Anatomy of the anterior and medial thigh

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Introduction0:00–0:35

The thigh is the part of the lower limb located between the hip and the knee. And it can be divided into anterior medial and posterior compartments that surround the femur.
These compartments are formed by the intramuscular septa that originate on the inner surface of the fascial lata and attached to the linear aspera of the femur.
And more importantly, each compartment contains its own muscles as well as blood vessels and nerves. Each muscle in the three compartments has a proximal origin and a distal insertion, a neurovascular supply and a specific action on the joints of the lower limb.

Anterior compartment0:35–0:58

So, the anterior compartment, which is the largest one includes the anterior thigh muscles, which can function as flexors of the hip and extensors of the knee.

Hip flexors0:58–4:49

First. The flexors of the hip include the Pectineus, iliopsoas and sartorius.
The Pectineus is an almost rectangular muscle located in the anterior part of the superomedial portion of the thigh. And it's often composed of a superficial and deep layer.
It originates on the superior ramus of the pubis and inserts on the pectineal line of the femur just inferior to the lesser trochanter.
Now, this muscle has a lot of nerve, mainly because of stool nerve supply. One supply is from the femoral nerve and the second supply is from a branch of the obturator nerve.
Finally, the pectineus has three main actions. It adducts flexes and medially rotates the thigh.
This is one muscle, two nerves and three actions. Second, the iliopsoas is the most powerful of the hip flexors.
It has most of its mass located in the posterior wall of the abdomen and greater pelvis. Actually, it consists of two parts.
Its broad lateral part is called the iliacus muscle which arises from the floor of the iliac fossa, ala of the sacrum, inner lip of the iliac crest and anterior sacroiliac ligaments.
And its long medial part is called the psoas major. It originates from the sides of the T 12 to L5 vertebrae and the discs between them as well as the transverse processes of all lumbar vertebrae.
Sometimes there's another component called the psoas minor which originates along the sides of T 12 and L1 vertebrae and intervertebral discs and attaches distally to the pectineal line and iliopectineal eminence.
Ok. So the iliacus and psoas major merge distally at the level of the inguinal ligament to form the Iliopsoas which crosses the hip joint to insert on the lesser trochanter of the femur.
Regarding innervation, the iliacus is supplied by the femoral nerve while the psoas major is supplied by the anterior rami of L1 to L3.
Now, given the fact that the iliopsoas is the only muscle attached to the vertebral column, pelvis and femur. It's easy to understand why it is the chief flexor of the thigh at the hip joint and one of the flexors of the lumbar part of the vertebral column.
The iliopsoas is also a postural muscle and stabilizer and it's active especially during standing when it helps maintain normal lumbar lordosis or curvature of the lumbar spine.
And third, the sartorius or the Taylor's muscle name given by the fact Taylors would sit in a cross legged position while sewing, which mimics the action of the muscle.
It's a long and ribbon like muscle situated superficially in the anterior compartment and within its own relatively well defined fascial sheath.
It originates on the anterior superior iliac spine and the superior part of the notch underneath it, from this point, it crosses the anterior thigh diagonally from lateral to medial, moving distally to the medial side of the knee.
And it inserts on the superior part of the medial surface of the tibia. Regarding innervation, it has the same nerve supply as the iliacus, which is the femoral nerve.
Now, its attachments make the sartorius the longest muscle in the body and allow it to flex both the hip and the knee joints.
It also weakly abducts the thigh and rotates it laterally. And when both sartorius muscles work together, they bring the lower limbs into the crosslegged sitting position.
Ok. Now, when it comes to extensors of the knee.

