In human anatomy, the femoral sheath is a band of fibrous tissue located in the femoral triangle of the upper thigh on both the left and right sides of the body. It essentially acts as a protective tubing through which the femoral artery, vein and lymph vessels pass on their way from the heart down to the legs. Each sheath is made of fascia, a special type of connective tissue. Its main job is to provide protection and guidance to the vessels as they transition from deep within the buttocks area to closer to the skin. This guiding and protective role is also echoed in a medical device that also carries the “femoral sheath” name. The device is a temporary, usually one-time use tube or synthetic covering that surgeons use to create a portal into a vein or artery of the upper thigh, usually for the purpose of introducing devices into the heart to diagnose or treat cardiac disease. The precise placement of this device is critical to its proper functioning, as well as to avoid complications like infection.
Relationship to the Femoral Triangle
Blood circulates through the body via a complex series of veins and arteries. The heart pumps and processes the blood, and these veins and arteries both deliver it to the extremities and channel it back into the heart for the process to start again. The femoral artery is primarily responsible for bringing blood to the legs. The femoral nerve, vein, and lymphatic tissues serve largely complementary roles to support this mission, and they largely run parallel to the artery. All of these elements convene at the top of each thigh in what’s known anatomically as the femoral triangle, named because of its basic shape; it’s a hollow, triangular-shaped space just below the abdomen and adjacent to the groin.
The sheath covers all of the femoral elements as they travel through this hollow triangle and down towards the leg. It helps them remain oriented and keeps them close together.
Core Form and Function
When viewed as a whole, the sheath forms a funnel that is oval in shape near the top and more rounded near the bottom. The blood and lymph vessels enter the funnel each in its own separate compartment formed by the fibrous tissue. The overarching purpose is to protect these vital vessels from damage as the leg moves relative to the hip.
One of the most important things about the sheath is its elasticity, which largely owes to the flexible fascia tissue of which it is made. Fascia refers to any sheet or band of connective tissue that provides support to the organs and tissues within the body. These tough but flexible tissues allow movement within defined ranges, similar to the effect of a girdle or a compression stocking. In exposed areas, such as behind the knees, the inner elbow, or the inner thigh, where nerves and blood vessels must pass close to the skin, fascia also provides protection from injury, as the thick tissues can't easily be penetrated.
As a Medical Device
The medical device known as a femoral sheath is a single-use piece of tubing that is placed into a femoral artery or vein, depending on what part of the heart needs treatment. This specialized type of catheter is usually measured in French, a medical term used to measure the outside diameter of catheters. Sheathes usually measure anywhere from 4 to 6 French, which is about 0.0523 to 0.067 inches (1.35 to 2 mm). They are as long as is required for the procedure, and are usually cut to order.
The exact placement of this catheter in relation to the anatomical sheath structure is very important. With entry into the vessel that is too high, the catheter will be too stiff to follow the vessel's turn into the body; too low, and it may follow the wrong subvessel. Specialized training is required to master these procedures.
Risks and Other Considerations of Sheath Insertion
The use of a catheter-style sheath involves risk to the vascular system, including infection, perforation of tissue, and loss of circulation for an extended period. The risk is mitigated by the important benefits provided, such as the examination of the vessels and valves of the heart, removal of plaque, or the placement of stents. The use of femoral sheaths is considered standard in cardiac surgery.