Video: Obturator externus muscle (3D)

At some stage or another, most of us often find ourselves sitting with our legs crossed. Whether it’s catching up with your girlfriends or just hanging out with the guys, it’s just a comfortable way to sit, right? To perform this action, we must be able to externally rotate our thighs. Today, we’ll learn about a muscle that assists in this movement in our tutorial on the functions of the obturator externus muscle.

Let’s begin with an overview of the anatomy of the obturator externus muscle. As we can see from our anatomical model here, the obturator externus is a flat fan-shaped muscle that originates from the external surface of the pelvis; therefore, we can best see it from an anterior perspective.

Looking at the bigger picture, the obturator externus muscle is part of a group of muscles known as the external rotators of the thigh, or the hip joint, which gives us a clue about its function. But more about that later.

Alternatively, you might also sometimes see it classified as one of the muscles belonging to the medial compartment of the thigh.

In order to understand the functions of the obturator externus, we need to first learn about the bones it attaches to and the joints that it crosses. If we take a closer look at our awesome 3D model here, we can see that the obturator externus muscle originates from the anterior surface of the obturator membrane and the bony boundaries of the obturator foramen.

Its muscle fibers converge posterolaterally to form a tendon, which passes posterior to the neck of the femur to insert at the trochanteric fossa of the femur, which is this depression we can see here, if we view our model from a posterior perspective.

By looking at these attachment points, we can clearly see that the obturator externus muscles crosses just one joint which is, of course, the hip joint, also known as the acetabulofemoral joint.

So now that we know the anatomy of our star muscle, we also need to have a look and see what nerve instructs it to carry out its functions. Conveniently, the obturator externus is innervated by the obturator nerve, which is formed by the L2, L3, and L4 nerve roots of the lumbar plexus. Specifically, it is innervated by the posterior branch of this nerve.

Now that we’re familiar with the structure and innervation of the obturator externus, let’s move on to talk about its functions.

The first movement of the obturator externus we’re going to talk about is external or lateral rotation of the thigh at the hip joint. As we can see from our animation, external rotation of the thigh involves rotation of the thigh outwards, away from the midline of the body. This movement is key when we want to cross our legs and take off our load. Together with the other external rotators of the hip, the obturator externus is important when walking. Specifically, it produces external rotation of the lower limb in the early swing of gait.

The second movement of the obturator externus is abduction of the thigh at the hip joint. This only occurs when the hip joint is already in a flexed position. Here, the obturator externus causes the thigh to swing away from the midline of the body which we referred to as abduction in the anatomy world. If you happen to do yoga, you’ll be versed in abducting your flexed thigh when doing movements like the classic tree pose.

Last, but certainly not least, the final function of the obturator externus is to help stabilize the hip joint by supporting the position of the head of the femur within the acetabulum.

So that brings us towards the end of our tutorial on the functions of the obturator externus muscle. Easy-peasy, right? Let’s summarize those functions one last time.

The first function of the obturator externus we saw was external rotation of the thigh at the hip joint, which involves rotation of the thigh outwards away from the midline of the body. The second function of this muscle was abduction of the flexed thigh. Here, the obturator externus causes the thigh to swing away from the midline of the body. The third and final function of the obturator externus was stabilizing the hip joint by keeping the head of the femur within the acetabulum.

And that’s us finished. Thanks for watching and feel free to check out our other 3D muscle function videos and lots more at kenhub.com. See you next time!