The Femur

The femur or thigh bone (Os femoris) is the largest and most massive of the long bones. It extends obliquely downward and forward, articulating with the acetabulum above and the tibia and patella below. It presents for examination a shaft and two extremities.

The shaft or body (Corpus femoris) is in general cylindrical, but flattened behind, and larger above than below. The anterior and lateral surfaces are continuous and strongly convex from side to side; there is often a central vertical rough line on the proximal part, but otherwise these surfaces are smooth. They are covered by the quadriceps femoris muscle. The posterior surface is wide, flat, and smooth in its proximal fourth. Below this part there is a rough elevation externally for the attachment of the femoral tendon of the biceps femoris, and a rough line internally to which the quadratus femoris is attached. The middle third is narrower, and is rough for the attachment of the adductor muscle. Just below this area an oblique groove crosses the surface, indicating the position of the femoral vessels. The internal border bears on its proximal part the internal trochanter or trochanter minor, a thick rough ridge, to which the ilio-psoas muscle is attached. From this a rough line curves up to the front of the neck and indicates the limit of the attachment of the vastus internus muscle. A narrow rough area about the middle gives attachment to the pectineus muscle, and the nutrient foramen is usually found just in front of this mark. The supracondyloid crest is situated below the groove for the femoral vessels, and gives origin to the inner head of the gastrocnemius. The external border is prominent in its upper part, and bears at the junction of its proximal and middle thirds the external or third trochanter (Trochanter tertius); this process is curved forward, and furnishes insertion to the tendon of the superficial gluteus muscle. At the lower part is found the supracondyloid or plantar fossa (Fossa plantaris), in which the superficial flexor arises; it is bounded externally by a thick rough margin, to which the outer head of the gastrocnemius muscle is attached.

The proximal extremity (Extremitas proximalis) is large and consists of the head, neck, and great trochanter. The head (Caput femoris) is placed at the inner side and is directed inward, upward, and somewhat forward. It is approximately hemispherical and articulates with the acetabulum. It is cut into internally by a deep notch, the fovea capitis, in which the pubo-femoral and round ligaments are attached. The articular surface is surrounded by a distinct margin. The neck (Collum femoris) is most distinct in front and internally. The great trochanter (Trochanter major) is situated externally; it presents three features. The anterior part or convexity is situated opposite to the head and rises little above the level of the latter; it gives attachment to the deep gluteus muscle, and in the fresh state its outer surface is coated with cartilage, over which a tendon of the middle gluteus passes, to be inserted into the crest, which is placed below and behind the convexity. The posterior part or summit is separated from the convexity by a notch; it is situated behind the plane of the head and rises to a much greater height. It furnishes insertion to part of the middle gluteus muscle. Its posterior border is continued downward as the trochanteric ridge, which forms the outer wall of the trochanteric fossa. A number of foramina are found in the concave area internal to the convexity.

The distal extremity (Extremitas distalis) is large in both directions and comprises the trochlea in front and two condyles behind. The trochlea consists of two ridges separated by a groove, and forms an extensive surface (Facies patellaris) for articulation with the patella. It is very unsymmetrical; the inner ridge or lip is much wider, more prominent, and extends up higher than the external one, and the two converge below. The condyles, internal and external (Condylus medialis, lateralis), are separated by the deep intercondyloid fossa (Fossa intercondyloidea), and articulate with the condyles of the tibia and the semilunar cartilages of the stifle joint. A ridge connects each condyle with the lower part of the corresponding lip of the trochlea. The intercondyloid fossa lodges the spine of the tibia and the crucial ligaments of the stifle joint, which are attached here.

The condyles are obliquely placed, with their long axes directed downward, forward, and inward. The articular surface of the external condyle is more strongly convex from side to side than that of the inner one, and the ridge which connects it with the trochlea is much narrower.

The internal epicondyle (Epicondylus medialis) is a rounded prominence on the internal surface of the internal condyle, to which the internal lateral ligament and the adductor muscle are attached. The corresponding external epicondyle (Epicondylus lateralis) is less distinct; it presents a mark where the lateral ligament is attached, below and behind which there is a depression (Fossa musculi poplitei) in which the popliteus muscle arises. Between the external condyle and trochlea is the extensor fossa (Fossa extensoria), in which the tendon of origin of the anterior extensor and peroneus tertius is attached.

Development.—The shaft and the distal end each ossify from one center, but the proximal end has two centers, one of which is for the great trochanter. The edge of the external trochanter also has a separate center. The proximal end fuses with the shaft at three to three and a half years, the distal at about three and a half years.