Knee extensors4:49–7:59

We're actually only talking about the quadriceps, femoris muscle, which in turn has four components. The three vasta muscles, vastus lateralis, vastus intermedius, and vastus medialis.
So named by their position around the femoral shaft and the rectus femoris, together, the four components form the largest and one of the most powerful muscles of the body which acts on both the hip and knee joint.
Now let's go through these one by one. The vastus lateralis is the largest of the four components.
It lies on the lateral side of the thigh and originates on the greater trochanter and lateral lip of the linear aspera of the femur vastus medialis covers the medial side of the thigh and originates on the intertrochanteric line and medial lip of the linear asper vastus intermedius lies between the vastus medialis and vastus lateralis and originates on the anterior and lateral surfaces of the shaft of the femur.
And finally, rectus femoris lies on top of Vastus intermedius and it received its name because it runs straight down the thigh.
Rectus, meaning straight in Latin. The muscle originates on the anterior inferior iliac spine and the ileum just superior to the acetabulum because there's power and unity, all tendons of the four parts of the quadriceps unite in the distal portion of the thigh to form the quadriceps, tendon moving distally, the quadriceps, tendon envelops, the patella and continues as a patellar ligament which crosses the knee joint and attaches to the tibial tuberosity.
The transition between the quadriceps, tendon and patellar ligament is marked by the patella which is embedded within it, making it the largest sesamoid bone in the body.
The medial and lateral vasta muscles also attach independently to the patella and form aponeuroses called the medial and lateral patellar retinacula.
The retinacula reinforced the joint capsule of the knee joint on each side of the patella en route to attachment to the anterior border of the tibial plateau.
The retinacula also play a role in keeping the Vella aligned over the patellar surface of the femur. The quadriceps, femoris is supplied by the femoral nerve, all in all the components of the quadricep muscle help extend the leg at the knee joint especially against gravity.
This action is important when rising from sitting or squatting during climbing and walking up stairs and running and jumping at the hip.
It aids in hip flexion through the action of rectus femoris as it is the only portion of the quadriceps that crosses the hip joint.
Additionally, the quadriceps is primarily responsible for absorbing the shock of heel strike, which is when the foot touches the ground heel first during walking or running.
And it functions as a hip fixator or stabilizer during bent knee sports such as skiing and tennis. Now, that was a muscle fatigue, inducing load of information.

Quiz7:59–8:14

Let's take a break and see if you can recall the origins and insertions of the anterior thigh muscles. Now, let's talk about the muscles of the medial compartment of the thigh which form the adductor group.

Medial compartment8:14–8:39

This group is made up of five muscles. Adductor magnus, adductor brevis, adductor, longus, gracilis, and obturator externus.
These function together to add up the thigh and stabilize the stance when standing on both feet or during side to side movement.
While standing first. Adductor magnus is the largest, most powerful and most posterior muscle in the adaptor group, it's a triangular muscle with the tip towards a pubic bone and a thick medial base.

Adductor magnus8:39–9:50

The base is divided into two parts. The superior segment is called the adductor part and it originates on the inferior remi of the pubis and ischium.
And then it fans out widely for an aponeurotic attachment to the gluteal tuberosity, entire length of linea, aspera and medial supracondylar line of the femur.
The inferior segment is called the hamstring part and it originates on the ischial tuberosity and attaches to the adductor tubercle of the femur.
Regarding innervation, the adductor part is supplied by the posterior division of the obturator nerve. While the hamstring part is supplied by the tibial division of the sciatic nerve.
The adductor portion, adducts and flexes the thigh where the hamstring portion extends the thigh. Second, a after brevis or the short abductor lies underneath the pectineus and ad after Longus where it arises from the body and inferior ramus of the pubis as it travels distally the muscle widens to attach to the pectineal line and proximal part of the linea aspera.

Adductor brevis9:50–10:50

When the obturator nerve emerges from the obturator canal to innervate muscles in the medial compartment, it divides into an anterior and posterior division.
With these two divisions passing anterior and posterior to the adapter brevis. In doing so, the obturator nerve and branches of its anterior division innervate the adductor brevis.
While this pattern of the anterior and posterior division sandwiching the adductor brevis is a useful tool to identify the adductor brevis on dissection and cross sectional imaging.
The main action of the adductor brevis is to adduct the thigh. Third adductor longus or the long adductor is a large triangular muscle that arises from the body of the pubis just inferior to the pubic crest where the apex of the triangle is, it then moves on to attach to the middle third of the linear asper of the femur where the base of the triangle is.

