The Lateral Knee: A Change of Scenery

Hello! It's a lovely fall day here in Chicago, and another refreshing midwest change of scenery is upon us. While I love all the city offers during the warm summer months, the change of seasons is always welcome; too much of the same thing can get a little stale. This has me thinking that I could use a break from writing about upper extremity (as I'm sure you could use a break from reading about it.) As beautiful as the arm is, and as much as there is to learn about its structure, I think this week might be the perfect time for an anatomical change of scenery. Grab yourself a hot mug of apple cider and let's talk about the leg!

Recent news photos from a perennial fall event, the Chicago Marathon, got me thinking about an area of the leg I've been wanting to write about. On the lateral side of the knee, we can see two incredibly beautiful tendons whose surface appearance increases in clarity when weight is placed on the leg. So it's easy to see these tendons, as well as some surrounding muscles, on runners.

Let's start with a photo showing a lateral view of a runner's knee. Once you've recovered from the shock of this gentleman's extremely short shorts, you'll notice that two tendons show very clearly where the thigh reaches the knee. What we're seeing here are the insertions of the iliotibial band and the biceps femoris tendon.

While the thigh is heavy with strong muscles that completely obscure most of the femur, its lateral-most surface is covered with a wide tendinous sheath known as the iliotibial band. Just deep and posterior to that, we find the biceps femoris muscle, one of the flexor muscles on the posterior surface of the thigh.

The pronounced landmark tendons in the photo above stem off these two structures. The biceps femoris tendon is an insertion tendon that comes from, of course, the more proximal biceps femoris muscle. This tendon is posterior to the iliotibial band tendon, and it inserts onto the head of the fibula, just distal to the knee joint. The iliotibial band tendon comes from the iliotibial band above and it inserts onto the lateral side of the tibial head. These two tendons, when they protrude (most visibly on a weight-bearing leg) form a beautiful little fossa just proximal to the lateral knee. (In anatomical terminology, a fossa is a depression; the word fossa comes for the Latin for ditch.)

These two tendons are usually visible, but to varying degrees, as we'll see below. But first let's examine the anatomy more closely:

Let's first establish that this is a lateral view of the knee and lower leg. The fact that digit number 5 (the pinky toe) is closest to us makes this clear up front. But if we could not see the foot, we'd still know this was a lateral view because we can see both ends of the fibula (the head at the proximal end and the lateral malleolus at the distal end.) In addition, if we were viewing the medial side of the lower leg, we'd be able to see the entire length of the medial tibia, which is not obscured by any soft tissue. 

On the lateral knee we can see the two tendons that show in the runner photo above. The iliotibial band tendon comes from an eponymous band above. This band originates at the tensor fasciae latae muscle at the ilium (a pelvic bone), and it inserts onto the tibia, hence the name ilio-tibial band. We can also see that this band inserts onto the tibia just posterior to the patella.

The other visible tendon here is that of the biceps femoris muscle. It can be seen in this diagram just posterior to the iliotibial band. This tendons extends more distally than that of the iliotibial band because it inserts onto the head of the fibula. This feature of the fibula is a very nice orientation landmark because not only is it the insertion point for biceps femoris, but it's also the origin point for a lower leg muscle, peroneus longus. (Peroneus longus is briefly touched upon in a previous post, A Lateral Ankle Tendon: Peroneus Longus or Peroneus Brevis?)

We can see in the photo above, as well as the photo below, how a weight-bearing leg shows these tendons so clearly:

We can see here that the iliotibial band tendon is more anterior than the biceps femoris tendon, and it doesn't extend as far distally. Also, the iliotibial band tendon is wider and flatter than the more cylindricl biceps femoris tendon. Notice also how the biceps femoris tendon forms the lateral wall of the popliteal fossa, which is the hollow area on the back of the knee.

These tendons are still visible on a relaxed leg but in a different way. A painting below by my talented friend Adam Nowak shows this. First let's look at the full painting:

The model's right leg is relaxing over the left leg, and we can still see the lateral knee structures mentioned above. But here the iliotibial band reads as a sunken area because just anterior to it (or above, in this image) the relaxed vastus lateralis muscle is sort of bulging out over the iliotibial band, casting a shadow over it. Posterior to the iliotibial band (or below it, in this image) the biceps femoris muscle also bulges out as it's pressed against the right leg. The band itself, being of less flexible tissue, maintains its shape and reads as a flat crease.

Here is a close-up:

Notice the iliotibial band in the model's relaxed right leg reads as more of a long depression than a ridge, and the vastus lateralis muscle, although not contracted, bulges outward as its weight makes it sort of spill over the iliotibial band. The painter pays close attention to anatomical detail, and it shows here. You can see more of Adam's beautiful work at Adam Nowak's Art Blog.

I do miss summer a little bit, and I could spend another long stretch of warm weather hunched in front of my computer with a glass of iced tea, writing more about the arms. But a change of seasons is good, as is a change of scenery. There is much more to cover on the human leg, so let's stick around awhile and absorb the view. Another post will be up soon, possibly the anterior thigh or lower leg. Thanks to Adam for the use of his image! Until next time, my friends.