is measured between the midpoints of the sacral promontory and upper border of the pubic symphysis, and on average is 10 cm in the adult male and 11.2 cm in the adult female. The transverse diameter is the maximum distance between similar points (assessed by eye) on opposite sides of the pelvic brim, and is on average 12.5 cm in the adult male and 13.1 cm in the adult female. The oblique diameter is measured from the iliopubic ramus to the opposite sacroiliac joint, and is on average 12 cm in the adult male and 12.5 cm in the adult female. These measurements vary with the individual and with racial group. In children, dimensions of the thorax and spine are significantly correlated with the width of the pelvic inlet, which are age-independent predictors of paediatric chest width and may be useful in assessing growth of the thorax and spine in children with early-onset spinal deformity ( ).

Articulated bony pelvis

The lesser pelvis encloses a true basin when soft tissues of the pelvic floor are in place. Skeletally, it is a narrower continuation of the greater pelvis, with irregular but more complete walls around its cavity. Of obstetric importance, it has a curved median axis, and superior and inferior openings. The superior opening is occupied by viscera. The pelvic floor, viscera and subjacent perineal sphincters close the inferior opening.

Cavity of the lesser pelvis

The cavity of the lesser pelvis is short, curved and markedly longer in its posterior wall. Anteroinferiorly, it is bounded by pubic bones, their rami and symphysis. Posteriorly, it is bounded by the concave anterior sacral surface and coccyx. Laterally, on each side its margins are the smooth quadrangular pelvic aspect of the fused ilium and ischium. The region so enclosed is the pelvic cavity proper, through which pass the rectum, urinary bladder and parts of the reproductive organs. The cavity in females must also permit passage of the fetus.

The pelvic cavity diameters are measured at approximately the mid-level. The anteroposterior diameter is measured between the midpoints of the third sacral segment and posterior surface of the pubic symphysis, and is about 10.5 cm in the adult male and 13 cm in the adult female. The transverse diameter is the widest transverse distance between the side walls of the cavity, and often the greatest transverse dimension in the whole cavity. It measures about 12 cm in the adult male and 12.5 cm in the adult female. The oblique diameter is the distance from the lowest point of one sacroiliac joint to the midpoint of the contralateral obturator membrane, and measures about 11 cm in the adult male and 13.1 cm in the adult female. All measurements vary with the individual and with racial group.

Pelvic outlet (inferior pelvic aperture)

Less regular in outline than the pelvic inlet, the pelvic outlet is indented behind by the coccyx and sacrum, and bilaterally by the ischial tuberosities. Its perimeter thus consists of three wide arcs. Anteriorly is the pubic arch, between the converging ischiopubic rami. Posteriorly and laterally on both sides are the sciatic notches between the sacrum and ischial tuberosities. The sciatic notches are divided by the sacrotuberous and sacrospinous ligaments into greater and lesser sciatic foramina ( Fig. 77.9 ). FLOAT NOT FOUND

With ligaments included, the pelvic outlet is rhomboidal. Its anterior limbs are the ischiopubic rami (joined by the inferior pubic (arcuate) ligament) and its posterior margins are the sacrotuberous ligaments, with the coccyx in the midline. The outlet is thus not rigid in its posterior half, being limited by ligaments and the coccyx, all slightly yielding. Even with the sacrum taken as the posterior midline limit (more reliable for measurement), there is typically slight mobility at the sacroiliac joints. Note also that a plane of the pelvic outlet is merely conceptual. The anterior, ischiopubic part has a plane that is inclined down and back to a transverse line between the lower limits of the ischial tuberosities, and the posterior half has a plane approximating to the sacrotuberous ligaments, sloping down and forwards to the same line.

Three measurements are made for the pelvic outlet. The anteroposterior diameter is usually measured from the apex of the coccyx to the midpoint of the lower rim of the pubic symphysis. The lowest sacral point may also be used (on average: male 8 cm, female 12.5 cm). The transverse (bituberous) diameter is measured between the ischial tuberosities at the lower borders of their medial surfaces (on average: male 8.5 cm, female 11.8 cm). The oblique diameter extends from the midpoint of the sacrotuberous ligament on one side to the contralateral ischiopubic junction (on average: male 10 cm, female 11.8 cm). All measurements vary among individuals and racial groups.

