Femur

The femur, or thigh-bone, is the longest and strongest bone in the body. It possesses a shaft and two extremities. The shaft is almost cylindrical in most of its length, and is curved with a forward convexity. The rounded head, which can easily be distinguished from the widely expanded lower end, projects from the medial side of the upper end of the shaft. This information is sufficient to enable the student to assign a given femur to its correct side of the body.

In the erect posture the femora are placed obliquely (fig. 264). Their heads are separated by the breadth of the true pelvis and their shafts incline downwards and medially, so that the medial aspects of the two knees can just touch. As the bones of the legs descend vertically from the knees, the obliquity of the femoral shafts results in the approximation of the feet in the erect attitude and the provision of a narrow base for the support of the weight of the body. The narrowness of the base detracts from the stability of the body but greatly facilitates movements and increases the speed with which they can be executed. The degree of obliquity of the shafts varies in different individuals, but is usually greater in the female on account of the greater breadth of the female pelvis.

Figure 455
The upper end of the femur (fig. 455) comprises a head, a neck, a greater and a lesser trochanter.

General features.—The head forms rather more than half a sphere; it is directed upwards, medially and somewhat forwards, to articulate with the acetabulum of the hip-bone. Its surface is smooth, and is marked a little below and behind its center by a small roughened pit.

The neck of the femur, which is about 5 cm. long, connects the head with the shaft and forms with the latter an angle of about 125�. This arrangement facilitates the movements of the hip-joint and enables the lower limb to swing clear of the pelvis. The neck is constricted at its middle and is wider at its lateral than at its medial end. Its two borders are rounded. The upper border is nearly horizontal and is gently concave upwards. The lower border is straight but oblique, and is directed downwards, laterally and backwards to meet the shaft near the lesser trochanter. The anterior surface of the neck is flattened and its junction with the shaft is marked by a prominent rough ridge, termed the trochanteric line. The posterior surface is convex backwards and upwards in its transverse axis, and concave in its long axis, and its junction with the shaft is marked by a rounded ridge, termed the trochanteric crest.

The greater trochanter is a large, quadrangular eminence, situated at the upper part of the junction of the neck with the body. Its posterosuperior portion projects upwards and medially (fig. 459) so as to overhang the adjoining part of the posterior aspect of the neck ; in this situation its medial aspect presents a roughened, depressed area, termed the trochanteric fossa. The free upper border of the trochanter lays one hands-breadth below the tubercle on the iliac crest, and is on a level with the center of the head of the femur. The anterior aspect of the trochanter presents a roughened impression ; its lateral aspect is divided into two areas by an oblique, flattened strip, wider above than below, which runs downwards and forwards across it. The lateral aspect of the trochanter can be palpated in the living subject, and, when the adjoining muscles are relaxed, the trochanter can be gripped between the thumb and fingers.

The lesser trochanter (fig. 455) is a conical eminence, which projects medially and backwards from the body at its junction medius with the lower and posterior part of the neck. Its summit and anterior aspect bear a roughened impression, but its posterior aspect, which lies at the lower end of the trochanteric crest, is smooth and even. It is placed too deeply to be felt in the living subject.

Figure 456
The trochanteric line is placed at the junction of the anterior surface of the neck with the shaft of the femur (fig. 457) It forms a prominent roughened ridge, which commences in a tubercle at the upper and medial part of the anterior aspect of the greater trochanter and runs downwards and medially. It reaches the lower border of the neck on a level with, but anterior to, the lesser trochanter, and thereafter, much narrowed, is continued downwards afid backwards on the shaft as the spiral line.

The trochanteric crest (fig. 455) is placed at the junction of the posterior surface of the neck with the shaft of the femur. It forms a smooth rounded ridge, which commences at the posterosuperior angle of the greater trochanter and runs down wards and medially to terminate below at the lesser trochanter. A little above its middle it presents a low rounded elevation, sometimes termed the quadrate tubercle.

