LL10 - Developmental Internal Rotation - Femoral and Obturator Nerves

In this short session, we're going to look at the effect on the lower limb

that the developmental internal rotation of the limb has

on the distribution of the femoral and the obturator nerves.

In the bottom left image, we can see that the fetus has the dermatomes

distributed to the limbs in a very logical order.

During development, the upper limb, in fact, externally rotates

but the lower limb internally rotates.

This is all part of the development of bipedalism that we see in humans

and this is well demonstrated in the lower right image.

But the most important effect, and a question that is often asked in exams,

is that the obturator nerve, which initially in early development

lies on the anterior aspect of the limb,

becomes posteromedial and the femoral nerve is swung onto the anterior surface

of the limb.

Now, both these nerves come from the same roots

and we can see this on the upper left image.

Both the femoral nerve and the obturator nerve

come from the L234 spinal nerves.

But what we have just previously described indicates that the posterior nerve,

that the femoral nerve comes from the posterior divisions and the obturator nerve comes from

the anterior divisions. The actual course of these nerves, of course, is also different

in that the femoral nerve approaches the upper limb posterior to the inguinal ligament, and

apart from its saphenous branch, which is a pure sensory branch, the nerve is distributed

within the anterior thigh, whereas the obturator nerve passes down through the pelvis and out

through the obturator canal, which is a small area in the obturator foramen. It supplies

the muscle compartment on the medial side of the leg, the adductor compartment, and

only one of its small sensory branches extends down to supply the knee joint.

And then we have the femoral nerve, which is a pure sensory branch, which is a pure

And then finally, on the upper right picture, we can see that during a dissection of the

serous muscle, the two nerves are exposed, and it is quite clear that the obturator nerve,

which is shown in green here, lies initially anterior to the femoral nerve. And with that

anatomical description, we'll end this session.

Please visit our website at incidentanatomy.net, where you can find the

complete collection of all our podcasts. You can also subscribe, download, or order

any of our material. You will also find full details of our range of mobile apps.