Other measurements

Apart from these main measurements, by consensus the basis of pelvic osteometry, other planes and measurements are used in obstetric practice. The plane of greatest pelvic dimensions is an obstetric concept. It represents the most capacious pelvic level, between the pelvic brim and midlevel plane, and corresponds with the latter anteriorly at the middle part of the pubic symphysis and posteriorly at the level of the second and third sacral segments.

The plane of least dimensions is said to be at about mid-pelvic level. Its transverse diameter is between the apices of the ischial spines. This measurement is about 9.5 cm in an adult female and is just wide enough to allow passage of the biparietal diameter of a fetal head (about 9 cm). Not surprisingly, most difficult parturition occurs here.

The above measurements are sometimes made in clinical practice using radiographs or magnetic resonance imaging (MRI) pelvimetry. Precise measurement is not possible without radiological techniques, and even these do not consider the adjacent soft tissues.

Pelvic axes and inclination

The axis of the superior pelvic aperture traverses its centre at right-angles to its plane, directed down and backwards ( Fig. 77.10 ). When prolonged (projected), it passes through the umbilicus and mid-coccyx. An axis is similarly established for the inferior aperture: projected upwards, it impinges on the sacral promontory. Axes can likewise be constructed for any plane, and one for the whole cavity is a concatenation of an infinite series of such lines (see Fig. 77.10 ).

The fetal head, however, descends in the axis of the inlet as far as the level of the ischial spines; it is then directed forwards into the axis of the vagina at right-angles to that axis. The form of this pelvic axis and the disparity in depth between the anterior and posterior contours of the cavity are prime factors in the mechanism of fetal transit in the pelvic canal.

In the standing position, the pelvic canal curves obliquely backwards relative to the trunk and abdominal cavity. The whole pelvis is tilted forwards, the plane of the pelvic brim making an angle of 50–60° with the horizontal. The plane of the pelvic outlet is tilted to about 15°. Strictly, the pelvic outlet has two planes: an anterior passing backwards from the pubic symphysis and a posterior passing forwards from the coccyx, both descending to meet at the intertuberous line. In standing, the pelvic aspect of the pubic symphysis faces nearly as much upwards as backwards and the sacral concavity is directed anteroinferiorly. The front of the pubic symphysis and anterior superior iliac spines are in the same vertical plane. While sitting, body weight is transmitted through the inferomedial parts of the ischial tuberosities, with variable soft tissues intervening. The anterior superior iliac spines are in a vertical plane through the acetabular centres, and the whole pelvis is tilted back with the lumbosacral angle somewhat diminished at the sacral promontory.

Pelvic mechanism

The skeletal pelvis supports and protects the contained viscera but is primarily part of the lower limbs, affording wide attachment for muscles of the thigh, leg and trunk. It constitutes the major mechanism for transmitting the weight of the head, trunk and upper limbs to the lower limbs. It may be considered as two arches divided by a coronal transacetabular plane. The posterior arch, chiefly concerned in transmitting weight, consists of the upper three sacral vertebrae and strong pillars of bone from the sacroiliac joints to the acetabular fossae. The anterior arch, formed by the pubic bones and their superior rami, connects these lateral pillars as a tie beam to prevent separation; it also acts as a compression strut against medial femoral thrust. The sacrum, as the summit of the posterior arch, is loaded at the lumbosacral joint. Theoretically, this force has two components: one thrusting the sacrum downwards and backwards between the iliac bones, the other thrusting its upper end downwards and forwards. Sacroiliac joint movements are regulated by osseous shape and massive ligaments. The first component therefore acts against the wedge, its tendency to separate iliac bones resisted by the sacroiliac and iliolumbar ligaments and pubic symphysis.

Vertical coronal sections through the sacroiliac joints suggest division of the (synovial) articular region of the sacrum into three segments. In the anterosuperior segment, involving the first sacral vertebra, the articular surfaces are slightly sinuous and almost parallel. In the middle segment, the posterior width between the articular markings is greater than the anterior, and centrally a sacral concavity fits a corresponding iliac convexity, an interlocking mechanism relieving the strain on the ligaments produced by body weight. In the posteroinferior segment, the anterior sacral width is greater than the posterior and here its sacral surfaces are slightly concave. Anteroinferior sacral dislocation by the second component (of force) is prevented, therefore, mainly by the middle segment, owing to its cuneiform shape and interlocking mechanism. However, some rotation occurs, in which the anterosuperior segment tilts down and the posteroinferior segment up. ‘Superior’ segmental movement is limited to a small degree by wedging but primarily by tension in the sacrotuberous and sacrospinous ligaments. In all movements, the sacroiliac and iliolumbar ligaments and pubic symphysis resist separation of the iliac bones.

