Dissector Answers - Anterior & Medial Thigh

Learning Objectives:

Upon completion of this session, the student will be able to:

1. Define the femoral triangle and adductor canal, their contents and the spatial relationships of the structures passing through them.
2. Identify the femoral and obturator arteries and veins and their branches. Give their areas of distribution.
3. Identify the muscles of the anterior and medial thigh, including their nerve and vascular supply. Describe their role in locomotion.
4. Predict what nerve or nerves are involved and the probable level of the injury, given a loss of function and/or cutaneous sensation involving the anterior and medial thigh regions.

Learning Objectives and Explanations:

1. Define the femoral triangle and adductor canal, their contents and the spatial relationships of the structures passing through them. (W&B 585-586)

Images from "Anatomy of the Human Body" by Henry Gray are provided by:

The borders of the femoral triangle are the inguinal ligament (superior), the sartorious muscle (lateral) and the adductor longus muscle (medial). It contains, from lateral to medial, the femoral nerve and branches, the femoral artery and branches, and the femoral vein and tributaries. (The image above shows the left femoral triangle, in case the "Orientation Penis" didn't make that clear.)

The following specializations of abdominal fascia in this region are also important:

• femoral sheath: a diverticulum of the transversalis fascia. It wraps the femoral vessels for the first 2 or 3 centimeters of their trip through the femoral triangle. The femoral sheath does not wrap around the femoral nerve. It has three compartments. The lateral compartment contains the femoral artery, the middle compartment has the femoral vein, and the medial compartment is designated as the femoral canal.
• femoral canal: the medial compartment of the femoral sheath. It usually contains fat, a few lymph vessels, and maybe a deep inguinal lymph node (node of Cloquet).
• femoral ring: the opening at the superior end of the femoral canal.

The adductor canal allows passage of the femoral vessels and the saphenous nerve through the middle one-third of the thigh. The quadriceps femoris muscles are separated from the adductor muscles by a deep groove. Put a roof on that baby, let's say the sartorious muscle, and you have the adductor canal. The canal ends at the adductor hiatus, which is a split in the adductor magnus muscle.

2. Identify the femoral and obturator arteries and veins and their branches. Give their areas of distribution. (W&B 600-605)

The femoral artery supplies a major portion of the thigh. (Analogously, the femoral vein drains a good deal of the thigh.) The femoral artery gives off the superficial epigastric artery, the superficial circumflex iliac artery, the superficial external pudendal artery (all three just distal to the inguinal ligament), the deep external pudendal artery, the deep femoral artery, and the descending genicular artery. The largest and most important of these is the deep femoral artery.

The deep femoral artery supplies the hip joint, proximal thigh, and posterior thigh, including the neck of the femur. It gives off two important branches. The medial femoral circumflex artery supplies the iliopsoas muscle, pectineus muscle, and the hip joint via ascending and descending branches. The lateral femoral circumflex artery supplies the lateral hip, thigh, and knee via ascending, transverse, and descending branches. The descending branch anastomoses with both the descending genicular branch of the femoral artery as well as the lateral superior genicular branch of the popliteal artery, to provide collateral circulation to the knee. (Latin, poples = ham of the knee, genu = knee)

The obturator artery supplies the medial thigh and hip, including the head of the femur (to a limited degree). It accomplishes this via anterior and posterior branches.

3. Identify the muscles of the anterior and medial thigh, including their nerve and vascular supply. Describe their role in locomotion. (W&B 590-595)

MUSCLE	INNERVATION	BLOOD SUPPLY	ACTION
iliopsoas	VPR L2-4, femoral n.	Iliolumbar a.	Flexor - aids in raising thigh for initial raising during locomotion
pectineus	Femoral n.	Medial femoral circumflex a.	Flexor - see above
rectus femoris	Femoral n.	Lateral circumflex femoral a.	Flexor of hip; Extensor of leg - provides forward extension of leg to meet ground and provide support for body weight.
vastus medialis	Femoral n.	Lateral circumflex femoral a.	Extensor of leg - see above
vastus intermedius	Femoral n.	Lateral circumflex femoral a.	Extensor of leg - see above
vastus lateralis	Femoral n.	Lateral circumflex femoral a., perforating branches of deep femoral a.	Extensor of leg - see above
gracilis	Obturator n. - anterior div.	Obturator a.	Adduction; also provides medial rotation of thigh to counteract the lateral rotation given by the extensor of the thigh, gluteus maximus m.
adductor longus	Obturator n. - anterior div.	Obturator a., deep femoral a.	Adduction; also provides medial rotation - see above
adductor brevis	Obturator n. - anterior div.	Obturator a., deep femoral a.	Adduction; also provides medial rotation - see above
adductor magnus	Obturator n. - posterior div., tibial n.	Obturator a., deep femoral a., medial circumflex femoral a.	Adduction; also provides medial rotation - see above

Question: Why do adductors medially rotate the femur?

Most of the adductor group of muscles attach on the posterior surface of the femur, so it is always a mystery how they medially rotate the thigh. If you look at an articulated skeleton while you read this, it will all become clear.

