Femoral neck fractures (Fig. 6.28) can interrupt the blood supply to the femoral head. The blood supply to the head and neck is primarily from an arterial ring formed by the branches of the medial and lateral circumflex femoral arteries around the base of the femoral neck. From here, vessels course along the neck, penetrate the capsule, and supply the femoral head. The blood supply to the femoral head and femoral neck is further enhanced by the artery of the ligamentum teres, a branch of the obturator artery, which is generally small and variable. Femoral neck fractures may disrupt associated vessels and lead to necrosis of the femoral head. Femoral neck fractures can be divided into three categories depending on the location of the fracture line: subcapital (fracture line passes across the femoral head-neck junction), transcervical (fracture line passes through the midportion of the femoral neck), and basicervical (fracture line passes across the base of the neck). Subcapital fractures have the highest risk of developing necrosis of the femoral head, and basicervical fractures have the lowest risk. Elderly patients with osteoporosis tend to have transverse subcapital fractures following low-energy trauma such as a fall from a standing height. Conversely, younger patients usually sustain more vertical fractures of the distal femoral neck (basicervical) after high-energy trauma such as a fall from a great height or due to axial load applied to an abducted knee, such as during a motor vehicle accident.
In the clinic
In these fractures, the break usually runs from the greater trochanter through to the lesser trochanter and does not involve the femoral neck. Intertrochanteric fractures preserve the femoral neck blood supply and do not render the femoral head ischemic. They are most commonly seen in the elderly and result from low-energy impact (Fig. 6.29).
Sometimes isolated fractures of the greater or the lesser trochanter can occur. An isolated fracture of the lesser trochanter in adults is most commonly pathological and due to an underlying malignant deposit.
In the clinic
An appreciable amount of energy is needed to fracture the femoral shaft. This type of injury is therefore accompanied by damage to the surrounding soft tissues, which include the muscle compartments and the structures they contain.
In the clinic
The normal flow of blood in the lower limbs is from the skin and subcutaneous tissues to the superficial veins, which drain via perforating veins to the deep veins, which in turn drain into the iliac veins and inferior vena cava.
The normal flow of blood in the venous system depends upon the presence of competent valves, which prevent reflux. Venous return is supplemented with contraction of the muscles in the lower limb, which pump the blood toward the heart. When venous valves become incompetent they tend to place extra pressure on more distal valves, which may also become incompetent. This condition produces dilated tortuous superficial veins (varicose veins) in the distribution of the great (long) and small (short) saphenous venous systems.
Varicose veins occur more commonly in women than in men, and symptoms are often aggravated by pregnancy. Some individuals have a genetic predisposition to developing varicose veins. Valves may also be destroyed when a deep vein thrombosis occurs if the clot incorporates the valve into its interstices; during the process of healing and recanalization the valve is destroyed, rendering it incompetent.
Typical sites for valvular incompetence include the junction between the great (long) saphenous vein and the femoral vein, perforating veins in the midthigh, and the junction between the small (short) saphenous vein and the popliteal vein.