Now we’ll complete our picture of the muscles around the knee by looking at three muscles at the back that we haven’t met yet, popliteus, gastrocnemius and plantaris.
Here’s the popliteus muscle. It arises from this area on the back of the tibia, and inserts up here on the lateral epicondyle of the femur. The tendon of popliteus passes through the capsule of the knee joint to reach its insertion. Popliteus is a minor flexor of the knee, and it can also produce medial rotation of the tibia.
Lying on top of popliteus is the small plantaris muscle. It’s a vestigial structure. It arises from the lateral epicondyle of the femur. The tiny tendon of plantaris runs down on the back of this big muscle, soleus. We’ll see where it ends up in the next section.
Lying on top of the two small muscles that we’ve just seen, is the much larger gastrocnemius muscle. Gastrocnemius arises by two heads, from the back of the medial and lateral condyles of the femur.
Gastrocnemius runs downward, and joins with the underlying soleus muscle, which we’ll see in the next section, to form the calcaneal tendon, or heel cord. Gastrocnemius has a slight flexing action at the knee, but its main action, by far, is at the ankle joint: we’ll see it again in the next section.
Now that we’ve seen all the muscles that arise or insert at the knee joint, let’s see how they all fit together.