Adductor longus10:50–11:26

In doing so it covers the anterior aspects of the adductor brevis and the middle of the adductor magnus. It's also supplied by the obturator nerve and branches of its anterior division and its main action is to add up the thigh.
Fourth gracilis, meaning slender and Latin is a long strap like muscle situated medially and superficially. Now, the muscle originates on the body and inferior ramus of the pubis.

Gracilis11:26–12:37

But its insertion on the superior part of the medial surface on the tibia is a bit more complicated. This is because gracilis joins the sartorius and semitendinosus, a muscle of the posterior compartment to form a common tendinous insertion called the Pez Anserinus or the goose's foot because it resembles, you know, a goose's foot.
Serinus goes and inserts on the superior part of the medial surface of the tibia and you can actually use the mnemonic, say grace before tea to remember the order of their insertion on the tibia.
Sartorius is the most anterior of the muscles followed by gracilis and then by the semitendinosus, which is the most posterior muscle of the Pez Anserinus.
And finally, gracilis is supplied by the obturator nerve and acts to abduct flex and medially rotate the thigh as well as add stability to the medial aspect of the knee.
In extension. And fifth, the obturator externus is a flat, relatively small fan shaped muscle that is deeply placed in the superior medial part of the thigh.

Obturator externus12:37–13:12

It extends from the external surface of the obturator membrane and the margins of the obturator foramen to the trochanteric fossa of the femur, passing directly underneath the acetabulum and neck of the femur.
It is supplied by the obturator nerve and helps to laterally rotate the thigh and study the head of the femur and the acetabulum.

Quiz13:12–13:28

Oh, that was a very longest section that could have been more brevis. Let's relax for a bit and try and recall the origins and insertions of the medial thigh muscles.
Now, before we move on to the other components, let's talk a bit about the particularities of anterior and medial compartments.

Femoral triangle13:28–15:33

First, the femoral triangle, distal to the inguinal ligament helps to understand structural relationships in the groin. And it's useful landmark in dissection.
It's bounded superiorly where the base of the triangle is by the inguinal ligament medially by the lateral border of the adductor longus and laterally by the medial border of the sartorius whose medial border together with the lateral border of the adductor longus forms a downward looking tip of the femoral triangle.
Moving on the muscular floor of the femoral triangle is formed by the iliopsoas laterally and the pectineus medially. The roof on the other hand is formed by the fascia lata and cribriform fascia, subcutaneous tissue and skin.
There's also a lot of stuff in the femoral triangle which you can remember by using the naval mnemonic from lateral to medial naval stands for a femoral nerve and its terminal branches, the femoral artery and several of its branches, femoral vein and its proximal tributaries.
The empty space where the femoral canal is and the deep inguinal lymph nodes and associated lymphatic vessels. Another important element within the femoral triangle is the femoral sheath which is a funnel shaped fascial tube that houses the proximal parts of the femoral artery vein and deep inguinal lymph nodes.
The tube is formed behind the inguinal ligament by a downward extension of the transversalis fascia anteriorly and iliopsoas fascia posteriorly, the sheath terminates inferiorly by blending with the outer layer of the femoral vessels.
And its purpose is to allow the femoral vessels to glide deep to the inguinal ligament during hip movement. Particular interest is usually given to the femoral canal which lies in the femoral sheath between the medial edge of the sheath and the femoral vein laterally.

