With reference to operations on and fractures of the femur, it should be remembered that the periosteum is much thicker in children than in adults, so that displacement is frequently prevented by it in children. The femoral artery lies close to the head of the femur, but from that point to the lower end of Hunter's canal is separated from it by a considerable mass of muscle, while in passing through the opening in the adductor magnus, and thereafter as the popliteal artery, it lies close to the bone. The main nutrient artery enters the centre of the shaft at the linea aspera, and a second enters 2 or 3 inches lower down. The bone is inclined downwards and inwards from hip to knee, the obliquity being greater in females, and it is slightly curved, with the convexity forwards. In section it is triangular in the middle one-third, and oval in the lower third. While the bone is generally deeply placed among the muscles, particularly in the upper half, it lies entirely in the anterior half of a transverse section at the junction of the middle and lower one-third. In this region also there are no important vessels or nerves on the outer side, and the shaft of the bone is Comparatively thin on its outer surface. Hence operations for osteomyelitis, wiring ununited fractures, etc., are generally performed through this outer aspect. The two lower limbs are very frequently of unequal length, the left being often the longer by about ¼ inch. This difference is generally due to the femur.

Fractures of the shaft of the femur may be due to either direct or indirect violence, the former most often affecting the lower one-third, the latter the upper one-third, while the two forms are of equal frequency in the middle one-third. As direct violence generally produces a transverse, while indirect produces an oblique fracture, it follows that fractures in the lower one-third are generally transverse, and those in the upper generally oblique, while oblique and transverse occur equally in the middle one-third. The femur is rarely fractured by muscular violence. In oblique fractures the obliquity is from above, downwards and forwards, this obliquity being combined with an inclination inwards in the upper one-third. In both upper and middle one-third where the fracture is oblique, the upper fragment tends to project forwards and a little outwards, being pushed forward by the lower fragment, and pulled by the action of the ilio-psoas. This tilting forward is most marked in the upper one-third. The lower fragment is drawn up behind the upper by the rectus, gracilis, sartorius, tensor fasciae femoris, hamstrings, and adductors, the latter also producing a slight inclination inwards. The lower fragment is also generally everted by the weight of the limb and external rotators. Fracture in the lower one-third generally occurs about 2 inches above the epiphysis, at the position where compact shaft and cancellous extremity meet. Where this fracture is oblique, and the obliquity favours the displacement, the lower fragment is apt to be tilted backwards by the gastrocnemius, and drawn up by the hamstrings, adductors, and other muscles mentioned above, arid as the femoral artery lies close to the bone in this region it is in some danger of being wounded. In such cases the limb is best treated in a flexed position, and this position of flexion is necessary in treating fractures of the upper one-third. Spiral fractures due to torsion forces are met with in the lower end of the femur and of the tibia, and are sometimes spoken of as helicoidal fractures of Leriche. Fractures of the femur in children are frequently transverse, and, the periosteum remaining intact, no sensible displacement may occur. In adults shortening frequently occurs as a result, but in estimating the amount of this the frequent normal difference in the length of the two limbs should be remembered.

Genu valgum, or knock-knee, is a deformity due to rickets, which affects the lower third of the femur, the shaft of the bone becoming bent with the convexity inwards. In consequence of this curve the epiphyseal line is tilted, the outer extremity being on a higher level than the inner, while the internal condyle appears to be lengthened in a downward direction owing to the tilting. When the patient attempts to stand erect with the legs straight, the head of the tibia rests on the uneven condylar surfaces, and is therefore thrown outwards, so that he stands with the knees touching or even crossing one another, and the feet wide apart. When, on the other hand, he sits, the tibia rests on the more posterior condylar surface, which is not affected by the lateral tilting, and so the deformity disappears. A patient with severe genu valgum makes use of this method of minimizing the deformity. Instead of attempting to walk with straight limbs, which would often be so divergent as to render walking impossible, he flexes both knees and hips, and so diminishes the divergence. In operating on genu valgum the bone is cut through by an osteotome, introduced through the soft tissues, at a point a finger's breadth in front of the adductor tubercle (to avoid the anastomotica magna), and a finger's breadth above the external condyle (that which is tilted upwards ; to avoid the epiphyseal line). A wedge-shaped incision is made through the bone (practically a transverse cut or fracture), the deformity is fully corrected, and the limb put in a splint until united.

Genu varum, or bow-leg, is a less definite condition also due to rickets, in which the femur presents a curve with the convexity outwards, which may involve the whole shaft or only part of it. The femoral curve is generally associated with one in the tibia, which in some cases is principally affected.

Amputation of _the thigh is generally performed, where possible, in the lower third. The skin flaps are cut long, are easily raised, and retract markedly. The anterior is generally the longer. The muscles are generally cut by a circular sweep, and retract unequally, the adductors, vasti, and crureus being limited in their retractive power by their attachment to the shaft of the femur. The femoral artery is generally cut in Hunter's canal, while the profunda, considerably reduced in size, lies close to the linea aspera of the femur, behind the tendon of the adductor longus. The other vessels cut are the descending branches of the external circumflex, lower perlorating, and long saphenous vein. In order to avoid splitting the femoral artery in cutting the flaps in an amputation in the middle third of the femur, it is advised to make them slightly lateral instead of directly antero-posterior. Care should be taken not to include the long saphenous nerve in the ligature of the femoral artery. The great sciatic nerve lies posteriorly amidst the hamstring muscles ; it is best pulled down, and cut short, to minimize risk of formation of stump neuroma. The other nerves cut are branches of the middle and internal cutaneous and muscular branches of the anterior crural, the anterior branch of the external cutaneous, the obturator, and small sciatic.