Particular features.-The head of the femur is entirely intracapsular and is encircled immediately lateral to its greatest diameter by the acetabular labrum. Its circumference is sharply defined., except on the anterior aspect, where the cartilage covered surface extends on to the front of the neck. The pit, which marks the head below and behind its center (fig. 455), gives attachment to the ligament of the head of the femur (ligamentum teres). The inferomedial part of the anterior aspect of the head is related to the femoral artery, from which it is separated by the tendon of the psoas major and the articular capsule.

The neck of the femur is roughened and pitted by numerous vascular foramina, especially on its anterior surface and on the upper part of its posterior surface. The angle which it makes with the shaft is widest at birth and diminishes steadily until the adult condition is reached. It is less in the female than in the male, owing to the increased breadth of the true pelvis and the greater obliquity of the shaft of the femur. The anterior surface of the neck is entirely intracapsular and on this aspect the capsular ligament extends laterally to the. trochanteric line. On the inferior surfaced the capsular ligament does not reach the trochanteric crest (fig. 460). and only a little more than the medial half of the neck lies within the capsule. The part of the anterior surface adjoining the head is covered with cartilage and is rented to the iliofemoral ligament in the erect posture. A faint groove crosses the posterior aspect in an upward and lateral direction ; it is produced by the obturator externus tendon as it passes to the trochanteric fossa. The nook of the femur does not lie in the same plane as the shaft, but is carried forwards as it passes upwards and medially. On this account the transverse axis of the head of the femur makes an angle with the transverse axis of the lower end of the hone, and this angle is known as the angle of femoral torsion.

Figure 457
The greater trochanter (fig. 456) provides insertion for most of the muscles of the gluteal region. The gluteus minimus is inserted into the rough impression on its anterior aspect. The gluteus medius is inserted into the oblique, flattened strip. which runs downwards and forwards across its lateral aspect. The area in front of this insertion is separated from the tendon by the trochanteric bursa of the gluteus medius; the area behind the insertion is covered by the deep fibers of the gluteus maximus, and a portion of the trochanteric bursa of that muscle may be interposed. The upper border of the trochanter gives insertion to the piriformis behind, and to the obturator internus in front, the trochanteric fossa receives the insertion of the obturator externus.

The lesser trochanter receives the insertion of the psoas major on its summit and on the medial part of its anterior aspect, the base of the trochanter is expanded and its medial or anterior surface gives insertion to the iliacus, which extends downwards for a short distance behind the spiral line. The upper fibers of the adductor magnus play over the posterior surface of the lesser trochanter and a bursa is sometimes interposed between them.

The trochanteric line marks the lateral limit of the capsular ligament of the hip-joint. Its upper part, including the tubercle already noticed (p. 383), receives the attachment of the upper band of the iliofemoral ligament; its lower part receives the lower band of the same ligament. The highest fibers of the vastus lateralis arise from the upper end of the line, and the highest fibers of the vastus medialis from its lower end.

The trochanteric crest, above the quadrate tubercle, is covered by the gluteus maximus muscle; below the tubercle it is separated from that muscle by the quadratus femoris and the upper border of the adductor magnus. The tubercle itself, and a portion of the bone below, receive the insertion of the quadrates femoris muscle.

Figure 458
The shaft of the femur (figs. 457 and 459) is narrowest middle expands little as it is traced upwards, but it widens appreciably near the lower end of the bone.

In its middle third the shaft possesses three surfaces and three borders. The anterior surface, which is smooth and gently convex in all directions, is easy to identify. It is placed between the lateral and the medial borders, which are both rounded and ill-defined. The lateral surface is directed more backwards than laterally, and is bounded in front by the lateral and behind by the posterior border. The posterior border is formed by a broad, rough ridge termed the linea aspera, which usually forms a crest- like projection, with distinct lateral and medial lips, along the longitudinal concavity of the shaft. In this situation the compact substance is increased in amount to compensate for the weakness caused by the curve of the bone. The medial surface is directed medially and slightly backwards; smooth, like the two other surfaces, it is bounded in front by the medial border and behind by the linea aspera.

