The Femur is a long bone with a shaft and two extremities. It articulates above with the acetabulum of the os innominatum and below with the head of the tibia and the patella.

Fig. 13. - Femur.

Upper Extremity Of The Femur

The Upper Extremity consists of a rounded head forming half a sphere, which is joined to the shaft, at an angle of 127.5 degrees, by the neck, a stout bar of bone, an inch or more in length. The cartilage-covered part of the head has a wavy outline where it joins the neck, and just below the summit is a small fossa for the insertion of the ligamentum teres. The two trochanters of the femur are situated on the posterior aspect of the upper end of the shaft, the great trochanter being placed externally and the small trochanter internally. Where the neck joins the shaft a distinct line is seen, the intertrochanteric line in front, and behind where it is more prominent it is called the intertrochanteric ridge (crista intertrochanterica). Just above the middle of this ridge is the quadrate tubercle. The great trochanter overhangs the neck above, and in the depression thus formed is found the digital fossa for the tendon of obturator ex-ternus. On its external surface is an oblique line running from above downwards and forwards. The small trochanter is a rounded eminence confluent with the shaft below.

The Shaft is cylindrical in shape and convex forwards, increasing in size gradually from above downwards. At its lower end it is flattened to support the condyles. The shaft is smooth except on its posterior surface, where a narrow longitudinal ridge is found-the linea aspera. This has distinct inner and outer lips, which separate inferiorly, each passing down to its own condyle and enclosing a smooth triangular space-the popliteal surface. Where the inner lip meets the condyle is a small tubercle-the adductor tubercle.

Lower Extremity Of The Femur

The Lower Extremity of the femur is flattened and recurved posteriorly to form two condyles, between them being the deep intercondylic notch. In front they are united to form a smooth, flat surface for the patella. The inner condyle is longer and narrower than the outer one; but as the femur in its normal position is placed obliquely - i.e., the upper extremities being widely separated by the pelvis-while the lower extremities are in apposition to one another, the inferior surfaces normally are in the same horizontal plane; whereas if the femur is held vertically, the inner condyle projects downwards below the outer one. The inner surface of the inner condyle and the outer surface of the outer condyle are subcutaneous, and each possesses a pronounced tuberosity for the attachment of ligaments.

Inferior Surface Of The Femur

The Inferior Surface of the femur is cartilage covered for articulation with the head of the tibia. It is more or less crescentic in form, the convexity being forwards. The anterior part is called the trochlea, and articulates with the patella. The inferior surfaces of the condyles are convex in both directions. That of the outer one is wider than the inner, and rises to a higher point on the anterior surface of the shaft. They each articulate with the tibia by means of a meniscus of cartilage, which separates the bones from one another.

Ossification

There is one primary centre for the shaft before birth, secondary centres appearing for the head, trochanter and lower extremity. (This latter may appear just before birth.) The whole bone is fused together by the twenty-second year.