Femoral canal15:33–17:19

The conical canal starts at the inguinal ligament and it extends distally to the proximal edge of the saphenous opening.
And just in case you forgot, the saphenous opening is an oval opening in the upper mid part of the fascial lata of the thigh covered by the thin perforated crub form fascia and which provides passage to the great saphenous vein to drain to the femoral vein and the femoral triangle, as well as the femoral branch of the genito femoral nerve.
When it comes to functions, the femoral canal allows the femoral vein to expand. When venous return from the lower limb is increased or when increased intraabdominal pressure causes a temporary stasis or blockage in the vein.
For example, this can occur during valsalva maneuvers which is when you ask the individual to exhale forcefully as if blowing up a balloon with a closed mouth and with the nose pinched shut.
The canal also contains loose connective tissue fat, a few lymphatic vessels and sometimes a deep inguinal lymph node called the lacunar lymph node.
Something else to know is that the proximal end of the femoral canal that opens up into the abdominal cavity is a femoral ring about the size of the tip of the little finger.
The femoral ring is bounded laterally by the vertical septum between the femoral canal and femoral vein immediately by the lacunar ligament and posteriorly by the superior ramus of the pubis, which is covered by the pectineus muscle and its fascia and anteriorly by the medial part of the inguinal ligament.
Another important landmark is the adductor or subsartorial canal, which is an approximately 15 centimeter long intermuscular passageway deep to the sartorius in the middle third of the thigh, it extends from the tip of the femoral triangle to the adductor hiatus.

Adductor canal17:19–18:37

The adductor canal is bounded anteriorly and laterally by the vastus medialis posteriorly by the adductors longus and magnus and medially by the Sartorius, which overlies the groove between the aforementioned muscles forming the roof of the canal.
Purpose wise, the adductor canal provides intermuscular passage for the femoral artery vein, nerve to vastus medialis and saphenous nerve as well as delivering the femoral vessels to the popliteal fossa inferiorly just proximal to the medial supracondylar ridge.
The canal leads to a passageway called the adductor hiatus. This hiatus is an opening between the aponeurotic adductor and tendinous hamstring insertion of the adductor magnus.
The adopter hiatus is a transition point for the femoral artery and vein to become the popliteal artery and vein during their course towards the popliteal fossa.

Quiz18:37–18:47

Now it's time we took a hiatus as well. Meanwhile, let's recall the boundaries and contents of the femoral triangle.
Now that we know these particularities, we can talk about the structures within the femoral triangle. First, up is the femoral nerve which enters the thigh deep to an area near the midpoint of the inguinal ligament, which is midway between the anterior superior iliac spine and pubic tubercle and enters the femoral triangle.

Femoral nerve18:47–19:41

Once in the thigh, it sends several branches to the anterior thigh muscles, articular branches to the hip and knee joints and terminates as a saphenous nerve.
The saphenous nerve then descends through the femoral triangle accompanying the femoral artery and vein in the adductor canal and goes superficial to the adductor hiatus and runs Antero inferiorly to supply skin and fascia on the anterior medial aspect of the knee leg and foot.

Femoral artery19:41–22:02

Next, there's the femoral artery which is the chief artery of the lower limb. The femoral artery is located in the anterior compartment and starts distal to the inguinal ligament as a continuation of the external iliac artery at the mid inguinal point, which is halfway between the pubic symphysis and anterior superior iliac spine and is different than the midpoint of the inguinal ligament.
It moves on to enter and bisect the femoral triangle passing deep to the midpoint of the inguinal ligament where it is situated between the femoral nerve laterally and the femoral vein medially.
The femoral artery continues its downward and medial trajectory from the femoral triangle through the adductor canal until it reaches the adductor hiatus.
Here, the artery enters the popliteal fossa where it continues as the popliteal artery, the femoral artery gives off plenty of branches along this trajectory.
The largest branch is the profunda femoris artery or deep artery of the thigh, which arises from the lateral or posterior side of the femoral artery and passes deep between the pectineus and adapter longus to become the main artery of the thigh.
In the middle third of the thigh, where it is separated from the femoral artery and vein by the adductor longus. The profunda femoris gives 3 to 4 perforating arteries that wrap around the posterior aspect of the femur supplying muscles in all three compartments of the thigh.
The medial and lateral circumflex femoral arteries then encircle the uppermost proximal femur. These arise from the lateral side of the profunda femoris.
In the upper third of the thigh, the medial and lateral circumflex, femoral arteries then encircled the uppermost shaft of the femur almost like in a warm life, giving hug and anastomose with each other and other arteries supplying the thigh muscles and superior end of the femur.
The medial circumflex, femoral artery supplies most of the blood to the head and neck of the femur via its branches called the posterior retinacular arteries or the lateral circumflex femoral artery mainly supplies muscles on the lateral side of the thigh.
Also important to the blood supply of the thigh is the obturator artery which branches from the internal iliac artery. Although 20% of the time, it's an accessory or replaced obturator artery from the inferior epigastric artery.

