Next Lesson - Bones of the Lower Limb
Core
There are four key areas within the lower limb. Moving down the limb, each area leads into the next, and knowing this helps you remember what each one contains. The femoral canal sits inside the femoral triangle, and the adductor canal starts at the lower point of the triangle. From top to bottom, we have:
- The femoral triangle
- The femoral canal
- The adductor canal
- The popliteal fossa
This is a large region located on the anterior aspect of the thigh. Knowing where this site is lets you find the femoral pulse and reach the femoral artery. The femoral artery can be used for procedures such as coronary angiography (an X-ray test, using dye, to look at the arteries of the heart), although NICE advises considering the radial artery (at the wrist) in preference for people with a heart attack (STEMI).
Borders of the Femoral Triangle
There are three main borders to know:
- Superior border - Inguinal ligament (the band running from the front of the hip bone to the pubic bone, in the groin)
- Lateral border - Medial aspect of Sartorius (a long, thin muscle running across the front of the thigh)
- Medial border - Medial aspect of Adductor Longus (a muscle of the inner thigh)
These can be remembered by the acronym SAIL: Sartorius, Adductor (longus), Inguinal Ligament
The femoral triangle also has a roof and a floor:
- Roof - Fascia lata (the tough sheet of connective tissue that wraps the thigh muscles)
- Floor - Pectineus (a muscle of the upper inner thigh), Iliopsoas (the main hip flexor muscle) and Adductor Longus (these muscles form the deepest layer; the triangle is a shallow space, so its contents lie close to the surface, just under the fascia lata)
Contents of the Femoral Triangle
There are four main structures found within the femoral triangle. Moving lateral to medial:
- Femoral Nerve
- Femoral Artery
- Femoral Vein
- Femoral Canal (containing lymphatic vessels and lacunar lymph nodes)
The femoral artery, vein and canal are all enclosed within a fascial layer - the femoral sheath.
Diagram - The yellow triangle highlights the location of the Femoral triangle. The numbers indicate the relative borders (1. Inguinal Ligament, 2. Medial aspect of Sartorius, 3. Medial aspect of Adductor Longus)
Creative commons source by Elisa Schorn, circa 1900, edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
An easy way to remember the contents of the femoral triangle is with the acronym NAVEL: Nerve, Artery, Vein, Empty space and Lymphatics. The last two letters stand for the contents of the femoral canal, so NAVEL covers the same four structures as the list above.
Another helpful acronym is NAVY - Nerve, Artery, Vein, Y-fronts (this helps you to remember that the nerve is most lateral, furthest from the genitalia).
Image - Visual representation of the NAVEL mnemonic, from left to right (lateral to medial)
SimpleMed original by Dr. Emily Smith
This is located medially within the femoral triangle and is where femoral hernias occur: part of the bowel, or the fat around it, is pushed down into the femoral canal. These hernias mainly affect women over 50. A hernia can form here because the canal contains a small empty space that other structures can slip into. The borders of the canal are rigid, so herniated abdominal contents are at high risk of strangulation, where the blood supply to the trapped tissue is cut off. Strangulation is a surgical emergency.
Borders of the Femoral Canal
The femoral ring is the proximal entrance to the canal. Its four boundaries are:
- Anterior border - Inguinal ligament
- Posterior border - pectineal ligament over the superior pubic ramus (the upper arm of the pubic bone), with pectineus behind
- Medial border - Lacunar ligament
- Lateral border - Femoral vein
Contents of the Femoral Canal
As mentioned before, the femoral canal contains multiple lymphatic vessels and deep lymph nodes (including the lacunar node). The empty space within the femoral canal lets the femoral vein (next to the canal) and the lymphatic vessels distend (widen) to cope with different levels of flow.
This region is found inferiorly to the femoral triangle - it is a continuation of the bottom point of the femoral triangle, and so sits in the anterior thigh.
Borders of the Adductor Canal
There are three borders:
- Anteromedial border - sartorius
- Lateral border - vastus medialis (the inner part of the quadriceps muscle, at the front of the thigh)
- Posterior wall - adductor longus proximally and adductor magnus distally
Contents of the Adductor Canal
As this canal is a continuation of the Femoral triangle, there are similarities in terms of content:
- Femoral Artery
- Femoral Vein
- Saphenous Nerve (a skin, or cutaneous, branch of the femoral nerve)
- Nerve to Vastus Medialis
Once the Femoral artery and vein leave the adductor canal, they become the popliteal artery and vein.
It is important to understand the location of the adductor canal, because hypertrophy (enlargement) of the muscles forming the borders of this canal can lead to Adductor Canal Compression Syndrome. This rare condition mostly affects young men. It can cause symptoms from a blocked artery (claudication, which is cramping leg pain on walking) or a compressed nerve (for example paraesthesia, which is pins and needles).
Diagram - This image shows a cross section of the left thigh. The highlighted triangle indicates the location of the adductor canal. The numbers indicate the muscles forming the borders of this canal (1. Sartorius, 2. Vastus Medialis, 3. Adductor Longus)
Public Domain Image by Henry Vandyke Carter, edited by Dr. Sachin Sudhakaran [Public domain]
This is a diamond-shaped region located posterior to the knee. This site allows access to the popliteal artery, so this is where the popliteal pulse is felt, although the artery lies deep in the fossa and the pulse can be hard to find. Two main causes of a lump in the popliteal fossa are Baker’s cysts (fluid-filled swellings, also called popliteal cysts) and popliteal aneurysms (abnormal widening of the popliteal artery).
Borders of the Popliteal Fossa
There are two superior borders and two inferior borders:
- Superomedial border - Semimembranosus (a hamstring muscle on the inner back of the thigh)
- Superolateral border - Biceps femoris (the outer hamstring muscle)
- Inferomedial - Medial head of Gastrocnemius (the main calf muscle)
- Inferolateral - Lateral head of Gastrocnemius
The floor of the popliteal fossa is formed by the back of the knee joint capsule, the popliteus muscle (a small muscle at the back of the knee) and the back of the femur (thigh bone), whilst the roof is composed of popliteal fascia and skin.
Contents of the Popliteal Fossa:
The main central bundle is ordered superficial to deep:
- Tibial nerve (branch of the sciatic nerve)
- Popliteal vein
- Popliteal artery
From medial to lateral, the usual side-to-side order is popliteal artery, popliteal vein, tibial nerve and common fibular nerve. The common fibular nerve (also known as the common peroneal nerve) follows the lateral margin with biceps femoris.
Diagram - This image illustrates the posterior aspect of the right lower limb. The yellow diamond highlights the region of the popliteal fossa. The numbers indicate the muscles that form the borders (1. Semimembranosus, 2. Biceps Femoris, 3. Medial head of Gastrocnemius, 4. Lateral head of Gastrocnemius)
Public Domain Source, edited by Dr. Sachin Sudhakaran [Public domain]
Edited by: Dr. Marcus Judge and Dr. Maddie Swannack
- 9800