In its upper third a fourth, or posterior surface is included between the upward continuations of the lips of the linea aspera, which diverge as they approach the upper end. The lateral lip is continuous with a broad, rough ridge, termed the gluteal tuberosity, which runs upwards and laterally towards the root of the greater trochanter. The medial lip continues upwards and medially as a narrow rough line, termed the spiral line, which can be traced across the upper part of the medial surface to the lower end of the trochanteric line. The posterior surface is therefore v-shaped in this part of the bone.

Figure 459
In its lower third also the shaft possesses an additional, posterior surface, which is included between the diverging downward continuations of the lips of the linea aspera. The lateral lip becomes continuous with the lateral, and the medial lip with the medial supracondylar line. These two lines form definite but not conspicuous ridges, and of the two the lateral is the more distinct. Near its upper end the medial supracondylar line is in part obliterated; it is in this situation that the femoral artery lies in close relation with the bone as it passes from the thigh to the popliteal fossa. The posterior aspect of the lower third forms a flattened, triangular area, which is termed the popliteal surface of the femur (fig. 459) ; in its lower and medial part it presents a rough and slightly elevated area.

Particular features.-The shaft (figs. 458 and 460) is thickly covered with muscles and cannot be felt satisfactorily through the skin. Its anterior and lateral surfaces give origin in their upper notch three-fourths to the vastus intermedius, below that muscle the articularis genu arises by one or two small slips from the front of the bone. The lower portion of the anterior surface for 5 or 6 cm. above the patellar articular surface is covered by the supra-patellar bursa, which intervenes between the bone and the muscles mentioned. The lower portion of the lateral surface is covered by the vastus intermedius. The medial surface is devoid of muscular attachments and is covered by the vastus medialis.

The vastus lateralis arises from a linear origin which commences in front at the root of the greater trochanter and follows it to the upper end of the gluteal tuberosity. It then descends along the lateral margin of the tuberosity to the lateral lip of the linea aspera, from the upper half of which its takes origin. The vastus medialis also arises from a linear origin. It commences at the lower end of the trochanteric line and follows the spiral line to the medial lip of the linea aspera. At the lower end of the linea aspera it follows the medial supracondylar line in its upper half.

Figure 460
The gluteal tuberosity may take the form of an elongated, roughened depression or it may project as a salient ridge. Occasionally it is sufficiently prominent to merit the name of a third trochanter. It receives the insertion of the deeper fibers of the lower half of the gluteus maximus muscle. The medial edge of the tuberosity provides insertion for the highest fibers of the adductor magnus ; the succeeding fibers of that muscle are inserted into the linea aspera and the upper part of the medial supracondylar line ; its lowest fibers form a stout tendon, which is inserted into the adductor tubercle and sends a membranous expansion to the lower part of the medial supracondylar line.

Between the gluteal tuberosity and the spiral line the posterior surface receives the insertions of the pectineus and the adductor brevis muscles. The pectineus is inserted into a line, sometimes slightly roughened, which descends from the root of the lesser trochanter to the upper end of the linea aspera. The adductor brevis is inserted lateral to the pectineus and extends downwards to the upper part of the linea aspera, where it is attached medial to the adductor magnus.

In addition to the attachment already described, the lines aspera receives the insertion of the adductor longus and the attachment of the lateral intermuscular septum, and gives origin to the short head of biceps femoris. The structures attached to the linea aspera may now be enumerated. From the lateral to the medial side they are : vastus lateralis, lateral intermuscular septum, short head of biceps femoris, adductor magnus adductor brevis (to upper part only); adductor longus and vastus medialis; but it should be noted that the tendinous fibers are interlaced and inseparable at their bony attachments. The perforating arteries cross the linen aspera from the medial to the lateral side, under cover of tendinous arches in the adductor magnus and the short head of the biceps side. The foramina for the nutrient arteries pierce the bone close to the linea aspera. They vary in number and position. One is usually placed near the upper end of the linen aspera, and a second which is not always present, near its lower end. The foramina are directed upwards through the compact substance.

