(3.49)
Now let’s look at the two collateral ligaments, the fibular collateral ligament on the lateral side, and the tibial collateral ligament on the medial side. The tibial collateral ligament goes from the medial epicondyle of the femur, to the anteromedial aspect of the proximal tibia.
The tibial collateral ligament blends with the capsule of the knee joint behind, and also in front. On its inner aspect, it’s firmly attached to the edge of the medial meniscus, which is here. Now let’s look at the rather different fibular collateral ligament. It goes from the lateral epicondyle of the tibia, to the head of the fibula.
The fibular collateral ligament stands out from the side of the knee joint. Unlike its tibial counterpart, it doesn’t blend with the joint capsule. It’s not attached to the meniscus.
When the knee joint is extended, both the collateral ligaments are tight. When it’s flexed, they become less tight. The function of the collateral ligaments is to keep the femoral and tibial condyles together,and thus to prevent the knee joint from bending from side to side like this, or like this.
In addition to the obvious knee movements - flexion and extension - it’s also possible for the tibia to rotate a little on the femur, like this. This rotation can happen only when the knee is flexed - when it’s extended the tightness of the collateral ligaments makes rotation impossible. The next structure we need to add in building up our picture of the knee joint is the quadriceps tendon, and along with it, the patella.
Here’s the distal end of the quadriceps muscle, which we’ll see in more detail later in this section. Here’s the quadriceps tendon. The patella, which is here, is enfolded within the tendon. The part of the tendon below the patella is known as the patellar ligament. On the medial side, and on the lateral side, the tendon is continuous with the capsule of the knee joint.
Between the quadriceps tendon and the femur is an extension of the knee joint cavity, the quadriceps bursa. It’s lined with synovial membrane. This lubricated pocket enables the quadriceps tendon to slide easily on the femur.
Now we’ll complete our picture of the knee joint by adding the fibrous capsule which encloses it.
Here’s the knee joint with the joint capsule intact. On the medial side the thin capsule is continuous with the tibial collateral ligament, but on the lateral side the capsule is separated from the fibular collateral ligament. On the back of the joint the capsule is thick and strong. The thickened posterior capsule prevents hyperextension of the knee joint.
Here we’ve divided the fibrous capsule to see its inner surface. It’s lined on the inside with synovial membrane all the way round the joint, except at the back. At the back, as we’ll see if we remove the capsule, the thin synovial membrane (here it is) passes forwards around the cruciate ligaments, covering them on the front.