Femoral head

The femoral head faces anterosuperomedially to articulate with the acetabulum ( Fig. 77.13 ). The head, often described as rather more than half a ‘sphere’, is not part of a true sphere but is spheroidal. Its smoothness is interrupted posteroinferior to its centre by a small, rough fovea, to which the ligament of the head of the femur (ligamentum teres) is attached. The head is intracapsular and is encircled, distal to its equator, by the acetabular labrum. Its articular margin is distinct, except anteriorly, where the articular surface extends on to the neck. The anterior surface of the head is separated inferomedially from the femoral artery by the tendon of psoas major, the iliopectineal bursa and the articular capsule.

Femoral neck

The femoral neck (see Fig. 77.13 ) is approximately 5 cm long, narrowest in its mid part and widest laterally, and connects the head to the shaft at an average angle of approximately 127° ( ) (angle of inclination; neck–shaft angle). The neck is also anteriorly rotated with respect to the shaft (angle of anteversion) some 10–15°, although values of this angle vary between individuals and between populations ( ). The contours of the neck are rounded; the upper surface is almost horizontal and slightly concave, while the lower is straighter but oblique, directed inferolaterally and backwards to the shaft near the lesser trochanter. On all aspects the neck expands as it approaches the articular surface of the head. Morphological variation of this bony expansion may cause painful impingement between the femoral neck and acetabular labrum at the extremes of flexion and medial (internal) rotation positions. The anterior surface of the neck is flat and marked at the junction with the shaft by a rough intertrochanteric line. The posterior surface, facing posteriorly and superiorly, is transversely convex, and concave in its long axis; its junction with the shaft is marked by a rounded intertrochanteric crest. There are numerous vascular foramina, especially anteriorly and posterosuperiorly.

The anterior surface is intracapsular, the capsule attaching laterally to the intertrochanteric line. Facets, often covered by extensions of articular cartilage, and various imprints frequently occur here. On the posterior surface the capsule does not reach the intertrochanteric crest; little more than the medial half of the neck is intracapsular. The anterior surface adjoining the head and covered by cartilage is related to the iliofemoral ligament. A groove, produced by the tendon of obturator externus as it approaches the trochanteric fossa, spirals across the posterior surface of the neck of the femur in a proximolateral direction.

Greater trochanter

The greater trochanter is large and quadrangular, projecting up from the junction of the neck and shaft (see Fig. 77.13 ). The leverage of many hip muscles is enhanced by their attachment to this prominent bony feature. Its posterosuperior region projects superomedially to overhang the adjacent posterior surface of the neck and here its medial surface presents the rough trochanteric fossa. The proximal border of the trochanter lies approximately a hand’s breadth below the iliac tuberculum, level with the centre of the femoral head. It has an anterior rough impression. Its lateral surface, continuous distally with the lateral surface of the femoral shaft, is crossed anteroinferiorly by an oblique, flat strip, which is wider above. This surface is readily palpable, especially when the muscles are relaxed.

Lesser trochanter

The lesser trochanter is a conical posteromedial projection of the shaft at the posteroinferior aspect of its junction with the neck. Its summit and anterior surface are rough, but its posterior surface, at the distal end of the intertrochanteric crest, is smooth. It is not palpable. The lesser trochanter serves as the primary attachment for the large iliopsoas muscle.

Intertrochanteric line

The intertrochanteric line, a prominent ridge at the junction of the anterior surfaces of the neck and shaft, descends medially from a tubercle on the upper part of the anterior aspect of the greater trochanter to a point on the lower border of the neck, anterior to the lesser trochanter, where there may also be a tubercle. This line is the lateral limit of the hip joint capsule anteriorly. The upper and lower bands of the iliofemoral ligament are attached to its proximal and distal ends and the associated tubercles. Distally, it is continuous with the spiral (pectineal) line.