Obturator artery22:02–22:31

The obturator artery passes through the obturator foramen to supply muscles of the medial compartment of the thigh, branching into an anterior and posterior division sandwiching the adductor brevis.
Now, the femoral vein is a continuation of the popliteal vein proximal to the adaptor hiatus. Ok.

Femoral vein22:31–23:19

So, from its origin at the adductor hiatus, the femoral vein ascends through the adductor canal, mostly posterior to the femoral artery.
It then goes on and enters the femoral sheath lateral to the femoral canal and ends posterior to the inguinal ligament where it becomes the external iliac vein in the inferior part of the femoral triangle.
The femoral vein receives the profunda femoris vein, the great saphenous vein and other tributaries. The most important one is a fronto Feoris vein or deep vein of the thigh, which is formed by the union of three or four perforating veins.

Quiz23:19–23:34

Ok. So now that we've reached the midpoint of the clip, just kidding, we're done.
Now, before we recap, let's see if you remember the location of the main arteries and veins of the thigh. All right, as a quick recap.

Review23:34–27:11

The muscles of the anterior compartment of the thigh are innervated by the femoral nerve. First.
The flexors of the hip include the pectineus iliopsoas which has a lateral part called the iliacus muscle and a medial part called the psoas major and the sartorius.
The second group, the extensors of the knee is represented by the four components of the quadriceps, femoris, vastus, lateralis, vastus intermedius, vastus medialis, and the rectus femoris, moving on the muscles in the medial compartment of the thigh, mainly innervated by the obturator nerve comprised the adductor group which is made up of five muscles, adductor magnus, adductor brevis, adductor longus gracilis, and obturator externus.
Then there's a femoral triangle, just distal to the inguinal ligament. It's founded superiorly by the inguinal ligament medially by the lateral border of the adopter longus and laterally by the medial border of the sartorius.
The muscular floor of the femoral triangle is formed by the iliopsoas laterally and the Pectineus medially. While its roof is formed by the fascia lata and cribriform fascia, subcutaneous tissue and skin.
The structures inside the triangle can be recalled from lateral to medial using the naval mnemonic, the femoral nerve, femoral artery, femoral vein, the empty space for the femoral Canalis and the deep inguinal lymph nodes.
The femoral sheath is a tube formed behind the inguinal ligament and it terminates inferiorly by blending with the outer layer of the femoral vessels.
The femoral canal starts at the inguinal ligament and extends distally to the proximal edge of the saphenous opening. And at its base is the oval femoral ring.
Another landmark is the adaptor canal which extends from the apex of the femoral triangle to the adductor hiatus. The adductor canal provides a passage through which the neurovascular bundle of the thigh traverses the middle third of the thigh and their way towards the popliteal fossa inferiorly.
The canal presents the adductor hiatus, an opening between the insertions of the adductor part and the hamstring part of the adductor magnus which provides passage for the femoral artery and vein.
The femoral nerve enters the femoral triangle deep to the inguinal ligament, sending several branches to anterior compartment muscles and terminating distally as a saphenous nerve.
The femoral artery starts distal to the inguinal ligament as a continuation of the external iliac artery and travels through the adductor canal and reaches the auctor hiatus.
Here, the artery enters the popliteal fossa from where it continues as a popliteal artery. The femoral vein is a continuation of the popliteal vein moving approximately from the adductor hiatus from where it descends through the adductor canal, enters the femoral sheath and then it ends posterior to the inguinal ligament where it becomes the external iliac vein.
Both the femoral vein and artery give branches that supply different structures in the thigh. Finally, we have the obturator artery which branches from the internal iliac artery and supplies the medial compartment