CHAPTER 80 Pelvic girdle, gluteal region and thigh
The pelvic girdle consists of the paired hip bones (each consisting of the ilium, ischium and pubis) and a single sacrum. The two pubic bones articulate anteriorly at the pubic symphysis and the sacrum articulates posteriorly with the two iliac bones: however, the bones are virtually incapable of independent movement except in the female during parturition. The pelvic girdle is massively constructed and serves as a weightbearing and protective structure, as an attachment for trunk and limb muscles, and as the skeletal framework of a birth canal capable of accommodating a large-headed fetus.
SKIN AND SOFT TISSUES
SKIN
Vascular supply and lymphatic drainage
Thigh
The skin of the thigh distal to the inguinal ligament and gluteal fold is supplied mainly by branches of the femoral and profunda femoris arteries. There is some contribution from the obturator, inferior gluteal and popliteal arteries and from direct cutaneous, musculocutaneous and fasciocutaneous vessels. For further details consult Cormack & Lamberty (1994).
SOFT TISSUE
Fascia
Deep fascia
Fascia lata
Iliotibial tract
Over the flattened lateral surface of the thigh, the fascia lata thickens to form a strong band, the iliotibial tract. The upper end of the tract splits into two layers, where it encloses and anchors tensor fasciae latae and receives, posteriorly, most of the tendon of gluteus maximus. The superficial layer ascends lateral to tensor fasciae latae to the iliac crest; the deeper layer passes up and medially, deep to the muscle, and blends with the lateral part of the capsule of the hip joint. Distally, the iliotibial tract is attached to a smooth, triangular facet (Gerdy’s tubercle) on the anterolateral aspect of the lateral condyle of the tibia where it is superficial to, and blends with, an aponeurotic expansion from vastus lateralis. When the knee is extended against resistance it stands out as a strong, visible ridge on the anterolateral aspect of the thigh and knee.
Saphenous opening
The saphenous opening is an aperture in the deep fascia, inferolateral to the medial end of the inguinal ligament, which allows passage to the long saphenous vein and other smaller vessels (Fig. 80.1). 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 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 superficial fascia 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.
Fascial compartments
There are three functional groups of muscle in the thigh, namely, anterior (extensor), posterior (flexor) and medial (adductor). The anterior and posterior groups occupy separate osteofascial compartments that are limited peripherally by the fascia lata and separated from each other by the femur and the medial and lateral intermuscular septa (Fig. 80.2). The adductor muscles, though distinct in terms of function and innervation, do not possess a separate compartment limited by fascial planes. Nevertheless it is customary to speak of three compartments: anterior, posterior and medial. The muscles of the three compartments are described below. Adductor magnus, adductor longus and pectineus could each be considered to be constituents of two compartments, i.e. adductor magnus in the posterior and the medial compartments, and adductor longus and pectineus in the anterior and the medial compartments.
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 (Fig. 80.3). 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 (great) 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 one 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. The femoral septum is traversed by numerous lymph vessels that connect the deep inguinal to the external iliac lymph nodes.
Iliac fascia
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. It is attached to the iliopubic ramus, where it receives a slip from the tendon of psoas minor, when that muscle is present. The external iliac vessels are anterior to the fascia but the branches of the lumbar plexus are posterior. 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 fascia, 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 (Fig. 80.3). The iliac fascia continues downward to form the posterior wall of the femoral sheath.
Obturator membrane
The obturator membrane (Fig. 80.4) 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.
BONE
HIP BONE
The hip bone is large, irregular, constricted centrally and expanded above and below (Fig. 80.5A,B). Its lateral surface has a deep, cup-shaped acetabulum, articulating with the femoral head, anteroinferior to which is the large, oval or triangular obturator foramen. Above the acetabulum the bone widens into an undulant plate surmounted by a sinuously curved iliac crest.

Fig. 80.5 Left hip bone. A, Outer aspect. B, Inner aspect. C, Anterosuperior view.
(From Sobotta 2006.)
Acetabulum
The acetabulum (Fig. 80.5A,C) 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. Occasionally a linear defect may be seen to cross the acetabular surface from the superior border to the acetabular fossa This does not correspond to any junction between the main morphological parts of the hip bone.
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. For a survey of these studies consult Whitehouse (1977). Additionally, Whitehouse’s observations, based on scanning electron micrography, indicate that the cortical bone is very porous, being only 75% bone, decreasing to 35% near the anterior superior iliac spine. Denser cortical bone starts at the margins of the crest and thickens rapidly below it on both aspects of the iliac blade.
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 (Holm 1980). 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.
Vascular supply
In the infant, nutrient arteries are clearly demonstrable for each component of the hip bone. Each nutrient artery branches in fan-like fashion within its bone of supply (Crock 1996). Later, a periosteal arterial network develops, with contributions from numerous local arteries (see under individual bones).
Ossification
Ossification (Figs 80.6, 80.7) 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 the ninth week; the ischial centre in its body in the fourth month, and the pubic centre in its superior ramus between the fourth and fifth months. At birth the whole iliac crest, the acetabular floor and 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 its tubercle.