Intertrochanteric crest

The intertrochanteric crest, a smooth and prominent ridge at the junction of the posterior surface of the neck with the shaft, descends medially from the posterosuperior angle of the greater trochanter to the lesser trochanter. A little above its centre is the low, rounded quadrate tubercle. It is covered by gluteus maximus, from which it is separated, medial to the tubercle, by quadratus femoris and the upper border of adductor magnus.

Gluteal tuberosity

The gluteal tuberosity, accepting the tendon of the gluteus maximus, may be an elongated depression or a ridge. It may at times be prominent enough to merit the title of a third trochanter.

Shaft

The shaft is surrounded by muscles and is impalpable (see Figs 77.11B , 77.12B ). The distal anterior surface, for 5–6 cm above the patellar articular surface, is covered by a suprapatellar bursa, between bone and muscle. The proximal two-thirds of the anterior and lateral surfaces are covered by vastus intermedius. The medial surface, devoid of attachments, is covered by vastus medialis.

The shaft is narrowest centrally, expanding a little at its proximal end, and substantially more at its distal end. Its long axis makes an angle of approximately 10° with the vertical, and diverges 5–7° from the long axis of the tibia. Its middle one-third has three surfaces and borders. The extensive anterior surface, smooth and gently convex, is between the lateral and medial borders, which are both round and indistinct. The posterolateral surface is bounded posteriorly by the broad, rough and often raised, linea aspera, usually a crest with lateral and medial edges. Its subjacent compact bone is augmented to withstand compressive forces, which are concentrated here by the anterior curvature of the shaft. The linea aspera gives at least partial attachment to adductors longus and brevis, adductor magnus, vastus medialis and lateralis, intermuscular septa (partially continuous with the fascia lata of the thigh), and the short head of biceps femoris, all inseparably blended at their attachments. Perforating arteries cross the linea aspera laterally under tendinous arches in adductor magnus and biceps femoris. Nutrient foramina, directed proximally, appear in the linea aspera, varying in number and site, one usually near its proximal end, a second usually near its distal end. The posteromedial surface, smooth like the others, is bounded in front by the indistinct medial border and behind by the linea aspera. In its proximal third the shaft has a fourth, posterior surface, bounded medially by the narrow, rough spiral line. Laterally, this surface is limited by the broad, rough gluteal tuberosity, ascending a little laterally to the greater trochanter and descending to the lateral edge of the linea aspera. In its distal one-third, the posterior surface of the shaft presents a further surface, the popliteal surface (see below) between the medial and lateral supracondylar lines. These lines are continuous above with the corresponding edges of the linea aspera. The lateral line is most distinct in its proximal two-thirds, where the short head of biceps femoris and lateral intermuscular septum are attached. Its distal third has a small, rough area for the attachment of plantaris, often encroaching on the popliteal surface. The medial line is indistinct in its proximal two-thirds, where vastus medialis is attached. Distally, the femoral vessels entering the popliteal fossa from the adductor canal cross the medial line obliquely. Further distally, the line is often sharp for 3 or 4 cm proximal to the adductor tubercle.

The popliteal surface, triangular in outline, lies between the medial and lateral supracondylar lines. In its distal medial part, it is rough and slightly elevated. Forming the proximal part of the floor of the popliteal fossa, the popliteal surface is covered by a variable amount of fat that separates the popliteal artery from bone. The superior medial genicular artery, a branch of the popliteal artery, arches medially above the medial condyle. It is separated from bone by the medial head of gastrocnemius. The latter is attached a little above the condyle; further distally, there may be a smooth facet underlying a bursa for the medial head of gastrocnemius. More medially, there is often an imprint proximal to the articular surface; in deep flexion, this is close to a rough tubercle on the medial tibial condyle for the attachment of semimembranosus. The superior lateral genicular artery arches up laterally proximal to the lateral condyle but is separated from bone by the attachment of plantaris to the distal part of the lateral supracondylar line.

