Hi everyone! This is Joao from Kenhub, and on this tutorial, we will look at the different functions of the vastus medialis muscle which you see now isolated on the screen. Now before we talk about the actual movements that this muscle is able to do on your knee, let me introduce you to the vastus medialis.
The vastus medialis is one of the four muscles that make up the quadriceps femoris which is this muscle that you see now on the screen. The quadriceps femoris is a superficial muscle that defines the anterior thigh. When you work out and you don't skip a leg day, this will be the muscle that will be clearly defined right in the front of your thigh. Now, let's isolate the vastus medialis again but before I do that, let's first remove this muscle here, the rectus femoris, which is part of the quadriceps femoris. That way, we can clearly see the vastus medialis in all its glory.
The vastus medialis is innervated by the femoral nerve which is this nerve that you see here highlighted on this image. The vastus medialis as the name suggests is the part of the quadriceps femoris that is found medially – so towards the midline of your body. It runs spirally around the femoral shaft originating at the linea aspera and the intertrochanteric line of the femur and then merges with the quadriceps tendon for the most part. The quadriceps tendon then inserts at the tibial tuberosity via the patellar ligament.
Now knowing what places the vastus medialis will be attaching to allows you to understand what joints this muscle will be moving when it contracts. And, yes, the knee is the joint that is affected. The knee is the meeting point for the distal end of the femur, the proximal end of the tibia and the patella. The bone that you can feel in front of your knee. So let's have a look at the functions that the vastus medialis is involved in at the knee joint.
In order to clearly show the first function, we will place the model in the sitting position showing the thigh flexed. The quadriceps femoris is the only extensor of the knee joint. For that reason, the vastus medialis will be involved in extending the knee joint. Like you see now on our animation which is essentially when with the thigh flexed, you bring your leg up, the muscle plays a role in every movement that requires your knee to be stretched such as walking, climbing stairs, getting up from a chair, etcetera.
Even though extension is the main function of this muscle, the vastus medialis is also involved to a small extent in internal rotation of the knee. In order to show you this movement, we have to flex the knee at a ninety-degree angle. The best way to do this is to first flex the thigh and then the knee. Remember that flexing the thigh is the movement caused when you bring your thigh towards the front of your body while flexing the knee is when you bring your lower leg towards the back of your body. So what you see now on the screen is what it would look like if you were sitting on a chair. When the knee is flexed, internal rotation is then possible which is when you rotate the lower leg towards the midline of your body.
So, essentially, these are the functions of the vastus medialis but before we conclude this tutorial, I would like to briefly summarize the functions of the vastus medialis that we learned.
We saw that the muscle is able to produce movement at the knee joint. It is able to extend the knee by bringing the lower leg up and it is involved to a small degree in internal rotation of the knee by moving the lower leg towards the midline of the body.
Now this is it for our tutorials on the functions of the vastus medialis. I will see you next time.