Between the ages of 8 and 9 years three major centres of 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 (Ponseti 1978). Fusion between the three bones within the acetabulum occurs between the 16th and 18th years. Delaere et al (1992) 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.
Pubis
Topography
The pubis (Figs 80.5, 80.6) is the ventral part of the hip bone and forms a median cartilaginous pubic symphysis with its fellow. The body of the pubis occupies the anteromedial part of the bone, and from the body a superior ramus passes up and back to the acetabulum and an inferior ramus passes back, down and laterally to join the ischial ramus inferomedial to the obturator foramen.
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.
Ilium
Topography
The ilium has upper and lower parts and three surfaces (Figs 80.5, 80.6). The smaller, lower part forms a little less than the upper two-fifths of the acetabulum. The upper part is much expanded, and has gluteal, sacropelvic and iliac (internal) surfaces. The posterolateral gluteal surface is an extensive rough area; the anteromedial iliac fossa is smooth and concave; the sacropelvic surface is medial and posteroinferior to the fossa, from which it is separated by the medial border.
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, 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 ill-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.
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, 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, 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 preauricular 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 Finnegan (1978) and Brothwell & Pollard (2001). The pelvic surface is anteroinferior to the acutely recurved 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. Its lower part faces medially and is separated from the iliac fossa by the arcuate line. Anteroinferiorly it extends to the line of union between the ilium and ischium. Though usually obliterated, it passes from the depth of the acetabulum to approximately the middle of the inferior limb of the greater sciatic notch.
Ischium
Topography
The ischium, the inferoposterior part of the hip bone, has a body and ramus. The body has upper and lower ends and femoral, posterior and pelvic surfaces (Figs 80.5, 80.6). Above, it forms the posteroinferior part of the acetabulum; below, its ramus ascends anteromedially at an acute angle to meet the inferior pubic ramus, thereby completing the boundary of the obturator foramen. The ischiofemoral ligament is attached to the lateral border below the acetabulum.
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 femoral 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 perineal muscles 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 sphincter urethrae. The lower border of the ramus provides an attachment for the fascia lata and a membranous layer of the superficial perineal fascia.
Ischial spine
The ischial spine projects downwards and a little medially (Fig. 80.8). 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.
SKELETAL PELVIS AS A WHOLE
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. 80.9). When prolonged (projected) it passes through the umbilicus and midcoccyx. 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 (Fig. 80.9). 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 symphysis pubis faces nearly as much upwards as backwards and the sacral concavity is directed anteroinferiorly. The front of the symphysis and anterior superior iliac spines are in the same vertical plane. In sitting, body weight is transmitted through 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.
SEXUAL DIFFERENCES IN THE PELVIS
In forensic practice, identification of human skeletal remains (which are sometimes fragmentary) usually involves determination of sex, and this is most reliably established from an examination of the pelvis. Even fragments of the pelvis may be useful in this respect. Several studies of metrical characteristics in various pelvic regions have been made, leading to the establishment of various indices. The ilium has received particular attention, e.g. one index compares the pelvic and sacroiliac parts of the bone. A line is extended back from the iliopubic ramus to the nearest point on the anterior auricular margin and thence to the iliac crest. The auricular point divides this chilotic line into anterior (pelvic) and posterior (sacral) segments, each expressed as a percentage of the other. Chilotic indices display reciprocal values in the sexes: the pelvic part of the chilotic line is predominant in females, and the sacral part in males. Detailed metrical studies of the ilium have indicated its limited reliability in ‘sexing’ pelves. However, the higher incidence and definition of the female preauricular sulcus is recognized. The desirability of correlating all available metrical data is to be emphasized; when a range of pelvic data can be combined, especially if they are metrical, 95% accuracy should be achieved. Complete accuracy has been claimed when the rest of the skeleton is available. Assessment of sex from isolated and often incomplete human remains is less reliable. For further details, consult Mays (1998) and Brothwell & Pollard (2001).
FEMUR
Topography
The femur is the longest and strongest bone in the human body (Figs 80.10, 80.11). Its length is associated with a striding gait, its strength with the weight and muscular forces it is required to withstand. Its shaft, almost cylindrical along most of its length, is bowed forward. It has a proximal rounded, articular head projecting medially from its short neck, which, in turn, is a medial extension of the proximal shaft. The distal extremity is wider and more substantial, and presents a double condyle that articulates with the tibia. In standing, the femoral shafts show an inclination upwards and outwards from their tibial articulations, with the femoral heads being separated by the pelvic width. Since the tibia and fibula descend vertically from the knees, the ankles are also in the line of body weight in standing or walking. The degree of femoral obliquity varies between individuals, but is generally greater in women, reflecting the relatively greater pelvic breadth and shorter femora. Proximally the femur consists of a head, neck, and greater and lesser trochanters.

Fig. 80.11 Femur: posterior aspect. A, Osseous features. B, Muscle attachments.
(From Sobotta 2006.)
Femoral head
The femoral head faces anterosuperomedially to articulate with the acetabulum (Fig. 80.12). 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. 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 ligamentum teres is attached to the fovea. The anterior surface of the head is separated inferomedially from the femoral artery by the tendon of psoas major, the psoas bursa, and the articular capsule.
