Video: Gluteus minimus muscle (3D)

Today, we're in the physiotherapy clinic, where we have a 35-year-old male being examined for what's known as a pelvic tilt. This describes a situation in which the pelvis tilts or drops to one side during the advancing or swing phase of gait, just as you can see here. What might cause this to happen, you ask? The answer lies with two specific muscles located in the gluteal region, and in this tutorial, we're going to cover the functions of one of them – the gluteus minimus.

We're going to go into detail on what this muscle does and why we need it. But, first, let's have a quick look at the anatomy of this muscle.

Here we can see the musculature of the gluteal region, which is where we're going to be focusing on in this tutorial. The gluteus minimus is one of the four superficial muscles in the gluteal region and is the smallest of the three gluteus muscles proper. That's why it's called minimus as this means small in Latin. The other three superficial muscles are the gluteus medius, the gluteus maximus, and the tensor fasciae latae. The gluteus minimus lies deep to these three muscles, so let's remove them in order to have a good look.

The gluteus minimus is a fan-shaped muscle and originates from a large attachment site on the gluteal surface of the ilium between the anterior and inferior gluteal lines. The fibers then run inferiorly to converge into a tendon which inserts at the anterior aspect of the greater trochanter of the femur. When we come to discuss the functions of this muscle, we will find that like the other gluteus muscles, it works on one primary joint. This is, of course, the hip joint, also commonly referred to as the acetabulofemoral joint which, as the name suggests, is formed by the articulation of the femoral head and the acetabulum of the pelvis.

Of course, to perform any function, a muscle needs innervation. In this case, the gluteus minimus muscle is innervated by the superior gluteal nerve, which we can see here. This nerve originates from the sacral plexus, specifically from the posterior divisions of spinal nerves L4, L5, and S1.

The gluteus minimus is in charge of three main functions. Luckily for us, these functions are the exact same as its big brother – the gluteus medius muscle. So, if you're familiar with those, this will be a piece of cake for you to learn.

Let's discuss our first function. The gluteus minimus is one of the most powerful abductors of the thigh – a movement which occurs at the hip joint. This means that when this muscle contracts, it will pull the greater tuberosity of the femur superiorly causing the femur to move laterally away from the midline of the body.

There are countless instances of when we might do this, but to give you an example, let's say you want to jump over a hurdle – like this guy here. Can you see the position that his left leg is in? This is abduction of the thigh, just like our model is showing.

The second function of the gluteus minimus muscle is internal or medial rotation of the thigh at the hip joint when in a flexed position. Internal rotation means that the thigh is being rotated towards the center of the body. This function is carried out by the anterior most fibers of the gluteus minimus as they have a greater mechanical advantage for this type of movement compared to their posterior counterparts. Internal rotation might seem quite a clumsy movement that we don't really perform that much out of choice. However, the ability of the gluteus medius and minimus muscles to internally rotate the femur is essential for counteracting the pull of external rotator muscles of the hip joint.

The importance of this role is not really appreciated until something goes wrong. For example, an individual with a weak gluteus minimus will typically walk with their feet turned out due to the lower limb being allowed to externally rotate by the passive pull of external rotators.

Last, but not least, the final function of the gluteus minimus muscle is stabilization of the pelvis. This is a crucial function and relates to our patient mentioned at the beginning of this tutorial. Let's take a closer look and explain.

In our animation, the model is standing on their right leg. If we were to take the weight of our left foot, this causes the pelvis to drop on the opposite side by means of adduction at the right hip joint. To counteract this instability, our right gluteus minimus contracts and causes the ipsilateral hip to abduct and return to the neutral or balanced position. This might seem insignificant at first, but it's an essential function in keeping our pelvis balanced during the gait cycle, and failure of this function to occur, perhaps due to nerve injury, is known as Trendelenburg gait.

And with that, we've covered all of the functions of the not-so-little gluteus minimus muscle. Let's just have a quick recap before we finish.

The gluteus minimus muscle is one of the strongest abductors of the thigh and the hip joint. When it contracts, it will pull the femur away from the midline of the body. The large fan-shape of the gluteus minimus means that when the anterior portion of fibers contract, they will pull the flexed thigh femur inward resulting in an internal rotation of the femur. And, finally, we demonstrated the role of the gluteus minimus muscle in stabilization of the hip joint during the gait cycle.

That's a wrap for this tutorial. I hope you enjoyed it and we'll see you next time.