The popliteal surface of the femur forms the floor of the upper part of the popliteal fossa. It is covered by a variable amount of fat, which separates the popliteal artery from the bone as it descends from the upper end of the medial supracondylar line to the intercondylar notch. The superior medial genicular artery arises from the popliteal artery as it lies in the intercondylar notch. It arches medially above the medial condyle but is separated from the bone by the medial head of the gastrocnemius, which takes origin from the rough elevation placed a little above the medial condyle. The superior lateral genicular artery arches upwards and laterally above the lateral condyle, but is separated from the bone by the plantaris muscle, which arises from a small roughened area on the lower part of the lateral supracondylar line.

The lateral supracondylar line is most distinct in its upper two-thirds; to which the short head of the biceps femoris and the lateral intermuscular septum are attached. Its lower part is marked by a small roughened area which gives origin to the plantaris and often encroaches on to the popliteal surface. The medial supracondylar line is feebly marked in its upper two-thirds, where it gives origin to the vastus medialis. Near its upper end it is crossed by the popliteal vessels as they enter the fossa from the subsartorial (adductor) canal. It is often sharp and prominent for 3 or 4 cm. above the adductor tubercle, and in this situation it gives attachment to a membranous expansion from the tendon of the adductor magnus muscle.

The lower end of the femur is widely expanded in order to provide a good bearing surface for the transmission of the weight of the body to the top of the tibia. It consists of two prominent masses of bone, termed the condyles, which are partially covered by a large articular surface. Anteriorly the two condyles are united and lie in line with the front of the shaft; posteriorly they are separated by a deep notch, termed the intercondylar notch, and they project backwards considerably beyond the plane of the popliteal surface.

Figure 461
The articular surface forms a broad /-shaped area for articulation with the patella, or knee-cap, above and the tibia below (fig. 461). The patellar surface extends over the anterior aspects of both condyles, but much the larger part of it covers the lateral condyle. It is concave from side to side, being grooved in its long axis to accommodate the convex posterior surface of the patella. The tibial surface is divided into medial and lateral parts by the intercondylar notch, but anteriorly each part is directly continuous with the patellar surface. The part forms a broad strip which covers the convex inferior and posterior aspects of the medial condyle, and is gently curved with the convexity of the curve directed medially. The lateral tibial surface covers the same aspects of the lateral condyle but forms a rather broader strip, which passes straight backwards.

The lateral condyle (fig. 462) is flattened on its lateral aspect and is not so prominent as the medial condyle, but it is stouter and stronger, for it is placed more directly in line with the shaft and probably takes a greater share in the transmission of the weight to the tibia. The most prominent point on its lateral aspect is termed the lateral epicondyle, and the whole of this surface can be felt through the skin in the living subject. A short groove, deeper in front than behind, separates the lateral epicondyle from the articular margin lateral epicondyle below and behind. The medial surface of the condyle forms the lateral wall of the intercondylar notch.

Figure 462
The medial condyle possesses a bulging, convex medial aspect, which can be palpated without difficulty. Its uppermost part is marked by a small projection, termed the adductor tubercle (fig. 457), because it gives insertion to the tendon of the adductor magnus muscle. The tubercle is an important bony landmark for the surgeon, and can be identified most readily when it is approached from above. The most prominent point on the medial surface of the condyle lies below and a little in front of the adductor tubercle and is termed the medial epicondyle. The lateral surface of the condyle is roughened and forms the medial wall of the intercondylar notch.

The intercondylar notch separates the two condyles below and behind. In front it is limited by the lower border of the patellar surface, and behind by the intercondylar line, which separates it from the popliteal surface. It lies within the capsular ligament of the knee-joint, but is covered with synovial membrane only over a very limited area.