Femoral neck
The femoral neck (Fig. 80.12) 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 135° (angle of inclination; neck–shaft angle): this facilitates movement at the hip joint, enabling the limb to swing clear of the pelvis. The neck also provides a lever for the action of the muscles acting about the hip joint, which are attached to the proximal femur. The neck–shaft angle is widest at birth and diminishes gradually until adolescence; it is smaller in females. The neck is laterally rotated with respect to the shaft (angle of anteversion) some 10–15°, although values of this angle vary between individuals and between populations (Eckhoff et al 1994). The contours of the neck are rounded: the upper surface is almost horizontal and slightly concave, 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. 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.
Greater trochanter
The greater trochanter is large and quadrangular, projecting up from the junction of the neck and shaft (Fig. 80.12). 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 tubercle, 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 palpable, especially when the muscles are relaxed. The trochanteric fossa occasionally presents a tubercle or exostosis.
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 line.
Shaft
The shaft is surrounded by muscles and is impalpable (Figs 80.10, 80.11). The distal anterior surface, for 5–6 cm above the patellar articular surface, is covered by a suprapatellar bursa, between bone and muscle. The distal lateral surface is covered by vastus intermedius. The medial surface, devoid of attachments, is covered by vastus medialis.
Distal end
The distal end of the femur is widely expanded as a bearing surface for transmission of weight to the tibia (Fig. 80.13). 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. However views differ as to the exact representation of these differences. One view holds that in both tibial portions of the femoral condyles the sagittal radius of curvature is ever decreasing (a ‘closing helix’). More recently it has been suggested that the medial articular surface describes arcs of two circles. The more posterior has a smaller radius. Laterally there may only be one arc of fixed curvature with a radius similar to that of the posterior arc of the medial femoral articular surface. These differences are believed to be important determinants of knee joint motion.
The lateral condyle (Figs 80.13, 80.14) is larger anteroposteriorly than the medial. Its most prominent point is the lateral epicondyle to which the lateral collateral ligament is attached. 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 lateral 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.
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 where articular, 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. 80.15). Force applied to the femoral head is therefore transmitted to the wedge and thence 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. 80.16). 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 produced by muscles attached to it. These two bars are proximal layers of arches between the sides of the shaft and transmit to it forces applied to the proximal end. A thin vertical plate, the calcar femorale, ascends from the compact wall near the linea aspera into the trabeculae of the neck. 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. Newell (1997), in a review of the calcar femorale, has described its three-dimensional anatomy in terms of the work of Dixon (1910), who was the first to recognize the deficiencies of the classic two-dimensional description of the architecture of the proximal femur. Dixon suggested 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.
Muscle attachments
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 genu are attached distal to this.
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 lateral collateral ligament (Fig. 80.14). 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 (Fig. 80.17) 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 (see trochanteric anastomosis). From this ring, ascending cervical branches 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, of importance in early childhood, reaches the head along the ligamentum teres 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 on developmental patterns of this supply in late fetal and early postnatal periods have revealed that although 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 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 profunda femoris). If two nutrient arteries occur, they may branch from the first and third perforators. Periosteal vessels arise from the perforators and from the profunda, 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 Crock (1980, 1996).
Ossification
The femur ossifies from five centres: in the shaft, head, greater and lesser trochanters and the distal end (Figs 80.10, 80.11, 80.18). Other than the clavicle, it is the first long bone to ossify. The process starts in the midshaft in the seventh prenatal week 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 the ninth month, in the head during the first six months after birth, in the greater trochanter during the fourth year and in the lesser between the 12th and 14th year. The centre in the cartilaginous head is restricted to it until the tenth year, so that the epiphysial line (Fig. 80.7) 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 (Trueta 1957). The epiphyses fuse independently: the lesser trochanter soon after puberty followed by the greater trochanter. The capital epiphysis fuses in the 14th year in females and 17th year in males,. The epiphysis at the distal end fuses in the 16th year in females, and 18th year in males. The distal epiphysial plate traverses the adductor tubercle.
JOINTS
PUBIC SYMPHYSIS
The pubic bones meet in the midline at the pubic symphysis, a secondary cartilaginous joint (Fig. 80.4).
SACROILIAC JOINT
The anterior sacroiliac ligament (Fig. 80.8), an anteroinferior capsular thickening, is particularly welldeveloped near the arcuate line and the posterior inferior iliac spine, where it connects the third sacral segment to the lateral side of the preauricular sulcus. It is thin elsewhere.
Interosseous sacroiliac ligament
The interosseous sacroiliac ligament is the major bond between the bones, filling the irregular space posterosuperior to the joint. It is covered superficially by the posterior sacroiliac ligament. Its deeper part has superior and inferior bands passing from depressions posterior to the sacral auricular surface to those on the iliac tuberosity. These bands are covered by, and blend with, a more superficial fibrous sheet connecting the posterosuperior margin of a rough area posterior to the sacral auricular surface to the corresponding margins of the iliac tuberosity. This sheet is often partially divided into superior and inferior parts, the former uniting the superior articular process and lateral crest on the first two sacral segments to the neighbouring ilium as a short posterior iliac ligament (see Fig. 42.52).
