Video: Tensor fasciae latae muscle (3D)

We’ve all heard the expression, “getting weak at the knees.” Whether its nerves before doing a big presentation or seeing a famous actor in person, these emotional situations can leave us in a hot mess on the floor, right? But what stops our knees from giving way during normal day-to-day activities? Are there muscles which help keep our knees extended? Ever heard of the tensor fasciae latae? No, it’s not something that you pick up at your local Starbucks. It’s rather a muscle which works to keep our knees from buckling under us, and we’re going to learn all about it now in this video on the functions of the tensor fasciae latae muscle.

So, the tensor fasciae latae is a muscle located in the lateral gluteal region and plays an important role in lots of everyday tasks. But before we explore all of that, let’s have a quick look at the anatomy of the muscle. Here we’re looking at an anterolateral view of the thigh region with our star muscle showing in full view for you to appreciate. The tensor fasciae latae originates from the outer lip of the anterior iliac crest and from the anterior superior iliac spine. The muscle body is fully enclosed by a thick fascial sheath, which is part of the deep fascia of the thigh known as the fascia lata from which it gets its name.

At the inferior most point of the muscle body, the fascia lata thickens to form a long and thick strip of fascia known as the iliotibial band or the IT band for short. The iliotibial band then runs inferiorly down the lateral thigh to insert at the lateral condyle of the tibia, specifically at a point known as the tubercle of the iliotibial tract, also known as Gerdy’s tubercle.

So now that we know about the attachments of this muscle, it’s only proper that we also take a look at its innervation, right? In this case, the tensor fasciae latae muscle is innervated by the superior gluteal nerve, which we can see here. This nerve originates from the posterior divisions of L4, L5, and S1 nerve roots of the sacral plexus.

Before we look at the functions, it’s also important to take a moment to note the main joints which the tensor fasciae latae acts upon. The first of these, of course, is the hip joint, also known as the acetabulofemoral joint, which is formed by the articulation of the head of the femur with the acetabulum of the hip bone. The attachment between the tensor fasciae latae and the iliotibial tract also allows this muscle to work on a second joint, which is the knee joint. This joint is formed by the femur with the proximal end of the tibia.

As far as the trade off between muscle size and function goes, the tensor fasciae latae is a real bargain. In fact, we can describe seven different functions from just this one relatively small muscle.

For our first function, let’s move to an anterior view where we can now see the role of the tensor fasciae latae muscle in internal or medial rotation of the femur at the hip joint. When this occurs, the femur is rotated inwards towards the pelvis. You might be thinking that it’s difficult to think of an example of when we would use this movement. However, it is actually quite important during the swing phase of gait, or the walking cycle.

When we take a step forward, the tensor fasciae latae assists in internal rotation of the hip joint for the stationary lower limb, which causes the contralateral hip bone and the lower limb to swing forward. This is what helps us to advance the nonweightbearing limb when we walk or run.

The second function of the tensor fasciae latae is stabilization of the pelvis. In our animation, the model is standing on the right leg. If we were to take the weight of our left foot, this causes the pelvis to drop to the opposite side by means of adduction at the right hip joint. To counteract this instability, our right tensor fasciae latae contracts and causes the ipsilateral hip to abduct and return to the neutral or balanced position. The gluteus medius and minimus are actually the prime movers of this action; however, it’s good to know that the tensor fasciae latae also assists with this.

The next function of the tensor fasciae latae is weak abduction of the femur at the hip joint. This means that when the tensor fasciae latae contracts, it is able to assist in moving the thigh away from the midline as we can see here. This is essentially the same movement as in the previous function; however, this time, the femur is not stationary as it was before.

Now let’s move on to the movements at the knee joint. To explain our next pair of functions, let’s put our model into roughly twenty-five degrees of knee flexion. This is roughly the boundary at which the function of the tensor fasciae latae changes in reference to the knee joint. This can be confusing, but all of it will make sense in a moment.

When the knee joint is in a flexed position of twenty-five degrees or less, the tensor fasciae latae assists in extension of the leg at the knee joint supporting the quadriceps femoris muscle which is the prime mover of the movement. This helps us to lock our knee into the fully extended position, just like we mentioned at the beginning of the tutorial. However, when the knee joint is flexed beyond thirty degrees, the tensor fasciae latae muscle instead assists in further flexion of the leg at the knee joint.

But why does this happen? Well, it’s all to do with the attachment of the IT band upon the lateral condyle of the tibia and the knee joint’s axis of flexion. At thirty degrees or more of flexion at the knee joint, the line of pull of the tensor fasciae latae passes posterior to the axis of rotation. This means that the muscle becomes a weak flexor. The opposite occurs when the knee is in position of less than twenty-five degrees flexion. Because now the line of pull of the tensor fasciae latae passes anterior to the axis of rotation, this means that the muscle becomes a weak extensor. A little complicated, I know, but interesting nevertheless.

Moving on to our second last function, the tensor fasciae latae also acts to externally or laterally rotates the leg at the knee joint when starting from a flexed position. It can do this because the attachment of the iliotibial band is located on the lateral aspect of the proximal tibia and means that the tensor fasciae latae is able to apply tension and cause the leg to rotate away from the midline. In practice, this function helps to protect the knee joint and prevent excessive internal rotation of the knee joint which could result in an acute or chronic injury.

Okay, so we’re almost there. One more function to discuss, and lucky for us, it’s relatively straightforward as we’re going to just mention the role of the tensor fasciae latae muscle in the stabilization of the knee joint. It physically does this by supporting the lateral aspect of the knee joint by tensing the iliotibial band, in addition to functionally promoting the position of the tibial condyles within the femur.

And we’re all done with functions. Those are a lot of information there, so let’s have a quick recap before we finish.

The first function of the tensor fasciae latae muscle that we looked at was internal rotation of the femur, which works to reduce the angle between the anterior thigh and the pelvis. The tensor fasciae latae helps to stabilize or balance the pelvis when the opposite side is unsupported such as when we’re taking a step forward while walking. In a similar type of movement, we also noted that the tensor fasciae latae is also a weak abductor of the femur at the hip joint, meaning that it desists in moving the thigh away from the midline of the body.

Turning our attention now to the knee joint, we saw that the tensor fasciae latae assists in extension of the leg when starting from a position of twenty-five degrees of flexion or less. But when starting from a flexed position of thirty-degrees or more, it does the opposite and assists with the flexion of the leg at the knee joint.

We also noted that due to its lateral attachment, the tensor fasciae latae muscle can externally or laterally rotate the leg at the knee joint when starting from a flexed position. And lastly, because the IT band attaches to both the femur and the tibia, it is able to stabilize the lateral aspect of the knee joint by pulling these bones together.

And that’s it for me for this tutorial. Thanks for watching and see you next time.