Particular features.-The patellar surface extends higher on the lateral than on the medial side, so that its upper border is oblique and runs downwards and medially (fig. 457). It is separated from the tibial surfaces by two faint grooves which cross the condyles obliquely. The lateral groove is the better marked (fig. 461) ; it runs laterally and slightly forwards from the front part of the intercondylar notch and expands to form a faint triangular depression, which rests on the anterior part of the periphery of the lateral semilunar cartilage (lateral meniscus), when the knee-joint is fully extended. The medial groove is restricted to the medial part of the medial condyle and rests on the anterior edge of the medial semilunar cartilage in the same position. Where this groove ceases the patellar surface is continued backwards on to the lateral part of the medial condyle as in the area adjoining the anterior part of the intercondylar notch. This area articulates with the medial vertical facet of the patella in forced flexion of the knee-joint; it is not distinctly outlined inmost femora. The tibial surfaces are convex from side to side and from before backwards. The anteroposterior curvature of the two surfaces is not of the same decree throughout the posterior part of each surface is the are of a circle, but its anterior portion is part of a cycloid (cycloid is the curve traced by a point on the circumference of a wheel rolling along a straight line). In full flexion of the knee-joint the sharply curved posterior parts of the tibia] surfaces rest on the tibia and the semilunar cartilages (menisci), while their anterior parts are in contact with the infrapatellar pad of fat. In full extension the anterior parts rest on the tibia, while the posterior parts are in contact with the posterior part of the articular capsule.

The medial condyle projects medially and downwards to such an extent that, despite the obliquity of the shaft, the lower surface of the lower end of the bone is practically horizontal. A curved strip, about 1 cm. wide, adjoining the medial margin of the articular surface, is covered with synovial membrane and lies within the capsule of the knee-joint.

The medial epicondyle, which lies above this area gives attachment to the medial (tibia) eollateral) ligament of the knee-joint. In front of the epicondyle the medial condyle is related to the medial patellar retinaculum (tendinous expansion of vastus medialis).

Figure 463
The lateral condyle is less prominent and its lateral surface projects but little beyond the lateral surface of the shaft. The lateral epicondyle gives attachment to the lateral (fibular collateral) ligament of the knee-joint, and above and behind it the bone bears an impression which gives origin to these fibers of the lateral head of the gastrocnemius that do not arise from the capsular ligament. The deepened anterior end of the groove which lies between the epicondyle and the articular margin gives origin to the popliteus (fig. 462) muscle; the posterior or upper end of the groove lodges the tendon of the muscle only in full flexion of the knee. In extension the tendon passes across, and sometimes grooves, the margin of the articular surface below. Immediately adjoining the articular margin a strip of the lateral condyle, 1 cm. broad is intracapsular, and is covered with synovial membrane, with the exception of the depression from which the popliteus arises.

Figure 464
The intercondylar notch separates the backwardly projecting protions of the two condyles, and is intracapsular but, to a large extent, extrasynovial. Its lateral wall, formed by the medial aspect of the lateral condyle, bears a flattened impression, which is placed on its upper and posterior part extends on tho the floor of the notch close to the intercondylar line. This impression gives attachement to the upper end of the anterior cruciate ligament of the knee-joint. The medial wall of the notch, formed by the lateral aspect of the medial condyle, bears similar but rather larger impression for the attachment of the upper end of the posterior cruciate ligament; it is placed anteriorly and extends on to the anterior part of the floor of the notch. These two impressions are relatively smooth, but rest of the notch is rough and pitted by vascular foramina. although occasionally the bursal recess between the two ligaments extends upwards to reach it. The intercondylar line gives attachment to the capsular ligament and, laterally; to the oblique posterior (oblique popliteal) ligament of the knee-joint. The anterior border of the notch receives the upper attachment of the infrapatellar synovial fold.

Structure.—The. shaft of the femur is a cylinder of compact bone; hollowed by a large medullary cavity. The wall of the cylinder is thick in the middle one-third of the shaft, where the bone is narrowest and the medullary cavity best formed ; but above and below this the wall becomes thinner, while the medullary cavity is gradually filled up with spongy substance, so that the upper and lower ends of the shaft, and the articular extremities more especially, consist of spongy substance, invested by a thin compact layer.