The posterior sacroiliac ligament
The posterior sacroiliac ligament (see Fig. 42.52) overlies the interosseous ligament: the dorsal rami of the sacral spinal nerves and vessels intervene. It consists of several weak fasciculi connecting the intermediate and lateral sacral crests to the posterior superior iliac spine and posterior end of the internal lip of the iliac crest. Inferior fibres, from the third and fourth sacral segments, ascend to the posterior superior iliac spine and posterior end of the internal lip of the iliac crest: they may form a separate long posterior sacroiliac ligament. This ligament is continuous laterally with part of the sacrotuberous ligament and medially with the posterior lamina of the thoracolumbar fascia.
The sacrotuberous ligament (Fig. 80.8, see Fig. 42.52) is attached by its broad base to the posterior superior iliac spine., the posterior sacroiliac ligaments (with which it is partly blended), to the lower transverse sacral tubercles and the lateral margins of the lower sacrum and upper coccyx. Its oblique fibres descend laterally, converging to form a thick, narrow band that widens again below and is attached to the medial margin of the ischial tuberosity. It then spreads along the ischial ramus as the falciform process, whose concave edge blends with the fascial sheath of the internal pudendal vessels and pudendal nerve. The lowest fibres of gluteus maximus are attached to the posterior surface of the ligament; superficial fibres of the lower part of the ligament continue into the tendon of biceps femoris. The ligament is pierced by the coccygeal branches of the inferior gluteal artery, the perforating cutaneous nerve and filaments of the coccygeal plexus.
The thin, triangular sacrospinous ligament (Fig. 80.8) extends from the ischial spine to the lateral margins of the sacrum and coccyx anterior to the sacrotuberous ligament, with which it blends in part. Its anterior surface is in fact the coccygeus muscle, i.e. muscle and ligament are coextensive. The sacrospinous ligament is often regarded as a degenerate part of coccygeus.
Accessory sacroiliac articulations are not uncommon. They develop behind the articular surface between the lateral sacral crest and posterior superior iliac spine and iliac tuberosity, and are acquired fibrocartilaginous joints resulting from the stresses of weightbearing. They have a joint capsule, are saddle-shaped, and may be single, double, unilateral or bilateral (Weisl 1954).
MUSCLES
MUSCLES OF THE ILIAC REGION
Psoas major
Psoas major is a long muscle that lies on either side of the lumbar vertebral column and the pelvic brim (Fig. 80.19). Its proximal attachments are complex. They include the anterior surfaces and lower borders of the transverse processes of all the lumbar vertebrae. There are five digitations, each from the bodies of two adjoining vertebrae and their intervertebral disc. The highest of these arises from the lower margin of the body of the 12th thoracic vertebra, the upper margin of the body of the first lumbar vertebra and the interposed thoracolumbar disc. The lowest arises from the adjacent margins of the bodies of the fourth and fifth lumbar vertebrae and the interposed disc. A series of tendinous arches extend across the narrow parts of the bodies of the lumbar vertebrae between the digitations already described. The lumbar arteries and veins, and filaments from the sympathetic trunk, pass medial to these arches. The upper four lumbar intervertebral foramina bear important relations to these attachments of the muscle. The foramina lie anterior to the transverse processes and posterior to the attachments to vertebral bodies, discs and tendinous arches. Thus, the roots of the lumbar plexus enter the muscle directly, the plexus is lodged within it, and its branches emerge from its borders and surfaces.
The complex vertebral attachments of psoas major sometimes display minor numerical variations.
Psoas minor
Psoas minor (Fig. 80.19) is absent in almost 40% of subjects. When present, it lies anterior to psoas major, entirely within the abdomen. It arises from the sides of the bodies of the twelfth thoracic and first lumbar vertebrae and from the disc between them. It ends in a long, flat tendon which is attached to the pecten pubis and ilio-pubic ramus and, laterally, to the iliac fascia.
Iliacus
Iliacus (Fig. 80.19) is a triangular sheet of muscle that arises from the superior two-thirds of the concavity of the iliac fossa, the inner lip of the iliac crest, the ventral sacroiliac and iliolumbar ligaments, and the upper surface of the lateral part of the sacrum (see Fig. 42.36). In front, it reaches as far as the anterior superior and anterior inferior iliac spines, and receives a few fibres from the upper part of the capsule of the hip joint. Most of its fibres converge into the lateral side of the strong tendon of psoas major, and the muscles then insert together into the lesser trochanter, but some fibres are attached directly to the femur 2.5 cm below and in front of the lesser trochanter.
MUSCLES OF THE GLUTEAL REGION
Tensor fasciae latae
Tensor fasciae latae (Fig. 80.19) arises from the anterior 5 cm of the outer lip of the iliac crest, from the lateral surface of the anterior superior iliac spine and part of the border of the notch below it, between gluteus medius and sartorius, and from the deep surface of the fascia lata. Proximal attachments may extend to the aponeurotic fascia superficial to gluteus medius. It descends between, and is attached to, the two layers of the iliotibial tract of the fascia lata and usually ends approximately one-third of the way down the thigh, although it may occasionally extend as far as the lateral femoral condyle.
