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Functions and anatomy of the quadratus femoris muscle shown with 3D model animation.
You’re taking a relaxing stroll along the beach, taking in the sea air, listening to the crashing waves before you, enjoying the warm summer sun in your face. Along the way, you take a second to look back at the footprints you've left behind. To your surprise, instead of your footprints pointing ahead as you would expect, you notice yours are actually pointing outwards, away from one another. This is known as out-toeing, which could also unfortunately be described as being duck-footed since it is similar to how our fine-feathered friend walks.
Being the ever curious anatomy student that you are, you are probably wondering what muscles might be at play here that cause your feet to point outwards like that. Well, I'm so glad you asked. In today's tutorial, we'll be investigating one muscle which can influence such a walking pattern as we explore the functions of the quadratus femoris muscle.
In order to better understand the actions that this muscle is capable of, let's first introduce the basic anatomy of the quadratus femoris.
The quadratus femoris actually belongs to a group of muscles known as the lateral or external rotators of the thigh along with five other muscles. The name of this muscle group gives you a hint of their main action, but before we get ahead of ourselves, let's look at where this relatively small muscle attaches.
The quadratus femoris muscle has its origin here, at the ischial tuberosity. It then extends transversely towards its insertion at the intertrochanteric crest of the femur. These attachment sites span across the acetabulofemoral joint, more commonly known to us as the hip joint, so it should be rather intuitive that this muscle will only act on this joint, and we’ll see how in just a minute.
The innervation for the quadratus femoris muscle is super easy to remember. This nerve is simply called the nerve to the quadratus femoris. Doesn’t get much easier than that! The nerve to the quadratus femoris is a branch of the sacral plexus and it may come in handy during exam time to know the nerve root levels of this nerve, which are L4, L5, and S1.
Now that we know a bit more about the quadratus femoris muscle, we can start investigating the actions that this muscle is capable of performing. We’ll start with the most obvious action. Remember how this muscle belonged to the muscle group called the external rotators of the thigh? So then it's not hard to imagine the quadratus femoris doing just that – that is, externally or laterally rotating the thigh, which occurs at the hip joint.
It’s important to remember that this action doesn't just only occur from a neutral stance, like what we just saw. If we have our model start with an internally or medially rotated hip joint, we can see how the quadratus femoris can externally rotate the thigh back to the neutral position. This dynamic relationship between the internal or external rotation is critical during certain phases of the gait cycle.
Let’s take a closer look. When we're standing with both feet side by side, our hip joints are in a neutral position with our toes pointing ahead of us. When we take a step forward, the hip joint of the planted limb undergoes internal rotation, swinging the pelvis forwards. If we look at the advancing limb, we see here that if the hip joint maintains a neutral position, this results in the limb pointing medially instead of directly ahead. To correct this, muscles like the quadratus femoris externally or laterally rotate at the hip joint causing the foot to turn to a forward-facing direction.
When we take another step forward, the same happens on the opposite limb. In the case of a tight external rotator or a weak antagonistic internal rotator, the lower limb can laterally rotate too much during the swing phase, which might be why you have those outwardly pointing footprints that we saw at the beginning of the video.
In addition to external rotation, the quadratus femoris muscle also functions to adduct the thigh at the hip joint. To see this, we'll start with the thigh in an abducted position. From here, we can now see the quadratus femoris adducts the thigh by drawing it towards the midline. So you could say that even the little quadratus femoris helps get you through those long cardio workouts by helping you adduct your thighs when doing jumping jacks.
In addition to these functions, the quadratus femoris also plays a very important role in the stabilization of the hip joint. More specifically, it stabilizes the head of the femur in the acetabulum of the hip bone. This stabilizes the hip joint so that larger muscles, like the gluteus maximus, can work. This means that while you're enjoying all sorts of activities, this muscle helps in keeping the joint stable to prevent injury. It may seem insignificant, but without this function, you may find yourself in a world of hurt.
And on that happy note, the functions of the quadratus femoris muscle have all been covered. But before we call it a day, let's quickly summarize what we learned.
We started by taking a stroll on the beach and looking at the role of the quadratus femoris in externally or laterally rotating the hip joint, then we saw how the quadratus femoris assists in adduction of the hip joint by drawing the thigh towards the midline, and, finally, we mentioned how the quadratus femoris help stabilize the head of the femur in the acetabulum of the hip bone – an important role in injury prevention.
And that's it! We’ve reached the end. Thanks for watching and please be sure to check out our other 3D muscle function videos.