Distal end

The distal end of the femur is widely expanded as a bearing surface for transmission of weight to the tibia ( Fig. 77.14 ). It bears two massive condyles, which are partly articular. Anteriorly, the condyles are confluent and continue into the shaft; posteriorly, they are separated by a deep intercondylar fossa and project beyond the plane of the popliteal surface. The articular surface is a broad area, like an inverted U, for the patella and the tibia. The patellar surface extends anteriorly on both condyles, especially the lateral. It is transversely concave, vertically convex and grooved for the posterior patellar surface. The tibial surface is divided by the intercondylar fossa but is anteriorly continuous with the patellar surface. Its medial part is a broad strip on the convex inferoposterior surface of the medial condyle, and is gently curved with a medial convexity. Its lateral part covers similar aspects of the lateral condyle but is broader and passes straight back. The tibial surfaces are convex in all directions. The medial and lateral tibial surfaces have dissimilar anteroposterior curvatures; as evident in Fig. 77.14 , the medial condyle curves more obliquely than the lateral. As described in Chapter 78 on the knee, these differences are believed to be important determinants in the mechanics of locking the knee in full extension.

Lateral condyle

The lateral condyle (see Fig. 77.14 ) is larger anteroposteriorly than the medial condyle. Its most prominent point is the lateral epicondyle to which the fibular collateral ligament is attached ( Fig. 77.15 ). A short groove, deeper in front, separates the lateral epicondyle inferiorly from the articular margin. This groove allows the tendon of popliteus to run deep to the fibular collateral ligament and insert inferior and anterior to the ligament insertion. Adjoining the joint margin is a strip of condyle, 1 cm broad. It is intracapsular and covered by synovial membrane except for the attachment of popliteus.

The medial surface is the lateral wall of the intercondylar fossa. Its lateral surface projects beyond the shaft. Part of the lateral head of gastrocnemius is attached to an impression posterosuperior to the lateral epicondyle.

Structure

The femoral shaft is a cylinder of compact bone with a large medullary cavity. The wall is thick in its middle third, where the femur is narrowest and the medullary cavity most capacious. Proximally and distally the compact wall becomes progressively thinner, and the cavity gradually fills with trabecular bone. The extremities, especially the articular areas, consist of trabecular bone within a thin shell of compact bone, their trabeculae being disposed along lines of greatest stress. At the proximal end the main trabeculae form a series of plates orthogonal to the articular surface, converging to a central dense wedge, which is supported by strong trabeculae passing to the sides of the neck, especially along its upper and lower profiles ( Fig. 77.16 ). Force applied to the femoral head is therefore transmitted to the wedge and from there to the junction of the neck and shaft. This junction is strengthened by dense trabeculae extending laterally from the lesser trochanter to the end of the superior aspect of the neck, thus resisting tensile or shearing forces applied to the neck through the head ( Fig. 77.17 ). Tensile and compressive tests indicate that axial trabeculae of the femoral head withstand much greater stresses than peripheral trabeculae. A smaller bar across the junction of the greater trochanter with the neck and shaft resists shearing caused by forces produced by local muscles such as the gluteus medius. A thin vertical plate, the so-called calcar femorale, ascends from the compact wall near the linea aspera into the trabeculae of the neck (see Fig. 77.17 ). Medially, it joins the posterior wall of the neck; laterally, it continues into the greater trochanter, where it disperses into general trabecular bone. It is thus in a plane anterior to the trochanteric crest and base of the lesser trochanter. demonstrated that the trabecular framework of the proximal femur was spiral, and that the ‘arches’ were simplified sectional profiles of this spiral. At the distal end of the femur, trabeculae spring from the entire internal surface of compact bone, descending perpendicular to the articular surface. Proximal to the condyles these are strongest and most accurately perpendicular. Horizontal planes of trabecular bone, arranged like crossed girders, form a series of cubical compartments.

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Muscle attachments

The greater trochanter provides attachment for glutei medius and minimus. Gluteus minimus is attached to its rough anterior impression and gluteus medius to its posterosuperior aspect and an oblique line on its lateral surface. The bone is separated from the tendons of gluteus minimus and medius by several bursae ( ). The area behind it is covered by deep fibres of gluteus maximus, with part of its trochanteric bursa interposed. The tendon of piriformis is attached to the upper border of the trochanter and the common (tricipital) tendon of obturator internus and the gemelli is attached to its medial surface. The trochanteric fossa receives the tendon of obturator externus. Psoas major is attached to the summit and anteromedial surface of the lesser trochanter, and iliacus to the medial or anterior surface of its base, descending a little behind the spiral line as its tendon fuses with that of psoas major. Adductor magnus (upper part) passes over the posterior surface of the lesser trochanter, sometimes separated by an interposed bursa.