Gluteus maximus
Gluteus maximus (Fig. 80.20) is the largest and most superficial muscle in the gluteal region. It is a broad, thick quadrilateral mass, which, with its overlying adipose fascia, forms the familiar prominence of the buttock. Gluteus maximus is thicker and more extensive in man than in any non-human primate, features that presumably correlate with the evolutionary transition to bipedality and a permanently upright posture. The muscle has a coarse fascicular architecture, with large bundles of fibres separated by fibrous septa. It arises from the posterior gluteal line of the ilium, and the rough area of bone, including the crest, immediately above and behind it; from the aponeurosis of erector spinae; the dorsal surface of the lower part of the sacrum and the side of the coccyx; the sacrotuberous ligament; and the fascia (gluteal aponeurosis) which covers gluteus medius. There may be additional slips from the lumbar aponeurosis or ischial tuberosity. The muscle may also be bilaminar. The fibres descend laterally; the upper part of the muscle, together with the superficial fibres of the lower part, ends in a thick tendinous lamina which passes lateral to the greater trochanter and is attached to the iliotibial tract of the fascia lata. The deeper fibres of the lower part of the muscle are attached to the gluteal tuberosity between vastus lateralis and adductor magnus.
A thin fascia separates the superficial surface of gluteus maximus from the overlying thick adipose subcutaneous tissue. The deep surface of the muscle is related to the ilium, sacrum, coccyx, sacrotuberous ligament, part of gluteus medius, piriformis, the gemelli, obturator internus, quadratus femoris, the ischial tuberosity, greater trochanter, and the attachments of biceps femoris, semitendinosus, semimembranosus and adductor magnus to the ischial tuberosity. Three bursae lie deep to gluteus maximus: trochanteric, over the greater trochanter; gluteofemoral, between the tendon of gluteus maximus and that of vastus lateralis; and ischiofemoral, over the gluteal tuberosity, which is less commonly present.
Gluteus medius
Gluteus medius is a broad, thick muscle (Fig. 80.20, Fig. 80.21A). It arises from the outer surface of the ilium between the iliac crest and posterior gluteal line above, and the anterior gluteal line below, and also from the strong fascia superficial to its upper part. The fibres converge to a flat tendon that attaches to a ridge that slants downwards and forwards on the lateral surface of the greater trochanter.

Fig. 80.21 A, Gluteus medius. B, Gluteus minimus and short external rotators of the hip.
(From Sobotta 2006.)
A deep slip of the muscle may be attached to the upper border of the trochanter. The posterior edge of gluteus medius sometimes blends with piriformis.
The posterior third of gluteus medius is covered by gluteus maximus, but it is superficial in its anterior two-thirds, where it is covered by a strong layer of deep fascia. Its deep surface is related to gluteus minimus. Branches of the deep divisions of the superior gluteal nerve and artery run between the medius and minimus muscles and are vulnerable during anterolateral and lateral approaches to the hip that involve splitting gluteus medius (see Fig. 80.22). Where the tendon glides on the anterosuperior part of the lateral surface of the trochanter, a bursa (trochanteric bursa of gluteus medius) separates it from the bone.
Gluteus minimus
Gluteus minimus lies deep to gluteus medius (Fig. 80.21B). The fan-shaped muscle arises from the outer surface of the ilium between the anterior and inferior gluteal lines and, behind, from the margin of the greater sciatic notch. The fibres converge below to the deep surface of an aponeurosis that ends in a tendon which is attached to an anterolateral ridge on the greater trochanter and contributes an expansion to the capsule of the hip joint.
Testing
The supportive effect of the glutei (medius and minimus) on the pelvis when the contralateral foot is raised depends on the following conditions. The two muscles, and their innervation, must be functioning normally. The components of the hip joint, which forms the fulcrum, must be in their usual relation. The neck of the femur must be intact, with its normal angulation to the shaft.
Piriformis
Piriformis (see Fig. 63.1, Fig. 80.21B) occupies a central position in the buttock, where it lies in the same plane as gluteus medius. It arises from the anterior surface of the sacrum by three digitations, which are attached to the portions of bone between the pelvic sacral foramina, and to the grooves leading from the foramina (see Fig. 42.36). It also arises from the gluteal surface of the ilium near the posterior inferior iliac spine, from the capsule of the adjacent sacroiliac joint, and sometimes from the upper part of the pelvic surface of the sacrotuberous ligament. The muscle passes out of the pelvis through the greater sciatic foramen, which it substantially fills. Here it constitutes an important surgical landmark in the identification of structures that emerge above and below it. It inserts into the medial side of the upper border of the greater trochanter of the femur via a rounded tendon that lies behind and above, but is often partially blended with, the common tendon of obturator internus and the gemelli. The muscle itself may be fused with gluteus medius.