If the femur was a perfectly straight and round cylinder and you attached something to the back of it, like the adductors attach, the cylinder would rotate laterally when you pulled medially on the back of it. However, the catch is - the femur is not a perfectly straight cylindrical shape. It bows anteriorly, quite a bit. Think of it as a bucket handle. If you grab a bucket handle, either from the back or the front, the bucket handle will move toward you when you pull. If you are an adductor and you grab the anteriorly bowed femur, it moves toward you, pivoting on both ends like a bucket handle (which connects to the bucket at both ends). Now, imagine you flex the hip, lifting the leg to take a step forward. The flexion of the hip makes the femur act even more like a bucket handle, so that the pull of the adductors lies in front of the pivot point of the head of the femur. Adductors pull the femur toward the pubic ramus, medially rotating the femur and counterbalancing the lateral rotational force of the big extensor of the hip - gluteus maximus.

4. Predict what nerve or nerves are involved and the probable level of the injury, given a loss of function and/or cutaneous sensation involving the posterior and medial thigh regions.

• Inability to adduct thigh: obturator nerve (L2, L3, and L4). It supplies the adductor muscles.
• Inability to extend leg: femoral nerve (L2, L3, and L4). It supplies the quadriceps femoris muscles.
• Impaired flexing of thigh: femoral nerve (L2, L3, and L4) OR obturator nerve (L2, L3, and L4). The former supplies the sartorius muscle, the rectus femoris muscle, the iliopsoas muscle, and the pectineus muscle, while the latter supplies the adductor muscles. All are involved in flexion of the thigh.
• Loss of cutaneous sensation on the anterior thigh: anterior femoral cutaneous nerve, from femoral nerve (L2, L3, and L4)
• Loss of cutaneous sensation on the lateral thigh: lateral femoral cutaneous nerve (L2 and L3)
• Loss of cutaneous sensation on the posterior thigh: posterior femoral cutaneous nerve (S1 through S3)

Cultural enrichment: Check out these sections from the 1918 version of Gray's Anatomy of the Human Body! Some of the terms are (of course) out-of-date, but the illustrations are timeless. The Femur - The Muscles and Fascia of the Thigh - The Veins of the Lower Extremity, Abdomen, and Pelvis - The Arteries of the Lower Extremity - Surface Anatomy of the Lower Extremity - Surface Markings of the Lower Extremity

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Questions and Answers:

5. The sartorius muscle inserts via the pes anserinus along with which other two muscles?

Pes anserinus is the common insertion of the gracilis, sartorius, and semitendinosus muscles.

6. Do you see deep inguinal lymph nodes in the femoral canal?

There are often several deep inguinal lymph nodes in the vicinity of the femoral canal. The one located within the canal is called the node of Cloquet. One deep inguinal node may sometimes be found below the femoral canal within the femoral triangle.

7. What is a femoral hernia?

A femoral hernia is a hernia through the femoral ring and canal. They often even continue through the saphenous hiatus.

8. Define the adductor canal.

See #1 above.

9. Identify the nerve to the vastus medialis. Source?

The vastus medialis muscle is supplied by the femoral nerve.

10. How does the relation of the femoral vein to the femoral artery change throughout the thigh?

At the inguinal ligament, the femoral artery is lateral to the femoral vein. At the adductor hiatus, the vein is posterior to the artery.

11. What are the relations of the popliteal vein to the popliteal artery in the popliteal fossa?

The popliteal vein lies posterior to the artery, but anterior (deep) to the tibial nerve.

12. Trace the deep femoral artery. What is its relation to the insertions of the adductor muscles?

The deep femoral artery passes between the pectineus muscle and the adductor longus muscle. It then travels inferiorly between the adductor longus muscle and the adductor brevis muscle.

13. Trace the lateral femoral circumflex artery. Note its three branches, and define the position and area supplied by each. Are there variations in origin?

In 14% of cases, this artery branches directly from the femoral artery. The ascending branch supplies the gluteus muscles and possibly the hip joint. The transverse branch supplies the vastus lateralis and possibly the hip joint. The descending branch supplies vastus lateralis and the knee.

14. What are the relations of the lateral femoral circumflex artery branches to the rectus femoris muscle and to the femoral nerve?

They pass immediately deep to rectus femoris muscle and femoral nerve, with femoral nerve branches accompanying.

15. How many perforating arteries do you find?

There are usually 4.

16. How do you distinguish a perforating artery?

They pass posteriorly through adductor brevis and adductor magnus to enter the posterior thigh.

17. What is the function of the patella?

The patella provides a bony surface that is able to withstand the compression placed on the quadriceps tendon during kneeling. It is also able to resist friction occurring when the knee is flexed and extended during running. The patella also provides additional leverage for the quadriceps, since it places the tendon more anteriorly, further from the joint's axis, causing it to approach the tibia from a position of greater mechanical advantage.

18. What muscles does the anterior division of the obturator nerve supply?

The anterior division of the obturator nerve supplies the gracilis muscle, the adductor longus muscle, and the adductor brevis muscle. Occasionally, the pectineus muscle is also supplied by the anterior division of the obturator nerve.

19. What usually supplies the pectineus muscle?

It is usually the femoral nerve innervating the pectineus muscle. Occasionally, the pectineus muscle is supplied by the anterior division of the obturator nerve.

20. What artery accompanies this nerve?

The medial femoral circumflex artery.

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