The most proximal fibres of vastus lateralis are attached to the proximal end of the intertrochanteric line, and those of vastus medialis to the distal end. Quadratus femoris is attached to the quadrate tubercle and the immediately distal bone. Vastus intermedius is attached to the anterior and lateral surfaces of the proximal three-quarters of the femoral shaft. Slips of articularis genus are attached distal to this.

The gluteal tuberosity receives the deeper fibres of the distal half of gluteus maximus and, at its medial edge, the uppermost fibres of adductor magnus. Distal to this, adductor magnus is attached to the linea aspera and, by an aponeurosis, to the proximal part of the medial supracondylar ridge. Its remaining fibres form a large tendon attached to the adductor tubercle, with an aponeurotic expansion to the distal part of the medial supracondylar ridge.

Pectineus and adductor brevis are attached to the posterior femoral surface between the gluteal tuberosity and spiral line. The pectineal attachment is a line, sometimes slightly rough, from the base of the lesser trochanter to the linea aspera. Adductor brevis is attached lateral to pectineus and beyond this to the proximal part of the linea aspera, medial to adductor magnus. Adductor longus, intermuscular septa and the short head of biceps femoris are also attached to the linea aspera. Vastus lateralis has a linear attachment from the anterior surface of the base of the greater trochanter to the proximal end of the gluteal tuberosity, and along the lateral margin of the latter to the proximal half of the lateral edge of the linea aspera. Vastus medialis is attached from the distal end of the intertrochanteric line along the spiral line to the medial edge of the linea aspera and thence to the medial supracondylar line, which also receives many fibres from the aponeurotic attachments of adductor magnus.

The medial head of gastrocnemius is attached to the posterior surface a little above the medial condyle. The short head of biceps femoris is attached to the proximal two-thirds of the lateral supracondylar line. Plantaris attaches to the line distally. Vastus medialis is attached to the proximal two-thirds of the medial supracondylar line.

Part of the lateral head of gastrocnemius is attached posterosuperiorly to the lateral epicondyle. Popliteus is attached anteriorly in the groove on the outer aspect of the lateral epicondyle. Its tendon passes deep to the fibular collateral ligament (see Fig. 77.15 ). The tendon lies in the groove in full knee flexion; in extension it crosses the articular margin and may form an impression on it.

Vascular supply

The blood supply of the femoral head is derived from an arterial ring around the neck, just outside the attachment of the fibrous capsule, constituted by the medial and lateral circumflex femoral arteries with minor contributions from the superior and inferior gluteal vessels. Branches from the arterial ring pierce the capsule (under its zona orbicularis) to ascend the neck beneath the reflected synovial membrane. These vessels become the retinacular arteries and form a subsynovial intracapsular anastomosis. Here the vessels are at risk with a displaced fracture of the femoral neck. Interruption of blood supply in this way can lead to avascular necrosis of the femoral head. If the fracture is intracapsular, not only is the intraosseous blood supply damaged but the retinacular vessels are also vulnerable. If the fracture is extracapsular, the retinacular vessels will remain intact and avascular necrosis of the femoral head is much less likely. The ascending cervical vessels give off metaphysial branches that enter the neck, while the intracapsular ring gives off lateral and inferior epiphysial branches. A small medial epiphysial supply reaches the head along the ligament of the head of femur by the acetabular branches of the obturator and medial circumflex femoral arteries, which anastomose with the other epiphysial vessels ( ). During growth, the epiphysial plate separates the territories of the metaphysial and epiphysial vessels; these vessels anastomose freely after osseous union of the head and neck. Observations of developmental patterns of this supply in late fetal and early postnatal periods have revealed that although the medial and lateral circumflex femoral arteries at first contribute equally, two major branches of the medial provide the final supply, both posterior to the neck. The supply from the lateral circumflex femoral artery diminishes and the arterial ring is interrupted. As the femoral neck elongates, the extracapsular circle becomes more distant from the epiphysial part of the head.

The trochanteric regions and subtrochanteric shaft are supplied by the trochanteric and cruciate arterial anastomoses. More distally in the shaft, nutrient foramina, directed proximally, are found in the linea aspera, varying in number and site: one is usually near its proximal end and a second usually near its distal end. The main nutrient artery is usually derived from the second perforating artery (see p. 1389 ). If two nutrient arteries occur, they may branch from the first and third perforators. Periosteal vessels arise from the perforators and from the profunda femoris artery, and run circumferentially rather than longitudinally. The distal metaphysis has many vascular foramina. Arterial supply here is from the genicular anastomosis. For further details, consult , .