Obturator internus
Obturator internus (see Fig. 63.1, Fig. 80.21B) is situated partly within the true pelvis and partly posterior to the hip joint. It arises from the internal surface of the anterolateral wall of the lesser pelvic cavity. Its attachments, which almost surround the obturator foramen, are to the inferior ramus of the pubis, the ischial ramus, and the pelvic surface of the hip bone below and behind the pelvic brim, to the upper part of the greater sciatic foramen above and behind, to the obturator foramen below and in front (Fig. 80.5B). It also arises from the medial part of the pelvic surface of the obturator membrane, from the tendinous arch that completes the obturator canal, and, to a small extent, from the obturator fascia that covers the muscle. The fibres converge towards the lesser sciatic foramen and end in four or five tendinous bands on the deep surface of the muscle. These bands make a lateral right-angled turn around the grooved surface of the ischium between its spine and tuberosity. The grooved surface is covered with a smooth layer of hyaline cartilage and is separated from the tendon by a bursa: ridges on the surface correspond to furrows between the tendinous bands. These bands leave the pelvis through the lesser sciatic foramen and unite to form a single flattened tendon that passes horizontally across the capsule of the hip joint. The gemelli fuse with this tendon before it inserts into an anterior impression on the medial surface of the greater trochanter anterosuperior to the trochanteric fossa. A long, narrow bursa is usually interposed between the tendon and the capsule of the hip joint, and occasionally communicates with the bursa between the tendon and the ischium.
Obturator externus
Obturator externus (Fig. 80.23) is a flat, triangular muscle covering the external surface of the anterior pelvic wall. It arises from the anteromedial two-thirds of the external surface of the obturator membrane, and from the adjacent bone of the pubic and ischial rami, extending for a short distance onto their pelvic surfaces between the margin of the obturator foramen and the obturator membrane. The whole muscle, and the tendon into which its fibres converge, spirals backwards, laterally and upwards, and thus crosses the inferior aspect and then the back of the neck of the femur and lower part of the capsule of the hip joint to end in the trochanteric fossa of the femur.
Gemellus inferior and gemellus superior
Quadratus femoris
Quadratus femoris (see Fig. 80.21B) is a flat, quadrilateral muscle lying between gemellus inferior and the upper margin of adductor magnus, from which it is separated by the transverse branch of the medial circumflex femoral artery. It arises from the upper part of the external aspect of the ischial tuberosity and inserts into a small tubercle a little above the middle of the trochanteric crest of the femur and into the bone for a short distance below. It may be absent.
MUSCLES OF THE THIGH
Anterior compartment
The muscles of the anterior compartment (Figs 80.2, 80.19) include sartorius and rectus femoris, which can act both at the hip and knee joints, and vasti medialis, lateralis, and intermedius, which act only at the knee. Articularis genu, a derivative of vastus intermedius, completes the group: it retracts the synovial capsule of the knee joint. Rectus femoris and the vasti extend the knee joint through a common tendon and hence are collectively termed the quadriceps femoris muscle. Adductor longus and pectineus are sometimes considered to be part of both the anterior and the adductor compartments.
Sartorius
Sartorius is a narrow strap muscle, and is the longest muscle in the body. It arises by tendinous fibres from the anterior superior iliac spine and the upper half of the notch below it. It crosses the thigh obliquely over to the medial side, then descends more vertically to the medial side of the knee. The muscle fibres terminate at this point and a thin, flattened tendon curves obliquely forwards and expands into a broad aponeurosis. The aponeurosis is attached to the proximal part of the medial surface of the tibia in front of gracilis and semitendinosus, together forming the ‘pes anserinus’ (Fig. 80.24). A slip from its upper margin blends with the capsule of the knee joint, and another from its lower margin merges with the superficial layer of the deep fascia on the medial side of the leg. This sheet of tissue passes inferiorly to lie superficial to and over the distal insertions of gracilis and semitendinosus. It has to be split by sharp dissection to reveal these two tendons if they need to be harvested, e.g. in cruciate ligament surgery (Fig. 80.24).
The main arterial supply to sartorius is derived from multiple branches of the femoral system, and enters the medial half of the muscle from its deep surface. Vessels supplying the proximal third of sartorius may arise from the common femoral, the main trunk of the profunda, the artery of the quadriceps, the superficial femoral or the lateral circumflex femoral artery. There may be an additional proximal supply from the superficial circumflex iliac artery. Those supplying the middle third of the muscle arise from the superficial femoral artery. The distal vessels arise from the superficial femoral within the adductor canal and from the descending genicular artery.
Quadriceps femoris
Quadriceps femoris (Figs 80.2, 80.19), the great extensor muscle of the leg, covers almost all of the front and sides of the femur. It can be divided into four parts, each named individually. One, rectus femoris, arises from the ilium and travels straight down the middle of the thigh, its shape and path determining its name. The other three arise from the shaft of the femur and surround it (apart from the linea aspera) from the trochanters to the condyles: vastus lateralis is lateral to the femur, vastus medialis is medial to it, and vastus intermedius lies in front of the femur. Rectus femoris crosses both hip and knee joints, while the three vasti only cross the knee joint.
Innervation of quadriceps group
Quadriceps femoris and articularis genu are supplied by the femoral nerve, L2, 3 and 4.
