Thigh

Thigh

Here, we will draw the innervation of the thigh.
Label the top of the page from left to right as abdomen; pelvis, thigh, and leg.
Next, start a table for the innervation of the thigh.
Indicate that the thigh divides into three compartments:
1st, the anterior compartment, which supplies the extensor muscles.  Indicate that the femoral nerve, supplied by L2-L4, innervates the anterior compartment.
2nd, the medial compartment, which supplies the adductor muscles.  Indicate that the obturator nerve, supplied by L2-L4, innervates the medial compartment.
3rd, the posterior compartment, which supplies the flexor muscles. Indicate that the sciatic nerve, supplied by L4-S3, innervates the posterior compartment.
Next, let's show the innervation of each compartment its primary muscle groups.
First, indicate that proximally, the femoral nerve helps innervate the iliopsoas muscle, which attaches within the iliac region; it is the primary hip flexor and assists in climbing stairs.
Then indicate that distally, the femoral nerve innervates the quadriceps femoris muscles, which lie within the anterior thigh; they provide knee extension, and assist in walking downstairs.
Now, show that the obturator nerve innervates the adductor muscles, which lie within the medial thigh and provide hip adduction.
Then show that the sciatic nerve innervates the hamstrings muscles, which lie within the posterior thigh and provide knee flexion and hip extension.
Finally, note that the peroneal division of the sciatic nerve innervates the biceps femoris short head and that the tibial division innervates the other hamstrings muscles: biceps femoris long head, semitendinosus, and semimembranosus.
A peroneal neuropathy at the fibular head will spare the short head of the biceps femoris, but will weaken the other peroneal innervated muscles.
END OF ESSENTIAL / START OF ADVANCED
Now, let’s address some advanced aspects of thigh innervation.
First, note that in regards to the iliopsoas muscle, the psoas muscles (psoas major and minor) are actually innervated by direct branches from ventral lumbar rami from L1 to L3 (and not the femoral nerve).
However, because the psoas muscles cannot be isolated and tested clinically, they are lumped in with the iliacus muscle, and all three are considered collectively as the femoral nerve-innervated iliopsoas muscle.
Next, indicate that the quadriceps femoris muscle group comprises: rectus femoris, vastus medialis, vastus intermedius, and vastus lateralis.
The adductors comprise adductor longus, adductor brevis, and adductor magnus.
In between the obturator and sciatic nerves, label adductor magnus; Indicate that the adductor magnus has both an adductor portion (as its name implies), supplied by L2-L4, and a hamstrings portion, supplied by L4, L5.
Next, let's include the lesser clinical muscles of the thigh. First, show that the femoral nerve innervates the sartorius muscle; it provides knee flexion in combination with hip abduction and lateral rotation.
Think of someone checking the bottom of his or her shoe to imagine the sartorius and its action Sartorius is the longest muscle in the body. It is a superficial muscle that crosses the thigh: it spans from the anterior superior iliac spine to the medial knee; Functionally, it serves to decelerate the lower extremity during climbing movements.
Then, show that the obturator nerve innervates the gracilis muscle, supplied by L2, L3; it provides hip adduction and also knee flexion and medial rotation.
Gracilis also lies superficially and spans the medial line of the thigh.
Now, show that the femoral nerve innervates the pectineus muscle, which assists in both hip flexion and adduction.
It lies in the femoral triangle; occasionally, the obturator nerve helps innervate the pectineus muscle, as well. The pectineus cannot be isolated and tested clinically.
Finally, show that the obturator nerve innervates the obturator externus muscle, which is one of the short rotators of the hip and which provides external rotation of the hip in hip extension and hip abduction in hip flexion.
Now, let's include the sensory branches of the thigh.
First, draw the lateral femoral cutaneous nerve (aka the lateral cutaneous nerve of the thigh), supplied by L2, L3. It provides sensory coverage to the lateral aspect of the thigh.
Then, from the femoral nerve, draw the medial and intermediate cutaneous nerves of the thigh, which cover the anterior thigh and which are collectively known as the anterior femoral cutaneous nerves.
Next, draw the saphenous nerve, which extends down the medial leg to the instep of the foot and provides sensory coverage to that same area. Lastly, show that the saphenous nerve produces the small but clinically important sensory branch called the infrapatellar branch, which innervates the anterior knee and which can be injured in knee arthroscopy.
Now, draw the posterior cutaneous nerve of the thigh, which S1-S3 supply; it covers the posterior thigh, and also some of the pelvic and proximal leg regions.
Note that the obturator nerve, itself, covers a small cutaneous area on the medial thigh.
Before we conclude, let's consider the anatomic relationships of the neurovascular structures of the femoral triangle because they are critical to know when performing femoral venous cannulation. Within the femoral triangle, the nerve lies most laterally; medial to it is the artery; and medial to it is the vein. The mnemonic NAVY is helpful because it incorporates the position of the midline genitalia, the "Y", into the acronym.