Hello, hello, everyone. This is Joao from Kenhub, and welcome to another anatomy tutorial where this time I'm going to be talking about the anterior thigh muscles and help you understand which muscles form the anterior side of the hip and thigh and how they work.
Now, without further ado, I want to tell you that the anterior thigh muscles are comprised by two main muscles, and these are the quadriceps femoris and the sartorius muscle.
Let’s start with the first one here on our list, the quadriceps femoris, seen now highlighted in green, here on these two images. What you need to know about this muscle is that this is a four-headed muscle of the thigh—hence the name, “quadriceps,” four-headed, and almost completely covers the anterior side of your femur.
As you can also see here on both of these images, that the quadriceps femoris is covering the anterior portion of your thigh bone. And you can also see here other muscles. These are known as the adductors of the thigh, and this is the tensor fascia latae.
Now, the other thing you need to know about the quadriceps femoris is that it ranks among the strongest muscles in the human body, and it significantly forms the lateral contours and the ventral side of your thigh as you can clearly see here.
Also, due to the name as you can see here, that this muscle has four heads, or is comprised, or is a collection, better said, of four muscles. And these are the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius. And we’re going to look at each one of these muscles, and where they are originating from, and also where they’re going to be inserting.
But before we do so, I want to start off in a different way here. I want to cover the innervation of the quadriceps femoris because all these four muscles that we just saw on the previous list are supplied or are innervated by one nerve, this one here that you can see on the image highlighted in green. This is known as the femoral nerve.
Now that we covered the innervation of the quadriceps femoris, let’s start with the individual head known as or individual muscle that is part of this larger muscle, the quadriceps, known as the rectus femoris.
Now, the rectus femoris has two origin points that we need to clarify here. And the first one is, as you can see here, this is the origin point for the rectus femoris. And here you can see that it’s inserting on the anterior inferior iliac spine of the pelvis and on the upper margin of the acetabulum on an area called the supraacetabular sulcus.
Now, in terms of insertion point, as you can see, the muscle is going to insert distally. So it’s going to go all the way down from the origin point and then going to be part or be part of this tendon here, which is the tendon of the quadriceps femoris. And here, you can see that the tendon is running over or above the ventral side and through the periosteum of this bone here, the patella. Now, then, we will go all the way down a bit further down and insert here, which is the tibial tuberosity or the tuberosity of the tibia. Now, the part below the patellar apex is referred to as the patellar ligament.
Now, let’s talk about the functions associated to the rectus femoris, and this muscle is responsible for flexion of the hip joint as well as extension of the knee joint. And in order to enable an extension of the knee joint, the quadriceps tendon must somehow be connected to the tibia. It indirectly is. The tendon inserts at the patella as we talked about on the previous slide. And from the patella, the patellar ligament runs to the tuberosity of the tibia. This way, as you can see and here also on this image where the muscle is performing its functions, you notice here that for this reason, for the insertion point of the rectus femoris, then we can see that it will influence the knee joint or extension of the knee joint.
Let’s move on to the next one, the next muscle here of the quadriceps femoris. And this one highlighted in green is known as the vastus medialis. And the vastus medialis, as you can see here in terms of origin point, you notice here a little bit of the origin point that this muscle is going to be around the shaft from the... it’s going to run spirally around the shaft of the femur from the linea aspera and the intertrochanteric line of the femur.
Now, we see a similar pattern here in terms of insertion point like we saw on the rectus femoris. This muscle will also distally insert distally. And the fibers insert as the quadriceps tendons as you can also see here in this image. And then will insert on the patella or runs on, above the ventral side and through the periosteum of the patella. And finally will insert on the tuberosity of the tibia like we saw on the rectus femoris, and the part below the patellar apex is referred, like I mentioned before, as the patellar ligament. So don’t forget this.
The next thing you need to know about the vastus medialis is a little about their functions. Now, in terms of functions, you need to remember two functions associated to the vastus medialis. One is extension of the knee joint, as you can see here represented in this ar... by this arrow. And another one is slight internal rotation of the knee joint. So when you move your foot to... towards the midline of your body.
Now, the next muscle that we’re going to be covering is this one also seen here highlighted in green. This is the vastus lateralis. As you can clearly see, this muscle is found a bit further to the lateral side of the quadriceps. And in terms of origin point, you can also see here that it’s going to be originating from or arising from the linea aspera and also the greater trochanter of the femur.
Now, take a look at the insertion point here. And you notice that this muscle is going to loop around the femur shaft and laterally runs as the quadriceps tendon to the patella. And the same pattern here that we talked about, so the muscle is go... or the muscle is going to insert as the quadriceps tendon on the patella. And it runs above the ventral side and through the periosteum of the patella and finally will be inserting on the tibial tuberosity.
