Video: Obturator internus muscle (3D)

And Kenhub has the ball! He’ll make the fantastic pass to Joao. Joao has the ball. He shoots. He scores! What a goal! And as the crowd celebrates, Declan, the anatomist, wonders to himself, “what muscles helped Joao score that goal?”

Well, one of the key players – excuse the pun – is the obturator internus which helps with external rotation of the thigh at the hip joint. This movement helps Joao shoot the ball into the goal with the side of his foot. Anyway, it's now time to leave the stadium and explore the functions of the obturator internus muscle in more detail.

Before we get into the key facts about the obturator internus, let's familiarize ourselves with this muscle as a whole. Using our anatomical model here, we can see that the obturator internus is a flat fan-shaped muscle that originates from the internal surface of the pelvis. Therefore, we can see it best from a posterior perspective. Together with the two gemelli muscles, it forms the triceps coxae.

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

Okay, an important step in understanding the functions of the obturator internus is learning the bones it attaches to and the joints it crosses. I just mentioned that the obturator internus originates from the internal surface of the pelvis, but if you want to pass your anatomy exams, then we’ll need to be a bit more specific.

If we take a closer look, we can see that the obturator internus originates from the ischiopubic ramus and the posterior surface of the obturator membrane. It's muscle fibers converge to form a tendon which bends ninety degrees around the ischium between the ischial spine and the ischial tuberosity and passes through the lesser sciatic notch to enter the gluteal region. The tendon of the obturator internus then travels posteroinferiorly to insert on the medial surface of the greater trochanter of the femur.

Now that we've learned the origin and insertion sites of the obturator internus, we can easily work out the joints that it crosses. It originates from the ischiopubic ramus, which is part of the hip bone and inserts at the greater trochanter of the femur; therefore, it crosses the hip joint. This means that the obturator internus acts on or performs movement at the hip joint, also known as the acetabulofemoral joint.

So we've determined that the obturator internus acts on the hip joint, but in order to carry out its functions, it needs a nerve to tell it what to do and when. The obturator internus is, funnily enough, innervated by the nerve to the obturator internus, which is formed by the L5, S1, and S2 nerve roots of the sacral plexus.

You’ll be pleased to hear that it's time to talk about the functions of the obturator internus muscle, and luckily for us, these are pretty easy. The first movement of the obturator internus 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. So if you think back to the beginning of our tutorial, this is the movement that Joao used to kick the ball with the side of his foot.

Together with other external rotators at the hip, the obturator internus is important when walking. Specifically, it produces external rotation of the lower limb in the swing phase of gait.

The second movement of the obturator internus is abduction of the flexed thigh at the hip joint. As we can see from our model, abduction describes the movement from the thigh away from the midline of the body. So you gentlemen who like to sit with their legs apart, give a little gratitude to the obturator internus for making this happen.

Last, but not least, the obturator internus also helps to stabilize the hip joint by keeping the head of the femur within the acetabulum.

So that brings us towards the end of our tutorial on the functions of the obturator internus. But before you go, let's summarize what we covered today.

The first function of the obturator internus 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 at the hip joint, which describes the movement of the thigh away from the midline of the body. The third and final function of the obturator internus 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!