Adductor compartment
The muscles of the adductor compartment, gracilis, pectineus, adductor longus, adductor brevis, and adductor magnus (Fig. 80.25), have evolved, as their nerve supply suggests, both from flexor and extensor columns. All five muscles cross the hip joint, but only gracilis reaches beyond the knee. They are known collectively as the adductors of the thigh, although their actions are more complex than this, e.g. acting from below they have important roles in balancing the trunk on the lower limb during walking.
Gracilis
Gracilis (Figs 80.2, 80.19) is the most superficial of the adductor group. It is thin and flat, broad above, narrow and tapering below. It arises by a thin aponeurosis from the medial margins of the lower half of the body of the pubis, the whole of the inferior pubic ramus, and the adjoining part of the ischial ramus. The fibres descend vertically into a rounded tendon, often harvested as a knee ligament graft, which passes across the medial condyle of the femur posterior to the tendon of sartorius. It then curves around the medial condyle of the tibia, where it fans out and is attached to the upper part of the medial surface of the tibia, just below the condyle, forming part of the pes anserinus. A few fibres from the lower part of the tendon continue into the deep fascia of the lower leg. Often there is a slip that blends with the tendon of the medial head of gastrocnemius. Unless divided this can lead to problems during surgical harvesting of the gracilis tendon.
Adductor longus
Adductor longus (Figs 80.2, 80.26), the most anterior of the three adductors, is a large, fan-shaped muscle that lies in the same plane as pectineus. It arises by a narrow tendon with a flattened (sometimes C-shaped) cross-section, which is attached to the front of the pubis in the angle between the crest and the symphysis. It expands into a broad fleshy belly which descends posterolaterally and inserts by an aponeurosis into the linea aspera in the middle third of the femur, between vastus medialis and adductors magnus and brevis, usually blending with all of them. Its proximal attachment is vulnerable to overload from sporting activity: this is one cause of sport-related groin pain.
Adductor brevis
Adductor brevis (Figs 80.2A, 80.26) lies posterior to pectineus and adductor longus. It arises by a narrow attachment from the external aspect of the body and inferior ramus of the pubis, between gracilis and obturator externus. Like adductor longus it is somewhat triangular, and expands as it descends posterolaterally to insert via an aponeurosis into the femur, along a line from the lesser trochanter to the linea aspera, and on the upper part of the linea immediately behind pectineus and the upper part of adductor longus.
Adductor brevis often has two or three separate parts, or may be integrated into adductor magnus.
The vascular supply to adductor brevis is variable. Usually the main supply is directly from the profunda femoris distally and from the ‘artery to the adductors’ more proximally. There is an additional proximal supply from the medial circumflex femoral artery. The deep surface receives branches from the obturator artery.
Adductor magnus
Adductor magnus (see Figs 80.2, 80.26), a massive triangular muscle, arises from a small part of the inferior ramus of the pubis, from the conjoined ischial ramus, and from the inferolateral aspect of the ischial tuberosity. The short, horizontal fibres from the pubic ramus are inserted into the medial margin of the gluteal tuberosity of the femur, medial to gluteus maximus; this part of the muscle, in a plane anterior to the rest, is sometimes called adductor minimus. The fibres from the ischial ramus fan out downwards and laterally, to insert via a broad aponeurosis into the linea aspera and the proximal part of the medial supracondylar line. The medial part of the muscle, composed mainly of fibres from the ischial tuberosity, is a thick mass which descends almost vertically, and ends in the lower third of the thigh in a rounded tendon, which can be palpated proximal to its attachment to the adductor tubercle on the medial condyle of the femur. The tendon is connected by a fibrous expansion to the medial supracondylar line.
Pectineus
Pectineus (Fig. 80.19) is a flat, quadrangular muscle in the femoral triangle. It may also be considered as part of the anterior compartment of the thigh. It arises from the pecten pubis, from the bone in front of it between the iliopubic ramus and the pubic tubercle, and from the fascia on its own anterior surface. The fibres descend, initially posteromedially and then posterolaterally to be attached along a line from the lesser trochanter to the linea aspera.
Adductor canal
The adductor canal (Hunter’s canal; subsartorial canal) is a trough-shaped intermuscular tunnel occupying the distal two-thirds of the medial aspect of the thigh (Fig. 80.2). It starts at the apex of the femoral triangle and extends distally as far as the distal attachment of the tendon of adductor magnus. It is triangular in section, and is bounded anterolaterally by vastus medialis, posteromedially by adductor longus, and distal to adductor longus, by adductor magnus. Its anteromedial boundary (often referred to as the roof) is a strong and dense fascia that extends from the medial surface of vastus medialis to the medial edge of the adductors longus and magnus, overlapping in its stride, the femoral vessels in the adductor canal. This fascia, on account of being overlain by sartorius, is termed the subsartorial fascia.
Posterior compartment
The muscles of the posterior compartment (see Figs 80.2, 80.22) receive their blood supply from the perforating branches of the profunda femoris, most importantly through the first perforator. This vessel has important anastomoses with the inferior gluteal artery (on or within semitendinosus) and with the medial circumflex femoral artery, while the third perforator anastomoses with the medial superior genicular artery within the short head of biceps. This anastomotic chain forms an important collateral arterial pathway when the femoral artery is blocked.