Now that we covered the origins and insertion for the vastus lateralis, it is time for us to move on to its functions, and you need to remember two. Two main functions associated to this muscle. And as part of the quadriceps, we would assume that it will extend the knee joint, and also another function associated to the vastus lateralis would be then a bit of rotation, external rotation of the knee joint. So when you move your foot away from the midline of your body.
Let’s move on to the final or the fourth muscle of the quadriceps, and this is the vastus intermedius. And in terms of origin point, you need to remember one. This muscle is going to begin in front of the femur. So it starts on or originates from the body of the femur. Then its tendon is going to go all the way to connect to the tendons of the other three. They’re going to form the tendon of the quadriceps that will run above the ventral side, and through also the periosteum of the patella, and then all the way to the tuberosity of the tibia.
Quick look at the functions associated to the vastus intermedius. One that we need to recall here associated or since this muscle is also a quadriceps muscle, then we’re going to assume that it’s going to be performing extension of the knee joint.
Let’s take a summary here of the of the quadriceps femoris before we move on to the sartorius. And what you need to know is this muscle is formed by four muscles including the rectus femoris, the vastus medialis, the vastus lateralis, and the vastus intermedius.
Now, in terms of functions, let’s also do a quick summary here of the quadriceps femoris. What you need to know is that all four muscles of this or that belong to the quadriceps will be helping with extension of the knee joint—very important and remember this. This is an important thing. When you hear about quadriceps femoris, think that all these muscles will be performing extension of this joint.
Now, if we look individually at the rectus femoris, one thing that we need to also highlight here about this one is this muscle is going to also be performing flexion of the hip joint. The vastus medialis will be performing a bit of internal rotation of the knee joint. And if you remember well, the vastus lateralis will be helping with a bit of external rotation of the knee joint.
Now, one important thing to clarify here is that the quadriceps tendon utilizes the patella, as we remember when we looked at the actual muscle. Now, it uses the patella, this bone, as a sesamoid bone, and this has two advantages. The first one is that the lever arm is lengthened which effectively increases the torque, torsional moment, what we call. And thus the muscle needs less power in order to move the bones, so this is an advantage why the muscle uses the patella as the sesamoid bone. The second one would be that the patella protects the knee joint from damage through the quadriceps tendon.
So this is a summary of the quadriceps femoris before we move on, now, to the last muscle of the anterior thigh muscles, seen here highlighted in green, and this is the sartorius muscle.
The sartorius is a long, slim, superficially running muscle of the thigh. Topographically, this muscle forms the lateral border of the femoral triangle where the large vessels of the thigh pass through. For this reason, the muscle serves as leading structure when surgically assessing the femoral artery.
Let’s start with the very first thing here on the highlighted muscle that you see here on the image on the right side, the origin point for this muscle, and you can clearly see here from this image right about here. This is the origin point. And if you remember well, when you learn the pelvis, this is the anterior superior iliac spine. And this bony structure, bony landmark of the pelvis or the hip bone, will serve as the origin point for the sartorius.
Now, let’s take a look at the insertion point. And as you can see clearly on this image that the sartorius runs spirally towards the knee region, and here, as you can see, right below... a little bit below the knee, there, it’s going to insert on the pes anserinus on the medial aspect of the tibia, medially from the tibial tuberosity. And, of course, I'm going to add here the pes anserinus. And in its entire course the muscle is covered by fascial duplication of the fascia latae, something to also highlight here as we talk about the insertion point of the sartorius.
Now, logically, it is important to add here. We talked about this when we started talking about the quadriceps, but it’s important to add here the innervation of the sartorius. And what you need to remember that this muscle is going to be supplied, like we saw for the quadriceps, this is also supply... or this muscle is also supplied by the femoral nerve. So a lesson to take home here is that all anterior thigh muscles are supplied or innervated by the femoral nerve.
Now, let’s move to the last topic of this tutorial, and we’re going to be covering the functions of the sartorius. And you can clearly see here on this image, image of the left side is showing the combination of all five movements of the sartorius that when executed simultaneously the legs would cross like a tailor’s seat, so hence the name as well sartorius.
Now, the sartorius contraction will cause flexion. One of the movements that you can see here on the image. You notice that the thigh is flexed due to the sartorius as well to the contribution of this muscle. And in addition, it is involved in abduction and external rotation represented in both of these arrows seen here. And in the knee joint, it forces flexion and also internal rotation as you can see indicated by the last arrow on the bottom.