Figure 465
The trabeculae in the ends of the femur are disposed along the lines of greatest pressure and tension. In the upper end (figs. 463, 464) the chief lamellae are arranged in the following manner. A series of bony plates at right angles to the articular surface of the head converge to a central dense wedge; this wedge is supported by strong lamellae which extend to the sides of the neck and are specially marked along its upper and lower borders. Any force therefore applied to the head of the femur is transmitted directly to the central wedge and thence to the junction of the neck with the shaft. This junction is in turn strengthened by a series of dense lamellae, which extend from the lesser trochanter to the lateral end of the superior border of the neck ; this arrangement will obviously oppose considerable resistance to either tensile or shearing force. A smaller bar stretching across the junction of the greater trochanter with the neck and shaft resists the shearing force of the muscles attached to this prominence. These two bars, one at the junction of shaft and neck, the other at the junction of shaft and greater trochanter, form the upper layers of a series of arches which extend across between the sides of the shaft and transmit to it forces applied to the upper end of the bone. A thin vertical plate of bone, named the calcar femorale (fig. 465), springs from the compact wall of the shaft in the region of the linea aspera and extends into the spongy substance of the neck. Medially, it is attached to the inner surface of the posterior wall of the neck of the bone ; laterally, it continues the plane of the posterior wall of the neck into the greater trochanter, where it shades off into the general spongy substance. It is thus situated in a plane anterior to the trochanteric crest and to the base of the lesser trochanter.

In the lower end, the trabeculae spring on all sides from the inner surface of the cylinder, and descend in a direction perpendicular to the articular surface, the trabeculae being strongest and having a more accurately perpendicular course above the condyles. In addition to this there are horizontal planes of spongy substance, which in this situation is mapped out into a series of cubical compartments.

Ossification (figs. 458, 460, 466).-The femur is ossified from five centers one each for the shaft, head; greater trochanter, lesser trochanter, and lower end. Except the clavicle, it is the first of the long bones to show traces of ossification. Ossification begins in the middle of the shaft in the seventh week of fetal life, and extends upwards and downwards. The secondary centers appear as follows : in the lower end, during the ninth month of fetal life (from this center the condyles and epicondyles are formed) ; in the head at the end of the first year ; in the greater trochanter during the fourth year ; and in the lesser trochanter between the thirteenth and fourteenth years. The epiphyses, derived from the secondary centers, fuse independently with the shaft after puberty ; the lesser trochanter joins first, then the greater, then the head, and, lastly, the lower end, which is not united until the twentieth year. It should be noted that the lower epiphyseal plate passes through. the adductor tubercle (fig. 408).

Figure 466
Applied Anatomy.-The lower end of the femur is the only epiphysis in which ossification has commenced at the time of birth. The presence of this center of ossification is, therefore, a proof, in a new-born child found dead, that the child has arrived at the full period of uterogestation, and is always relied upon in medico-legal investigations. The position of the epiphyseal plate should be carefully noted. It is on a level with the adductor tubercle, and the epiphysis does not, therefore, form the whole of the synovial covered portion of the lower end of the bone. It is essential to bear this point in mind in performing operations on the lower end of the femur, since growth in length of the bone takes place chiefly from the lower epiphyseal cartilage, and any interference with it in a young child would involve such ultimate shortening of the limb, from want of growth, as to render the limb almost useless. Separation of the lower epiphysis may take place up to the age of twenty ; but, as a matter of fact, few cases occur after the age of sixteen or seventeen. The epiphysis for the head is entirely intracapsular.

Fracture of the neck of the femur is usually termed intracapsular fracture, but this is not always a correct designation, as, owing to the attachment of the articular capsule, the fracture is partly within and partly without the capsule when the fracture occurs at the lower part of the neck. It generally takes place in old people, principally women, and usu ally from a very slight degree of indirect violence. Probably the main cause of its occurrence in old people is the senile degenerative change which takes place in the bone. Merkel believes that it is mainly due to the absorption of the calcar femorale. As a rule the fragments become united by fibrous tissue, but frequently no union takes place, and the opposed surfaces become smooth and eburnated.

Fractures at the junction of the neck with the greater trochanter are usually termed extracapsular, but this designation is also incorrect, as the fracture is partly within the capsule, which is attached in front to the intertrochanteric line below the line of fracture. These fractures are produced by direct violence to the greater trochanter, as from a fall laterally on the hip.

The fractures of the lower end of the femur include transverse fracture above the condyles, the most common; and this may be complicated by a vertical fracture between the condyles, constituting the �T� shaped fracture. In these cases the popliteal artery is in danger of being wounded.

 

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