Semitendinosus
Semitendinosus (see Fig. 80.2B), notable for the length of its tendon, lies posteromedial in the thigh. It arises from an inferomedial impression on the upper area of the ischial tuberosity (Fig. 80.5), by a tendon it shares with the long head of biceps femoris, and from an aponeurosis connecting the adjacent surfaces of the two muscles for 7.5 cm from their common origin. The belly is fusiform and ends a little below midthigh in a long, rounded tendon that runs on the posterior surface of semimembranosus. The tendon curves around the medial condyle of the tibia, passes over the medial collateral ligament of the knee joint (from which it is separated by the bursa of the pes anserinus), and inserts into the upper part of the medial surface of the tibia behind the attachment of sartorius and distal to that of gracilis (Fig. 80.24). At its termination it is united with the tendon of gracilis and gives off a prolongation to the deep fascia of the leg and to the medial head of gastrocnemius. A tendinous intersection is usually present near the midpoint of the muscle, which may also receive a muscular slip from the long head of biceps femoris. These connections with the medial head of gastrocnemius and biceps can cause difficulty when harvesting the tendon surgically for a graft.
Semimembranosus
Semimembranosus (see Fig. 80.2B), so named because of the flattened form of its upper attachment, is posteromedial in the thigh. It arises by a long, flat tendon from a superolateral impression on the ischial tuberosity (Fig. 80.5). Inferomedially the tendinous fibres intermingle to some extent with those of biceps femoris and semitendinosus. The tendon receives, from the ischial tuberosity and ramus, two fibrous expansions that flank adductor magnus. It then broadens and descends deep to semitendinosus and the long head of biceps femoris. Muscle fibres arise from the tendon at about midthigh and converge to a second aponeurosis on the posterior aspect of the lower part of the muscle, which tapers to the heavy, rounded tendon of the distal attachment. The tendon divides at the level of the knee into five components. The main one is attached to a tubercle (sometimes called the tuberculum tendinis) on the posterior aspect of the medial tibial condyle. The others are: a series of slips to the medial margin of the tibia, immediately behind the medial collateral ligament; a thin fibrous expansion to the fascia over popliteus; a cord-like tendon to the inferior lip and adjacent part of the groove on the back of the medial tibial condyle, deep to the medial collateral ligament; and a strong expansion which passes obliquely upwards to the femoral intercondylar line and lateral femoral condyle and forms much of the oblique popliteal ligament of the knee joint.
Semimembranosus overlaps the popliteal vessels and is itself partly overlapped by semitendinosus throughout its extent (see Fig. 80.2). Its deep surface lies on adductor magnus. The sciatic nerve lies laterally and surprisingly close to the surface. The distal end of the muscle partially overlies the medial head of gastrocnemius before passing anteromedially to it. An important bursa lies between the semimembranosus tendon and gastrocnemius, and often communicates with the knee joint and with a smaller bursa between the tendon and the posterior tibial margin.
Biceps femoris
Biceps femoris (see Fig. 80.2) occupies a posterolateral position in the thigh. It has two proximal attachments. One, the long head, arises from an inferomedial impression on the upper area of the ischial tuberosity (Fig. 80.5), via a tendon which it shares with semitendinosus, and from the lower part of the sacrotuberous ligament. The other, the short head, arises from the lateral lip of the linea aspera, between adductor magnus and vastus lateralis. This attachment extends proximally almost to gluteus maximus and distally along the lateral supracondylar line to within 5 cm of the lateral femoral condyle, and from the lateral intermuscular septum. The long head forms a fusiform belly that descends laterally across the sciatic nerve. The fibres end in an aponeurosis which covers the posterior surface of the muscle. This aponeurosis receives on its deep surface the fibres of the short head, and gradually narrows to a tendon (the lateral hamstring). The main part of the tendon splits round the fibular collateral ligament and is attached to the head of the fibula. The remainder splits into three laminae. The intermediate lamina fuses with the fibular collateral ligament, while the others pass superficial and deep to the ligament to attach to the lateral condyle of the tibia.
Actions of posterior femoral muscles
Acting from above, the posterior femoral muscles flex the knee. Acting from below, they extend the hip joint, pulling the trunk upright from a stooping posture against the influence of gravity, biceps being the main agent. When the knee is semi-flexed, biceps femoris can act as a lateral rotator and semimembranosus and semitendinosus as medial rotators of the lower leg on the thigh at the knee. When the hip is extended, biceps is a lateral rotator and semimembranosus and semitendinosus are medial rotators of the thigh. As is the case with quadriceps femoris, the adductors and gluteus maximus, the hamstrings are quiescent in easy symmetrical standing. However, any action that takes the centre of gravity in front of a transverse axis through the hip joints, e.g. forward reaching, forward sway at the ankle joints, or forward bending at the hips, is immediately accompanied by strong contraction of the hamstrings. (This is in marked contrast to gluteus maximus, which contracts only when there is a call for powerful extension at the hip joint.)