Anatomy 101: Knee (Extension)
Last month we took a look at what happens when your knee goes into flexion.
We looked at the structure of what happens with the bones and how the muscles around that joint control and guide the knee into flexion. This month we are going to look into the flip side of things. We are going to look at extension, or better what happens when we stand up from a squatted, or seated position.
Section I: Structure
When it comes down to the bones of the knee nothing changes from knee flexion you still have the femur, tibia (or better the tibial plateau) fibula, and the ligaments (which we will get into next month) all remain the same.
What does change is the forces that are acting on the knee and this changes the requirements of the firing patterns of the muscles that are involved.
Section II: Muscles
Now here is where the difference comes into play. The forces acting on the knee joint during extension change and are placed on the “front” of the leg to “make the leg straight” again. These muscles are:
- Rectus Femoris
- Vastus Intermedius
- Vastus Lateralis
- Vastus Medialis
Now something interesting points that I need to really emphasize here are that during extension (pure extension) the hamstring muscle group and the entire lower leg muscle group must fire to help the knee stay in place or else there will be a dislocation of the joint. Also, these five muscles also play an active role in hip flexion (some do internal rotation and others aid in external rotation of the hip as well, we will get into that in a few months). One more point to take in at this point is that the Vastus Lateralis, Vastus Medialis, Vastus Intermedius, and the Rectus Femoris all connect to a shared tendon that encapsulates the Patella (knee cap) and its insertion (connection to the bone farthest from the head) is at a boney process on the tibia called a tuberosity.
Now there are a couple more muscles that aid in extension of the knee, but they are very weak at doing so they are:
- Tensor Fascia Latae, and
These two muscles are more involved in hip movement and control, but they do some work when it comes to knee ext