In general, the pattern of venous drainage of the head and neck corresponds to that of the arteries, though there may be a single large cervical vein posteroinferiorly.

Innervation

The periosteal innervation is derived proximally from nerves that supply the hip joint, distally from those supplying the knee, and in all areas from nerves that innervate muscles attached to the bone.

Ossification

The femur ossifies from five centres: in the shaft, head, greater and lesser trochanters and the distal end ( Figs 77.18 – 77.19 ). Other than the clavicle, it is the first long bone to ossify.The process starts in the mid-shaft during embryonic stages 22 and 23 (postfertilization days 52–58) and extends to produce a miniature shaft that is largely ossified at birth. Secondary centres appear in the distal end (from which the condyles and epicondyles are formed) during postmenstrual weeks 33–36; in the greater trochanter during the fourth year; and in the lesser trochanter between the twelfth and fourteenth years. In the infant, the femoral head is entirely cartilaginous: it cannot be seen on plain radiographs and is best visualized using ultrasound ( Fig. 77.20 ). The centre in the cartilaginous head is restricted to it until the tenth year, so that the epiphysial line (see Fig. 77.7 ) is horizontal and the inferomedial part of the articular surface is on the neck. The medial epiphysial margin later grows over this part of the articular surface. Thus, the mature epiphysis is a hollow cup on the summit of the neck. The epiphysial line follows the articular margin except where it is separated superiorly from the articular surface by a non-articular area where blood vessels enter the head ( ). The epiphyses fuse independently: the lesser trochanter soon after puberty, followed by the greater trochanter. The capital epiphysis fuses in the fourteenth year in females and seventeenth year in males. The epiphysis at the distal end fuses in the sixteenth year in females, and eighteenth year in males. The distal epiphysial plate traverses the adductor tubercle.

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Acetabular labrum and impingement injury

The shape of the bones of the hip normally limits large and potentially damaging contact stress on adjacent connective tissues, especially during the extremes of movement. Consider, for example, the normal shape of the femoral head and neck region. Similar to the shape of a light bulb, the spherical femoral head narrows gradually at its junction with the neck of the femur. This tapering limits large contact stress between the femoral neck and the margin of the acetabulum. However, tapering may be lost because of natural variation or underlying pathology, resulting in a specific deformity that has been referred to as a cam deformity because the head and neck of the femur, together, resemble a camshaft. Although often subtle, this deformity may be detected radiographically (see arrow in Fig. 77.23 ). In some patients with a cam deformity, extreme and repeated motions of the hip, typically involving combinations of flexion, medial rotation and adduction, can create damaging impingement between the hard and bulbous femoral neck and the softer acetabular labrum. The anterosuperior section of the labrum is particularly vulnerable to this type of injury, which is a painful and often motion-limiting condition referred to as femoro-acetabular impingement syndrome. The repeatedly traumatized section of the labrum can become enlarged, fragmented or torn. When the acetabular labrum is torn, a hip joint may become unstable as a consequence of the loss of the natural suction seal around the joint. In some advanced cases, the impingement trauma may create lesions at the chondrolabral junction, resulting in damage to the adjacent articular cartilage, potentially predisposing the hip joint to degenerative arthritis (osteoarthrosis) ( ). Treatment may involve arthroscopic repair of the acetabular labrum and cartilage, as well as reshaping the area of the femoral head and neck responsible for the impingement. FLOAT NOT FOUND

Iliocapsularis

Iliocapsularis (also called iliacus minor or iliotrochantericus) is a little-known but constant muscle that lies immediately deep to the tendon of iliopsoas and overlies the anterior hip capsule ( , ). Typically present as just a few strands of fibres, it originates from the anteromedial hip capsule and anteroinferior iliac spine, and is attached just distal to the lesser trochanter. Although the function of the muscle is uncertain, it may draw the capsule taut as a way of reducing its impingement during hip flexion. For reasons not understood, the size of the iliocapsularis has been shown to be larger in hips with radiological evidence of developmental hip dysplasia ( )